Improving compressive strength for recycled aggregate concrete

Abstract

As Hong Kong will be running out of the landfill areas in the next eight to ten years, development of recycled aggregate concrete technology is imperative. Hence, the behaviors of the recycled aggregate (RA) in the recycled aggregate concrete (RAC) need to be fully explored. Currently, applications of RAC mainly confined to sub-base systems of roadwork such as pavements and some other non-structural purposes. The application of RAC to high grade concrete is rare resulted from its low compressive strength and high variability. This paper proposes a new approach in mixing concrete, namely, the two-stage mixing method, intended to improve the compressive strength for RAC and hence lower its strength variability. Based upon our experimental work and results, improvements of 21% and 31% in strength to RAC with 30% RA substitute in 14 and 28 days respectively were achieved. The effect can be attributable to the porous nature of the RA and hence the pre-mix process can fill up some pores, resulting in a denser concrete and thus leading to a higher strength when compared with the traditional mixing approach.