Effect of biomineralized Bacillus subtilis on recycled aggregate concrete containing blended hydrated lime and brick powder

Using RCA in concrete reduces the consumption of natural raw materials, protects the environment and manages waste disposal. Since a high volume of aggregates is used in the concrete, the usage of RCA from construction and demolition waste (CDW) would increase the sustainability in the production of concrete. This research used bio-immobilization techniques to improve the strength and durability properties of RAC with blended HBr. In this order, 50% and 100% NCA was replaced with RCA to prepare RAC mixtures with and without bacteria. In addition to this, 10% cement was replaced with HBr in RAC mixes. The tests were carried out in terms of compressive strength, water absorption, rapid chloride penetrability, water permeability, and durability against sulphate resistance. Further, FESEM and EDS analyses were conducted to investigate the morphology of all the concrete mixtures. The durability test was conducted on 28 days, 56 days, and 120 days of concrete mixes. The outcomes show that the durability properties regarding water absorption, RCPT, and water permeability were increased by 33%, 62.3%, and 51%, respectively. Compressive strength was also enhanced by 35.76% from calcite precipitation in 50% BRAC-HBr concrete mix at the age of 120 days. The strength performance of BRAC-HBr concrete mixes in an acid environment was increased due to the mineral precipitation which can prevent the sulphates from penetrating. Further, the outcomes of the EDS analysis confirmed the existence of bacterial crystals in terms of CaCO3 while the sulphate salts were observed in the FESEM micrograph. Additionally, the benefit-cost ratio shows that it is economically possible to produce 50% BRAC-HBr concrete with improved RAC properties that have been prepared using bacteria.