Self-healing of concrete cracks by immobilizing non-axenic bacteria with enhanced recycled aggregates

To solve the problems such as poor compatibility with the cementitious matrix and high cost of current bacterial carriers, a type of self-healing concrete by immobilizing non-axenic bacteria into recycled aggregate (RA) with enhancement was proposed. The reasonable enhancement time of RA and its effect on the compressive strength of concrete were first investigated. Then, the crack-healing capacity and the crack-filling precipitations of concrete immobilizing non-axenic bacteria were studied. The test results show that the reasonable enhancement time of the RA using biodeposition of non-axenic bacteria is 7 days. The water absorption and crushing index of recycled coarse aggregate (RCA) decrease by 27% and 20%, respectively. The compressive strength of concrete prepared with the enhanced RCA increases by 12.9%. After 28 days of healing, the average values of healed crack widths and completely healed percentages of cracks of the concrete specimens by immobilizing non-axenic bacteria into RA with enhancement are up to 0.28 mm and 60%. The maximum width value of healed cracks reaches 1.26 mm. The water permeability coefficients of the concrete specimens can decrease by up to 99.7% compared to that without crack-healing. The crack-filling precipitations of self-healing concrete by immobilizing non-axenic bacteria exhibit regular cubic shapes. The crystals of these precipitations are calcite.