EVALUATION OF LONG TERM AGING EFFECTS ON PVC CHEMICAL AND THERMAL SEAMS
By: Fred P. Rohe & Mark A. C. Wolschon
In 1991, Ian Peggs asked me the question “What are the long term effects of wedge welding of PVC geomembranes?” At the time, I was not sure of what the answer to that question was.
To find an answer, EPI proceeded with an experiment in the long-term behavior of Thermal Wedge Welded PVC seams. We decided to also compare chemically welded PVC seams according to the same parameters. Mark Wolschon, Quality Control Manager at EPI, has been in charge of the research from the start, and has managed the sampling program and supervised all of the testing.
This program was established to evaluate the peel strength and durability of PVC seams in service over an extended period of time. The procedure was setup to analyze the changes that natural environmental conditions might have on the peel strength of PVC seams, and to determine if there were any detrimental changes caused by the welding procedure. The test area is located at Environmental Protection Inc., Mancelona, MI., which is situated in northwest Lower Michigan, approximately on the 45th parallel. Ambient temperatures range from 85°F to -20°F.
The geomembrane material used was 30 mil PVC liner, manufactured by Occidental Chemical Corporation, lot #60034, received by EPI on 12-18-1991. The original material certification and receiving inspection records are included in the records of this program.
The seams were fabricated under normal factory conditions. Two seventy-five foot test strips were fabricated. The first was a factory chemical welded (CW) seam, and the second was a dual track wedge welded (WW) seam.
Both strips were the cut into three 25' sections and numbered. Seam sections 1,2 & 3 are the chemical welded seams, and 4, 5, & 6 are the wedge welded seams.
After initial production of the seams each sample had five 1” wide specimens removed, which were tested for peel strength per ASTM D-413.
a) The test strips were placed in position on June 22, 1992. Sample numbers #1 and #4 (one each of the CW and WW seams) were buried approximately 8 to 12 inches deep in native sandy loam soil.
b) Samples #2 and #5 were placed exposed on the surface of the ground along side #1 and #4 with the edges secured in the soil.
c) Sample stripes #3 and #6 were archived in storage in an unheated warehouse at EPI.
At six-month intervals, five one-inch specimens will be retrieved for peel testing. The peel strength test results will be recorded for comparison with earlier test results. Testing will continue until all samples are exhausted.
DATES OF TESTING
Initial Fabrication 02/27/92
1 after installation 08/15/92
Wedge Welded Seams;
Each of the three samples was tested for peel strength. Both tracks of the dual track weld were tested in each sample.
All of the year 2000 wedge welded samples tested (buried & exposed) resulted in a seam edge break for each of the specimens. None of the specimens peeled in the seam area.
All of the samples are continually gaining peel strength. There has been NO evidence of any brittleness, even in the exposed samples, to this point. There has been no deterioration of the PVC geomembrane caused by the thermal welding.
Chemically Welded Seams;
A set of chemically welded seams was also compared with the thermally welded seams.
The archived chemically welded sample shows an expected uniform increase in peel strength over the term of the test. The buried and exposed samples also show a continuing increase in peel strength.
We know from other experiments that the chemical weld continues to develop increased strength over time. We also know that as the material ages it tends to increase in tensile strength and decrease in flexibility. The peel strength of the welds is tending to follow the same pattern, and will eventually reach film tear bond and break at the seam edge when tested for peel strength.
This is an ongoing experiment, and new data will be added to these charts as each succeeding test is done. We have additional sample material available to any qualified test lab interested in doing analytical evaluation of these welds. Contact Fred Rohe or Mark Wolschon for more information.