Cementitious binders and reclaimed asphalt aggregates for sustainable pavement base layers: Potential, challenges and research needs

Abstract

Reclaimed asphalt pavement (RAP) has been increasingly used in the past few decades as a replacement of natural aggregates in pavement layers. However, low replacement level is employed, and consequently, large quantities of RAP are still left unused. Researchers often neglect foundation pavement layers, but it has higher prospects to consume recycled materials due to their increased thickness. RAP has inferior properties compared to natural aggregates; therefore, cementitious binders are used to produce a (sub)base layer using high volumes of RAP. This paper reviews the use of RAP aggregates with cementitious materials for pavement foundation layers. Special attention is given to the use of alkali-activated materials (AAM) as a binder in substitution for Portland cement (PC). This review discussed the properties of fresh and hardened RAP in cementitious matrices, as well as changes in the microstructure. The biggest challenge on the use of RAP on both systems, RAP-PC and RAP-AAM, is the bond issues caused by the presence of asphalt on the surface of the aggregates. Some researches addressed how physical or chemical pre-treatments to the RAP could improve the adherence to the paste, but few studies focused on the optimisation of the binder. A literature survey indicated that an optimised mix design, durability studies and life cycle assessment (LCA) are important research needs towards the development of RAP-AAM. Despite the lack of research evidence, RAP-AAM is a promising solution for foundation pavement layers.