Improvement of recycled concrete aggregate using alkali-activated binder treatment

This paper presents a study on improving recycled concrete aggregate (RCA) using alkali-activated binder treatment for producing Portland cement concrete (PCC). The recycled concrete aggregate was treated with cement paste (CP), alkali-activated high-calcium fly ash paste (AHF), and alkali-activated high-calcium fly ash paste incorporating dolomite powder (AHFD) and the corresponding workability and mechanical properties of the PCC mixed with the treated RCA were investigated. The natural concrete aggregate (NCA) was replaced with RCA at the levels of 0, 25, 50, 75, and 100% by weight. Experimental results showed that the RCA had higher water absorption and lower dry-rodded density than those of NCA. However, the water absorption of RCA can be improved by using various surface treatments. The microstructure improvement of PCC with treated RCA was confirmed by the results obtained from XRD, MIP, SEM/EDS, TGA/DTG analyses. The surface treatments of RCA using coating materials significantly improved the workability of concrete; whereas the strength improvements were not so evident. The treatments with CP and AHFD pastes gave reasonably high strength concrete, but that with AHF gave low strength due to shrinkage and cracking of coated paste. In general, the use of treated RCA to replace NCA is a suitable choice as an alternative material to replace the natural nonrenewable resource components as well as makes concrete more sustainable and environmentally friendly.