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October 4, 1991 PVC Calendering FML Materials Sheet Integrity - Pinholes   An understanding of sheet integrity must begin with an understanding of the process, formulation, and raw materials. In calendering, the raw materials are fed to a simple mixer, gradually heated and homogenized by passage through an internal mixer/and or a roller mill, then the hot mass is fed to the calender where it is compressed between heated rollers to form a film of desired thickness. The hot film is peeled from the calender, cooled and woundup. Contemporary PVC calendars have four (4) rolls and are usually in an inverted L configuration. Sheeting 84" wide and higher are capable of being produced in a thickness range of .003" to .050". Calendering offers the following advantages: Very high outputs. Output is controlled by mixing capacity. Excellent thickness control. ± 5% of nominal. Low strain in the membrane.Attractive appearance. A four (4) roll plastic calender, reforms the sheet three times ensuring exclusion of air in the membrane. The calendering process then produces membrane of homogenous composition, uniform physical dimensions ensuring membrane integrity within the parameters of its design. In the range of thicknesses used in the geomembrane industry (.010" - .060") pinholes are a non event. To ensure the manufacture of pinhole free membrane, two procedures are followed: A backlit vertical viewing station - full width, 2 yards long - is installed in the calender train, prior to the windup. This allows for continuous monitoring. Periodic sampling - full width, two yards long - every third roll. The sample is placed over a viewing table, which is backlit, hand tension applied and the membrane examined. The following are some examples of applications where PVC films or sheeting are used and where sheet integrity is of prime importance. geomembranes (.010" - .060")swimming Pool liners (.015" - .040")roofing membranes shower pan liners medical collection bags for liquids and solids vapour barriers (.004")tarpaulins inflatable aquatic designs (.008 - .010")medical enteral feeding and plasma bags baby pants shower curtains  Some examples of product or application specifications are shown here: a) ASTM D3083 - PVC sheeting for Pond Canal Reservoir Lining        1 pinhole allowed per 10 sq. yards (backlit viewing) b) ASTM D4551 - PVC Plastic Flexible Concealed Water Containment Membrane        For .030 and .040 sheeting        No pinholes allowed (backlit viewing) 3.Federal Specification L-P-375C Types I and II Plastic Film, Flexible, Vinyl Chloride.        2 pinholes/sq. yd. for film thickness .004" - .008" NO pinholes allowed for sheeting thickness .010" - .020" 4. CGT specification for Inground Swimming Pool Vinyl        No pinholes allowed. 20 mil membrane (backlit viewing) Conclusion Process, formulation, raw materials, quality control testing, all combine to produce a defect free, pinhole free geomembrane. PAUL LUSSIER , Canadian General-Tower, Ltd. For more information call   800-OK-LINER  today!

POSITION PAPER ON THE USE OF PVC LINER IN LANDFILLS AND WASTE WATER TREATMENT PLANTS FOR THE MICHIGAN DEPARTMENT OF NATURAL RESOURCES In the choice of a flexible membrane liner or cap, it is generally accepted that there is not a universal material that provides the best performance in every requirement for this application. It is the position of OxyChem, in offering this flexible PVC liner material, that OxyFlex™ PVC offers the best overall performance in applications involving landfill liners, landfill caps and waste water treatment liners, based upon actual performance of PVC liners and technical data relating to these particular end uses. In this paper, I will address the concerns that you have voiced in the choice of PVC over other FML materials. I will try to keep this as brief as possible and still state the facts in a clear fashion. There is much more material concerning this subject, some of which I have attached for more in depth reading. Of course, I would welcome an opportunity to further discuss these issues at your convenience. I will address the following topics for which you have a concern. 1. Light degradation 2. Loss of plasticizer 3. Insufficient strength in material under 50 mils 4. Pinholes in material under 50 mils 5. Insufficient seam strength 6. Chemical compatibility It is a fact that long term exposure to UV radiation can lead to the reduction of physical properties of PVC materials. It should be noted that PVC films are routinely used in outdoor applications such as graphic/decorative decals, examples being automotive pinstripes, truck fleet marking decals, tents, industrial tarpaulins and outdoor advertising. PVC is the material of choice for all theses applications, one reason being its excellent outdoor performance characteristics. To examine this particular application, the FML is exposed only as long as it takes to place it at the site and cover it with a protective soil cover. This usually is a short period of time, say 3 or 4 months. However, to determine the actual endurance of OxyFlex PVC as compared to HDPE, a 40 mil sample of the OxyFlex PVC and a 60 mil sample of HDPE were exposed to 1,000,000 Langleys (a unit of light measurement) in real time EMMAQUA testing in Arizona by the outside test firm, DSET. This testing correlates to 4 to 6 years of actual outdoor exposure depending upon the particular area of the country. Even after this exposure, the PVC exceeded the requirements for NSF Standard 54 for the properties tested; 100% modulus, tensile and elongation. The HDPE, on the otherhand, could not be tested for physical properties because the material was destroyed in the testing by the sunlight. The US Bureau of Reclamation was commissioned by the EPA to conduct the same real time EMMAQUA test using 5" wide seam samples, which included PVC and HDPE materials. Again the HDPE samples were destroyed by the sunlight, but the PVC samples were still sound. Light exposure of the PVC during installation would have no measurable effect on its physical properties. The next concern, loss of plasticizer, again has lead to some misconceptions. To better understand what plasticized PVC is, one needs to understand the relationship between PVC resin and plasticizer. Plasticizer is a liquid which is very compatible with the PVC resin molecule. The plasticizer imparts the flexibility into the PVC liner. Both the plasticizer and the PVC resin are very long chained organic molecules and as such are difficult to separate once mixed, due both to their chemical affinities and their size. The plastizer acts as a lubricant allowing the PVC molecules to slide over each other. This allows them to slide back and forth when put under stress. This gives the PVC the ability to rebound when stresses are removed. The HDPE and the VLDPE on the other hand, are long crystalline chains, which once stress is introduced, do not rebound but stay in their elongated form causing extreme thinning and stress cracking associated with HDPE. It is true that plasticizer can be extracted from PVC using certain concentrated organic solvents. In situations where the liner would be exposed to this environment, we would not recommend OxyFlex PVC. However, in the typical landfill the levels of organic solvents are very low, usually less then 1%. These very small levels would not have the same effect on liners because the other components would interact in a complex manner. PVC liners have been in use since the 1950's and samples of the liners have been examined and remain totally functional after many years. Dr. Henry Haxo recovered 20 mil PVC liner from the Lycoming County Pennsylvania Landfill. The sample was taken (July, 1984) from near a leachate collection sump during the excavation of a leachate pipe and in all probability had been fully immersed in leachate for the entire 6 years the facility had been in service (since June, 1978). A full set of physical property tests along with analytical tests were performed on the field sample and compared with similar test results from a new unexposed 20 mil PVC sample obtained from the same manufacturer. The exposed sample test results were also compared with the NSF Standard 54 test values for 20 mil PVC liner. Quoting from the Haxo report: "The PVC FML remains flexible and useful with almost 90% retention of all original physical properties. It can also be seen that the physical properties after the exposure exceeded the minimum values specified for a 20 mil PVC in the NSF Standard 54, Flexible Membrane Liners." In another report, a 20 mil PVC FML that was used to line a 5 acre pond, was tested after 17 years under water with no earth cover. Again, the material still met all the requirements for the NSF Standard 54 for Flexible Membrane Liners. In testing of 30 mil OxyFlex PVC, using the EPA Method 9090, the recognized test method for liner compatibility, the PVC again passes the requirements for the NSF Standard 54 after testing. The PVC was immersed in a leachate from the Grand Central Landfill for a period of 120 days at 23°C and 50°C. Additional testing is in progress for 40 and 50 mil OxyFlex PVC. The results of which will be available in December, 1989. According to Bob Landreth of the EPA, "It has long been recognized in the industry that PVC materials have the longest history of containing municipal solid waste leachate." The next concern is the insufficient strength of material under 50 mils. This is a little puzzling to me since a reference to a specific physical property is not made. PVC liners at 20 mil have been successfully used in the containment industry for over 35 years with a great deal of success. I realize that thicker liners are now specified to provide an extra margin of safety. The puncture resistance of PVC liners compared to HDPE has been shown to be superior in real world three dimensional stress testing. In a paper by Ronald K. Frobel of the US Department of the Interior, he reports in testing conducted on various FML for puncture resistance placed under pressure over a subgrade configuration that: "The HDPE reaches its yield point rapidly and ruptures over a sharp protrusion, whereas the PVC continues to elongate and form over a protrusion. " In a similar study commissioned by the EPA, 30 mil PVC was compared to 100 mil HDPE. The results were the same. Even with the gauge differential, the 30 mil PVC material did not puncture, whereas the 100 mil HDPE failed at cone heights of 1 inch. The manufacturers of HDPE do recommend that 60 mil HDPE liners be used to help in bonding the seams due to difficulty in bonding this crystalline material and the stress cracks that occur at the seams. This may have carried over into all FML. The physical properties of PVC along with test results such as those above are the basis for our recommendation for OxyFlex PVC FMLs under 50 mils. The gauge recommendation will vary depending upon the specific application. Next, concerning pinholes in PVC film. I would like to know what study was done to provide this information. The chance of pinholes in OxyFlex PVC FML of 20 to 60 mil is nonexistent. Our technology allows us to produce millions of pounds of PVC films yearly in the thickness down to 3 mils for other applications, where the need for a pinhole free film is critical. Many of our PVC films are used in inflatable applications, swimming pools and other medical applications which require film integrity to perform, at much lower gauges than used in FMLs. To suggest that PVC FMLs have a pinhole problem is total unfounded and not true. Seam strength is certainly a major consideration in choosing a FML liner. PVC liners, because of their flexibility, can be factory seamed into much larger panels than more rigid polymers. This reduces the number of field seams by 80% compared to a HDPE liner. Because the factory seams can be made under a controlled environment, the factory seams have higher bond strength. Additionally the field seams, using a solvent or adhesive, are very simple to accomplish and conduct QA testing. OxyFlex PVC is formulated specifically to allow the material to obtain a seam bond stronger than the virgin material. HDPE on the other hand, requires sophisticated equipment to seam. Even then the grinding process used and the stresses induced into the liner at the seam points has lead to numerous failures due to stress cracks of the HDPE. Also checking the seam integrity is difficult and time consuming. A memorandum issued by the EPA states the following: " As a result of documented failures of liner seams to contain waste at some surface impoundments, EPA is evaluating the potential for stress cracking of high/medium density polyethylene (HDPE) liner materials." The report continues: "Two HDPE properties may also weaken the long-term stress-crack resistance of the polymer significantly. First, as an HDPE liner ages, the amount of crystallinity increases, and the number of tie molecules decreases. And second, elevated temperatures promote oxidation of stabilizers added to the HDPE to retard the liner's breakdown. HDPE liners are seamed using heat to fuse together adjacent sheet along the edges where they overlap. Material next to the seams may be made more brittle and weaker due to the very high temperature required for fusion. " The report goes on to offer practices to reduce the chance of this occurrence and how to look for and report stress crack failures. PVC, since it is not a crystalline polymer is not subject to stress cracking failures. Lastly, the concept of chemical compatibility. I have already touched upon this in my discussion on loss of plasticizer. I would like to elaborate on this slightly. The OxyFlex PVC passes the typical landfill leachate with flying colors in the EPA 9090 testing. In this test the FML in immersed in the leachate for ultimate contact. In reality the FML is covered by a protective soil cover of 1 foot or more. This forms a barrier and protects to liner from intimate exposure to the leachate, further improving its performance. In laboratory testing, OxyFlex PVC has been exposed to pH's ranging from 2 to 12. The material was tested for three months at temperatures of 73°F, 100°F and 158°F. Physical testing of the material showed no significant change in any physical property. The OxyFlex PVC met the requirements for NSF Standard 54 for PVC Flexible Liner after the exposure period. I would agree that for an application where the PVC FML is exposed to concentrated organic solvents which would attack the polymer, we would not recommend it. However, for landfill liners and caps, waste water treatment plants and related applications, this is not the case and OxyChem guarantees it! In summary, I would like to quote from a article by Buranek and Pacey presented to the Geosynthetic '87 Conference on geomembranes: "The choice of liner system materials continues to be very limited. HDPE and LLDPE have excellent durability, chemical/biological resistance, and weldability; however, their mechanical properties leave much to be desired. Specifically; the are too stiff and therefore very difficult to handle in the field; their sensitivity to notches and scratches limits the design strains to 5-8% in spite of their ability to elongate 500-700% in the un-notched state; and they have relatively high coefficients of thermal expansion/contraction and consequently are very difficult to place in varying temperature conditions (it is common for exposed HDPE/LLDPE geomembrane to be taut and perfectly wrinkle-free after a cool night and completely "cross-hatched" with large wrinkles by that afternoon). Some manufacturers are working to develop new products which will combine the durability, chemical/biological resistance and weldability of HDPE/LLDPE with the excellent mechanical properties of other materials, say PVC. " HDPE suffers from being a crystalline material susceptible to stress cracking. It can be a time bomb waiting to go off in a landfill. When you consider that the thermal expansion of HDPE is three times that of PVC, it is not a logical choice in a environment such as Michigan which can have large temperature swings. And when it does stretch, it cannot rebound, but becomes very thin at points where it does yield, unlike PVC. Our stand is that there is no FML presently that meet all the requirements. We continue development to find one. But lets examine the benefits of OxyFlex PVC FML: 1. PVC has superior puncture resistance in actual usage. It conforms to ground settling and irregular subgrades without yielding. 2. PVC has a reliable proven history of performance in gauges down to 20 mil since the 1950s. 3. PVC has the ability to produce a strong reliable seam consistently. 4. PVC provides excellent chemical resistance in landfill and waste water treatment applications. 5. PVC offers UV protection which assures that the polymer does not lose its original physical properties while it is being installed. 6. PVC has the flexibility for efficient installation in the field. 7. PVC allows for large factory seamed panels, which reduces the number of field seams by 80% I certainly appreciate this opportunity to explain OxyChem's position on PVC flexible membrane liners. I look forward to further discussions on this subject in person on some future date at your convenience. David C. Lauwers Manager, Product Development Occidental Chemical Corporation Vinyls Division For more information call 800-OK-LINER today!

