Page 330 - Materials Chemistry, Second Edition

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The Sanitary Landfill 301
10.4.9 SURVIVABILITY TESTS
Several tests are available to determine the survivability of unexposed polymeric liners. For exam-
ple, puncture tests are useful to estimate the survivability of geomembranes in the field. During a
puncture test, a 5/16 in. steel rod with rounded edges is pushed down through an anchored mem-
brane (Figure 10.5). A very flexible membrane that is shown to have high strain capacity under ten-
sion may have great survivability in the field. High-density polyethylenes provide a high penetration
force but experience high brittle failure. Thus, puncture data may not adequately predict field
survivability (U.S. EPA, 1989).
10.4.10 PERMEABILITY

Even if a liner is installed correctly, i.e., without punctures and defects, liquid will inevitably
diffuse through. However, such rates are extremely low. U.S. EPA data (1988) for water vapor
transmission across various geomembranes is given in Table 10.5. Permeability of a geomem-
brane is evaluated using ASTM E96, the Water Vapor Transmission test (ASTM, 2000). A sam-
ple of the membrane is attached to the top of a small aluminum cup containing a known volume
of water. The cup is then placed in a chamber of controlled humidity and temperature. The
chamber is typically set to 20% relative humidity while the humidity in the cup is 100%; thus,
a concentration gradient is set up across the membrane. Moisture diffuses through the membrane
and with time the liquid level in the cup will fall. From these measurements, the rate at which
moisture is moving though the membrane is measured and the permeability of the membrane is
calculated with a simple diffusion equation (Fick’s first law)
J D(dC/dx) (10.2)
2
2
where J is the flux (mol/cm sec), D the diffusion coefficient (cm /sec), C the concentration
3
(mol/cm ), and x the length in the direction of movement (cm).

FIGURE 10.5 Puncture apparatus for geomem-
brane testing.