Abstract
Moisture damage–related distress is a primary concern limiting the application of cold-mix asphalt (CMA) as an alternative to hot-mix asphalt in the field. Thus, a simple and effective method is needed in the materials selection process to identify moisture susceptible materials. This study presents a modification to the boiling test procedure specified in ASTM D3625 based on the concept that a mix designer can limit moisture damage by controlling coating quality. The test was modified to present CMA-specific sample preparation guidelines and to remove subjectivity from the test by quantifying coating according to image analysis. Coating quality was evaluated with the coating loss ratio, defined as an index to compare coating before and after the boiling of cured loose mixtures. The relationship between coating quality and moisture resistance was verified with two separate tests: the AASHTO TP-91 binder bond strength test and the AASHTO T-283 tensile strength ratio test. The binder bond strength test provided a direct measure of the bond between binder and aggregate and how it was influenced by moisture. The effect of coating quality on bulk mixture performance was evaluated through comparison with the tensile strength ratio test. All compacted mixtures were produced with a newly developed CMA mix design method to maintain air void levels between samples. Results show that image analysis can be effectively applied to quantify the results of the boiling test, and rankings from all three tests are consistent; this efficacy suggests that the evaluation of coating quality with the modified boiling test can be used as an effective initial evaluation of the potential for CMA moisture susceptibility.
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