Applying Microbial-Induced Calcium Carbonate Precipitation Technology to Improve the Bond Strength of Lightweight Aggregate Concrete after High-Temperature Damage

Abstract

High temperatures and external force can easily lead to a decline in the bond strength of reinforced concrete components. Microbial-induced calcium carbonate precipitation (MICP) technology has considerable potential for repairing concrete. Given this, this study utilized MICP technology to improve the bond strength of heat- and pull-damaged lightweight aggregate concrete (LWAC). The specimens of a control group (Group A) and two experimental groups (Group B and Group C) were prepared. The experimental group was prepared using lightweight aggregates (LWAs) that had been immersed in a nutrient solution and a bacterial solution. The control group was prepared using LWAs that were not immersed in a nutrient solution or bacterial solution. These specimens healed themselves in different ways after exposure to high temperatures (300 °C and 500 °C) and pull-out damage. Groups A and B adopted the same self-healing method; that is, their specimens were placed in a computer-controlled incubator at 40 °C. Group C used different self-healing methods. The specimens in this group were soaked in a mixed solution of urea and calcium acetate at 40 °C for two days and then taken out and placed in an incubator at 40 °C for two days. A cycle took four days until the expected self-healing age was reached. After being exposed to 300 °C and self-healed for 90 days, the residual bond strengths of the secondary pull-out tests in Groups A, B, and C were 20.63, 22.13, and 25.69 MPa, respectively. Moreover, compared with Group A, the relative bond strength ratios of the secondary pull-out tests in Groups B and C increased by 5.8% and 20.3%, respectively. This demonstrates that MICP technology could effectively improve the bond strength of LWAC after high-temperature and pull-out damage.