Article from PLASTICS ENGINEERING January ’87 pp. 29-32 Calendering is still king for high-volume PVC sheet Though calenders are expensive, calendering remains the Preferred method of producing large amounts of polyvinyl chloride sheet at high rate. Few new calenders are expected to be built in coming years, and most calenders now in use are relatively old. But they are continually being upgraded with new technology. Stephen J. GustAmerican Hoechst CorporationOttowa, Illinois  The calendering process came into being in the 19th century with E.M. Chaffee’s patent for a multiple-roll device to make rubber sheet. Of course, the process, still used to manufacture golf ball windings and elastic bands for clothing had to be tried on thermoplastics. PVC sheet was first successfully calendered in Germany in the 1930s. By the end of that decade, calendering was being used there for both rigid and plasticized compounds (the tough differentiation between the two types is that plasticized compounds contain at least 20-percent plasticizer). German Processors greatly expanded their production of rigid PVC sheet during the 1940s and 1956s, while U.S. companies of that era concentrated on plasticized PVC, moving slowly into calendering rigid PVC. Today, calendering is practiced worldwide. with rigid PVC production approaching a billion pounds annually. Roughly 95 percent of all calendered production is PVC. But over the last 15 years, the total number of PVC calenders in operation in the United States has remained nearly constant. Only about 25 of the 150 PVC calenders now operating are used for rigid production. A few of the 150 are new, but many are the same ones that have been operating for all of the 15 years. Despite the age of current calender lines, major productivity increases and product quality changes have been made, for calendering technology has been forced by competition both at home and abroad to strive for better rates and quality.   Figure 1.) Calenders, originally designed for use in the rubber industry, were adapted for use with thermoplastics such as PVC. "Globs" of fluxed resin are squeezed into thin, flat sheets at very high rates.   Why use a calender? A calender forms molten Plastic into a homogeneous flat sheet. During the process, usually one and sometimes both surfaces are given a textured finish. Just to make the sheet flat and bring it down to the proper thickness, calenders have four or more rolls, each over two feet in diameter and over four feet in length (Fig.1). With a calender's massive size and weight comes a massive investment, which may lead manufacturers to consider any of a number of alternative processing meehods, Indeed, why use a calender at all if other methods are available? Calendered sheet is usually made between 2 and 50 thousandths of an inch thick. Sheet may also be produced on an extruder followed by a polishing roll stack, or on a calenderette, which, like a polishing roll stack, has two or three methods (see the Table) indicates that calendering is the only option where high rates are required and less-than-perfect clarity is permissible.  Table. Comparison of sheet manufacturing methods.                 Manufacturing method   Parameter Calender Calenderette Extruder         Cost per method, millions 4 1 to 3 1 of dollars       Rate, pounds per hour 500 to 8000 500 to 1500 500 to 1000 Thickness control, percent +/- 5 +/- 4 +/- 10 Problems High cost Low rate; lack Low rate; material     of versatility degradation Benefits High rate; Good accuracy; Low cost; good   versatility low cost optical quality;       thin and heavy       gauge capability The calendering process At the beginning of the calendering process, the major raw materials in a formula are automatically weighed and added to a blender. Smaller amounts of materials, usually pigments and stabilizers, are masterbatched (combined with some of the larger additives for greater accuracy) ahead of time so they too can be automatically weighed and added. Next, the blend is fed to a fluxing machine, a kneader for example, which "melts" it and drops it onto a holding mill from which a continuous strip is cut off to feed the calender's first bank. The bank is continuously formed into a rough sheet by the first nip (roll clearance). At the second nip, another lesser bank is formed and the sheet is thinned and widened. The sheet is taken off the last calender roll by a series of small stripper rolls and guided through a set of embossing rolls, and then over and under a series of cooling rolls, before finally being wound on a tube or cut into sheets for shipment. As simple as the sequence of operations may seem, each phase is complex and has evolved to its present state over many years. (See Fig. 2 for the entire process.)  Figure 2.) Most current calenders have been in use for over 15 years. Many that originally batch-processed rubber were adapted to make textured or laminated PVC sheet continuously and automatically from beginning to end. The Formulas Because of the complexity of controlling a calender, most formulas are closely related to and even specifically designed for the type of calender and auxiliary equipment in the calender line. Ingredients are usually kept secret but tvpicallv fall into the following categories: PVC, impact modifiers, stabilizers, process aids, lubricants, and plasticizers. PVC resin for rigid compounds, made either by the suspension (emulsion or colloid) or mass (bulk polymerization) processes, is best in the 1.7-to-2.0 relative-viscosity range. Homopolymer grades are used alone and in combination with 2 to 10 percent acetate copolymer. Impact modifiers, the mini shock absorbers used to improve PVC's poor impact resistance. come from a large selection of ABS, MBS, CPE, or acrylic polvmers chosen on the basis of their impact efficiency, clarity, weatherability, and stress-whitening, as well as their processing characteristics. Stabilizers are needed. When heated, PVC naturally tends to degrade, first by yellowing, then by turning dark brown and losing its physical properties. Stabilizers-added to a formula between 0.1 and 5 percent-retard degradation by tying up hydrochloric acid (HCL) generated by the heat of processing. Many types of stabilizers are used. Metallic salts, mixed metal salts, organotins, and tin mercaptides are the major categories. The amount and type- and therefore the efficiency- of a stabilizer chosen for use in a particular calender line must be tempered by FDA and EPA requirements on the use of heavy metals. At the same time, processability must be balanced against cost. Even reactive problems with the stabilizer in processing or calendering must be accounted for. In spite of the fact that PVC is one of the least stable polymers, it enjoys one of the highest production volumes of any thermoplastic because of effective stabilization and the use of flow modifiers. Process aids assist stabilization and increase the melt strength of the sheet during calendering and post processes such as thermoforming. Added to PVC formulas in small amounts, process aids help fluxing and reduce process temperatures, thereby decreasing the amount of expensive stabilizer needed. Acrylic process aids are used most because of their strength and versatility. Figure 3.) In four- and five-roll designs, both top and bottom feed, the most  popular for PVC is the four-roll inverted L.   Lubricants are added to reduce the tendency of PVC to stick to the hot metal of mill and calender rolls. Lubricants also save on stabilizer use because they reduce frictional heat buildup between particles during fluxing and between molecules during calendering. Lubricants are classified as either external or internal, depending on where they are most effective. Stearic acid, organic and inorganic stearates, and soaps of many kinds are mostly classified as internal lubricants. Paraffin and polyethylene waxes are almost entirely external, but montan waxes combine both internal and external properties. As little as 0. 1 to 0.5 percent lubricant is normal. Thicker sheet requires less lubrication because it generates less frictional heat on the calender. Plasticizers make PVC more flexible but therebv lower melt viscosity, moduli, and transition temperatures. When plasticizers are used in amounts less than 5 percent. they are generally considered lubricants. If they are used in quantities greater than 20 percent, the formula is classified as flexible, that is, plasticized PVC. In either case, the effect on calenderability is nearly the same as lubricants. Two common plasticizer groups are phthalates such as diocryl phthalate and epoxides such as epoxidized soybean oil.  Blending Blending the raw materials is one of the most underrated aspects of calendering technology. The reason, perhaps, is at U.S. manufacturers first concentrated on flexible compounds rather than rigid ones. Blending flexible compounds is done differently, usually in large batch blenders, first heated and then cooled for better absorption and storage of masterbatched plasticizer and pigment. So, when U.S. manufacturers finally under took compounding of rigid PVC formulas, there was a tendency not to spend capital dollars on the high-intensity mixers used extensively in Europe. Because of their high speed, not only do they blend thoroughly and quickly but fuse ingredients in place preventing separation. U.S. compounders had been relying on ribbon blenders, which are much less efficient. Banburys, from the Farrel Corp, were used to flux batch by batch and essential mixing was accomplished in the fluxing step. But with the newer continuous fluxing machines, little effective mixing is done after a compound leaves a blender.  Processing Fluxing Ingredients leave a blender as a free flowing powder at room temperature, sometimes with regrind blended in. Fed to batch or continuous machines, the blends are formed into homogeneous melt streams under high pressure and temperatures around 150° C.  Heating and delivery The output from a fluxing machine is seldom totally adequate as a direct feed to a calendar. Either a two-roll mill or an extruder is used to form strands, chunks, ribbons or other acceptable forms. A mill or an extruder, in series with the fluxing machine, does double duty in partially degassing the melt and serving as a reservoir to help prevent running calender rolls together-an expensive error in both repair and downtime if stock momentarily runs out. At this stage of the process, melt is maintained and delivered to the calender at around 140° to 160° C.  Calender Rolls The most common calender roll configurations, shown in Fig. 3, all squeeze a plastic melt into a flat sheet. The inverted L is a favorite for PVC. In calendering, PVC tends follow the hotter and faster roll. The progression is, therefore, to have each roll hotter and faster than the previous one in the stack. Heated either by steam or hot oil, roll temperatures range from 150° C to 200° C. Fluxed material delivered to the first calender nip is regulated to form a 6 inch-diameter rolling bank. The sheet passing the first nip forms another bank about 2 inches in diameter between the second and third rolls and so on until, at the final nip. the desired thickness is obtained from the smallest bank possible to minimize stress in the sheet. Forces created by melt in the nip are sufficient to cause the calendar rolls to deflect affecting sheet profile adversely. And roll-separating forces are a function of roll speed, the type of roll surface, sheet thickness, and a compound's rheology. Making the rolls of forged steel that has twice the elastic modulus of cast iron helps minimize deflection but at a significant cost increase. Even with forged steel, further correction of roll contour is necessary to make flat sheet. There are three available means of adding extra correction: crowning, roll bending, and roll crossing. All can be used at once, if necessary. Normally only the last roll is corrected by crowning: machining a bow of several thousandths of an inch along the length of the roll compensates for some of the bending. Roll deflection from compound to compound may not be constant, and bending the last roll, bowing it in either a positive or negative direction in additional compensation, is accomplished by applying force outboard or inboard of the main bearings (bottom of Fig. 4). Figure 4.) Roll crossing and roll blending are two methods that are used for correcting sheet profile.   Rotating the axis, skewing one roll with respect to another (top of Fig. 4). is called roll crossing. It increases a sheet's edge thickness while keeping the thickness at the center of the sheet constant.  Sheet takeoff and post-processing Stripping. Thickness of sheet coming from the last nip is purposely oversize. This is to make up for as much as a 2/3 gage reduction that occurs when the sheet is stretched-from 30 to 150 percent-as it is stripped from the last calender roll by a series of at least two small rolls. Therefore, the design and operation of these stripping rolls affects shrinkage and flatness of the sheet. Embossing and laminating. To create a leather-like grain or other surface, the sheet coming from the stripper rolls is passed between a textured steel roll nipped by a rubber roll that forces the PVC into the grain. To laminate another sheet or a fabric to the calendared sheet, it may be nipped against the sheet on the last calender roll or a laminating station may be installed in place of the embossing rolls. Cooling. Passing the sheet alternately over and under a series of cooling rolls brings it to room temperature. The sheet is then trimmed to width and wound on a tube or cut to length and stacked as sheets. Edge trim. taken at this stage, is recycled.  Improving the system Because of the extremely high cost of building new calender lines, it is doubtful that there will be a large number of new lines forthcoming without more high-volume products. Immediate efforts will be directed toward increasing quality and consistency coming from present calendars through better blending, improving fluxing and delivery methods, and updating calender and takeoff process controls. The more consistent the input, the more smoothly the process runs and the more consistent and reliable is the output. Closed-loop weighing and blending is now becoming the norm and with improved blending available, present fluxing systems become adequate. But providing a more uniform feed to the calender remains a challenge. Stronger materials and better designs could result in newer calenders with smaller rolls and more precise bearings. In the main, however, existing calenders will be overhauled and provided with better drives and bearings. Closed-loop thickness control is currently practiced but is still being refined as improving sensor technology for feedback control becomes available. On-line defects sensed by lasers, for example, will enable 100 percent inspection as quality requirements will, in general, continue to tighten. With those improvements already in place and others constantly on the way to meet growing competition, calendering will remain the most efficient way to make high-volume PVC products.   For more information call   800-OK-LINER  today!

Flexible Poly (Vinyl Chloride) For Long Outdoor Life JOHN H. OREM and J. KERN SEARS Monsanto Chemical Company St. Louis, Missouri 63166 A review of the compounding requirements for producing flexible PVC with quite satisfactory outdoor life is presented. Testing criteria and the importance of incorporated additives of specific types are reviewed. Data on multi-location outdoor weathering are shown. The prime importance of thickness and additive migration is proposed. Plasticized polyvinyl chloride's ability to withstand outdoor exposures is influenced by many factors. These include the flexibility, the thickness of the fabricated product, the additives which are incorporated into the formulation and the amount of thermal degradation that is initiated during compounding and fabrication. This latter point, while being of less importance, must be remembered. At Monsanto Company, for many years we have been exposing plasticized PVC in Florida, Arizona and more recently Puerto Rico. In this paper, we will give bench marks for the service life under different conditions which may be expected from clear and from pigmented flexible PVC. These formulations will utilize general purpose plasticizers, primarily DOP (di-2-ethyl hexyl phthtalate). Following papers will discuss our intensive evaluations of more varied formulations.   TERMS AND THE STANDARD FORMULATION One sun hour is an accumulated hour during which the sun is shining with an intensity of O.823 Langleys per min ( g cal/cm 2 /min). Much of our testing has been, and continues to be, done in Miami, Florida. In this area there are approximately 110 sun hours per mouth. This is a total of 1200 to 1300 sun hours per year. A Langley is 1 gram calorie/cm 2 /minute. In Miami, Florida, with a 45° due south exposure, the specimens receive approximately 150,000 Langleys per year. One watt is 0.07 gram calories per minute. Failures of exposed specimens are measured or recorded in several different ways including: Time-To-Fifth Spot. Clear films show incipient failure by development of very small random brown spots characteristic of UV degradation. The "first failure" is recorded as the time to the fifth spot on these clippings. The first few spots may appear fortuitous in some cases and unrelated to general failure. Final Failure. Spotting and accompanying embrittlement continue until the film loses integrity and tends to tear from the rack or until it is completely brown. This is the "final failure" time. Brittleness Temperature. The brittleness temperature is measured before exposure and then on the samples as they are received at regular intervals from the exposure site. Measurements are run up to 22° C. The ASTM 1790-62 (Masland Cold Crack) method, with the use of semi-micro specimens, is followed in determining brittleness temperatures. Elongation. Elongation is measured on the samples before exposure. As the samples are received from the testing site, their elongations are again measured. The data for this paper was collected from unsupported film that was exposed direct to the sun facing due south at 45° from the horizontal. Today, Monsanto Company's Plasticizer Research Laboratory utilizes the following as its starting standard formulation for evaluating plasticizer performance under outdoor conditions.  PVC “s” type (IV 1.13) 100.0 Plasticizer 50.0 Epoxy stabilizer 3.0 Barium cadmium liquid stabilizer 2.0 Phosphite stabilizer 0.1 UV absorber 1.0 Stearic acid 0.5 THICKNESS Throughout this discussion, we will be showing the influence of thickness on the weathering of flexible PVC films and sheets. Darby and Graham (1) attribute this to the volatilization and leaching of the stabilizers. Degradation commences on the surface where radiation intensity is the greatest. The thicker sections provide a larger reservoir of stabilizer. Stabilizer readily, and constantly, migrates from the reservoir to the film's surface. Thicker films and sheets having larger reservoirs contain more of the preventative-stabilizer. This results in the longer life. In Fig. 1, the actual results of our Florida aging program show the benefits of thickness. This work was done using DOP as the plasticizer and includes the results of exposed formulations with and without ultraviolet light absorber. The benefits of UV absorbers will be discussed later during our comments on stabilizers. From the actual results that went up to a 20 mil (0.5 mm) thickness, we extrapolated to 60 mil (1.5 mm) thickness; this is shown in Fig. 2.  PLASTICIZERS All plasticizers, and all plasticizer concentrations, do not perform in the same manner. Generally, more volatile plasticizers will yield films with a shorter outdoor life expectancy. Clear films, including a UV absorber, plasticized at 50 phr (parts per hundred resin) were exposed in 4, 10 and 20 mil thicknesses in Florida. In this evaluation, four general purpose plasticizers were studied. Two were highly branched diisodecyl phthalate (DIDP) and diisononyl phthalate (DINP). One was singly branched, DOP. The fourth plasticizer, heptyl-nonyl-undecyl phthalate, was essentially linear. This study revealed the benefit of using the less branched phthalate plasticizers for products to be used outdoors. DIDP and DINP, the two highly branched plasticizers, plasticized 4 mil films were entirely brown after 24 mo exposure. The 10 and 20 mil specimens using DIDP browned at 30 months. Heptyl-nonvl-undecvl phthalate and DOP, however, had not shown any browning after 36 months. A limited outdoor Feathering study in Florida by Darby and Graham (2) showed 35 phr plasticizer to be the most beneficial for long-term durability. This was based on work using two plasticizer systems without UV absorber. One was DOP and the other plasticizer system was 90 percent DOP and 10 percent 2-ethyl hexyl diphenyl phosphate. Also seen in this particular study was the synergistic influence of the phosphate plasticizer in thin films of 4 mil thickness. Looking first at DOP, and using elongation as the measure for outdoor life, we find these 4 mil films plasticized at 20 phr had a life of 13 months. The 35 phr plasticizer level survived for 23 months. At a 50 phr plasticizer concentration, the outdoor life fell to 15 months, and at 70 phr it was only 11 months. Now, we see the influence of the phosphate synergism on plasticizer level and the outdoors. At the lower two concentrate where films are relatively stiff, the service life increase from the addition of this phosphate plasticizer is 9 to 15 percent. Of considerable interest, the soft and flexible films, those with 50 and 70 phr of plasticizer, have a dramatic increase in life expectancy. The small addition of phosphate plasticizer yields a 50 percent increase in outdoor serviceability. Later work from the same laboratory shows the response of films containing a UV absorbers and plasticized at 50 phr, to outdoor aging when the plasticizer system is varied from all DOP to all 2-ethyl hexyl diphenyl phosphate. We see this benefit of the phosphate synergism in 20 mil thicknesses as well as in the thin 4 mil films. The optimum level of phosphate plasticizer is 10 to 15 percent of the total plasticizer system.  