Evaluation of the Effect of Bacillus Pumilus Precipitate on the Strength and Durability of Concrete

Microbiologically induced calcite precipitate (MICP) also called bio-mineralization is a process by which living organism’s forms inorganic solids. The basic principles of MICP involves the formation of urease by the Bacillus species and the hydrolyze urea produce ammonia and carbon dioxide, and the ammonia released to the surroundings subsequently increases pH leading to accumulation of insoluble calcite (CaCO3). Bacillus pumilus is a common soil bacterium which can induce the precipitation of calcite. The effect of different concentrations of B. pumilus on the compressive strength and durability of concrete was studied. It was found that the concrete treated with bacteria (i.e. concrete mixed with bacteria and concrete cured in bacteria suspension) performed better than the control concrete. Though the treated concrete were stronger than the control in terms of compressive strength, the strength increase was more pronounced at early ages (7 & 14 days) than at later ages (21 & 28 days); the best performance at 28days was an increase of about 6% above the compressive strength of the control for concrete mixed with bacteria, at a suspension density of 1.5x108 cells/ml. The durability performance improved with increase in the concentration of B. pumilus, though there was no significant difference between the performance of concrete mixed with bacteria and concrete cured in bacteria suspension. At 28 days, the weight loss was 16.5%, 11.8%, 17.8% and 14.2% for concrete mixed with bacteria at concentration of 0, 1.5E8, 12E8 and 24E8 cells/ml respectively. Similarly, at 28 days, the weight loss was 16.5%, 15.5%, 15.7% and 15% for concrete cured in cementation reagent containing various B. pumilus suspension at density of 0, 1.5E8, 12E8 and 24E8 cells/ml respectively. Furthermore, the general trend for loss of weight under acidic condition was increase in loss of weight with duration of immersion but the rate of loss decreased with age. The depositions of calcite inside the micro cracks of concrete by B. pumilus were analyzed under scanning electron microscope (SEM). The unique imaging and microanalysis capacities of SEM established the presence of calcite precipitation inside cracks, bacterial impressions and new calcite layer on the concrete surface of concrete. This calcite layer improves the compressive strength and impermeability of the concrete, thereby increasing its resistance to acidic environment especially at 1.5 x 108cells/ml B. pumilus suspension. Keywords: Bacillus Pumilus, Concrete, Compressive strength and Durability

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

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

Effect of Treatment Compositions on the Plasticity of Tropical Red Soil Treated with Bacillus Coagulans

The study evaluated the effect of four treatment compositions on the plasticity of tropical red soil (Lateritic soil) admixed with Bacillus coagulans (B. coagulans). Samples for Atterberg limits test were prepared using four treatment compositional variables. They include 25% B. coagulans suspension and 75% cementation reagent, (25%B /75%C); 50% B. coagulans suspension and 50% cementation reagent (50% B /50%C); 75% B. coagulans suspension and 25% cementation reagent, (75%B /25% C) with the above three being in equivalent volumes of the corresponding liquid limit(LL) and 50% of the optimum moisture content (OMC) of compaction, to be both  B. coagulans suspension and cementation reagent (i.e. 50% OMC B /50%OMC  C) of the natural soil. Results showed that the LL for; 25%B /75% C, 50% B /50% C and 75% B /25%C generally increased from 0 up to peak values at 1.8 x 109 cells/ml and then declined at 2.4 x 109 cells/ml. In the case of samples treated with 50% OMC B/50% OMC C, the LL initially decreased from 0 up to 6.0 x 108 cells/ml and thereafter increased significantly. Plastic limit (PL), Plasticity index (PI) and Linear shrinkage (LS), recorded improvement. Regression analysis for the best treatment composition (i.e 75%B /25%C) has regression coefficient of 91.8%. Based on the four treatment compositions considered, 75%B/25%C enhanced the soil workability significantly and is suggested for geotechnical engineering applications such as road pavements that are lightly trafficked