Retrospective Evaluation of Cured-in-Place Pipe - (NEPIS)(EPA ...

condition with no signs of structural distress. For one of these samples, retesting five additional coupons
provided results that did meet the ASTM minimum value. It is considered likely that poorer liners will
have more spatial variability in structural parameters and hence the test results may depend on the chance
of where the coupons are taken. Higher quality liners are more likely to have full resin impregnation and
even curing and should provide more consistent test results.
6.4.6 Buckling Tests. Sections of the two 8-in. liners that were recovered together with the host
pipe were removed from the existing clay pipe and installed in a surrogate steel host pipe for external
pressure testing. The 2-ft length that was available for testing was shorter than would be necessary to
avoid end effects that tend to provide higher buckling pressures. However, the annular gap around the
liner in the surrogate pipe was much higher than that in the site condition, which would tend to lower the
buckling resistance. The Denver liner held 40 to 45 psi (equivalent to 96 to 102 ft head of water) for
nearly an hour without buckling. The Columbus liner held 50 psi (equivalent to 115 ft head of water) for
15 minutes without buckling. In both cases, the level of applied external pressure did cause some leakage
through the liner.
The depth (from the surface to the crown of the pipe) of the Denver pipe was 5 ft and the depth of the
Columbus pipe was 6 ft. Thus, the short-term buckling pressures applied to the specimens were 15 to 20
times the maximum water pressure that would be applied if the groundwater table was at the ground
surface.
6.4.7 Surface Hardness Tests. Surface hardness tests were performed following ASTM D2240
(Durometer Shore D) and ASTM D2583 (Barcol hardness) and the results are tabulated in Table 6-5.
Table 6-5. Summary of Hardness Values
Measurement Set
Age of
Liner
Location
TTC Shore D Values
Interior Exterior
TTC Barcol Values
Interior Exterior
Insituform
Barcol
Values
Crown 62.8±3.3 77.5±3.1 43.2±1.5 45.9±1.2 38±3
Denver 8-in. 25 Spring line 58.9±3.0 79.6±1.4 38.5±0.9 39.4±1.2 -
Invert 56.4±2.3 74.3±1.7 38.9±1.3 42.3±0.8 -
Denver 48-in.
downstream (2010)
23 Crown 65.2±3.4 78.9±1.6 16.5±1.5 29.3±1.3 -
Denver 48-in.
upstream (2010)
23 Crown 46.6±2.3 62.7±3.1 14.9±1.8 18.5±2.4 -
Crown 63.3±0.8 83.0±1.8 7.0±0.8 14.3±1.7 -
Columbus 8-in. 5 Spring line 62.3±0.8 81.7±1.8 6.5±0.8 14.0±1.6 -
Invert 62.4±2.2 79.5±0.9 6.8±0.8 13.0±1.7 -
Columbus 36-in. 21 Upper haunch 65.7±3.6 78.9±2.3 18.9±2.2 22.3±2.0 -
The measurements for the exterior surface of the liner gave significantly higher readings than those for
the inner surface of the liner when using the Shore D hardness test. On the Shore D scale, average inner
surface values ranged from 46.6 to 65.7 and exterior surface values ranged from 62.7 to just over 83. In
the Barcol hardness measurements, the differences in hardness of the inner surface compared to the
exterior surface values varied significantly. In some cases, the values were quite similar and in others the
exterior values were around double the interior values. It is not clear at present how much of these
differences are due to the presence of and/or degradation of the inner surface layer and how much they
may represent deterioration due to exposure to the waste stream.
100