STABILIZERS When formulating flexible PVC films and sheets for outdoor use, the complete stabilizer system must be considered. Darby and Graham (2) showed the influence of epoxidized soybean oil, several metal salts of organic acids, a phosphate ester and an ultraviolet absorber, 2-hydroxy-4-methoxy benzophenone, on weathering. For background, we will briefly review this work. The influence of stabilizers on outdoor durability of flexible PVC was measured using epoxy cadmium stabilizers individually and in synergistic mixtures with 2-hydroxy-4-methoxy benzophenone. "Epoxy-cadmium" indicated a synergistic mixture of an epoxy compound, a barium cadmium salt of an organic acid and a phosphate ester. When only the epoxy compound and barium cadmium salt were used, decomposition occurred quite early. This was seen by discoloration, serious tack formation and the loss of elongation. The addition of an ultraviolet light stabilizer, such as 2-hydroxy-4-methoxy benzophenone, had essentially no benefit in this stabilizer system. However, triphenyl phosphite by itself yielded a longer life than either of the above stabilizers. When 2-hydroxy-4-methoxy benzophenone was added to the triphenyl phosphate, there was a large improvement in the weathering life of the film. Although the epoxy and barium cadmium constituents were not necessarily needed to achieve good outdoor durability, they are definitely required to insure adequate heat stability during the processing of the flexible polyvinyl chloride. Our data were obtained with formulations using conservative stabilizer levels.  PIGMENTS AND COLORANTS Outdoor life expectancy of flexible PVC may be aided through pigmentation. H. C. Jones (3) found increasing increments of anatase and rutile titanium dioxide definitely improved reflectance characteristics of plasticized PVC. His accelerated weathering studies revealed rutile titanium dioxide to be decidedly superior to the anatase as a light stabilizing agent. In his work, Mr. Jones was interested not only in whether the pigments absorbed in the UV range, but also what happens to the absorbed energy. He found, "When an untreated rutile absorbs UV the absorbed energy goes into a photochemical reaction that liberates active oxygen. For this reason, rutile for use in plastics is given a surface treatment which inhibits this photochemical reaction and causes the absorbed UV energy to be dissipated as heat. DeCoste and Hansen (4) showed colored pigments strongly assisting in the maintenance of mechanical properties by protecting the plasticized polyvinyl chloride compositions from degradation. Combinations of pigments are beneficial to long-term outdoor aging because they can shield in the visible and the ultraviolet range - the use of rutile titanium dioxide with a selected colored pigment was quite good. Many exposures have revealed the benefits of titanium dioxide in films of three thicknesses: 4 mils (0.1mm), 10 mils (0.25mm), 20 mils (0.5mm). Without titanium dioxide and without an ultraviolet absorber all failed in 22 months. However, with titanium dioxide the 4 mil film had a life of 32 months, and the 10 mil film's life was 47 months. More pronounced, was the effect on the 20 mil flexible sheet; with titanium dioxide, it survived 76 months, more than 6 years, in Florida. Similar outdoor studies were made with blue and black films. Both colorants, phthalocyanine blue at 0.9 phr and channel black at 1 phr, definitely extend the weathering life of flexible PVC films and sheets. The 20 mil blue film survived 80 months, over six and a half years, before failing the room temperature brittleness test.  Table 1. Weather-Ometer Exposures of Flexible PVCa Containing Titanium Dioxides Exposure, days Anstaso   Ruttie     Rb bb R b             1 P.H.R.   1 P.R.R.   0 73.4 2.4 78 2.5 10 71.7 0.8 78.1 2.2 20 65 7.3 75.3 4.9 30 36.5 20.3 73.8 6.7 40 24.1 15.2 79 7.9 50 20,1 11.8 69.11 9.9 60 19.1 10.2 67.6 10             3 P.H.R.   3 P.H.R.   0 86.8 2.7 89,4 3.5 10 82 1.5 88.1 4 20 78.8 4.6 64.4 7.4 30 70 11.3 82.4 9.1 40 44.7 19.5 80.8 10.5 50 40.8 16.2 79.4 11.8 60 38.8 14 79.9 11.9             5 P.H.R.   5 P.H.R.   0 89.5 2.6 91.4 3.4 10 83.9 1.7 90 4.7 20 80.9 4.6 86.2 7.8 30 72.5 9.8 84.1 9.7 40 49.8 17.4 81.9 11.2 50 46.6 13.9 80.8 12.5 60 45.2 12.6 81.2 12.7 a Formula (parts by weight): PVC resin (Geon 101), 100:plasticizer (DOP), 50:stabilizer (Mark M), 3:lubricant (stearic Acid), 0.5 titanium dioxide, as indicated. B Hunter color measurements (reflectance and “b” value) made over standard black background. As has been stated many times, the use of black pigments is encouraged to achieve the ultimate in outdoor life with flexible PVC products. Twenty mil sheets withstood 5 years of Florida exposure before reaching the 0° C brittleness temperature. Extrapolating this, we would expect a 60 mil, black pigmented, flexible PVC sheet to withstand more than ten years outdoor exposure in most environments.   CONCLUSION Flexible PVC can be produced that will provide quite satisfactory outdoor life. In formulating, one should attempt to use a plasticizer concentration in the range of 35 parts per hundred parts of PVC. Consider using a good phosphate ester as 10 percent of the plasticizer system to take advantage of the synergistic effect, particularly where plasticizer levels above 35 phr have to be used. Wherever possible, use some pigmentation; black formulations will give the longest outdoor life. Blues significantly extend life. The incorporation of treated rutile titanium dioxide is very beneficial. Ultra-violet light absorbers must be included in clear films. In addition to the epoxy and barium cadmium containing stabilizers, include a phosphate ester in the stabilize system. The thicker the film, the longer will be its expected outdoor life. Throughout this work we have reported the weathering life and extrapolated life expectancy using brittleness temperature along with other methods of measurement. Cold Crack measuring is very sensitive to surface deterioration and, therefore, quite sensitive to weathering. To conserve exposed samples, we use semi-micro specimens (32mm x 4mm) for determining the Masland Cold Crack temperature.  REFERENCES 1. Joseph R. Darby and Paul R. Graham, "Outdoor Durability of Plasticized Polyvinyl Chloride," Modem Plast., January 1962. 2. Ibid., Darby and Graham 3. H. C. Jones, "Improving Weatherability of Plastics With White Pigments. Modern Plas., January 1972. 4. J. B. DeCoste, and R. H. Hansen, "Colored Poly(Vinyl Chloride) Plastics for Outdoor Applications." SPE J., 18,431 (1962.)   For more information call   800-OK-LINER   today!

William R. Morrison & J. Jay Swihart Bureau of Reclamation, Denver, Colorado 80225. USA ABSTRACT The Bureau of Reclamation has been using polyvinyl chloride (PVC) plastic in its buried membrane canal lining work for over 20 years. Results of tests conducted on samples of inservice linings indicate that the factory-fabricated seams retain excellent shear and peel strength properties with no apparent signs of deterioration. The practice of using a 1 - m overlap unbonded PVC field seam has proven adequate for most irrigation canal lining applications, but would not be suitable for applications requiring 100% seepage control. Results of laboratory investigations conducted in conjunction with a study on the underwater lining of operating canals with PVC indicate that an adhesive formulated for the repair of vinyl swimming pool liners can be used to make underwater PVC field seams. Results of these investigations also indicate that field seams made in the dry can achieve enough early peel and shear strength development (within 15 min) for placement underwater.  INTRODUCTION Reclamation has used PVC linings for seepage control in irrigation canals for over 20 years. The earliest PVC plastic lining installation was a small experimental section installed in 1957, on the Shoshone Project in Wyoming.1 The first PVC installation under construction specifications (604C-72) was on the Helena Valley Canal, Montana, in 1968. The plastic lining was an alternative to the hot, spray-applied asphalt membrane material.2 (Because the energy crisis in the 1970s caused a significant increase in the cost of petroleum products, coupled with a limited source of supply, the asphalt membrane material was deleted from our specifications.) Over the years, Reclamation has obtained samples of PVC from various installations to determine the aging characteristics of these materials.3 Results of tests conducted on PVC scams from two installations are discussed in this paper. Laboratory tests were also conducted on PVC seams as part of the research program to develop methods and materials for the underwater lining of operating canals. Reclamation has a number of leaky, unlined irrigation canals that cannot be easily dewatered for lining because of water delivery commitments. Underwater installation of a PVC lining protected with a concrete cover is currently being evaluated. In addition, PVC seams were evaluated among other seams under a laboratory study Reclamation conducted for the Environmental Protection Agency (EPA) entitled 'Evaluation of Flexible Membrane Liner Seams after Chemical Exposure and Simulated Weathering'.4 The results for the PVC seams are presented in this paper.  FIELD PERFORMANCE OF PVC PLASTIC CANAL LINERS PVC plastic linings were originally used in the rehabilitation of old, unlined canals, especially in areas unsuitable for compacted earth or concrete linings.5 Plastic linings finding wider use in new construction.6.7 The work involves four basic steps: excavation, subgrade preparation, installation of the plastic membrane, and placement of the earth cover (0.3 - 0.5 m in depth) to protect the membrane from the elements and physical damage. Because of the requirement of an earth cover, membrane linings are restricted to canals having low-velocity flows (0.3 -1 m/s). Also the side slopes should be no steeper than 2.5(H): 1(V) and preferably 3(H): 1(V) to minimize cover stability problems. PVC is manufactured in roll goods approximately 2 m wide. The roll goods are factory fabricated into sheets wide enough to cover the canal prism and up to several hundred meters in length depending upon its thickness. For most canal lining work, sheets of PVC lining can be joined simply by lapping the downstream end of one sheet of 0.9 m over the upstream end of the adjacent sheet. The PVC plastic has a tendency to adhere to itself and, with the weight of the earth cover, a sufficiently bonded joint is obtained where 100% seepage control is not required. The watertightness of the unbonded field seam is discussed in more detail in the next section. Where a more positive seal is required, the PVC is overlapped a minimum of 0.3 m and a solvent cement (recommended by the manufacturer) applied to a minimum width of 50 mm. A continuous study is being conducted by Reclamation to evaluate the performance of buried PVC membrane canal linings. Results from two installations-Bugg Lateral, Tucumcari Project, New Mexico, and the Helena Valley Canal, Helena Valley Unit, Montana- are presented. Bugg Lateral In the spring of 1961, a small test of 0.25 mm PVC was installed on the Bugg Lateral, Tucumcari Project, New Mexico. The test section was about 228 m in length, and it is the oldest Reclamation installation for which performance data are available for this material. The hydraulic properties of the canal are summarized in Table 1 . TABLE 1           Hydraulic Properties of Plastic-Lined Canals     Protective Flow Velocity Bottom width Normal water depth Cover Canal depth (m3/s)   (m/s)   (m)   (m)   (m)   Helena Valley -26   0.64   2.7   28-Jan   0.3   Bugg Lateral 2.66   0.57   4-Feb   4-Jan   0.4               Note: Ratio of side slopes in both canals is 2 (horizontal) to 1 (vertical).   Samples were obtained in 1965 (4 years of service), 1970 (9 years of service), 1975 ( 14 years of service). 1980 (19 years of service), and 1988 (after 27 years of service). A photograph taken during the 1980 field sampling is shown in Fig. 1. Results of the sampling indicated the lining was intact below water level, but had suffered some damage from root penetration above the waterline.   TABLE 2           Results of Laboratory Tests Conducted on PVC Seam Samples from Bugg Lateral.   Tucumcari Project, New Mexico           Typical       Physical Specification original 4 Years 9 Years 27 Years property requirements results of service of service of service Thickness 0.25 0.26 0.26 0.25 0.25 (mm) 10%         Tensile 3 4 4.1 4 5.5 Strength           (kN/m)           Bonded seam 1.95 4 4 3.8 5.8 Strength in           shear (kN/m)           Bonded seam Not NDa ND ND 3.5 Strength in peel Required         (kN/m)           aNot determined. Helena Valley Canal In the fall and winter of 1968-69, a reach of the Helena Valley Canal, 1930 m in length, was lined with 0.25-mm thick PVC plastic. This was the first PVC lining installation under a Reclamation construction specification (604C-72). The PVC was furnished in sheets 12.8 m wide by 122 m in length. The sheets were accordion folded in both directions for delivery to the job site. Samples of the lining containing a factory seam were obtained after 9 and 14 years of service. Results of laboratory tests conducted on the factory seam are summarized in Table 3. Test results indicate that as with the Bugg Lateral lining, the factory seams retained their integrity after 14 years of service. LABORATORY TESTS FOR UNDERWATER LINING OF OPERATING CANALS Reclamation has been conducting research to develop new technologies for lining canals while they are in operation. The basic concept consists of placing a PVC geomembrane covered with gravel, soil or concrete while the canal remains in operation. The canal would be lined in two or more passes necessitating an underwater field seam in the PVC geomembrane down the centerline of the canal. A 1-m overlapped unbonded seam was planned for this location. As previously mentioned, Reclamation routinely, uses this type of seam (in the transverse direction only) for its PVC-lined canals. Leakage through the unbonded seam was expected to be relatively small since PVC tends to bond slightly to itself under pressure. Seepage measurements obtained for some of these canals, although limited, has supported this expectation. For underwater lining, a study was undertaken to quantify the seepage for this type of seam and to examine the effects of hydraulic head, cover depth and cover material. Additional important information was obtained, quite accidentally, concerning the effect of an irregular subgrade. These results led to a second phase of the study where a new adhesive for bonding PVC under water was examined. Conventional solvents for field seaming in the dry were also examined. TABLE 3         Results of Laboratory Tests Conducted on PVC Seam Samples from Helena Valley Canal. Helena Valley Unit, Montana                 Specification     Physical requirement Typical 9 years 15 years property results original of service of service Thickness (mm) 0.25 0.27 0.25 0.25   10%       Tensile strength 3 5.8 5 5.7 (kN/m)                   Bonded seam 2.2 5 4.6 5.1 strength in shear       (kN/m)                   Bonded seam Not NDa ND 3.7 strength in peel required       (kN/m)         a Not determined.         Phase 1-Unbonded field Seams The test apparatus for determining seepage through the overlapped seam measures (width by length by height) 1.2 m by 2.4 m by 0.6 m and is shown in Fig. 2. The gravel drain collects the seepage while the geotextile provides a smooth subgrade for the PVC liner. A more representative subgrade material (i.e. something less permeable than gravel) would obviously reduce seepage; however, an investigation into various subgrade materials was beyond the scope of this study. Three cover conditions were examined including 25 mm of sand (No. 50 in size), 25 mm of sand plus 50 mm of concrete blocks (200 mm by 600 mm), and 25 mm of sand plus 150 mm of concrete blocks. The voids (approximately 10 mm wide) between the concrete blocks were filled with sand. With the aid of a stand-pipe, tests were run at hydraulic heads of 0.3, 0.9, 1.5 and 2.1 m. Each test was run for a minimum of 24 h to allow stabilization of hydraulic gradients within the gravel drainage layer. Some tests were run for up to 2 weeks to evaluate observed decreases in seepage with time. The results are summarized in Table 4. Test sets A and B are duplicates with 25-mm sand/50-mm concrete cover and demonstrate the variations seen for identical test conditions. These test sets were meant to approximate the 75 mm of concrete cover. The seepage at 2.1 m of head represents 15-30 liters per day per linear meter of seam and was considered acceptable. A gradual decrease in seepage was seen with time, caused either by fines moving through the overlapped seam and plugging the geotextile and/or gravel drain, or by settlement and compaction of the sand between the concrete blocks. TABLE 4         See page through Overlapped Unbonded Seam in PVC Geomembrane Test Set Cover Hydraulic head Seepage         (m) (liters m d)   A 25 mm of sand plus 0.3 0     50 mm concrete 0.9 0       1.5 2 2.1 15         B 24 mm of sand plus 0.3 1     50 mm concrete 0.9 5       1.5 -       2.1 30   C 25 mm of sand plus 0.3 1     150 mm concrete 0.9 4       1.5 5       2.1 15   D 25 mm of sand 0.3 15       0.9 60       1.5 80   E 25 mm of sand plus 0.3 60     50 mm concrete 0.9 400     (wrinkle in geotextile) 1.5 - Test set C used 150 mm of concrete blocks rather than the 50 mm used in test sets A and B. No measurable differences in seepage were detected. Test set D had only the 1.5 mm of sand cover (no concrete blocks) and demonstrated 20 times more seepage than test sets A and B which had 25 mm of sand and 50 mm of concrete cover. This increase in seepage has two causes. The first is the difference in cover load 25 mm versus 75 mm, and the second is the difference in seepage paths. The sand/concrete combination has not only longer but also fewer seepage paths, as the seepage can only occur through the sand between the concrete blocks. Test set E again had 25 mm of sand plus 50 mm of concrete cover: however, a defect was inadvertently introduced into the subgrade by a fold (wrinkle) in the geotextile. This defect increased seepage by a factor of about 100. As subgrade defects will be impossible to avoid entirely in the field, methods for bonding the seams underwater are needed to assure maximum water conservation. TABLE 5       PVC Seam Strength Using Special Vinyl Liner Adhesive   Peel Strength Shear Strength Cure condition (kN/m) (kN/m)   Air 2.6 10   Underwater 3 12.2   Requirementa 1.8 9.8   a Specification requirements for factory seams   Phase II-Bonded field seams Phase II of the study examined solvents adhesives for field seaming of PVC geomembranes both underwater and in the dry. The biggest challenge was finding a solvent which could be used underwater, as there has been very little experience in this area. Discussions with manufacturers led to the selection of a specially modified bodied tetrahydrofuran solvent used to repair vinyl swimming pool liners. Test results for PVC seams made both underwater and in air with the special vinyl adhesive are summarized in Table 5. Tests were conducted to determine peel and shear strength after a 24-h cure. Test results indicate that the seams are quite satisfactory and even meet the requirements for factory seams using conventional solvents in the dry. There was also concern about the rate of seam strength development for the transverse field seams that would be needed every 60 m. These seams would be fabricated in the dry with conventional solvents but then very quickly (perhaps within 15 min) subjected to shear stress as they were placed underwater in the canal prism. Seam specimens were fabricated in air with a manufacturer-supplied solvent cement and tested for shear and peel strength after cure times ranging from 5 min up to 4 h. The shear strength developed very quickly (within 5 min) and then decreased with time until reaching equilibrium after 1-2 h. Conversely, the peel strength developed rather slowly and required-30- 60 min to develop fully. Shear strength is the more critical as shear is the predominant stress on the seams during installation and service. Tests were also performed to ensure that specimens, made with conventional solvent and initially cured in air, would continue to cure underwater. Seam specimens were partially cured in air for 5 min and then cured in water for 3 days. These specimens did indeed develop full shear and peel strengths. RESULTS OF EPA STUDY In 1986, Reclamation completed a study for EPA entitled 'Evaluation of Flexible Membrane Liner Seams After Chemical Exposure and Simulated Weathering'. In this study, 37 geomembrane seams, both factory and field were evaluated. The PVC seams included in the study are listed in Table 6. The seams were subjected to six chemical solutions, brine and water immersion, freeze/thaw cycling, wet/dry cycling, heat aging, and accelerated outdoor aging for periods of up to 1 year. Effects of these environmental conditions were evaluated using shear and peel strength tests before and after exposure. The tests were performed under dynamic load at room temperature and under static dead load at 50° C. The rate of grip separation for both the peel and shear tests was kept the same (50 mm/min) to determine if there was any direct correlation between the two properties. Also, a 25-mm wide test specimen was used in both tests. Results of tests conducted on seams subjected to water immersion, freeze/thaw cycling, wet/dry cycling, and heat aging are summarized in Table 7. These environmental conditions are those often encountered in Reclamation's hydraulic applications. TABLE 6           Type of PVC Seams Evaluated in EPA Study     Sample Type of Manufacturer Seaming Seam   No Seam Fabricator Method Width   1 Factory A,C Solvent adhesive 25   2 Factory A,D Thermal-dielectric 19   3 Field Aa Solvent adhesive 50   4 Filed Ab Solvent adhesive 88   5 Filed Bc Solvent adhesive 75 a Solvent adhesive furnished by fabricator C.   b Solvent adhesive furnished by fabricator D.   c Solvent adhesive furnished by manufacturer B.   