Evaluation of crack self-healing capacity of rice husk ash concrete incorporating bacillus subtilis

Abstract

Cracking reduces the durability of concrete structures by providing pathways for water and aggressive ions to penetrate the cementitious matrix. This study evaluates the crack self-healing capacity of rice husk ash (RHA) concrete incorporating Bacillus subtilis. RHA was used to replace 15% of cement by mass, while Bacillus subtilis powder was added at 0.2%, 0.3% and 0.4% by mass of binder. Calcium lactate pentahydrate was used as the bacterial nutrient. Compressive strength was tested at 7, 28 and 56 days, and crack self-healing was examined on reinforced beam specimens cracked at 7 days of age and monitored after 1, 5 and 28 days under continuous water curing. The results showed that Bacillus subtilis improved the performance of RHA concrete, with the 0.3% mixture giving the highest compressive strength of 47.5 MPa at 56 days. Visual observations showed the progressive formation of white mineral deposits along the crack path, which is consistent with the mineralization behavior expected in bacteria-based self-healing systems. However, the chemical and mineralogical composition of these deposits was not directly verified in the present study. The 0.3% mixture showed the most distinct and uniform crack-filling behavior, whereas the 0.4% dosage did not provide further improvement. Crack width strongly affected healing efficiency: cracks of about 0.1 mm were almost completely closed after 28 days, while cracks larger than about 1.0 mm were only partially filled. These findings demonstrate the potential of combining RHA and Bacillus subtilis to enhance crack self-healing in concrete.