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To evaluate the strength of the bond area formed by solvent-cementing of thermoplastic pipe and fittings, tests are conducted at 2 hours, 16 hours and 72 hours. Because the data is statistical in nature, more than a single specimen must be tested to provide a representative strength at each cure time. Considering that 3 tests are run, each consisting of multiple specimens, a method was developed for testing joined plaques rather than pipe and fittings. This method, known in the industry as “lap-shear” is much less time intensive than actual pipe joint preparation, and in theory, provides a good approximation of the anticipated strength of a pipe/fitting joint. A study of this test method was conducted to investigate variables in preparation technique and their effect on strength. The results indicate an extreme sensitivity to minor variations in preparation. The interpretation of this data with respect to joint strength is also discussed. An explanation of these significant deviations encountered due to the changes in preparation is provided, based on thermodynamic considerations of the mixing/dissolution process and work input to sample/solvent system. This paper presents an analysis of the sample preparation technique, in both a theoretical and qualitative context of solution thermodynamics and an evaluation of the minor changes in methodology that can cause major differences in test results. Notable results of the study include changes in shear strength on the order of 12–100% based solely on sample handling within the first 30 seconds, and a lack of sensitivity to the composition of the cement within normal ranges. The solution thermodynamics analysis provides some insight as to the relative significance of the variables in the preparation method.
solvent-cement, PVC, poly(vinyl chloride), shear, bond, diffusion
Director, Physical & Mechanical Testing, NSF International, Ann Arbor, MI