Effect of treatment method of recycled concrete aggregate by pristine graphene on mechanical and durability properties of concrete

Using recycled concrete aggregates (RCAs) in concrete has emerged as a promising approach to minimize the environmental impact associated with construction and demolition waste, while simultaneously enhance the sustainability of concrete. Enhancing the quality of RCAs is crucial to instill greater confidence among material suppliers and promote the systematic utilization of RCAs in the construction industry. This study presents the use of pristine graphene suspension at 0, 0.1 and 0.2% concentrations in water for improving properties of RCAs, thereby improving mechanical and durability properties of resulting concretes incorporating 100% RCA as coarse aggregates. For this investigation, two treatment methods, including pre-spraying and pre-soaking, were used to treat the RCAs. Nano-silica with the same concentration and treatment method was also utilized to compare the results. Various strength tests including axial compressive, splitting tensile and flexural were performed. In addition, material properties such as water absorption and drying shrinkage were assessed. Microanalysis using scanning electron microscopy (SEM) and micro-CT was also employed. It is shown that, for both treatment methods investigated and nanomaterial concentrations, pristine graphene is more effective than nano-silica in increasing the strength properties and reducing the water absorption and drying shrinkage due to a lower level of material porosity. It is also found that, for a given nanomaterial concentration and type, concrete with pre-soaked RCA exhibits higher strengths and lower water absorption and drying shrinkage compared to the concrete with pre-sprayed RCA. A lower porosity and reduced number of microcracks are observed in pre-soaked RCA concrete compared to pre-sprayed RCA concrete. The results are promising and point that the treatment of the RCAs reduce their water absorption and, thereby improving mechanical and durability performance of the concrete.