A Performance Enhancement Technique for Recycled Concrete Aggregates

Recycled concrete aggregates (RCAs) typically derived from construction and demolition waste differ from natural aggregates as the former contains hardened cement paste. The residual cementitious mortar is comprised of fine aggregates, hydrated, and un-hydrated cement particles, which have a higher porosity due to the existing cracks and voids. This leads to an increase in water absorption, reduced density, reduced aggregate crushing, and reduced impact strengths when compared to virgin aggregates. Furthermore, the interfacial transition zone between the old adhered mortar and the new cement matrix creates an additional weak link. This results in decreased mechanical and durability strength parameters of the hardened recycled aggregate concrete (RAC). Construction and demolition waste consists of approximately 40% of waste concrete. Recycling this waste to produce RCAs promotes several advantages. A sustainable alternative to that of virgin aggregates is generated, and there is a reduction in energy consumption and CO2 emissions during the quarrying of raw materials. Within this study, an innovative technique was developed to treat the coarse RCAs using a waterproofing agent. The water absorption was reduced by 50% while the bulk density and specific gravity had almost a 1% increase after treatment. The treated coarse RCAs were used to create new concrete at 0%, 30%, 50%, 70%, and 100% replacement ratios to natural concrete aggregates (NCAs) to investigate the fresh and hardened concrete parameters. The treated RAC showed improvement in workability, hardened density, and compressive strength when compared to the untreated RAC.