Test results indicated that except for heat aging, the samples performed satisfactorily with very little change occurring to either the shear or peel strength. The heat aging samples exhibited stiffening due to plasticizer loss from the material. Of the two factory seaming methods used for the PVC, the seams made with the solvent adhesive exhibited higher shear strength, whereas those made dielectrically produced higher peel strength values. The higher shear strength was primarily due to the wider factory seam for the solvent adhesive seam. All failures occurred in the parent material, except for the peel tests on the PVC solvent adhesive seam, where the failure occurred within the seam itself. No appreciable difference was noted in the performance of the two seaming methods however. TABLE 7                       Results of EPA Study on PVC Seams                     Sample 1   Sample 2   Sample 3   Sample 4   Sample 5     Test Condition Shear Peel Shear Peel Shear Peel Shear Peel Shear Peel Original   10 2.6 9.3 6.7 8.3 2.7 9.3 3.4 10.4 4.3 Water immersion at 23°C 6 months 9.9 2.8 9.1 6.6 8.5 3.1 10.5 3.8 10.6 4.3   12 months 10 2.9 9.3 7.3 9 2.7 10.7 3.9 11.7 4.4 Heat aging at 60°C 4 weeks 9.2 3.1 9.3 6.5 8.8 3.8 10.4 4.2 10 4     8 weeks 9.1 3.1 9.2 6.9 9.4 3.2 9.3 4.3 11.3 5.1   13 weeks 10 3.3 9.5 6.9 9.1 4.1 10 4.4 11.4 3.9 Freeze/thaw at: 10 cycles 10.1 2.7 8.9 6.7 8.4 2.4 9.6 4 10.5 4.4   20 cycles 9.7 2.8 9.3 7.3 9.3 3 10 4 12.4 4.7   50 cycles 10.1 2.8 8.4 7.2 8.9 2.7 9.1 3.8 10.4 4.7 Wet/dry at: 10 cycles 10.2 2.7 9.4 6.9 8.4 2.6 10.3 3.8 11.2 6   20 cycles 9.9 2.7 8.5 6.5 8.8 3.3 9.5 3.7 10.2 3.2   50 cycles 9.9 2.7 10.1 6.7 8.2 2 10.6 4.3 10.7 4.6 Note: Test values are expressed as kN/m width of seam. One freeze/thaw cycle consisted of freezing for 16 h at 6.7?C and thawing for 8 h in room temperature water. One wet/dry cycle consisted of 16 h water immersion followed by 8 h of drying at 37.7?C. CONCLUSIONS The Bureau of Reclamation has been using PVC in its buried membrane canal lining work for over 20 years. Results of tests conducted on samples of inservice linings indicate that the factory seams retain excellent shear and peel strength properties with no apparent signs of deterioration. A 1-m overlap, unbonded PVC field seam appears to be adequate for most irrigation canal lining applications, but would not be suitable for landfills or hazardous waste installation where 100% seepage control is required. Results of laboratory tests also indicate that the solvent-bonded field seams can achieve early peel and shear strength development which is advantageous for underwater lining applications. Laboratory tests conducted on an adhesive sealant formulated for the repair of vinyl swimming pool liners indicated that it can be used to make underwater PVC field seams. Results of laboratory tests involving various environmental aging conditions indicate that there is no appreciable difference in the performance of solvent or dielectrically made factory seams.  REFERENCES 1. Hickey, M. E. Investigations of plastic films for canal linings. Research Report No. 19. A Water Resources Technical Publication. Bureau of Reclamation, Denver, Colorado, 1969.2. Geier, F. H. & Morrison, W. R. Buried asphalt membrane canal lining, Research Report No. 12. A Water Resources Technical Publication. Bureau of Reclamation, Denver, Colorado, 1968.3. Morrison, W. R. & Starbuck, J. G. Performance of plastic canal linings. Bureau of Reclamation Report No. REC-ERC-84-1. Denver, Colorado, 1984.4. Morrison. W. R. & Parkhill, L. O. Evaluation of flexible membrane liner seams after chemical exposure and simulated weathering, US Environmental Protection Agency. Report No. EPA/600/S2-87/0l5, Cincinnati, Ohio, 1987.5. Wilkinson, R. W. Plastic lining on the Riverton Irrigation Project. Proc. ASCE Irrigation and Drainage Speciailty Conference. Flagstaff, Arizona, 1984.6. Starbuck, J. G. & Morrison, W. R. Flexible membrane for closed basin conveyance channel. San Luis Valley Project, Colorado, Proc. International Conference on Geomembranes. Denver, Colorado, 1984.7. Weimer, N. F. Use of polyvinyl chloride liners for large irrigation canals in Alberta. Canadian Geotechnical Journal. 24 (1987) (2) 252-9.    REC-ERC-84-1 PERFORMANCE OF PLASTIC CANAL LININGS January 1984 Engineering and Research Center U. S. Department of the InteriorBureau of Reclamation   Table18. -Physical properties test results for PVC membrane linings on Bugg Lateral. Tucumcari Project, New Mexico, installed spring 196l.- Continued     Sample Sample Sample   Specifications No. B-6764 No. B-7022 No. B-7023 Physical property requirements (14 years (19 years (I 9 years     of service, of service, of service,     BWL) BWL2 ) AWL1) Thickness, mm (mils) 0.25 (10) 0.24 (9.6) 0.24 (9.6) 0.21 (8.2) percent change ±10 -14.3 -14.3 -26.8           Tensile strength, N/mm (lbf/in) 3.0 (1 7) 4.2 (24.2) L3 4.6 (26.4) L 5.0 (28.6) L     4.6 (26.1) T4 5.2 (29.8) T 4.7 (26.9) T percent change -5.5 L +3.1 L +1 1.7 L     +14.5 T +30.7 T +18.0 T           Elongation percent 225* 268 L 211 L 151 L     274 T 188 T 188 T percent change -35.0 L -48.9 L -63.3 L     -40.7 T -59.3 T -59.3 T           Modulus at 100 percent Not required 2.4 (13.8) L 3.6 (20.5) L 4.6 (26.0) L elongation, N/mm (lbf/in) 2.4 (13.8) T 4.2 (23.9) T 4.2 (23.9) T percent change +21.1 L +79.8 L +128.1 L     +34.0 T +132.0 T +132.0 T           Elmendorf Tear, grams 1500* 3000 L 3000 L 450 L     2865 T 2200 T 1300 T percent change +63.9 L +63.9 L -75.4 L     +25.1 T -3.9 T -43.2 T           Impact resistance Not more than 2 5 tested Not Not   specimens out determined determined   of 10 shall fail 5 failures       at -18ºC (0ºF)               Plasticizer content, percent Not required 34.1 27 21.6 percent change -14.3 -32.2 -45.7           Bonded seam strength, 65 Not Not Not percent of parent material determined determined determined           1 AWL denotes above normal waterline   2 BWL denotes below normal waterline   3 L denotes longitudinal direction     4 T denotes transverse direction     * Minimum, each direction         Canal data: Established     seepage   b = 5.00 ft, d =4.40 ft, s:s =1.5:1, and   rate   WP =20.86 ft. (7.4806 gal/ft3) (2169 ft2)   Length =104.25 ft.     Average seepage rate for section is 8.2 = 0.0005 (ft3/ft2)/d gal/d.   Reach 5A, station 599+00, PVC lined: Seepage section has a wetted surface of (104)(2y0.86) = 2169 ft2. Canal data: For more information call   800-OK-LINER   today!

T he First Pan American Geosynthetics Conference & Exhibition2-5 March 2008, Cancun, Mexico Eliminating costly tests for PVC geomembranes by using new ASTM D 7177 air channel test for field seams. D.S. Rohe, Environmental Protection, Inc. Mancelona, MI, USA ABSTRACT Air channel strength testing of dual track thermal welds of PVC geomembranes has been developed to provide quality assurance for the full length of PVC geomembrane field welds, eliminating the need for cutting holes in the liner to perform destructive peel testing.  The testing method was adopted as ASTM D 7177 Standard Specification in June 2005 and has been published for use since the 2006 construction season.  This paper will present a detailed case history of the installation quality control and engineering quality assurance programs implemented on the 787,800 square foot 40 mil PVC geomembrane lagoon system installed at the Village of Manton Wastewater Treatment Lagoon improvement project in Manton, MI, USA.  The design engineers at Fleis & Vandenbrink Engineers worked with the Michigan Department of Environmental Quality to eliminate the outdated and highly inaccurate water balance test by requiring air channel testing for PVC geomembrane field seams.  The 40 mil PVC geomembrane was installed using dual track thermal welding and all field seams were air channel tested for seam continuity and peel strength.  The success of this project has provided the basis for implementing this new testing technology in lieu of the water balance test, saving the customer precious time and ultimately precious funding. Introduction In Michigan, there have been numerous projects to rehabilitate old existing waste water lagoons.  Many of these lagoons were constructed over thirty years ago and simply used native soils or natural clay as a bottom liner.  At the time, clay was a suitable option for a liner system to minimize infiltration into the soil and potentially the water table.  With the advances in geosynthetic technology over the past few decades, there are now a plethora of better liner systems. Using Government grants and funding through the United States Department of Agriculture (USDA) Rural Development, many communities have been able to rehabilitate their waste water treatment plants to include a new geosynthetic liner system.  In the spring of 2006 the Village of Manton, Michigan began this process. Contractors Fleis & Vandenbrink Engineers from Grand Rapids, Michigan were retained by the Village and given the task of designing the new system and construction oversight for the project.  The project was advertised for public bid proposals.  Team Elmer's was selected as the Prime Contractor to complete the project and selected Environmental Protection, Inc. (EPI) as the PVC geomembrane fabricator and installer.  The project specifications also required an independent third party construction quality assurance firm specifically to inspect the geomembrane liner installation and testing.  STS Consultants, Ltd. was retained for this purpose as the independent third party construction quality assurance (CQA) firm.  Design The existing lagoon system was made up of three large lagoons.  The new design would require two of the existing lagoons be renovated to include two settling lagoons (lagoons number two and four) and one aeration basin (lagoon 1a).  The third existing lagoon would be removed from service but left intact for future expansion.  The excavation phase began by draining each lagoon.  Once the lagoon had drained down to a workable level, the contractor began with the sludge drying and removal.  After the sludge removal was complete, the subgrade was excavated down to the existing clay liner system.  Since this project was a rehabilitation of existing lagoons, the engineer also designed a gas venting system into the subgrade that would allow any gases from organic degradation to vent outside the liner and not be trapped below the liner system.  A sand cushion layer was then placed over the clay subgrade in preparation for the PVC geomembrane. The new design specified 40 mil PVC geomembrane be used as the primary liner system in the rehabilitated lagoons.  For the three new lagoons, a total of 787,800 square feet of 40 mil PVC geomembrane would be required to completely line the lagoons.  EPI fabricated the 40 Mil PVC geomembrane into panels as large as 15,000 square feet (75 feet wide & 200 feet long) for this project.  By fabricating large custom sized panels, the amount of field seams required would be minimized. The sequence was essentially the same for each lagoon.  Once the PVC geomembrane was installed and all testing had been completed, the excavation contractor began placing the cover soil.  One foot of cover soil was placed over the entire liner system using heavy equipment and GPS guided bulldozers for finish grading.  The side slopes were also covered with rip rap to maintain the cover soil and minimize erosion.  Once the excavation, liner placement and cover soil phase was completed, each individual lagoon was placed back into service prior to beginning work on the next lagoon.  This sequence allowed the Village of Manton to continue uninterrupted service during the rehabilitation process.  Geomembrane discussion Project specification required the Minnesota Water Balance Test to be conducted if all the requirements of the air channel testing were not met to the satisfaction of the Owner.  The water balance test essentially consists of filling each lagoon with clean water and measuring any change in the water level.  Any water level changes are compared against a control to determine the integrity of the lagoon liner system.  The control is typically a barrel placed in or near the lined area or a weather station.  Measurements are taken for four weeks and compared with atmospheric gains and losses to determine the lagoon leakage rate.  The downside of the water balance test is the time it takes as well as the required clean water to fill the lagoons to six feet in depth.  The accuracy of the test itself makes the determination of liner integrity a real challenge.  The time involved for the contractor as well as the challenge of securing the clean water to fill the lagoons is quite costly.  Following are the details of how the water balance test was not required due to the high level of testing and quality control required on this project. Prior to the lagoons being prepared, the geomembrane panels were delivered to the site and each fabricated geomembrane panel was labeled with its size and a unique serial number for quality control purposes.  During installation, the panels were deployed beginning in the morning and technicians began seaming once enough panels were in place to begin.  Seaming was performed using a hot air welding machine that produced a dual track thermal fusion weld with an unbonded center channel for testing.  Prior to production seaming, the machines were configured and trial welds were made.  These trial welds were tested with a portable tensiometer to ensure seam strengths.  All field seams were dual track welded, including the ?butt seams? that have the overlap from factory seams.  These factory seams of each panel have the potential to leak at the intersection of field to factory seams if the welding machine is not properly configured.  Special care was taken to ensure the field seams that included factory seam overlaps were sealed at each joint. The project specifications required the 40 mil PVC geomembrane to be installed with all production field seams constructed using dual track thermal fusion welds.  The dual track weld leaves an unbonded area between two parallel welds that can be air pressure tested.  With this technique, the entire length of seam can be evaluated to ensure continuity as well as seam strength.  Minimum required peel strength was 15 pounds per inch width and minimum required shear strength was 77.6 pounds per inch width.  All of the trial welds and destruct samples were tested in peel and shear modes according to ASTM D 6392 Standard Test Method for Determining the Integrity of Nonreinforced Geomembrane Seams.  Every destruct taken passed the requirements for peel and shear, with peel strength averaging around forty pounds per inch width. Thermal fusion welding allows for the air channel testing to be performed once the seam is completed and the material returns to ambient temperature.  This allowed the installation personnel to begin air channel testing shortly after each seam was completed.  The air channel testing was typically done in the afternoon, after enough seam was completed to efficiently test.  Ambient temperatures were typically between 80°F and 100°F.  The geomembrane liner temperatures were normally 20°F to 40°F above the ambient temperature due to the dark coloration of the liner.The specifications for this project required all seams be air channel tested according to GRI Test Method GM6 .  The project specifications did not require the test pressure in the air channel to meet the ASTM D 7177 requirements. The ASTM D 7177 testing requirements specify a minimum pressure at a particular geomembrane sheet temperature.  Due to the high ambient temperatures, the ASTM requirements actually correlated to the GRI GM6 test requirement which was actually slightly lower than the ASTM requirements.  In accordance with the ASTM D 7177 test method which requires the seam to maintain the minimum pressure at a given sheet temperature, this test method will verify seam strength as well as continuity.  EPI used the minimum requirements of the ASTM method since they were more specific to PVC geomembrane than the requirements of GM6 and provided more confidence to the CQA.  GRI GM6 requires the seam of 40 mil PVC geomembrane to maintain a pressure of 20-30 psi and have no more than a five psi drop over a two minute holding period.  The air channel pressures used for this project were between 20 psi and 30 psi and typically on the higher end at 25 psi to 27 psi.  Given the sheet temperatures at the time of the tests, the pressures used would ensure the seam strength of the entire length of seam according to ASTM D 7177 .  Any seam that did not hold the required pressure was investigated to find the leak point and then tested in each direction from the leak.  The leak point was then capped with a repair patch after the air channel testing was completed.  That repair patch was then tested using the air lance method according to ASTM D 4437 .  Lagoon 2 ( Figure 1 ) was ready to be lined in June of 2006.  304,625 square feet of 40 mil PVC Geomembrane liner was supplied for this lagoon.  From approximately 4,500 lineal feet of field seam in this lagoon, nine destructive samples were taken.  Over 1,225 lineal feet of field seam from this lagoon were from the factory end to factory end type of field seam.  This means there was a "T" from the factory seam every 6.25 feet on both panels being seamed.  It was critical that these end to end seams were also dual track welded and air channel tested to ensure the integrity of the seams.  Special care was taken by the seaming technicians when setting up the welder to make sure this type of seam was completely sealed.  Then the air channel test also verified the strength of the seam as well as continuity. Figure 1.)  Lagoon 2 panel layout.   There is a potential for each of the "T" seams to have a very tiny leak at the junction of three sheets of material.  This is another reason why air channel testing every seam is critical to the integrity of the liner system and not just using air channel testing for the long flat edge to flat edge seams.  While destructive samples will give you a decent representative sample, they are not comprehensive.  For example, if a destruct is taken in the first half of any given seam and the welding machine has a malfunction in the second half of the seam, it is possible for that section of seam to go unchecked for strength.  With dual track welding and air channel testing according to ASTM D 7177 , the entire length of seam will be pressurized and any section of seam that is less than the required peel strength will quite literally peel open from the inside out.  This is in essence peel testing 100% of the seam from the inside out.  This technological advance in non-destructive testing is also a destructive test over the entire length of seam giving all parties involved a much higher level of confidence in the final liner system. Lagoon 1a ( Figure 2 ) was the next lagoon to be lined in July of 2006.  A little more than 76,000 square feet of PVC Geomembrane liner was required for this aeration basin.  There were two destruct samples taken from nearly 880 lineal feet of field seam in this lagoon.  Only about 225 lineal feet of field seam from this lagoon were from the factory end to factory end.  Given the critical nature of these types of seams they were also dual track welded and air channel tested to ensure there were no leaks.                    Figure 2.) Lagoon 1a panel layout.                                    Figure 3.) Lagoon 4 panel layout.   Lagoon 4 ( Figure 3 ) was the last lagoon to be rehabilitated in August of 2006.  406,625 square feet of 40 mil PVC Geomembrane liner was provided for this lagoon.  There were 16 destruct samples taken from almost 8,000 lineal feet of field seam in this lagoon.  Close to 1,700 lineal feet of field seam from this lagoon were from the factory end to factory end.  All seams were dual track welded and air channel tested to ensure their strength and integrity.  Conclusion With the very short construction season in Michigan, which is typically April through October, waiting 30 days for a water balance test on each lagoon would have been a real challenge for the contractor to complete the project on schedule.  Therefore, completing the air channel testing on all field seams and not being required to undertake the water balance test was a significant savings to everyone involved.  In the end, this savings directly benefitted the community and the Village of Manton.  This project provides a great example of how more stringent quality control procedures and requirements can actually be a cost savings in the long run.    References GRI Test Method GM6. Standard Practice for Pressurized Air Channel Test of Dual Seamed Geomembranes, Geosynthetic Research Institute, Folsom, Pennsylvania, USA. ASTM D 4437, Standard Practice for Determining the Integrity of Field Seams Used in Joining Flexible Polymeric Sheet Geomembranes, American Society for Testing and Materials, West Conshohocken, Pennsylvania, USA. ASTM D 6392. Standard Test Method for Determining the Integrity of Nonreinforced Geomembrane Seams Produced Using Thermo-Fusion Methods, American Society for Testing and Materials, West Conshohocken, Pennsylvania, USA. ASTM D 7177. Standard Specification for Air Channel Evaluation of Polyvinyl Chloride (PVC) Dual Track Seamed Geomembranes, American Society for Testing and Materials, West Conshohocken, Pennsylvania, USA.   For more information call   800-OK-LINER   today!

