Effect of Different Factors on Bonding Properties of Bitumen–Aggregate Combinations

Abstract

The bond between bitumen and aggregate is important in ensuring suitable performance of flexible pavements in different environmental conditions. The bonding properties of bitumen–aggregate samples can be affected by different factors (i.e., aggregate types, bitumen types, temperature variations, aging phenomenon, and moisture conditioning). This study illustrated the effects of different factors on the bonding properties of bitumen–aggregate samples and aimed to identify the significant factors. The experimental variables in this study were aggregates (limestone and granite), bitumen (traditional black bitumen, clear binder), aging duration, curing conditioning, and curing times. Bitumen bond strength (BBS) tests and rolling bottle tests (RBTs) were performed to determine the pull-off tensile strength (POTS) and stripping degree of bitumen–aggregate samples, respectively. BBS test results illustrated that aging initially improved the bond strength of the samples, but further increases in aging duration attenuated bond strength because of bitumen embrittlement. In general, temperature changes showed an inverse relation to the bond strength of the samples. Failure type changed from cohesive to mix failure or adhesive failure at low temperatures. BBS results also showed that bonding between bitumen and aggregate was dominated by bitumen type when cohesive failure was observed, and in cases of adhesive failure or cohesive-adhesive failure, aggregate types had a significant effect on bonding properties. Cohesive-adhesive failure or adhesive failure was observed at low temperatures and in wet conditioning. RBT results showed that a bitumen–granite mixture showed high moisture susceptibility. Statistical analysis suggested that all variables of this study except aggregate types were statistically significant and affected bond strength in dry conditioning. In wet conditioning, all the variables were significant, and curing time was the most influential variable. Partial eta squared values were highest for bitumen type, indicating the importance of this factor for bitumen–aggregate bond strength.