Degradation Resistance of Bio-Concrete Containing Rice Husk Ash and Bacillus Subtilis under Acidic, Sulfate, and Elevated Temperature Exposure

Abstract

This study investigated the degradation resistance of bio-concrete containing rice husk ash (RHA) and Bacillus subtilis when exposed to acidic, sulfate, and elevated temperature environments. Concrete mixes with 0%, 5%, 7.5%, and 10% RHA and B. subtilis [6 MacFarland] were tested for pore solution pH, residual compressive strength at 30 – 100°C, mass loss in 5% H₂SO₄ for 28 days, and strength loss in 5% Na₂SO₄ for 90 days.  Results showed that RHA reduced pore pH from 12.6 to 11.3 due to pozzolanic consumption of Ca(OH)₂, but all mixes remained above pH 11.0, ensuring bacteria viability. Compressive strength increased up to 80°C for all mixes, with 10% RHA + 6 MF achieving 46 N/mm² at 80°C, 41% higher than the control. Acid attack mass loss decreased from 20% to 11%, while sulfate-induced strength loss decreased from 22% to 8% for the same mix. The improved performance is attributed to microbially induced calcite precipitation (MICCP) and secondary C-S-H formation, which densified the matrix and reduced permeability. The findings indicate that the synergy between RHA and B. subtilis enhances durability in aggressive environments, making 10% RHA + 6 MF bio-concrete suitable for infrastructure exposed to acid, sulfate, and moderate heat.