North American and European Flexural Testing Methods – Impact on CIPP Flexural Properties
Will you get the 50 year plus life you expect from your CIPP installation? A video inspection and thickness measurement of your completed installation will not tell you this. Each CIPP installation encounters variables that affect its initial cured-in-place mechanical properties. The present state-of-theart in mechanical inspection techniques uses a destructive flexural test to determine the initial flexural strength and modulus of each installation. This data, along with the final thickness is then used to confirm that the installation complies with the liner’s design, such as by F1216 Appendix X1 calculations.
Normally variation can be expected between the results obtained for specimens from lab prepared samples and results obtained for specimens from field prepared samples. It is also not unusual for results obtained from different labs to present additional scatter. The sources of this latter variation have not been well documented and consequently create unnecessary doubt in the method used to determine these properties.
This paper describes the ASTM D790 test method that is used to determine flexural strength and modulus; and examines the sources of variation that exist from specimen preparation techniques as opposed to CIPP sampling techniques. The D790 method provides guidance on test specimen selection based upon the material to be tested. CIPP is not a specific material configuration in the D790 method. As a result, it is left to the user (or test lab) to interpret which D790 material configuration most closely matches the CIPP material. This ambiguity in D790 can lead the tester to choose from a wide selection of different specimen types. This paper documents the results of experiments designed to quantify the effect of 1) specimen types and 2) testing directions on the flexural modulus and strength of CIPP field samples.