Since its inception, CIPP has developed from a proprietary, to a standards based technology with numerous systems available to choose from. Globalization has shaped the trenchless industry and many of the CIPP systems in use today were developed outside of North America.
The measurement of flexural properties is one of the most common QA/QC techniques to verify the satisfactory curing of a CIPP installation. North American procedures rely on measurements taken in the longitudinal direction while European procedures measure flexural properties primarily in the hoop direction. This paper examines the differences between the two methods for measuring flexural properties and illustrates the differences in actual test data taken from CIPP field samples.

The life extension capabilities of CIPP for pipe rehabilitation are well established. The measured long-term flexural modulus creep retention factor (CRF) of CIPP has been employed to design numerous installations where the actual life extension has later been demonstrated. The CRF is determined by the CIPP system manufacturer through type testing of the resin/felt material.

Accepted industry consensus is that field prepared CIPP samples can exhibit lower short-term flexural properties than the short-term flexural properties which are determined by CIPP system suppliers during type testing. Factors such as installation conditions or crew experience can contribute to flexural properties of field samples occasionally falling below the specified design minimums. This characteristic of CIPP field installations has been referred to as natural variation.

One commonly observed anomaly which can be related to lower short-term flexural properties in CIPP field samples is ineffective resin saturation of the needled felt. Since in needled felt CIPP systems, the resin itself is responsible for achieving the ultimate flexural properties, failure to fully saturate the voids within the felt with resin can result in lower flexural performance.

Current design practice assumes that CIPP field samples which exhibit short-term flexural properties lower than those determined during type testing will nonetheless exhibit long-term creep performance which is similar to the creep behavior originally determined by the system supplier during type testing.

This paper describes the findings of a research project examining the relationship between resin saturation effectiveness of needled felt CIPP field samples and short-term and long-term flexural properties.

Cured-place-pipe (CIPP) has demonstrated that it can be an effective rehabilitation technology when implemented within an appropriately managed project. Numerous specifications have been written to describe the processes which are required to ensure that the Owner is left with rehabilitated assets which will deliver the expected life extension of the asset. The processes included in these specifications typically reflect a balance between, on one side, the risk of a failure to meet design objectives and on the other, the cost, both in direct dollars and indirectly in administration and management, to minimize that risk.

While the first CIPP installation was completed in 1971, the first industry standard practice, ASTM F1216 was not published until 18 years later. Even though the standard has seen regular revisions since then, the recommended inspection practices have largely remained the same even while anecdotal evidence to support more rigorous practices has accumulated. Only very recently has published research based upon actual data from installations demonstrated the prevalence and magnitude of natural variation (lower mechanical properties and/or wall thickness) in CIPP installations.

In this vacuum, the content of owner specifications has come to reflect the individual specification writers experience or lack thereof with CIPP and their perception of the risk of not meeting design objectives. Using statistical and economic analysis of actual project experiences, this paper will demonstrate the risks and costs of a CIPP quality assurance process which has been informed by five decades of research and industry experience.

Creep is a time-dependent phenomenon wherein a material experiences continually increasing strain under a constant load. ASTM D2990 is the test method employed when investigating the creep properties of plastics and has been applied in industry to the study of cured-in-place pipe (CIPP) material. In the application of D2990 to CIPP material, several situations may be encountered where subjective interpretation of the standard is required. Such situations include determining loading conditions to provide data relevant to real-world CIPP design and selecting the appropriate curve-fitting equations to accurately predict long-term properties. In long-term creep testing, loading conditions should be set below the yield point of the material while being greater than the expected working load.

This would be to ensure that the majority of recorded strain is creep-related and that experiment durations remain practical. Under ASTM D790 and ASTM D638, the yield point is defined as the end of the linear portion of the stress-strain curve where the material exhibits an increase in strain without an increase in stress. Issues arise when trying to determine the yield point of composite materials such as watermain CIPP because their stress-strain curves do not typically show an initial linear region or a point of zero slope.

This paper seeks explore other methods for determining an effective yield point of CIPP watermain which can be used as a reference for future long-term creep tests.

Short term flexural testing for quality assurance of Cured-In-Place Pipe (CIPP) is one of the necessary tests to verify that the installed liners meet the material properties requirements specified in the Owner specification and the structural design of the liner. Research has demonstrated considerable variation can occur in flexural test results from CIPP samples. This variation in flexural test results can further be increased by the uncertainty already inherent in the ASTM D790 test method. In our previous papers related to this subject, we investigated the influence of test specimen geometry, stress distribution on the test specimen, and the effect of through-thickness resin curing on the flexural test results.

In this work, we summarized our previous work to identify the impact of using different specimen surface conditions and test methods on the measured flexural modulus and flexural strength, and continue the investigation on determining if specific test specimen preparation tools had an effect on the surface roughness and dimensional accuracy of the finished specimens, which in turn impacts the flexural properties of the CIPP. Many common tools are used by laboratories to prepare flexural test specimens; however, a standardized sample preparation technique has not been established within the CIPP industry. Six sample preparation tools were identified and used to prepare flexural test specimens in accordance with ASTM D790. Several criteria, including dimensional accuracy and surface roughness, were quantified to evaluate the effectiveness of the different tools to prepare ASTM D790 compliant test specimens.

The discussion from this research focuses on resin and felt CIPP systems; spray-on systems, UV systems, reinforced systems will be presented in future discussion.