Microwave-Assisted Production of Aggregates from Demolition Debris

Abstract

Concrete recycling is an increasingly common method of disposing of demolition rubble and can provide a sustainable source of concrete aggregates. However, Recycled Concrete Aggregates (RCA) currently produced are usually of low quality and generally considered not suitable for use in ready mix concrete. The presence of the contaminants (impurities) in the concrete debris and the presence of the mortar adhered to the RCA particles have been identified as the main causes lowering the quality of RCA compared to Natural Aggregates (NA). The current study was aimed to investigate the possible methods to eliminate the abovementioned causes and thereby increase the quality of RCA. Based on a comprehensive literature review conducted to investigate the capability of different surface removal techniques for removal of the contaminants from the concrete surface, the focus was placed on the microwave decontamination technique that had been reported to have a relatively better removal speed and performance. A comprehensive numerical study was conducted to examine the phenomenon leading to delamination of the concrete surface when exposed to microwaves and to develop an easy-to-use simulation technique to be used in practical predictions and control of the microwave decontamination of concrete. In addition, besides the concrete surface decontamination, a novel microwave-assisted technique to remove the adhering mortar from RCA was developed during the current study. The capability of this method to remove the adhering mortar from RCA was numerically and experimentally investigated and compared with the other RCA beneficiation methods proposed in available literature. Moreover, an industrial microwave heating system that can be used in concrete surface decontamination and RCA beneficiation methods was designed and installed during the current study. The results of this study demonstrated that incorporating the microwave-assisted decontamination and RCA beneficiation techniques into the conventional concrete recycling procedure may significantly increase the quality of RCA.