Carbon-conditioned recycled aggregate in concrete production

This paper investigates the use of carbon-conditioned recycled aggregate (RACO2) in concrete production. Experimental work is conducted for RACO2 with varying chamber pressure (0 kPa, 75 kPa, 150 kPa), chamber duration (0 min, 30 min, 90 min) and RACO2 replacement percentages (0%, 30%, 100%) for concrete production. Average of three results on compressive, tensile and flexible strength and modulus of elasticity at 28 curing days are compared. The process of carbon-conditioning refers to the pressurised exposure of recycled aggregate to carbon dioxide (CO2) for a certain period of time before concrete mixing. The entraining of CO2 assists to facilitate the negative properties of recycled aggregate that produces a deprived final recycled concrete as well as providing a superior calcium carbonate chemical reaction. Carbon-conditioning reduces porosity and water absorbency of recycled aggregate. In addition to improve recycled aggregate quality, CO2 emissions from the aggregate also help filling openings in the concrete composition, generating an improved bond matrix from the formation of calcium carbonates (Zhan et al., 2014). These two traits assist in enhancing the recycled concrete properties. This paper demonstrates a great potential in the use of RACO2 in improving physical and mechanical properties of recycled concrete and provides insight for effective use of recycled aggregate for concrete production. The effective use of recycled aggregate can reduce the amount of landfill that is utilised for construction and demolition waste.