Evaluating the strength of concrete when using recycled aggregates and fly ash

Abstract

ABSTRACT:

Recently, the research and production of recycled aggregate concrete (RCA) has achieved many technically feasible results and contributes to environmental protection when resource depletion becomes more and more pressing issues. In this study, recycled aggregate (RA) is old concrete used to replace natural stone aggregate (NA) with different ratios. The RCA mixes are designed using the ACI method and the DMDA method. All concrete mixes were compared about fresh properties by value slump, compressive strength of the cube specimens at 28 days. Furthermore, RCA mixes using FA designed by the DMDA method were also evaluated for strength development over time, compressive strength of drilled specemens in the floor with variable thickness and relationship between compressive strength and UPV. Studying results show that: RA reduces the workabilities of concrete but FA has the opposite effect. Compressive strength of concrete decreases with the ratio of RA to NA. Concrete mixes using FA develop slowly in strength. On the other hand, when evaluating the compressive strength of RCA through the drilled specimens and the upv method show different behaviors compare to types of concrete with only NA.

Keywords: Recycled aggregates (RA); recycled concrete aggregates (RCA); fly ash (FA); ultrasonic pulse velocity (UPV)