Role of asphalt binder film thickness on the behaviour of RAP-incorporated concrete

Abstract

This study investigates the role of asphalt binder film thickness around the Reclaimed Asphalt Pavement (RAP) aggregates in influencing concrete behaviour. For fundamental understanding, the RAP aggregates were prepared in the laboratory at different asphalt binder (AB) dosages simulating the field oxidation. These aggregates were then characterised for their physical & morphological properties, hydrophobicity, and leaching behaviour, and later related to concrete's fresh, mechanical, and durability characteristics. The results indicated that the performance of concrete is strongly governed by the asphalt coating on RAP and the concrete behaves differently as a function of AB content — with different AB contents (0–3 %), the reduction in concrete compressive strength, flexural strength, and elastic modulus were found to be in the range of 29–58 %, 21–54 %, and 25–71 %, respectively. At dosage ≤ 2 %, AB sealed the micro-pores on aggregate surfaces, softened the edges and corners, reduced the surface roughness, and eventually enhanced the concrete workability by 43 %. However, excess binder beyond 2 %, caused the RAP to agglomerate, leading to an increase in the aggregate’s angularity and a decrease in its overall sphericity, subsequently reducing the concrete consistency. In addition, the excess binder reduced the asphalt cohesive strength which in turn negatively impacted the concrete performance. The leachate (organic compound) concentration was also observed to be a function of the AB content which interfered with the hydration kinetics of cement paste leading to the formation of 69–207 % thicker interfacial transition zone. Conversely, increasing the AB to 3 % significantly enhanced the concrete toughness index by 136 %.