Effect of Bacillus subtilis and Paenibacillus polymyxa on the Compressive Strength and Self-Healing of Type IP Concrete

The influence of Bacillus subtilis (Solution A) and Paenibacillus polymyxa (Solution B) bacteria on the properties of conventional concrete with a design compressive strength of f′c = 210 kg/cm2 and on the repair of microcracks and fissures was evaluated. Yura Type IP and Frontera Type IP cements were used, together with aggregates from the Chiguata and La Poderosa quarries (Arequipa, Peru). Two mix design methods were applied: ACI 211 and the fineness modulus of the combined aggregates. For microcrack repair, injections of Solutions A and B were applied, followed by either water curing or curing in the corresponding bacterial solution. For water replacement, both solutions were used at concentrations of 10%, 15%, and 20%. Compressive strengths were measured at 7, 14, 21, and 28 days. The results indicate that bacterial incorporation, together with reductions in the effective water-to-cement ratio associated with bacterial solution replacement, was associated with improvements in compressive strength and microcrack repair through mechanisms consistent with calcium carbonate (CaCO3) precipitation. For the injection group, a maximum strength of 196.09 kg/cm2 was obtained. For the water replacement group, a maximum strength of 335.71 kg/cm2 was reached, representing a 59.9% increase over the standard design. The P. polymyxa solution consistently outperformed B. subtilis across all groups and concentrations evaluated. These findings suggest that bacterial solutions—particularly P. polymyxa—may represent a promising complementary strategy to improve concrete performance and durability under the evaluated experimental conditions.