Characterization of Asphalt Mixtures Containing Double-Coated Recycled Concrete Aggregates

Abstract

Asphalt mixtures made with recycled concrete aggregates (RCAs) derived from construction and demolition (C&D) wastes exhibits inferior properties to mixtures containing natural aggregates only. This is mainly because of old cement mortar attached to RCA surfaces, and other impurities such as bricks and tiles. This study developed a new state-of-the-art coating technique to improve the behavior of RCA–asphalt mixtures. The technique was based on combining two treatments: coating and heating. It is therefore called the double-coating technique (DCT). The coarse RCA was first coated with bitumen emulsion to upgrade its durability. However, postcoating, some areas of RCA surfaces were found not coated with bitumen emulsion. Therefore, asphalt mixtures made with such particles were cured in an oven maintained at 155°C for 90 min. The bitumen is expected to be less viscous at 155°C, and flowed through the uncoated areas and sealed them. A second treatment was applied to minimize the expected moisture degradation and improve adhesion between RCAs and bitumen. The treated RCA is called double-coated recycled concrete aggregate (DCRCA). Mixes with 0%, 20%, 40%, and 60% DCRCAs were evaluated. The use of DCRCAs was found to improve the resistance of asphalt mixes against permanent deformation. The fatigue life (number of cycles to failure) also was improved by the addition of DCRCAs in asphalt mixtures. The number of load cycles of DCRCA mixes was 12%, 23%, and 141% higher than that of the control mix. The DCRCA mixes exhibited either comparable or better dynamic modulus than that of control mix. Although the use of RCAs in flexible pavement construction is not yet permitted in Australia, the results presented in this work indicate the suitability of DCRCAs to be used in asphalt mixtures production.