Mechanical properties, drying shrinkage, and nano-scale characteristics of concrete prepared with zeolite powder pre-coated recycled aggregate

The utilization of recycled coarse aggregates (RCAs) obtained from construction & demolition wastes in concrete material has been a feasible sustainable development strategy. However, the poor properties of RCAs have some adverse effects on the performance of concrete. In this study, the properties of RCAs are enhanced by zeolite powder-cement (ZP-C) slurry pre-coating, and the compressive strength, dry shrinkage, microstructures and nano-mechanical properties of concrete containing natural coarse aggregates (NCAs), RCAs and the enhanced RCAs (ERCAs) are investigated. The results show that the incorporation of RCAs or ERCAs is detrimental to the development of concrete properties, compared with the NCAs. The compressive strengths of the concrete containing ERCAs are higher than that of the concrete containing RCAs, and the dry shrinkage strain of the former is lower than that of later, under the same conditions. Meanwhile, the width of enhanced interfacial transition zone (EITZ) between ZP slurry layer and new cement matrix (CM) decreases by 46.9%, compared with old ITZ (OITZ) between old CM and new CM. In the nanoindentation test, the elastic modulus of EITZ is higher than that of OITZ. The outcome of this study exploits the synergy between natural ZP and RCA to effectively solve the problem of poor effect of conventional strengthening methods on old demolition concrete wastes to improve the mechanical and drying shrinkage properties of recycled aggregate concrete while promoting resource conservation and recycling.

Automated summary

The study shows that enhancing the properties of RCAs with zeolite powder-cement pre-coating can improve the compressive strength and reduce the dry shrinkage strain of concrete, thereby enhancing its overall performance. Compared to concrete containing RCAs, concrete containing ERCAs displays better performance in terms of compressive strength and dry shrinkage strain.