Self-healing of concrete containing commercial bacteria by means of water and chlorides permeability

Abstract

Microbial-induced calcium precipitation (MICP) has shown adequate potential to act as a healing product through Calcium Carbonate (CaCO3) precipitation inside cracks. This work studies the self-healing capability of conventional concrete incorporating two dosages of Bacillus subtilis encapsulated in diatomaceous earth and a liquid solution consisting of a combination of Bacillus, denitrifying, and photosynthetic bacteria. The two bacterial agents used are commercial or industrial products from other sectors. For these mixes, disks of size ϕ100×50 mm were pre-cracked at the age of 21 days by splitting test until reaching residual cracks of 100 to 450 µm. At the age of 28 days, self-healing was promoted during 28 days in three exposures, continuous water immersion at 20°C, a high humidity environment at 20°C and 95% of relative humidity, and 7 days immersed in water at 20°C and 21 days in the high humidity environment. Self-healing was analyzed with water permeability by comparing the results before and after healing. Afterward, chlorides’ penetration was performed to study the possible healing protection on cracked disks compared to uncracked reference disks. As a result, after 7 days of immersion in water, the mixes with bacteria presented acceptable healing results. Some healed cracks could also significantly reduce the penetration of chlorides towards the interior of the concrete matrix.