Air Channel Test ASTM D 7177 Eliminates Water Balance Test of PVC Geomembrane Lined Surface Impoundment  Fred P. Rohe and Daniel S. Rohe, Environmental Protection, Inc.   ABSTRACT This paper will present a detailed description of the installation quality control and engineering quality assurance programs implemented on the 73,000 square meter (787,800 Ft2) PVC geomembrane lagoon system installed at the Village of Manton Wastewater Treatment Lagoon improvement project in Manton, MI USA.   Air channel strength testing of dual track thermal welds of PVC geomembranes has been developed to provide quality assurance testing for the full length of PVC geomembrane field welds.  This method effectively peel tests every inch of a field weld and eliminates the need for cutting holes in the liner to remove samples in order to perform destructive peel testing on only a small portion of the seam.  The testing method was adopted as ASTM D 7177 Standard Specification for Evaluation of Polyvinyl Chloride (PVC) Dual Track Seamed Geomembranes in June 2005 and was first used extensively in the 2006 construction season.  The designers at Fleis & Vandenbrink Engineers worked with the Michigan Department of Environmental Quality to eliminate the outdated and obsolete water balance test by requiring air channel testing for PVC geomembrane field seams.  The success of this project has provided the basis for implementing this new testing technology in lieu of the water balance test, saving customers precious time and ultimately precious funding for construction of PVC lined surface impoundments.  INTRODUCTION There is an old cliche about spending more initially for a quality product and saving money in the long run.  This paper provides information about how quality PVC geomembrane welding and testing can provide immediate cost savings today to owners, operators and communities. Thermal welding of PVC material is not a new development. The process has been used for many years in all types of PVC fabrication. However over the past 5 years or so, there have been new developments and improvements in the equipment and techniques for thermal welding of thin, flexible PVC films used as geomembranes.  In the process of developing these new techniques and working countless hours in the field with new equipment, it became very apparent to the authors that air channel testing of PVC dual track welded seams was also a strenuous test of the strength and quality of the full length of every weld.   While heat welding any thermoplastic geomembrane today is relatively simple, welding long lengths of seam without the slightest imperfection in its peel strength is still quite challenging.  This came to light on some of the first projects while developing these PVC air channel testing techniques. For instance, a field seam that had a destructive sample removed (and that sample passed independent laboratory peel testing) failed when air channel tested along its entire length.  A large section of that same tested seam had not bonded completely, had passed air lance testing, but began to split open when air channel tested.  It was then that the authors were more convinced than ever that air channel testing of PVC geomembranes could in fact measure the strength, and therefore the quality, of the entire length of a weld. The authors also discovered that thermal welding long lengths of seam (> 60-100M) (200-300 ft.) that easily passes an air lance test, would invariably fail an air channel test in some small area, unless the operator was thoroughly trained and the welding machine properly set up.  Temperature, speed, and contact pressure are critical to developing a consistent weld in any geomembrane.  Welding too hot and traveling too fast are the major detriments to the successful, consistent welding of PVC.  They also discovered that too much air pressure at very high sheet temperatures would cause failure in an otherwise passing PVC weld.  This is not the case in testing HDPE geomembranes. Persisting in their belief that air channel testing could provide real time strength testing of PVC welds led others into this research and the eventual development of ASTM D 7177 Standard Specification for Air Channel Evaluation of Polyvinyl Chloride (PVC) Dual Track Seamed Geomembranes.  This procedure only applies to the air channel strength testing of PVC geomembrane welds.  While there have been serious attempts to develop a similar procedure for testing the full length of other thermoplastic geomembrane welds (i.e. HDPE), none have been successful or standardized. The Manton project recognized that superior testing of the PVC geomembrane seams by checking both the continuity and strength would render a costly and time consuming water balance test unnecessary. (Not to mention that a water balance test does not identify the defect, it only tells you the lagoon is leaking, but not where.)   The project specifications required the Minnesota Water Balance Test be conducted, if all the requirements of the air channel testing were not met to the satisfaction of the Owner.  The water balance test essentially consists of filling each lagoon with clean water and measuring any change over a 30 day period.  Any water level changes are compared against a control to determine the integrity of the lagoon liner system.  The control is typically a barrel placed in or near the lined area or a weather station.  Measurements are taken for four weeks and compared with atmospheric gains and losses to determine the lagoon leakage rate.  The downside of the water balance test is the cost of the time it takes, as well as the cost of pumping clean water to fill the lagoons to six feet in depth, and then discharge it again.     CASE STUDY The Village of Manton in northwest lower Michigan has a wastewater treatment facility utilizing three ponds.  The ponds were originally constructed using clay soil as a liner.  In 2006 it became necessary to rehabilitate the lagoons and reduce the amount of leakage from the ponds.  Elmer's Crane & Dozer, Inc. of Traverse City, MI USA was selected as prime contractor for the project.  They performed all of the earth work on the site. Elmer's selected Environmental Protection, Inc. (EPI) of Mancelona, MI USA to fabricate and install the PVC geomembrane liner system.  STS Consultants, Inc. was retained as the independent third party construction quality assurance (CQA) firm to oversee liner installation and testing.  73,000 M2 of 40 mil PVC geomembrane was required to completely line the lagoons.  EPI fabricated the 40 Mil PVC into panels as large as 1,400 M2 (15,000 square feet -75 feet wide & 200 feet long). These large custom sized panels were used to reduce the amount of field seams required.  The existing lagoon system was made up of three large ponds.  The new design would require two of the existing lagoons be renovated to include two settling lagoons (lagoons number two and four) and one aeration basin (lagoon 1a).  The third existing lagoon would be removed from service but left intact for future expansion. In succession, the lagoons were each drained, dewatered, and sludge removed, then excavated down to the original clay liner.  Since this project was a rehabilitation of existing lagoons, the engineer also designed a gas venting system into the subgrade that would allow any gases from organic degradation to vent outside the liner and not be trapped below the liner system.  A sand cushion layer was then placed over the clay subgrade in preparation for the PVC geomembrane.  The sequence was essentially the same for each lagoon.  Once the PVC geomembrane was installed and all testing had been completed, the excavation contractor began placing one foot of cover soil over the entire liner system using heavy equipment and GPS guided bulldozers for finish grading.  The side slopes were also covered with rip rap to maintain the cover soil and minimize erosion.  Once the excavation, liner placement, and cover soil phase was completed, each individual lagoon was placed back into service prior to beginning work on the next lagoon.  The use of the air channel strength test instead of the 30 day water balance test also saved a minimum of one month between the completion of one lagoon and the start of draining the next.  This sequence allowed the Village of Manton to continue uninterrupted service during the rehabilitation process.  WELDING Once the lagoon subgrade was completed, the PVC geomembrane panels were deployed and welded together using Leister Twinny hot air welding machines that produce a dual track weld with an un-bonded air channel between the welds.  Fig. 1 provides a close up view of the nip rollers and hot air nozzle that create the two parallel welds with an un-bonded air channel between. Prior to production welding, each machine was configured and trial welds were made.  Minimum required peel strength was 2.6 kN/M (15 lb/in width) of specimen and the shear strength requirement was 14 kN/M (77.6 lbs/in width).  All trial welds and destructive samples were tested according to ASTM D 6392 Standard Test Method for Determining the Integrity of Nonreinforced Geomembrane Seams.  There was approximately 3,700 lineal meters (12,000 feet) of field seam produced on this project.  The CQA Engineer removed 26 destructive samples (> 1 sample per 150 M of seam).  All destructive samples were tested in EPI's lab, and 50% of the samples (13) had a portion also sent to an independent laboratory (TRI / Environmental, Inc., Austin, TX).  All samples met specification requirements when tested according to ASTM D 6392 . FIG 1.) Dual Track Hot Air Welder   AIR CHANNEL TESTING  Air channel testing of the dual track field seams was conducted immediately after the welding was completed and the material had cooled to ambient temperatures. The specifications for this project required all seams be air channel tested according to GRI Test Method GM6 .  ASTM D 7177 testing requirements specify a minimum pressure for each particular geomembrane sheet temperature.  On this project, the ASTM requirements correlated to the GRI GM6 test requirement (GM6 was actually slightly lower than the ASTM requirements.)  In addition, the ASTM D 7177 test method will verify seam peel strength, as well as continuity.  EPI used the minimum requirements of the ASTM D 7177 method since they were more specific to PVC geomembrane than the requirements of GM6, and provided more confidence to the CQA.  When the air channel is inflated (FIG. 2) to the appropriate test pressure for the material temperature, a peel stress equivalent to 2.6 kN/m (15 lb/in width) is applied to the interior of BOTH sides of the dual track weld.  Thus both welds are being tested at the same moment.  The peel stress from the interior of the weld is similar to the stress applied to a test specimen in a tensiometer when it is peel tested from the exterior of the weld channel. FIG. 2.)  Exaggerated view of an inflated dual track PVC geomembrane thermal weld produced with a Leister Twinny hot air welder. Significant research was done on this test method comparing air channel peel pressures to actual laboratory peel specimen test results.  "Air Channel Testing of Thermally Bonded PVC Seams", by Thomas, et al. (2003) describes the testing used to develop the relationships between air pressure in the PVC channel and the temperature of the PVC material at the time of testing.  These field tests results were then correlated with laboratory test results to develop a relationship between air channel pressures and peel strength of the weld.  Further refinements involved testing in cold temperatures with very stiff material, and testing at very high material temperatures.  The resulting information produced the following Table 1 which is referred to in ASTM D 7177 :   Table 1.  Pressure Required to Verify 2.6 kN/M (15 lb/in) Peel Strength for PVC SheetTemperature °C SheetTemperature °F Air PressureKPa Air PressurePSI Hold Time(seconds) 4.5 40 345 50 30 7 45 324 47 30 10 50 310 45 30 13 55 290 42 30 15.5 60 276 40 30 18 65 262 38 30 21 70 241 35 30 24 75 228 33 30 26.5 80 214 31 30 29.5 85 193 28 30 32 90 179 26 30 35 95 165 24 30 37.5 100 152 22 30 40.5 105 138 20 30 43.5 110 131 19 30 The air channel pressures used for this project were between 138 and 214 KPa (20 psi and 31 psi) and typically on the higher end at 165 to 193 KPa (24 psi to 28 psi).  Given the sheet temperatures at the time of the tests, the pressures used would ensure the seam strength of the entire length of seam according to ASTM D 7177 .  Any seam that did not hold the required pressure was investigated to find the leak point and then tested in each direction from the leak.  The leak point was then capped with a repair patch after the air channel testing was completed.  That repair patch was then tested using the air lance method according to ASTM D 4437 . Understanding the relationship of air pressure to material sheet temperature is critical in testing flexible PVC geomembranes.  If the pressure is not high enough, the only test is of continuity, so the pressure needs to be high enough to stress the weld in a peel mode.  Conversely, if the pressure is too high (which is often the case at very high material temperatures, i.e. above 32 °C) a passing seam can be compromised.  With excessive air pressure in the PVC channel at very high sheet temperature, we are expecting the weld to have much higher peel strength than the standard specification requires, and we cause a seam to fail an air channel test when it would normally pass a destructive peel test.  There is an inverse relationship of material sheet temperature to air channel pressure when testing PVC geomembrane peel strength. The ideal scenario would be to have every seam be leak free and without defects over 100% of its length prior to testing.  However, the ideal is tough to deliver under field conditions.  Rain, dirt, wind, operator error, burn outs all contribute to problems welding a perfect seam.  On this project 71% of the seams were welded and tested over their complete length, welded error free, without holes.  As operators and equipment improve, this rate will also improve.   AIR CHANNEL TESTING T-SEAMS ALL field seams must be tested and T-seams can be difficult if not welded properly.  T-seams are defined as a point in the seam where three layers of material overlap each other.  This occurs at the point that a dual track field weld crosses a factory seam, usually at a 90 degree angle.  The PVC geomembrane factory welded panels on this project were made up of strips of PVC material 193 cm (76 inches) wide.      FIG. 3.) Panel Layout Dwg Lagoon 2   Referring to Fig.3, each panel is made up of 12 strips of 193 cm (76 inch) wide PVC, each 61 M (200 feet) long.  The factory seams are vertical in Fig.3.  There are eleven factory seams in each panel.  The lines shown on Fig. 3 are the field seams.  There is approximately 1,200 M (4,000 feet) of simple two panel overlap field seam in this lagoon (the vertical field seams shown).  Approximately 400 M (1,225 feet) of seam (the horizontal seams shown in Fig. 3) are typical T-seams where the end of one factory panel over laps the end of another factory panel.  Since the factory seams don't normally line up exactly from the end of one panel to the end of the next panel, one of these horizontal seams could have a potential of 146 Ts in that weld.  There is an additional T-seam created at the end of each field seam.  The field T-seam must be specially prepared so that there is no un-bonded edge where the welder crosses the previously welded field seam.   FIG. 4.) Specimen from PVC geomembrane T-Seam   The air channel test over each "T" requires great care in welding (FIG. 4) in order to eliminate leaks and be able to proficiently perform air channel testing.  There is a potential at each "T" to have a very tiny hole at the junction of the three layers of material.  This is another key reason why air channel testing of every seam is critical to the integrity of the liner system finding and eliminating these holes.  Special care is taken by the welding technicians when setting up the welder to make sure this type of overlap is completely sealed, so the air channel test can be used to verify strength and continuity of these seams also. On this project the factory seams had no loose edge, so the process for welding T-seams in PVC was relatively easy. Slowing the welding machine's rate of travel allowed the melted PVC material to flow together at the junction of the three layers of material, providing the necessary seal and weld strength.  If there is a loose edge on the factory seams, then each loose edge will need to be trimmed, similar to the process used on field welds which intersect other seams.  On this project all factory panel end seams were tested over their entire length.   CONCLUSIONS The downside of the water balance test is the cost of the time it takes, as well as the cost of pumping clean water to fill the lagoons, and then discharging it again.  If the test indicates that the pond is leaking, there is no way to know where the leak may be.  On the Manton project, eliminating the water balance test of each lagoon saved at least 90 days from the construction schedule and the pumping millions of gallons of water. Air channel testing for continuity and peel strength on all PVC field welds gives the regulators, engineers and owner the assurance that every inch of field seam exceeds the minimum specified strength requirements.  Investing in a superior welding and weld testing system saved the community of Manton significant construction time and significant real dollars.   REFERENCES ASTM D 7177. Standard Specification for Air Channel Evaluation of Polyvinyl Chloride (PVC) Dual Track Seamed Geomembranes, American Society for Testing and Materials, West Conshohocken, Pennsylvania, USA. ASTM D 4437, Standard Practice for Determining the Integrity of Field Seams Used in Joining Flexible Polymeric Sheet Geomembranes, American Society for Testing and Materials, West Conshohocken, Pennsylvania, USA. ASTM D 6392. Standard Test Method for Determining the Integrity of Nonreinforced Geomembrane Seams Produced Using Thermo-Fusion Methods, American Society for Testing and Materials, West Conshohocken, Pennsylvania, USA. GRI Test Method GM6. Standard Practice for Pressurized Air Channel Test of Dual Seamed Geomembranes, Geosynthetic Research Institute, Folsom, Pennsylvania,  USA.  Thomas, R.W. and Stark, T. D., Air Channel Testing of Thermally Bonded PVC Seams, September 4, 2002 Thomas, R. W., Stark, T. D., and Choi, H., Air Channel Testing of Thermally Bonded PVC Seams, Geosynthetics International Journal, Industrial Fabrics Association International (IFAI), Vol 10, No. 3, October 2003, pp. 645-659. Thomas, R.W. and Stark, T. D., Air-Channel Testing of Thermally Bonded PVC Geomembrane Seams, Geotechnical Fabrics Report, Industrial Fabrics Association International, Vol 20, No. 8, October 2003, p. 10. Stark, T. D., Choi, H., and Thomas, R. W., Low Temperature Air Channel Testing of Thermally Bonded PVC Seams, International Association of Geosynthetic Installers, Industrial Fabrics Association International (IFAI), Vol 4, Issue 1, Winter 2004, pp. 5-7.   For more information call   800-OK-LINER   today!

