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

Looking for correlations to the low modulus value, it can be noted that the flexural strength recorded for
Set 1 of the Denver 48-in. upstream liner was also the lowest value measured. However, the tensile test
data (representing different coupons from the same sample) were at the upper end of the range of the
remaining results. For the Columbus 36-in. liner with the low flexural modulus value (which was
installed as an emergency change order to an existing contract), the flexural strength and tensile strength
were all near the bottom of the range for all the liner samples, but were not the lowest values. However,
the tensile modulus for the Columbus 36-in. liner was the lowest value recorded.
The 1995 sample of the Denver 48-in. liner was measured with an average flexural modulus of 490,000
psi, which was the highest value recorded in the data included in this study. The remaining modulus
values measured in this study (excluding the Denver 48-in. upstream liner and the Columbus 36-in. liner)
range from 263,707 psi to 366,563 psi. An additional flexural modulus value of 464,652 psi was a
recorded value from the QA/QC testing during installation of the Columbus 8-in. liner.
Hence, the two flexural modulus values measured by other laboratories (464,652 and 490,000 psi) are
significantly higher than the TTC measured values (182,622 to 340,044 psi). This introduces the
possibility that some differences in modulus may occur through variations in sample creation,
preparation, testing procedures, and/or interpretation. In particular, for the Columbus 8-in. QA/QC
sample, the sample is usually prepared by curing an extension of the liner within the manhole. This does
not have the same installation and curing conditions as within the sewer line itself and such samples are
generally expected to have higher test results than coupons cut from within the sewer.
For tensile strength, the average values range between 2,300 psi and 4,020 psi. The Columbus 8-in. liner
tended to exhibit high tensile strengths (3,696 psi to 4,020 psi) and the Denver 48-in. liner tested by
Insituform had a low tensile strength of 2,300 psi. The remaining tensile strengths were all grouped in a
close range between 2,990 psi and 3,208 psi. There is no minimum value for tensile strength provided in
the ASTM F1216 standard.
For tensile modulus, the average values range between 315,259 psi and 426,787 psi. There is no
minimum value for tensile modulus provided in the ASTM F1216 standard and it does not appear to be a
commonly recorded test value.
Tensile elongation at break is sometimes used within the industry to help identify issues relating to liner
composition, but it is reported to be an imprecise measure due to the effect of surface irregularities in the
sample on the elongation at break. A high elongation at break may point to a lower degree of resin
saturation in the liner, but good records of liner wet out and examination of specific gravity data are
considered more reliable. For the test results reported in this study, the tensile elongation (strain) at break
ranges from 1% to around 11%. In this study, the high elongations at break were observed for the
Columbus 8-in. liner samples, but this did not appear to correlate well with poor performance in the other
test values. The most common range for tensile elongation at break for the samples tested ranged from
around 1.5% to around 6%.
The flexural and tensile testing results raise issues about the variability of samples within the same liner
and potential variability in test results among different laboratories. However, some level of correlation
between test results is observed for some of the parameters measured. As the research progresses to other
sites, it will be important to find out which of the parameters are the most sensitive to deterioration of the
liner structural condition and performance, as well as which are the most cost-effective and reliable to
measure.
Most of the liner samples met the original specifications for structural performance in flexure. Even the
two samples that were below the originally specified flexural modulus values appeared to be in good
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