Study of Factors Affecting Curing of Asphalt Emulsion Tack Coats

Abstract

Asphalt emulsion is the most widely used tack (bond) coat material in the U.S. A critical aspect when using asphalt emulsion is the rate of curing, which can cause project delays and affect final performance of the tack coats. The main objective of this study is to investigate factors that may affect the curing time of asphalt emulsion tack coat. Six factors including emulsion type, humidity, curing temperature, type of substrate, residual rate of application, and dilution rate were varied in this study. Curing time is quantified using a mass loss test in which the mass of each sample was recorded at 30-minute intervals until a constant (terminal) mass is reached. A moisture loss rate is calculated in reference to the terminal mass as a function of time. Results show a significant effect of dilution rate, humidity, and temperature on the rate of curing, whereas the effects of emulsion type, rate of application, and substrate type are less significant. In general, the rate of curing is found to decrease with increased dilution rate, humidity, and lower temperature, particularly when factors are compounded (low temperature and high humidity). Findings indicate that from a practical perspective, limiting the practice or extent of dilution should be considered if rapid curing is desired. Although the type of emulsion is not shown to significantly affect curing rate, the residual properties of the residue may affect tracking propensity and bond strength independent of curing time.