Experimental investigation on the strength and durability properties of bacterial self-healing recycled aggregate concrete with mineral admixtures

Abstract

Microcracks are the inherent feature of concrete and this feature also persists in recycled aggregate concrete (RAC) just like a conventional concrete. Due to external loading and chemical reactions, microcrack spreads, causing harmful species to enter the concrete causing durability of the concrete to deteriorate. In this study, the precipitations of bacterially induced CaCO3 were introduced in RAC as a strategy to repair cracks on their own. Recycled coarse aggregate (RCA) was used at the 50% and 100% levels by replacing natural coarse aggregate (NCA). In addition, 10% weight of cement was replaced in bacterial recycled aggregate concrete (BRAC) mixes with microsilica (MS) and metakaolin (MK). The competency of self-healing was assessed through compressive strength, ultrasonic pulse velocity (UPV) measurements, water permeability and microscopic inspection of crack healing. The maximum crack width of 0.63 mm was fully healed after 56 days of healing incubation. Depending on the cracking age regain in compressive strength was found to be in the range of 57% to 93% and the variation ratio (Rk) of the permeability coefficient was observed in the range of 143% to 181% in different BRAC mixes. The microstructure investigations were conducted using SEM with EDS and XRD techniques from which the morphology of bacterial precipitations and their composition were explored. Based on the results of the study, it is suggested that cracks in RAC can be self-repaired by bacterially attained self-healing phenomena and hence, its durability can be improved.