Development of highly conductive and self-sensing cement concrete using PVA/nano CB-impregnated recycled coarse aggregate

This paper aims to develop a novel method of preparing self-sensing concrete with recycled coarse aggregate (RCA) impregnated by polyvinyl alcohol (PVA) solution containing nano carbon black (Nano CB). The four-electrode method was adopted to investigate the influence of modified RCA substitution ratio, temperature and water content on the electrical resistivity of as-fabricated modified RCA concrete. In addition, the effects of modified RCA substitution ratio and loading rate on the piezoresistivity were explored. The results indicate that the modification have successfully attached Nano CB to the surface of RCA, and the micro-pores on the RCA surface have been filled with PVA/ Nano CB slurry, meanwhile, the water absorption decreased by 28.8%, and the crushing value decreased by 42.3%. The workability and compressive strength of concrete are improved by the modification of RCA as well. As the RCA substitution ratio increases, the resistivity of concrete first decreases slowly, then sharply and finally stabilizes. The percolation threshold of modified RCA concrete is approximately 60% substitution ratio of modified RCA (1.76 wt.% Nano CB by weight of cement). Moreover, the conductivity of modified RCA concrete possesses positive temperature sensitivity and humidity adaptability. Under cyclic loading of stress, the order of the maximum FCR value and the stress sensitivity of modified RCA concrete is: percolation zone > conductive zone > insulation zone. The specimens with modified RCA substitution ratio of 60% (in percolation zone) exhibit the best piezoresistive response compared to specimens with substitution ratios of 40% (in insulation zone) and 80% (in conductive zone). In addition, regardless of the modified RCA substitution ratio, the stress sensitivity of specimens decreases with the increase of loading rate.