Bioconcrete: Harnessing the Endogenous Microbiota of Reinforced Concrete for Crack Remediation

Abstract

Reinforced concrete (RC) is the most widely used construction material in the world, but its susceptibility to cracking ultimately shortens the structure’s operational lifetime. When cracked, water can enter RC and undergo cycles of freezing and thawing, causing further damage and corrosion of the reinforcement. While many conventional crack remediation strategies are effective in the short term, they are high maintenance and can be environmentally hazardous due to the emission of volatile organic carbons or chemical runoff. Microorganisms capable of calcium carbonate precipitation (MICP) have been studied as a potential remediation strategy that alleviates the shortcomings of traditional chemical-based RC patching methods; however, previous studies have struggled to maintain microbial survival likely because the bacterial species originated from non-RC environments. In this study, native microorganisms capable of MICP were isolated from preexisting RC structures using traditional microbiological techniques for use in a bioactive mortar in bench-scale model cracked RC specimens. Overall, out of the 24 MICP isolated organisms, the 5 fastest growing from traditional growth curves and most promising calcium carbonate producers via XRD analysis were evaluated for their ability to reduce water ingress in cracked RC specimens against the commonly used MICP organism, Sporasarcina pasteurii, after immersion in water. Optimal biomortar composition was found to be a 3:8 mixture of MICP culture and sterile sand for the bottom half of the crack and a 5:2:0.4 mixture of sterile sand, MICP organism, and binder for the top of the crack. Overall, water ingress experimentations revealed that one of the five isolated MICP organisms outperformed S. pasteurii by reducing water ingress in treated specimens by 2.8 times; however, the other isolates did not reduce ingress.