Test Method on Adhesive Property of Joint Sealant in Supporting Layer of Ballastless Slab Track

Abstract

The current test method cannot predict the properties of a joint sealant accurately, and therefore this paper proposes a new test method to evaluate its adhesive property. Field investigation was conducted to examine the main forms of joint sealant failure and its actual working conditions. Our findings enabled us to develop a new test method for evaluating the adhesive properties of sealants. A testing procedure, a standard substrate, and optimal testing parameters were determined in the light of analyses of test results. We conducted differential scanning calorimetry (DSC) and X-ray photoelectron spectroscopy (XPS) tests to research the adhesive mechanism of the sealant. Results showed that adhesive failure is the main failure form, and it is caused mainly by horizontal joint expansion. Using peak load as the standard evaluation index, we noted that quartz substrate has the weakest bonding interface with joint sealants. The adhesive strength of sealants has a positive correlation with the isocyanate index and elongation rate, and a negative correlation with temperature. The optimal elongation rate was determined to be 100 mm/h, at which there is good repeatability and stability. Sealants with high isocyanate index can present two glass transition points and react more easily with SiO2, but may also result in a rougher surface that could reduce the chemical interaction between polyurethane and SiO2.