Influence of Bacillus coagulans on the Compressive Strength and Durability of Concrete

Abstract

This study investigates the influence of Bacillus coagulans on the compressive strength and durability of concrete. Concrete cubes were prepared in three different ways. The first set was prepared without bacteria treatment as control. Second set was prepared by mixing concrete with B. coagulans suspension at various densities and then cured in water while the third set was prepared without the bacteria but cured in cementation reagent containing various B. coagulans suspension densities. 1.5  10⁸ cells/ml, 12.0  10⁸ cells/ml, and 24.0 10⁸ cells/ml B. coagulans suspension densities of bacteria were investigated for bacteria-treated-concrete. The 100mm concrete cubes were tested for compressive strength and durability under Sulfuric acid environment. Tests were conducted between 7 and 28days at 7days interval. In general, concrete treated with bacteria were much stronger than the control at early ages up to 14days. Although they were still stronger at 28 days, the percentage increase in strength were much lower. At 28 days, the compressive strength of the untreated concrete was 32N/mm². For concrete mixed with bacteria, the highest compressive strength was 34N/mm²obtained at 12.0 x 10⁸ cells/ml bacteria density while 37N/mm² was obtained at the same density for concrete cured in bacteria suspension. The durability study indicated that concrete treated with bacteria performed better than the control. For both mixing and curing with bacteria, the best result of loss of strength at 28days were obtained at bacteria density of 1.5  10⁸ cells/ml; 12.0% and 13.7% respectively compared to 16.5% for the control. Analysis of variance (ANOVA) test shows that concrete immersed in bacteria reagent has more significant effect on the compressive strength than those prepared by mixing the bacteria with the concrete. Microbial calcite precipitation was viewed using a scan electron microscope (SEM), which established the presence of calcite precipitation inside pores with bacterial impression and a new calcite layer on the surface of the concrete formed.

Keywords: Bacillus coagulans, Concrete, Compressive strength and Durability