Performance of concrete containing pristine graphene-treated recycled concrete aggregates

Upcycling recycled coarse aggregates (RCAs) in concrete is a promising way to decrease the environmental effect of construction and demolition waste and improve concrete sustainability. Pretreatment of RCAs helps to enhance the quality of the resulting concrete and results in an increased level of confidence for material suppliers to systematically use RCAs to replace virgin aggregates for concrete production. This study demonstrates the utilization of pristine graphene for pretreating RCAs with the aim of effectively alleviating the loss of mechanical and durability performance of concretes when compared to virgin aggregate concretes. The RCAs were presoaked in water solution containing graphene concentration ranging from 0 to 0.5 %. Then, 50 % of natural coarse aggregates were replaced with the RCAs for concrete production. Different properties of concrete including slump, axial compression, splitting tension, water absorption and drying shrinkage were measured. In addition, microanalysis of the aggregates was performed by x-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). Based on results, treating the RCAs with 0.2 wt% pristine graphene results in increased workability (13 %), compressive strength (21 %) and tensile strength (12 %) and decreased water absorption (22 %) and drying shrinkage (20 %) of the RCA concrete. Increasing the concentration of the graphene beyond 0.2 wt % is found to decrease the workability and strength properties and increase the water absorption and drying shrinkage. This is attributed to the agglomeration of the graphene at high concentrations, leading to non-uniform filling effects and ineffective microcrack and void filling. It is also found that 0.2 wt% is the optimum pristine graphene concentration, which can lead to an RCA concrete with similar mechanical and durability properties to the conventional concrete.