Organic “High-Build” Spray-in-Place Liners – An Emerging Class of Rehabilitation Methods

By Erez N. Allouche, PhD, P. Eng. and Eric J. Steward, Trenchless Technology Center, Louisiana Tech University | June 2009 Vol. 64 No. 6

Mechanical properties
A series of tests of both polyurethand and polyurea linings were performed in accordance with ASTM D638 to determine the stress versus strain relationship of the materials used in the construction of the test panels. Coupon samples were cut from each panel in both, lateral and longitudinal directions. The samples were then tested to evaluate their tensile modulus and limiting tensile strain as per ASTM 638. For the 15 samples of polyurea, the elastic modulus was found to range between 150,000 psi and 230,000 psi, with an average value of 189,000 psi. Strain at failure was found to be 0.049. The average tensile modulus for the polyurethane was determined to be 425,000 psi, and the strain at failure 0.02. Graphical representations of the experimentally measured stress-strain curves for the polyurea and polyurethane formulations tested are shown in Figures 3 and 4, respectively.

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Fig 4. Stress-strain curve for polyurethane (as per ASTM 638)
Apparatus, experimental set-up (subhed)
The testing frame consists of two main components; the pressure side and the opening side. The pressure side of the frame was designed to apply a uniform pressure to one side of the panel (Figure 5). The opening side of the frame contains a circular opening, which simulates a deficiency in the host pipe wall. This opening is the region of the panel where failure occurs. Both portions of the frame contained a rigid formation of rectangular steel tubes attached to a machined flat steel plate (Figure 6). On the pressure side, the steel plate has a welded steel extension collar that creates a 24 x 24 x 1 inch cavity where the water pressure can be developed. The collar has a square groove machined inside of the bolt pattern to fit a rubber seal (Figure 5). The seal assists in maintaining the pressure inside the cavity by eliminating any minor deformities in the panel.

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Fig. 5: Pressure half of frame with the seal installed

The opening side of the frame consists of either a 3-inch or 4.5-inch diameter opening in the center of a rigid steel plate. This opening simulates a portion of material either heavily corroded or missing altogether from the host pipe wall. The two halves of the frame are connected using 26 threaded one inch diameter rods.