Civil and Environmental Research www.iiste.org ISSN 2224-5790 (Paper) ISSN 2225-0514 (Online) Vol.10, No.7, 2018 1 Evaluation of the Effect of Bacillus Pumilus Precipitate on the Strength and Durability of Concrete Oriola, Folagbade Olusoga Peter* Department of Civil Engineering, Nigerian Defence Academy, Kaduna, Nigeria Sani, John Engbonye Department of Civil Engineering, Nigerian Defence Academy, Kaduna, Nigeria Anebi, Morgan Adah Department of Civil Engineering, Nigerian Defence Academy, Kaduna, Nigeria Abstract 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 (CaCO 3 ). 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 1.5x10 8 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 10 8 cells/ml B. pumilus suspension. Keywords: Bacillus Pumilus, Concrete, Compressive strength and Durability 1. Introduction Ordinary Portland Cement (OPC) Concrete which is the mixture of cement, fine aggregate, coarse aggregate and water is without argument, the most commonly used construction material because it is cheap, easy to make and convenient to place or cast to shape. However, it has limitations of deteriorating due to micro cracks and pores which are formed within the concrete matrix. (Claisse et al., 1997, Ravindranatha et al., 2014a). These micro cracks causes concrete to be susceptive to ingress of liquid and gases which can attack the constituents of concrete. Degradation mechanisms of concrete often depend on the way potentially aggressive substances can penetrate into the concrete, possibly causing damage. The permeability of the concrete is dependent on the porosity and on the connectivity of the pores. The more open the pore structure of the concrete, the more vulnerable the material is to degradation mechanisms caused by penetrating substances. Khan (2003) confirmed that durability of concrete is related to the characteristics of its pore structure. Furthermore OPC Concrete have a very high potency to crack which can easily leads to reduction in the strength and durability of concrete (Chahal et al., (2012) and Arunachalam et al., (2010). Therefore, the requirements for high durability for structures exposed to harsh environments such as sea buoys, offshore structures, tunnels, highway bridges, sewage pipes and structures for solid and liquid wastes containing toxic chemicals and radioactive elements may not be achieved using OPC concrete. However, based on continuous research carried out, various modifications have been made to try to overcome these deficiencies of cement concrete; one of such developments is bacteria concrete. Due to microbial activities of bacteria, microbiologically induced calcite precipitation (MICP), a highly impermeable calcite layer is formed which fills the micro cracks and pores in concrete and contributes to increase in the strength and improvement in the