Bioconcrete: Enhancing Compressive Strength in Self-Constructed Homes

Self-constructed homes, commonly built without technical supervision, often rely on empirically prepared concrete mixes that result in high variability and substandard mechanical performance. This study evaluated the effect of incorporating Bacillus subtilis and Bacillus cereus into such non-standard concrete to improve its compressive strength. Two widely used field dosages were identified through surveys with master builders, reaching compressive strengths of 4.98 MPa and 11.77 MPa at 28 days, both below the 17 MPa minimum required by building codes. These mixes were replicated as controls, and the bacterial strains previously isolated and cultured were added at concentrations of 10³, 10⁵, and 10⁷ CFU/mL. The incorporation of Bacillus subtilis at 10³ CFU/mL improved compressive strength by 6.57%, while Bacillus cereus at 10⁷ CFU/mL achieved a 36.91% increase, reaching 16.11 MPa. This improvement is attributed to calcium carbonate precipitation via microbial biomineralization. Notably, Bacillus cereus remained active at ambient curing temperatures near 10 °C, typical of high-altitude environments, and proved more effective under such conditions. These findings highlight the potential of microbial additives, particularly Bacillus cereus, as a low-cost and context-adapted solution to enhance concrete performance in self-constructed homes.