Evaluation of The Moisture Susceptibility of Asphalt Mixtures Using the Direct Tension Test at the Binder and Mastic Scales

Abstract

The objective of this research is to study the interaction between different binders, aggregates, and mineral fillers in terms of their ability to resist moisture damage using an innovative direct tension test which is conducted at the binder and mastic levels. The direct tension test is used to study the adhesion between the binder or mastic and the aggregate surface as well as the cohesive strength of the binder or mastic. This is done by testing at various extension rates that cause adhesive and cohesive failures. The study uses non-modified and SBS-modified binders, locally used aggregates and fillers such as limestone and hydrated lime respectively, in addition to recycled concrete aggregates (RCA) and recycled asphalt pavement (RAP). The results show that the test method can evaluate the effect of moisture conditioning on the fabricated samples and differentiate between binders, aggregates, and fillers in the context of moisture damage susceptibility. The advantages of the developed test are that it is easy to conduct, repeatable, uses affordable equipment, and allows to measure strength as well as strain data. It is concluded that the non-modified binder performs better than the SBS-modified binder in resisting moisture damage when paired with limestone and RCA. Replacing limestone coarse aggregate with RCA worsens the moisture susceptibility, whereas incorporating RCA filler limits the loss of the adhesive bond strength after moisture conditioning. The positive effect of incorporating hydrated lime, which is a common anti-stripping agent used to improve adhesion, is dependent on the type of aggregate and binder it is used with.