CURING OF CHEMICALLY WELDED PVC SEAMS By Fred P. Rohe and Sam Lewis | Environmental Protection, Inc., Mancelona MI  Chemical welding and heat welding are the two most common methods of producing seams in geomembrane fabrication. While heat welded seams reach full strength almost as soon as they cool, chemically welded seams require a period of time for curing in order to reach full strength. Since heat welding is not always practical for use on thin gauge geomembrane material, chemical welding has been used successfully on thin gauge geomembrane materials since the 1950's. Currently, there is an increasing requirement for destructive testing of geomembrane seams at the earliest possible time. The curing of chemically welded PVC seams takes place over a long period of time. The age of the sample will affect the test results and should affect the engineer's interpretation of these results. On July 25, 1988, Environmental Protection, Inc. began a study of the curing of chemically welded PVC seams. A 100 foot long seam of 20 mil PVC was fabricated using normal EPI factory fabrication techniques. This seam was then cut into 24" long test sample blanks. These samples were then tested at the following intervals: 20 minutes, 1 hour, 2 hours, 4 hours, 7.5 hours, 23 hours, 30.5 hours, 46.5 hours, and then at a rate of one per day until the end of one month. The samples were tested for bonded seam strength using ASTM D-3083 NSF modified, and they were tested for seam peel adhesion following ASTM D-413 as modified by NSF. The results from these tests were then plotted on two graphs: shear vs. age, and peel vs. age. The natural logarithm was taken of the data and was also plotted on two graphs: ln shear vs. In age, and ln peel vs. ln age. These graphs were found to be highly linear with a correlation coefficient of .95 for ln shear vs. ln age, and .80 for ln peel vs. In age. A linear regression analysis was then performed for both log-log graphs to find the equations for the best fit lines. These lines were then superimposed on the log-log plots. The equations for the best fit lines was then exponentiated to find the best fit curves for the real data. While the applicability of these results is limited to the materials and methods used by EPI, they do show that chemically welded PVC seams will increase in shear and peel strengths over time. ASTM requires 40 hours of conditioning time in the laboratory prior to testing PVC seams for shear and peel. As can be seen from the data presented here, this may not be sufficient time for the seam to reach its ultimate strength. However, based on the age of the sample, a prediction could be made using this curve as to what the ultimate strength of the seam will be. While it is sometimes necessary to test the seams when still fairly new, the results of these tests should not be taken as representative of the ultimate strength of a chemically welded PVC seam. Caution should be used in evaluating the data on the testing of seams that are not completely cured. Figure 1.) shows the best fit curve for the shear strength vs. time of this test. The minimum shear strength of 36.8 lbs. per inch reach in approximately 2 hours. The shear strength to increase over time to a strength of 53.3 lbs. per inch width.   Figure 2.) shows the best fit curve for peel strength vs. time. The peel strength reached the minimum requirements in approximately 96 hours. The strength continued to increase throughout the time of the test reaching an ultimate peel strength of 12.1 IBS. per inch width at the conclusion of the test.   Figure 3.) illustrates the shear strength of the seam vs. its age. The minimum required bonded seam strength of 36.8 lbs. per inch was achieved in approximately 2 hours. The seam continued to cure and increase in strength to a final value of 57 lbs. at the end of the 30 day test.   As part of EPI's quality control process a second long term test on the curing of a chemically welded 20 mil PVC seam was conducted in December of 1988. Again, a l00 foot seam was fabricated using normal EPI processes. The seam was cut into 24 inch samples immediately after fabrication, and tested at the same intervals as the July long term test. Calculation of the data to plot the best fit curve was performed in the identical manner of the original test.  Figure 4.) illustrates the best fit curve of the peel strength vs. the age of the seam. The ultimate peel strength of this seam is approximately 2.5 lbs. per inch width higher than the original test. Also, the seam reached its initial minimum requirements for peel strength much sooner than the original test. Although the ultimate value of the second test was slightly higher, when superimposed on each other, the best fit curves for the increase of peel strength are virtually identical. This observation also holds true for the shear strength of the seam in that, when superimposed, the shear strength best fit curves are also almost identical from these two tests.     For more information call   800-OK-LINER  today!

XR-5 Geomembrane installation over structural Geofoam fill by Fred P. Rohe  The city of Detroit is in the process of reclaiming its river front. Over the years the area has been dominated by business and industry but the area has become an embarrassment. The Detroit Riverfront Conservancy was created with the mission of revitalizing the waterfront area. The first phase of this undertaking was the Louis Arena to the Douglas MacArthur bridge to Belle Isle. People are to run, walk, bike and roller-blade on the new RiverWalk, which will also include places for people to sit and take in the scenery. A portion of the RiverWalk passes directly between the General Motors (GM) Renaissance Center buildings and the Detroit River. GM retained Albert Kahn Associates to design a suitable plaza and promenade to blend as part of the RiverWalk project. The plaza includes a granite world map showing the GM facility locations world wide. John Carlo, Inc. was selected as the prime contractor to build the plaza as a showpiece for the GM Center.    Planter boxes were lined to create a tree-lined tiered walkway.   Material The area selected for the plaza has seen many varied uses over the past century. There are many unknowns regarding the soils and other materials deposited there. It was known that the area had experienced some subsidence and the fill in the area was over soft soils. The area is bounded on one side by a service areaway and on the other by a concrete sea wall at the river’s edge. The site’s close proximity to the Windsor Tunnel under the Detroit River to Canada was another important consideration.The plaza area needed to be raised approximately four meters above the existing parking lot area it is replacing. The designers selected expanded polystyrene Geofoam for use as fill material. The 1.5 pounds/square foot density Geofoam would save weight, reduce lateral pressures on the adjacent structures, and speed construction at the congested work site. Hydrocarbons have a devastating effect on contact with expanded polystyrene foam. In order to protect the Geofoam from damage by an accidental spill of fuel or other hydrocarbon materials, the designers utilized a geomembrane. 8130 XR-5 was selected to cover the top of all areas where Geofoam was installed. XR-5 is a PVC coated fabric formulated using Elvaloy, a chemical resistant polymer which imparts flexibility to the geomembrane. Protective sand layer was broadcast-spread over geomembrane liner.    Discussion The GM Renaissance Center Plaza and Promenade is a public area in downtown Detroit. GM will be displaying vehicles at the plaza as well as hosting many outdoor events in the area. The plaza will also be heavily landscaped to provide an enhanced look to the park like setting. The plaza is also directly adjacent to a busy city street with all types of vehicles all types of vehicles traveling in the congested area. There is legitimate concern for a possibility of an accidental fuel spill. Therefore it was necessary to take precautions to protect the Geofoam from any adverse exposure to chemicals that would dissolve the foam. Environmental Protection, Inc. (EPI) was selected to provide over 4,700 square meters of XR-5 geomembrane liner for this project. Over one acre of XR-5 was prefabricated to fit the varying shapes of the plaza and the many planter boxes and planting areas that were incorporated into the design. Each area of the plaza where Geofoam was installed had to be covered with geomembrane. The XR-5 material was installed directly over the foam, or over a sand cushion that was installed on top of the foam in some areas. The liner extended up vertically 30 to 50 centimeters on the perimeter concrete walls. The geomembrane was secured to the concrete using an aluminum batten bar 0.3175 centimeters by five centimeters. The batten was anchored to the concrete wall using Ramset three centimeter long powder-actuated fasteners located approximately 15 centimeters centre to centre. Since the geomembrane now acts to collect any fluid, including rainwater, a drain age system had to be implemented above the liner and drain piping to direct the water away from the plaza. The liner was sealed to these drain pipes using prefabricated EPI Tapered Pipe Boots. Boots were custom fabricated of XR-5 for each pipe diameter used on the project. EPI also prefabricated inside and outside corners to simplify the installation of the XR-5 around the many column foundations and intricate corners in the planter areas. Installation of the XR-5 had to be coordinated with the many other subcontractors working on the site. The area was so congested that the installation had to be done in phases in order to allow enough area for everyone to operate efficiently.  Summary The XR-5 geomembrane provided an excellent solution for protection of the EPS Geofoam on this project. The material was easily fabricated to fit the unusual shapes and dimensions of the plaza and its many planters. Installation was rapid, with very little field welding required. While unlikely, it is possible that an accidental spill could cause serious damage to the Geofoam underlying the GM Renaissance Center Plaza and Promenade. The foresight to provide protection for the EPS foam will ensure that this area will be use-able and useful to the visitors to the Detroit river front for many years to come. References: Curtis, R., Page, D., Peaslee, G. “EPS Geofoam Technology Project”, The Bridge, April/June 2004, Michigan Technological University, Houghton, MI 49931. “Reclaiming The Riverfront.” “GM Riverfront Plaza & Promenade”, The Liner Letter, Vol. 4 – Issue 5, July 7, 2004. Wehrmeyer, S., “Geofoam: Providing new solutions to old challenges”, Geotechnical Fabrics Report, June/July 2001. Nystrom, J., “Applications: Geofoam takes a new track”, Geotechnical Fabrics Report, September 1999. Reuter, G., Rutz, J., “Applications: A lightweight solution for landslide stabilization”, Geotechnical Fabrics Report, September 2000.     For more information call   800-OK-LINER  today!

