Self-healing potential of cave-isolated bacteria in cement-based materials under different exposure conditions

Incorporating bacteria capable of precipitating calcium carbonate (CaCO₃) in cementitious materials has been studied as a sustainable self-healing mechanism for cracks, promoting improved structural durability and reducing maintenance needs. However, most studies focus on well-known bacterial strains under limited exposure conditions. Bacteria originating from extreme environments, such as caves, tend to exhibit higher resilience to harsh conditions, including the high alkalinity of cementitious matrices, potentially enhancing self-healing efficiency. This study evaluates the self-healing potential of Bacillus subtilis CV16, a strain isolated from the Pedra da Cachoeira cave (Brazil), in mortars, with a calcium source (calcium lactate), subjected to different exposure conditions (air exposure, immersed in potable water, immersed in lime-saturated water, and under dry-wet cycles). The healing ratio was quantified using two complementary methods: visual crack closure via stereoscopy (R W ) and functional sealing via permeability tests (R K ). The results indicated that bacterial addition promoted crack healing, with this effect being enhanced in the presence of water. The R W analysis revealed the highest healing ratio in mortars under dry-wet cycles, reaching 98 % after 168 days. Significant visual healing was also observed in bacterial samples submerged in lime-saturated water (77 %) and potable water (50 %). In contrast, all reference mortars remained below 35 % healing, together with air-exposed samples with bacteria. Permeability tests confirmed these functional results, showing that bacterial mortars in water-exposed conditions (submerged or in cycles) achieved near-complete sealing (over 95 %). Specimens exposed to air showed no significant differences compared to the reference samples. The material precipitated in the cracks was identified as calcite, aragonite, and vaterite. The study concludes that bacterial treatment has potential applications in structures exposed to moisture, such as reservoirs and dams, although its effectiveness may be limited in dry environments. This research reinforces the feasibility of bacterial self-healing as a promising strategy to extend the service life of cementitious materials and reduce environmental impacts in the construction industry. • The exposure condition influences self-healing cracks in cement-based materials. • Cave-isolated bacteria can crack sealing through CaCO₃ precipitation. • B. subtilis CV 16 does not need urea to precipitate CaCO3. • Self-healing was enhanced in water and CO2 exposure (dry–wet cycles).