Improving the chloride transport resistance of concrete through targeted coating of aggregates with layered double hydroxides

Aggregate surface modification is a promising strategy for enhancing the chloride resistance of concrete in marine environments. In this study, a simple method of surface modification – coating coarse aggregates with layered double hydroxides (LDH) – was developed. The microstructure and properties of the surface-modified coarse aggregate were characterised. The effectiveness of the surface-modified aggregate on improving chloride transport resistance was assessed using rapid chloride migration and natural diffusion tests. In addition, its influence on the microstructure of interfacial transition zone (ITZ) was examined. The results indicated that surface modification of coarse aggregate was successfully achieved by coating with LDH, imparting a considerable chloride adsorption capacity. The chloride transport resistance was significantly enhanced for concretes with different water-to-cement ratios (0.3 and 0.5). In addition, the level of enhancement increased with an increase in the replacement ratio of surface-modified coarse aggregate. The surface modification decreased the ITZ thickness and refined the pore structure of ITZ. Accordingly, both the imparted chloride adsorption capacity and improved ITZ microstructure jointly contributed to the enhanced chloride transport resistance of concrete.