William R. Morrison & J. Jay Swihart Bureau of Reclamation, Denver, Colorado 80225. USA ABSTRACT The Bureau of Reclamation has been using polyvinyl chloride (PVC) plastic in its buried membrane canal lining work for over 20 years. Results of tests conducted on samples of in-service linings indicate that the factory-fabricated seams retain excellent shear and peel strength properties with no apparent signs of deterioration. The practice of using a 1 - m overlap unbonded PVC field seam has proven adequate for most irrigation canal lining applications, but would not be suitable for applications requiring 100% seepage control. Results of laboratory investigations conducted in conjunction with a study on the underwater lining of operating canals with PVC indicate that an adhesive formulated for the repair of vinyl swimming pool liners can be used to make underwater PVC field seams. Results of these investigations also indicate that field seams made in the dry can achieve enough early peel and shear strength development (within 15 min) for placement underwater.  INTRODUCTION Reclamation has used PVC linings for seepage control in irrigation canals for over 20 years. The earliest PVC plastic lining installation was a small experimental section installed in 1957, on the Shoshone Project in Wyoming.1 The first PVC installation under construction specifications (604C-72) was on the Helena Valley Canal, Montana, in 1968. The plastic lining was an alternative to the hot, spray-applied asphalt membrane material.2 (Because the energy crisis in the 1970s caused a significant increase in the cost of petroleum products, coupled with a limited source of supply, the asphalt membrane material was deleted from our specifications.) Over the years, Reclamation has obtained samples of PVC from various installations to determine the aging characteristics of these materials.3 Results of tests conducted on PVC scams from two installations are discussed in this paper. Laboratory tests were also conducted on PVC seams as part of the research program to develop methods and materials for the underwater lining of operating canals. Reclamation has a number of leaky, unlined irrigation canals that cannot be easily dewatered for lining because of water delivery commitments. Underwater installation of a PVC lining protected with a concrete cover is currently being evaluated. In addition, PVC seams were evaluated among other seams under a laboratory study Reclamation conducted for the Environmental Protection Agency (EPA) entitled 'Evaluation of Flexible Membrane Liner Seams after Chemical Exposure and Simulated Weathering'.4 The results for the PVC seams are presented in this paper.  FIELD PERFORMANCE OF PVC PLASTIC CANAL LINERS PVC plastic linings were originally used in the rehabilitation of old, unlined canals, especially in areas unsuitable for compacted earth or concrete linings.5 Plastic linings finding wider use in new construction.6.7 The work involves four basic steps: excavation, subgrade preparation, installation of the plastic membrane, and placement of the earth cover (0.3 - 0.5 m in depth) to protect the membrane from the elements and physical damage. Because of the requirement of an earth cover, membrane linings are restricted to canals having low-velocity flows (0.3 -1 m/s). Also the side slopes should be no steeper than 2.5(H): 1(V) and preferably 3(H): 1(V) to minimize cover stability problems. PVC is manufactured in roll goods approximately 2 m wide. The roll goods are factory fabricated into sheets wide enough to cover the canal prism and up to several hundred meters in length depending upon its thickness. For most canal lining work, sheets of PVC lining can be joined simply by lapping the downstream end of one sheet of 0.9 m over the upstream end of the adjacent sheet. The PVC plastic has a tendency to adhere to itself and, with the weight of the earth cover, a sufficiently bonded joint is obtained where 100% seepage control is not required. The watertightness of the unbonded field seam is discussed in more detail in the next section. Where a more positive seal is required, the PVC is overlapped a minimum of 0.3 m and a solvent cement (recommended by the manufacturer) applied to a minimum width of 50 mm. A continuous study is being conducted by Reclamation to evaluate the performance of buried PVC membrane canal linings. Results from two installations-Bugg Lateral, Tucumcari Project, New Mexico, and the Helena Valley Canal, Helena Valley Unit, Montana- are presented. Bugg Lateral In the spring of 1961, a small test of 0.25 mm PVC was installed on the Bugg Lateral, Tucumcari Project, New Mexico. The test section was about 228 m in length, and it is the oldest Reclamation installation for which performance data are available for this material. The hydraulic properties of the canal are summarized in Table 1 . TABLE 1           Hydraulic Properties of Plastic-Lined Canals     Protective Flow Velocity Bottom width Normal water depth Cover Canal depth (m3/s)   (m/s)   (m)   (m)   (m)   Helena Valley -26   0.64   2.7   28-Jan   0.3   Bugg Lateral 2.66   0.57   4-Feb   4-Jan   0.4               Note: Ratio of side slopes in both canals is 2 (horizontal) to 1 (vertical).   Samples were obtained in 1965 (4 years of service), 1970 (9 years of service), 1975 ( 14 years of service). 1980 (19 years of service), and 1988 (after 27 years of service). A photograph taken during the 1980 field sampling is shown in Fig. 1. Results of the sampling indicated the lining was intact below water level, but had suffered some damage from root penetration above the waterline.   TABLE 2           Results of Laboratory Tests Conducted on PVC Seam Samples from Bugg Lateral.   Tucumcari Project, New Mexico           Typical       Physical Specification original 4 Years 9 Years 27 Years property requirements results of service of service of service Thickness 0.25 0.26 0.26 0.25 0.25 (mm) 10%         Tensile 3 4 4.1 4 5.5 Strength           (kN/m)           Bonded seam 1.95 4 4 3.8 5.8 Strength in           shear (kN/m)           Bonded seam Not NDa ND ND 3.5 Strength in peel Required         (kN/m)           a Not determined. Helena Valley Canal In the fall and winter of 1968-69, a reach of the Helena Valley Canal, 1930 m in length, was lined with 0.25-mm thick PVC plastic. This was the first PVC lining installation under a Reclamation construction specification (604C-72). The PVC was furnished in sheets 12.8 m wide by 122 m in length. The sheets were accordion folded in both directions for delivery to the job site. Samples of the lining containing a factory seam were obtained after 9 and 14 years of service. Results of laboratory tests conducted on the factory seam are summarized in Table 3. Test results indicate that as with the Bugg Lateral lining, the factory seams retained their integrity after 14 years of service. LABORATORY TESTS FOR UNDERWATER LINING OF OPERATING CANALS Reclamation has been conducting research to develop new technologies for lining canals while they are in operation. The basic concept consists of placing a PVC geomembrane covered with gravel, soil or concrete while the canal remains in operation. The canal would be lined in two or more passes necessitating an underwater field seam in the PVC geomembrane down the centerline of the canal. A 1-m overlapped unbonded seam was planned for this location. As previously mentioned, Reclamation routinely, uses this type of seam (in the transverse direction only) for its PVC-lined canals. Leakage through the unbonded seam was expected to be relatively small since PVC tends to bond slightly to itself under pressure. Seepage measurements obtained for some of these canals, although limited, has supported this expectation. For underwater lining, a study was undertaken to quantify the seepage for this type of seam and to examine the effects of hydraulic head, cover depth and cover material. Additional important information was obtained, quite accidentally, concerning the effect of an irregular subgrade. These results led to a second phase of the study where a new adhesive for bonding PVC under water was examined. Conventional solvents for field seaming in the dry were also examined. TABLE 3         Results of Laboratory Tests Conducted on PVC Seam Samples from Helena Valley Canal. Helena Valley Unit, Montana                 Specification     Physical requirement Typical 9 years 15 years property results original of service of service Thickness (mm) 0.25 0.27 0.25 0.25   10%       Tensile strength 3 5.8 5 5.7 (kN/m)                   Bonded seam 2.2 5 4.6 5.1 strength in shear       (kN/m)                   Bonded seam Not NDa ND 3.7 strength in peel required       (kN/m)         a Not determined.         Phase 1-Unbonded Field Seams The test apparatus for determining seepage through the overlapped seam measures (width by length by height) 1.2 m by 2.4 m by 0.6 m and is shown in Fig. 2. The gravel drain collects the seepage while the geotextile provides a smooth subgrade for the PVC liner. A more representative subgrade material (i.e. something less permeable than gravel) would obviously reduce seepage; however, an investigation into various subgrade materials was beyond the scope of this study. Three cover conditions were examined including 25 mm of sand (No. 50 in size), 25 mm of sand plus 50 mm of concrete blocks (200 mm by 600 mm), and 25 mm of sand plus 150 mm of concrete blocks. The voids (approximately 10 mm wide) between the concrete blocks were filled with sand. With the aid of a stand-pipe, tests were run at hydraulic heads of 0.3, 0.9, 1.5 and 2.1 m. Each test was run for a minimum of 24 h to allow stabilization of hydraulic gradients within the gravel drainage layer. Some tests were run for up to 2 weeks to evaluate observed decreases in seepage with time. The results are summarized in Table 4. Test sets A and B are duplicates with 25-mm sand/50-mm concrete cover and demonstrate the variations seen for identical test conditions. These test sets were meant to approximate the 75 mm of concrete cover. The seepage at 2.1 m of head represents 15-30 liters per day per linear meter of seam and was considered acceptable. A gradual decrease in seepage was seen with time, caused either by fines moving through the overlapped seam and plugging the geotextile and/or gravel drain, or by settlement and compaction of the sand between the concrete blocks. TABLE 4         See page through Overlapped Unbonded Seam in PVC Geomembrane Test Set Cover Hydraulic head Seepage         (m) (liters m d)   A 25 mm of sand plus 0.3 0     50 mm concrete 0.9 0       1.5 2 2.1 15         B 24 mm of sand plus 0.3 1     50 mm concrete 0.9 5       1.5 -       2.1 30   C 25 mm of sand plus 0.3 1     150 mm concrete 0.9 4       1.5 5       2.1 15   D 25 mm of sand 0.3 15       0.9 60       1.5 80   E 25 mm of sand plus 0.3 60     50 mm concrete 0.9 400     (wrinkle in geotextile) 1.5 - Test set C used 150 mm of concrete blocks rather than the 50 mm used in test sets A and B. No measurable differences in seepage were detected. Test set D had only the 1.5 mm of sand cover (no concrete blocks) and demonstrated 20 times more seepage than test sets A and B which had 25 mm of sand and 50 mm of concrete cover. This increase in seepage has two causes. The first is the difference in cover load 25 mm versus 75 mm, and the second is the difference in seepage paths. The sand/concrete combination has not only longer but also fewer seepage paths, as the seepage can only occur through the sand between the concrete blocks. Test set E again had 25 mm of sand plus 50 mm of concrete cover: however, a defect was inadvertently introduced into the subgrade by a fold (wrinkle) in the geotextile. This defect increased seepage by a factor of about 100. As subgrade defects will be impossible to avoid entirely in the field, methods for bonding the seams underwater are needed to assure maximum water conservation. Phaonded Field Seams Phase II of the study examined solvents adhesives for field seaming of PVC geomembranes both underwater and in the dry. The biggest challenge was finding a solvent which could be used underwater, as there has been very little experience in this area. Discussions with manufacturers led to the selection of a specially modified bodied tetrahydrofuran solvent used to repair vinyl swimming pool liners. Test results for PVC seams made both underwater and in air with the special vinyl adhesive are summarized in Table 5. Tests were conducted to determine peel and shear strength after a 24-h cure. Test results indicate that the seams are quite satisfactory and even meet the requirements for factory seams using conventional solvents in the dry. There was also concern about the rate of seam strength development for the transverse field seams that would be needed every 60 m. These seams would be fabricated in the dry with conventional solvents but then very quickly (perhaps within 15 min) subjected to shear stress as they were placed underwater in the canal prism. Seam specimens were fabricated in air with a manufacturer-supplied solvent cement and tested for shear and peel strength after cure times ranging from 5 min up to 4 h. The shear strength developed very quickly (within 5 min) and then decreased with time until reaching equilibrium after 1-2 h. Conversely, the peel strength developed rather slowly and required-30- 60 min to develop fully. Shear strength is the more critical as shear is the predominant stress on the seams during installation and service. Tests were also performed to ensure that specimens, made with conventional solvent and initially cured in air, would continue to cure underwater. Seam specimens were partially cured in air for 5 min and then cured in water for 3 days. These specimens did indeed develop full shear and peel strengths. RESULTS OF EPA STUDY In 1986, Reclamation completed a study for EPA entitled 'Evaluation of Flexible Membrane Liner Seams After Chemical Exposure and Simulated Weathering'. In this study, 37 geomembrane seams, both factory and field were evaluated. The PVC seams included in the study are listed in Table 6. The seams were subjected to six chemical solutions, brine and water immersion, freeze/thaw cycling, wet/dry cycling, heat aging, and accelerated outdoor aging for periods of up to 1 year. Effects of these environmental conditions were evaluated using shear and peel strength tests before and after exposure. The tests were performed under dynamic load at room temperature and under static dead load at 50° C. The rate of grip separation for both the peel and shear tests was kept the same (50 mm/min) to determine if there was any direct correlation between the two properties. Also, a 25-mm wide test specimen was used in both tests. Results of tests conducted on seams subjected to water immersion, freeze/thaw cycling, wet/dry cycling, and heat aging are summarized in Table 7. These environmental conditions are those often encountered in Reclamation's hydraulic applications. TABLE 6           Type of PVC Seams Evaluated in EPA Study     Sample Type of Manufacturer Seaming Seam   No Seam Fabricator Method Width   1 Factory A,C Solvent adhesive 25   2 Factory A,D Thermal-dielectric 19   3 Field Aa Solvent adhesive 50   4 Filed Ab Solvent adhesive 88   5 Filed Bc Solvent adhesive 75 a Solvent adhesive furnished by fabricator C.   b Solvent adhesive furnished by fabricator D.   c Solvent adhesive furnished by manufacturer B.   Test results indicated that except for heat aging, the samples performed satisfactorily with very little change occurring to either the shear or peel strength. The heat aging samples exhibited stiffening due to plasticizer loss from the material. Of the two factory seaming methods used for the PVC, the seams made with the solvent adhesive exhibited higher shear strength, whereas those made dielectrically produced higher peel strength values. The higher shear strength was primarily due to the wider factory seam for the solvent adhesive seam. All failures occurred in the parent material, except for the peel tests on the PVC solvent adhesive seam, where the failure occurred within the seam itself. No appreciable difference was noted in the performance of the two seaming methods however. TABLE 7                       Results of EPA Study on PVC Seams                     Sample 1   Sample 2   Sample 3   Sample 4   Sample 5     Test Condition Shear Peel Shear Peel Shear Peel Shear Peel Shear Peel Original   10 2.6 9.3 6.7 8.3 2.7 9.3 3.4 10.4 4.3 Water immersion at 23°C 6 months 9.9 2.8 9.1 6.6 8.5 3.1 10.5 3.8 10.6 4.3   12 months 10 2.9 9.3 7.3 9 2.7 10.7 3.9 11.7 4.4 Heat aging at 60°C 4 weeks 9.2 3.1 9.3 6.5 8.8 3.8 10.4 4.2 10 4     8 weeks 9.1 3.1 9.2 6.9 9.4 3.2 9.3 4.3 11.3 5.1   13 weeks 10 3.3 9.5 6.9 9.1 4.1 10 4.4 11.4 3.9 Freeze/thaw at: 10 cycles 10.1 2.7 8.9 6.7 8.4 2.4 9.6 4 10.5 4.4   20 cycles 9.7 2.8 9.3 7.3 9.3 3 10 4 12.4 4.7   50 cycles 10.1 2.8 8.4 7.2 8.9 2.7 9.1 3.8 10.4 4.7 Wet/dry at: 10 cycles 10.2 2.7 9.4 6.9 8.4 2.6 10.3 3.8 11.2 6   20 cycles 9.9 2.7 8.5 6.5 8.8 3.3 9.5 3.7 10.2 3.2   50 cycles 9.9 2.7 10.1 6.7 8.2 2 10.6 4.3 10.7 4.6 Note: Test values are expressed as kN/m width of seam. One freeze/thaw cycle consisted of freezing for 16 h at 6.7?C and thawing for 8 h in room temperature water. One wet/dry cycle consisted of 16 h water immersion followed by 8 h of drying at 37.7?C. CONCLUSIONS The Bureau of Reclamation has been using PVC in its buried membrane canal lining work for over 20 years. Results of tests conducted on samples of inservice linings indicate that the factory seams retain excellent shear and peel strength properties with no apparent signs of deterioration. A 1-m overlap, unbonded PVC field seam appears to be adequate for most irrigation canal lining applications, but would not be suitable for landfills or hazardous waste installation where 100% seepage control is required. Results of laboratory tests also indicate that the solvent-bonded field seams can achieve early peel and shear strength development which is advantageous for underwater lining applications. Laboratory tests conducted on an adhesive sealant formulated for the repair of vinyl swimming pool liners indicated that it can be used to make underwater PVC field seams. Results of laboratory tests involving various environmental aging conditions indicate that there is no appreciable difference in the performance of solvent or dielectrically made factory seams.  REFERENCES 1. Hickey, M. E. Investigations of plastic films for canal linings. Research Report No. 19. A Water Resources Technical Publication. Bureau of Reclamation, Denver, Colorado, 1969.2. Geier, F. H. & Morrison, W. R. Buried asphalt membrane canal lining, Research Report No. 12. A Water Resources Technical Publication. Bureau of Reclamation, Denver, Colorado, 1968.3. Morrison, W. R. & Starbuck, J. G. Performance of plastic canal linings. Bureau of Reclamation Report No. REC-ERC-84-1. Denver, Colorado, 1984.4. Morrison. W. R. & Parkhill, L. O. Evaluation of flexible membrane liner seams after chemical exposure and simulated weathering, US Environmental Protection Agency. Report No. EPA/600/S2-87/0l5, Cincinnati, Ohio, 1987.5. Wilkinson, R. W. Plastic lining on the Riverton Irrigation Project. Proc. ASCE Irrigation and Drainage Speciailty Conference. Flagstaff, Arizona, 1984.6. Starbuck, J. G. & Morrison, W. R. Flexible membrane for closed basin conveyance channel. San Luis Valley Project, Colorado, Proc. International Conference on Geomembranes. Denver, Colorado, 1984.7. Weimer, N. F. Use of polyvinyl chloride liners for large irrigation canals in Alberta. Canadian Geotechnical Journal. 24 (1987) (2) 252-9.    REC-ERC-84-1 PERFORMANCE OF PLASTIC CANAL LININGS January 1984 Engineering and Research Center U. S. Department of the InteriorBureau of Reclamation   Table18. -Physical properties test results for PVC membrane linings on Bugg Lateral. Tucumcari Project, New Mexico, installed spring 196l.- Continued     Sample Sample Sample   Specifications No. B-6764 No. B-7022 No. B-7023 Physical property requirements (14 years (19 years (I 9 years     of service, of service, of service,     BWL) BWL2 ) AWL1) Thickness, mm (mils) 0.25 (10) 0.24 (9.6) 0.24 (9.6) 0.21 (8.2) percent change ±10 -14.3 -14.3 -26.8           Tensile strength, N/mm (lbf/in) 3.0 (1 7) 4.2 (24.2) L3 4.6 (26.4) L 5.0 (28.6) L     4.6 (26.1) T4 5.2 (29.8) T 4.7 (26.9) T percent change -5.5 L +3.1 L +1 1.7 L     +14.5 T +30.7 T +18.0 T           Elongation percent 225* 268 L 211 L 151 L     274 T 188 T 188 T percent change -35.0 L -48.9 L -63.3 L     -40.7 T -59.3 T -59.3 T           Modulus at 100 percent Not required 2.4 (13.8) L 3.6 (20.5) L 4.6 (26.0) L elongation, N/mm (lbf/in) 2.4 (13.8) T 4.2 (23.9) T 4.2 (23.9) T percent change +21.1 L +79.8 L +128.1 L     +34.0 T +132.0 T +132.0 T           Elmendorf Tear, grams 1500* 3000 L 3000 L 450 L     2865 T 2200 T 1300 T percent change +63.9 L +63.9 L -75.4 L     +25.1 T -3.9 T -43.2 T           Impact resistance Not more than 2 5 tested Not Not   specimens out determined determined   of 10 shall fail 5 failures       at -18ºC (0ºF)               Plasticizer content, percent Not required 34.1 27 21.6 percent change -14.3 -32.2 -45.7           Bonded seam strength, 65 Not Not Not percent of parent material determined determined determined           1 AWL denotes above normal waterline   2 BWL denotes below normal waterline   3 L denotes longitudinal direction     4 T denotes transverse direction     * Minimum, each direction         Canal data: Established     seepage   b = 5.00 ft, d =4.40 ft, s:s =1.5:1, and   rate   WP =20.86 ft. (7.4806 gal/ft3) (2169 ft2)   Length =104.25 ft.     Average seepage rate for section is 8.2 = 0.0005 (ft3/ft2)/d gal/d.   Reach 5A, station 599+00, PVC lined: Seepage section has a wetted surface of (104)(2y0.86) = 2169 ft2. Canal data:   For more information call   800-OK-LINER  today!

