Experimental Study on the Influence of Water Absorption of Recycled Coarse Aggregates on Properties of the Resulting Concretes

In this paper, three recycled coarse aggregates (RCAs) with different 24-h water absorptions (5.67, 3.12, and 1.98 wt%) were used to produce recycled coarse aggregate concretes (RCACs). Different water absorption rates were obtained by modifying the surface of RCAs with low and high concentration of alkaline organosilicone modifier that is stable in concrete. A normal aggregate concrete mixture was also prepared to serve as control mixture. The effect of RCA absorption on the microstructure (interfacial transition zone), mechanical properties (compressive strength, modulus of elasticity, and concrete-rebar bonding strength), and durability (shrinkage and water permeability) of the resulting RCAC was investigated. Test results showed that the surface modification of RCA was effective in reducing the water absorption. From micrographs, RCAC prepared with low concentration of surface modifier (No. 2 RCA) showed mechanical interlocking with the surrounding cement matrix. Among RCAC, No. 2 RCA (with low concentration of surface modifier) showed better mechanical and durability performance due to the mechanical interlocking which served as effective force transmission medium between aggregate/cement matrix. It can therefore be concluded that RCA prepared with low concentration of surface modifier improved the properties of RCAC. In addition, it may be used as a potential tool to reduce possible slump loss in fresh concrete thereby resulting in consistent mix and providing greater flexibility in mix design.