Abstract
The bond strength of asphalt binder and aggregate is an important parameter to evaluate the mixture ability to resist moisture damage. An innovative approach was utilized where adhesive failures of asphalt-aggregate constituents were computed in direct tension using the Pneumatic Adhesion Tensile Testing Instrument (PATTI). Hydrated Lime (HL) and Pavement Modifier (PMD) were used as anti-stripping fillers in asphalt mastics, while Evotherm (EV) was incorporated as the Warm Mix Asphalt (WMA) additive. Three long-term conditioning levels were performed namely; unconditioned, conditioned long-term aged (LTA) + 1 freeze-thaw (F-T) cycle and LTA + 3F-T cycles prior to testing. The Accelerated Laboratory Vacuum Saturator (ALVS) was integrated to subject asphalt constituents to the combined effects of pore pressure and high temperature. The conventional moisture conditioning and aging procedures were also modified to better mimic the actual field condition. An interesting observation pertaining to the moisture-damage mechanism was made in this study where moisture penetrated into the asphalt-aggregate interface via holes on the asphalt film. Compared to asphalt mastics, more holes were observed to develop on the binder specimens. The percentage adhesive failure of asphalt constituent test specimens was quantified using 2-D imaging technique. The percentage adhesive failure of asphalt specimens increased with LTA and F-T cycle, while tensile strength reduced with moisture conditioning. Asphalt mastics specimens exhibited relatively lower percentage adhesive failure than binder specimens attributed to the addition of fillers that stiffened and reduced binder moisture susceptibility. The image analysis results showed that the percentage adhesive failure for specimens prepared with polymer modified binders was lower than unmodified binder specimens. Samples using PMD exhibited slightly lower percentage adhesive failure than HL specimens. The percentage of failure reduced further with the incorporation of EV, regardless of aggregate type. Specimens using limestone also showed superior moisture resistance than granite specimens in moist condition.
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