PVC in Arch Dam Repair The use of a geomembrane for an arch dam repair By G. Zuccoli, C. Scalabrini and A. Scuero, General Manager*, Technical Manager* and Technical Manager** Reprinted from Water Power & Dam Construction, February 1989  A geomembrane was recently used in Italy to repair the upstream face of a double curvature arch dam. The authors describe the process and give details of a number of tests that were conducted in the laboratory to verify properties of the membrane used. Publino dam, a 40 m-high double curvature arch dam with a crest length of 250 m, was built in 1951. It is located at an elevation of 2135 m. The dam, which is provided with a de-icing plant on the upstream face, has a reservoir capacity of 5 x 106 m3. It is used as seasonal storage for hydroelectric power generation and pumping. Publino dam can be reached from the valley floor by both cable and narrow gauge railways: most of the route is in tunnels, for an overall length of 11 km. In 1988 widespread deterioration of the surface of the upstream face of the dam was observed. Further investigation showed that up to 30 percent of the 5500 m2 cement rendering had become detached. This condition indicated that the permeability of the structure would rapidly increase if no remedial work were carried out. Although the losses at full storage capacity were only 0.25 l/s. Sondel (the owners of the structure) decided to carry out the rehabilitation of the upstream face as a preventive measure. rather than wait for any further deterioration. It was considered that any delay in this work would make the necessary operations expensive, in terms of both the extent of the operation and the loss of hydro production. Refurbishment method On the basis of work carried out previously by ENEL (the Italian national power authority) on gravity dams. Sondel decided to use a synthetic, waterproof, drained membrane to protect the upstream face. Experience had shown that these membranes could be installed rapidly with mechanical anchorage and with minimal preparatory operations on the underlying concrete support. The system adopted was the same as that already used on the Miller, Lago Nero, Piano Barbellino and Cignana Molato dams. In this system, the impermeable facing is a geocomposite consisting of a very thick flexible synthetic PVC membrane (characterized by high resistance to aging) which was prefabricated and heat-welded to a polyester geotextile during production. Paired stainless-steel sections (ribs), placed vertically and fitted to the body of the dam with small anchors, fasten the geomembrane to the dam face. These pairs of sections also act as non-pressurized drainage collectors for water condensing, behind the membrane. The water collected is conveyed to the heel of the dam, where a perimeter drainage pipe conveys it through the drainage gallery, downstream of the body of the dam. The membrane is manufactured in sections of sufficient length to cover the whole height of the dam, thus avoiding horizontal joints. The vertical joints and the corresponding mechanical anchorages are covered with an additional strip of the same membrane. The mechanical anchorage of the membrane makes it possible to keep the protective facing independent of the facing behind so that construction and expansion joints in the original structure are waterproofed at the same time. (The anchorage ribs are simply placed on either side of the joint, and covered with the waterproof facing.) The system constitutes an efficient drainage system for the body of the dam: the presence of the layer of geotextile draws off the water present within the body of the dam, which tends to stabilize its moisture content. The finished appearance of the installation is satisfactory from an aesthetic point of view: the membrane is a uniform grey colour. The membrane adheres well to the face thanks to the mechanical anchorage, which avoids any sagging or bulging of the material. The solution adopted does not involve any stability reappraisal, since the membrane itself, and the ribs which support it, are comparatively light. The drainage collector, installed along the upstream perimeter of the foundation of the Publino dam, is a stainless steel omega-sectioned bar, fixed externally to the body of the dam. This bar also acts as the sealing element for the base of the membrane sections, as well as connecting with all the vertical ribs. The water collected is drained off through one of the original drainage pipes inserted in the body of the dam. Climatic conditions From an operational point of view, the system adopted allows work to be carried out even in harsh climatic conditions, which would make the adoption of other solutions (such as mortar with resins) difficult, uncertain, and more expensive. In fact, all the components of the system are manufactured and prepared in the factory under controlled climatic conditions. The only operations which take place on site are of a mechanical nature: with other solutions there could be problems with chemical behaviour (polymerization, gelling, and so on) and physical behaviour (viscosity, distribution, and so on), which are often the cause of poor results. Transportation The overall quantity of material necessary for the geocomposite solution is relatively small. This makes the solution particularly suitable in cases of difficult access to the site, as at Publino dam. Also, limited volume of equipment is necessary for this method: only suspended platforms (quickly and easily constructed and dismantled) and small tools (drills, welder, and so on) are required. Installation In the case of the Publino dam, it was planned to waterproof the entire face, which meant that the reservoir had to be completely emptied. Normally the time required for installing the stainless steel sections is approximately 40 percent of the total time needed for the whole operation. However, this installation can be carried out at various stages, according to the water level in the reservoir, using, platforms suspended from the crest of the dam. At Publino, in June and July 1988, the deteriorated parts of the cement rendering were removed from the face, the upstream heel of the dam was cleaned, the perimeter drainage pipe was constructed and the lower vertical sections of the support for the geomembrane were installed (working in horizontal bands).   At the same time, other general work was carried out, such as the complete overhaul of the bottom outlet valve. By the beginning of August, the reservoir was back in operation. The installation of the vertical sections continued, using platforms suspended above the water level, which was continually rising. Placement of the vertical sections continued until October 1988. At the beginning of the summer 1989 season, corresponding with the minimum water level, the reservoir be completely emptied for another month, for the installation of the geocomposite. Therefore, the rehabilitation will be completed over two seasons (representing a total of eight months). The careful planning, of such work should cause minimum interference with the running of the plant and consequently low operational losses. Concrete face preparation It was possible to accelerate the overall installation time because the thick geomembrane (2.5 mm) heat bonded to a 500 g/m2 geotextile, does not require laborious preparation of the concrete face. At Publino, only the deteriorated part of the rendering was removed (using light electric scrapers). The surface after scraping, although rough, is generally considered suitable for laying the geomembrane. A very small amount of patching was done (approximately 3 percent of the total surface), using pozzolan cement, on those parts of the face which were particularly pitted, exposing aggregate with sharp edges. This was decided on the basis of experimental investigations carried out by ENEL at their Hydraulic and Structural Research Centre (ENEL-CRIS). Durability of the system The solution adopted has until now proved to be very reliable, since similar installations carried out up to ten years earlier (for example Lago Miller, 1976) have not shown any deterioration compared with their initial performance. Whenever the partial substitution of the waterproof geomembrane becomes necessary, the operation is very quick and inexpensive compared with the initial installation. The geocomposite The geocomposite chosen for the Publino dam is designated Sibelon CNT 3750, which consists of a 2.5 mm-thick geomembrane manufactured with a PVC mix, heat-bonded during production to a 500 g/m2 polyester felt geotextile. Great care was taken over the choice of the plasticizer added to the basic mix, so as to obtain a geomembrane with good performance in view of the difficult climatic conditions. The material constituting the membrane has been subjected to an extensive series of laboratory tests, both in Italy, at independent University institutes and independant research centres, and abroad, at laboratories belonging to public institutions. These tests have confirmed the good balance of the material. The geomembrane incorporated in the composite has shown the following mechanical characteristics: very low permeability (Darcy coefficient k less than 1 x 10-12 cm/s); non-degradability; good tensile strength (exceeding 285 percent elongation at breaking load); excellent flexibility and elasticity (almost complete spring back, even at loads close to breaking load); good resistance to low temperatures (no sign of cracking after folding test at -35° C); excellent bending fatigue limit (no breakage after 1 x l06 repeated flexions); good resistance to abrasion; optimal chemical inertia; ice-repellence; resistance to damage by flora and fauna: and, good performance of the heat-welded joints. These mechanical characteristics are further enhanced when the geomembrane is heat-bonded to the geotextile. The functions of the heat-bonded to the geotextile are: to increase the dimensional stability of the geomembrane; to provide diffused drainage of the waterproofed surface, drawing off and then draining the waters of infiltration and condensation; and, to cushion the geomembrane and protect it from possible puncture on the rough surface of the existing face. An interesting laboratory elasticity test was carried out. A sample of geomembrane (2 mm thick, and 20 cm in diameter) used on the Lago Nero dam, was placed on a rigid 5 mm-thick support with a slit in the centre, 50 mm long and 5 mm wide. Hydraulic pressure of 20 bar was applied to the sample. A 1.9 mm deflection was measured on the part of the membrane which corresponded with the slit: this returned to its original position within about 10 min of the pressure ceasing. The performance of the membrane remained constant over several repetitions of the test. This test carried out on a sample without a geotextile, shows the excellent resistance of the membrane even if it were fixed directly onto very rough or pitted surfaces. Another laboratory test carried out by ENEL-CRIS involved the application of cycles of hydraulic pressure up to 20 bar on pieces of geomembrane 2 mm thick, bonded to a 200 g/m2 weight geotextile, placed on samples of very rough surfaces which were taken from the deteriorated faces of existing dams. The membrane behavior was as follows: no perforation or laceration occurred, indicating that the membrane had remained waterproof: and, immediately after the test, the PVC material showed the imprint of the underlying surface, but within one hour of the end of the test, the membrane had returned to its original smooth condition. Also in connection with the application of PVC geomembranes to dams, ENEL-CRIS carried out a series of tests regarding the aging of the material, analyzing samples, of membrane taken from dams that had been functioning for more than ten years. The samples were taken from areas above the maximum storage level, which had therefore been exposed to the light constantly. Compared to the initial values, the results of the mechanical tests showed a deterioration of about 22 percent in the tensile strength and approximately 20 percent in the elongation at breaking load: this performance is excellent, considering the high initial values used as the reference. The possible chemical alteration of the polymer with time was tested by infrared spectrophotometry. Absorption tests were carried out on two different samples, exposed and not exposed to ultraviolet rays: the resulting graphs showed the same pattern. It can be concluded that, as far as aging in natural conditions is concerned, the PVC geomembranes used so far show no sign of deterioration in their chemical structure, and therefore in the chemical additives which give the material its mechanical performance. Conclusions Waterproofing the upstream face with a mechanically anchored PVC geomembrane offers a number of advantages:  efficient protection of the construction and expansion joints:  drainage of the body of the dam: and,  simple and rapid installation which does not require expensive surface preparation and is long-lasting. In addition, the installation costs are competitive, but, since the membrane does not require maintenance and is durable over a long period of time, the overall costs are well below those of a traditional facing. Acknowledgment Planning of the Project and work on the waterproof facing were carried out by CARPI, and the preparation of the face was carried out by the same company in direct collaboration with Sondel. Bibliography Scuero, A., "RCC Dams, Upstream Face Waterproofing" ASCE Specialty Conference. San Diego, USA: March 1988. Cazzuffi, D., "The use of geomembranes in Italian Dams": Water Power & Dam Construction, March 1987. Koerner, R. M., Designing with Geosynthetics". Prentice-Hall. Englewood Cliffs, New Jersey, USA: 1986 Monari, F. "Waterproof Covering for the Upstream Face of the ‘Lago Nero’ Dam", Proceedings International Conference on Geomembranes, Denver, Colorado, USA: 1984.   For more information call   800-OK-LINER  today!

There has been much written regarding the use of PVC vinyl products in water pipe, medical applications, toys, packaging and other consumer applications.  Some fanatical groups are advocating the ban of vinyl and chlorine throughout the world. Their claims of dangers of vinyl, based on outdated studies, inconclusive reports, and "junk science" continue to be disproved by sound scientific research conducted by reputable scientists and by the vinyl industry. Here are a few examples: New Phthalate study is PVC’s Koop d’etat The PVC industry had the world's attention June 22, 1999, and for a change it was happy to be in the spotlight. Former U.S. Surgeon General C. Everett Koop pronounced phthalates completely safe in medical devices and toys. His declaration was reported widely in the popular press. This is the same press that a year ago had never heard of phthalates, but just seven months ago helped bully retailers into pulling soft vinyl toys from store shelves. A variety of commentators picked up on Koop's study, and Koop himself authored an opinion piece for the Wall Street Journal. Much of the coverage made a connection between his study and a report on the safety of silicone breast implants. The commentators criticized the trend toward "junk" science that attacks products with anecdotal evidence that doesn’t stand up to the rigors of scientific inquiry. In this celebrity-crazed era, a stamp of approval from Koop seems to be just the prescription that the vinyl industry needed. Koop was arguably the most visible surgeon general in U.S. history. He used the office as a bully pulpit, and in the process won a gold-plated reputation as an advocate for public health. Critics attacked the Koop study, arguing that the American Council on Science and Health, which organized the project, was funded by, and therefore a pawn of, chemical industry interests. Given Koop's stature, it will be difficult to make that charge stick. The key now will be for the vinyl industry to sustain its success. It needs to reinforce Koop's conclusion and create a public perception that vinyl products are safe. It needs to convince a few former customers to shift course publicly and go back to using PVC. In the meantime, it should continue to support research into the safety of PVC, as well as research and development efforts to make vinyl resin production, use and disposal as safe as possible. This article is from Plastic News Magazine, July 5, 1999 as shown in the Viewpoint.   TV: In an interview on CBS This Morning , Dr. Koop stated that the medical profession has over 40 years of historical data showing the safety of vinyl products used in health care applications.  He stated that the use of phlalate plasticizers in medical applications has proven to be a safe and cost effective practice, and that consumers should not be concerned with its use in health care.  Here's another... NEW ORLEANS - Baxter International Inc. , a leading supplier of medical products, wants to set the record straight regarding its use of flexible PVC. The Deerfield, III.- based firm was thrust into the spotlight in April when, after shareholders expressed concern about alleged health problems resulting from PVC use, Baxter officials said the company would continue its effort to find alternatives to vinyl products. In a June 24 speech at Flexpo 99 in New Orleans, Baxter technical director K.Z. Hong said the company had been reviewing alternate materials for several years. "We’re constantly searching for better materials," Hong said. "People were asking us why we were resisting change, and that’s totally contrary to the truth." Hong said Baxter has replaced rigid and semirigid PVC applications such as blister packaging and drip chambers as superior replacement materials were developed. Flexible PVC also has been replaced in applications including bags for pre-mix drugs and some blood products such as platelets. But in most flexible PVC applications, competing materials haven't been able to match the variety of attributes PVC can offer, he said. Materials aiming for PVC’s medical uses include thermoplastics elastomers and metallocene or single-site-enhanced grades of polyethylene and polypropylene, as well as numerous blends, alloys and multilayer laminates made from those materials. Hong laid out those criteria in a three-tiered, pyramid-shaped diagram, with basic attributes on the bottom and difficult ones on top. By volume, 80 percent of medical PVC applications require materials that can reach the third level. Hong also repeated Baxter’s belief that PVC is not harmful in medical uses. Greenpeace and other activist groups have claimed that phthalates used in plasticizers can leach out of PVC blood bags and intravenous tubing and enter the bloodstream. Most potential replacement materials are significantly more expensive than PVC. But Hong said the cost factor has been exaggerated in some accounts. "There's been a misleading impression that we've overemphasized the cost, and that makes Greenpeace think we're only thinking of dollar signs," Hong said. "That's totally untrue. The first item on our list of material-selection criteria is the safety of the end users. The material must first do no harm to patients." Hong added that PVC has more than 40 years of safe and effective clinical use working in its favor. That history adds up to at least 5 billion patient days of acute exposure to PVC products and at least 1 billion patient days of chronic exposure. "The PVC experience has been very unique," Hong said. "The material is unchallengeable today, but maybe tomorrow that will change." Baxter has done a good job of handling the PVC issue so far, according to Robert Brookman, vice president of Teknor Apex, a PVC compounder headquartered in Pawtucket, R.I. "Initially, I was shocked at what [Baxter] said, when it sounded like they were actively seeking to replace PVC," Brookman said. "But when the company followed up and straightened things out, I felt more comfortable with it." Brookman added that PVC’s history of widespread medical use, combined with research such as former U.S. Surgeon General C. Everett Koop's recent study, are proof of the material's safety. "This argument doesn't have a leg to stand on," Brookman said. "There's no sound data that shows PVC is medically harmful." This article was written by Frank Esposito and published in the Plastic News Magazine, July 5, 1999 edition.