Mechanical properties of CIPP: A comparative analysis of testing methods, sample geometry, and liner materials
Topic(s) : Material and Structural Behavior - Simulation & Testing
Co-authors :
Ana SKENDER (CROATIA), Marina FRANČIĆ SMRKIĆ , Viktorija UKALOVIĆAbstract :
The cured-in-place pipes (CIPP) have been used as a trenchless (“no dig”) rehabilitation method for water and sewer pipelines since the 1970’s. This technology is often used to address issues such as leaks, corrosion, and structural damage to concrete pipelines. A thermoset resin-saturated liner (flexible tube) is inserted into the damaged pipe by mechanical pulling or inversion. The liner is inflated to the inner surface of the pipe by air or water pressure and then cured by heat or ultraviolet (UV) light to obtain a hardened liner inside. The heat curing method is a traditional, low-cost curing method with a significant carbon footprint and energy consumption. The UV curing method, on the other hand, is characterized by fast curing, a lower carbon footprint and higher costs. The liner serves as a resin carrier and can be a synthetic fibre needle felt liner or GRP (glass reinforced polymer) liner. The fibre reinforcement reduces the thickness of the inner pipe and at the same time increases its mechanical properties. Resin systems mostly used are styrene-free Vinylester or styrenated Polyester.
Laboratory tests are performed on samples taken from full-length liners to verify that the installed liner fulfils the performance requirements. The modulus of elasticity serves as an indicator of the load-bearing capability. In this paper, the apparent modulus of elasticity of CIPP was determined in the ring stiffness test, from the 3-point bending test and the tensile test. The expressions used to calculate the moduli are valid if linear elastic behaviour and small deflections are assumed. Each test method includes a specific sample geometry and test conditions. For example, the standard recognizes 3-point bending tests on curved samples cut in the circumferential direction or on flat longitudinal samples. The apparent values of the flexural modulus determined on curved samples are then converted to the flexural modulus that would be obtained on an equivalent flat specimen using a theoretical correction factor. This correction factor is derived under the assumption that the sample does not slip on its supports. The results of 3-point bending tests on curved samples of needle felt and GRP liner with different span-to-diameter ratios are presented in this paper. The findings of this study provide an understanding of the mechanical properties of CIPP as determined by various tests related to the effects of sample geometry, test conditions and liner material.
Laboratory tests are performed on samples taken from full-length liners to verify that the installed liner fulfils the performance requirements. The modulus of elasticity serves as an indicator of the load-bearing capability. In this paper, the apparent modulus of elasticity of CIPP was determined in the ring stiffness test, from the 3-point bending test and the tensile test. The expressions used to calculate the moduli are valid if linear elastic behaviour and small deflections are assumed. Each test method includes a specific sample geometry and test conditions. For example, the standard recognizes 3-point bending tests on curved samples cut in the circumferential direction or on flat longitudinal samples. The apparent values of the flexural modulus determined on curved samples are then converted to the flexural modulus that would be obtained on an equivalent flat specimen using a theoretical correction factor. This correction factor is derived under the assumption that the sample does not slip on its supports. The results of 3-point bending tests on curved samples of needle felt and GRP liner with different span-to-diameter ratios are presented in this paper. The findings of this study provide an understanding of the mechanical properties of CIPP as determined by various tests related to the effects of sample geometry, test conditions and liner material.