International Journal of Engineering and Applied Sciences (IJEAS) ISSN: 2394-3661, Volume-3, Issue-4, April 2016 81 www.ijeas.org Abstract— This paper presents the results of a study carried out to investigate the ability of ureolytic bacteria to enhance the compressive strength of concrete. The urease producing aerobic alkalophilic bacteria Bacillus subtlis strain MU12 was used in the present study. Ureolytic bacteria used in the present studies were isolated from various sources like cowshed, poultry farm, milk, soil and pigeon dung. All the isolates were screened for ureolytic activity on the basis of urease test. These isolated cultures were purified on phenol red agar plates. Four different cell concentration (10 4 , 10 5 ,10 6 ,10 7 cells/ml) of bacteria were used in making the concrete mixes. Tests were performed for compressive strength of concrete cubes at 7 days, 14 days and 28 days. Inclusion of MU12 @ 10 7 cells/ ml in cement concrete enhanced the compressive strength in 7 th and 14 th days concrete samples. Index Terms— Urease, Calcium Carbonate Precipitation, Characterization, Endospore. I. INTRODUCTION Concrete is an absolutely essential component of construction materials used in infrastructure and most buildings. Despite its versatility in construction, it is known to have several limitations. A lot of research has been carried out around the globe to improve properties of concrete. Recently, it has been found that microbial mineral precipitation resulting from metabolic activities of favorable microorganisms in concrete can improve the overall behavior of concrete. In this technique ureolytic bacteria (microorganism) are used hence the concrete is called Bacterial or Microbial concrete. The “Microbial concrete” can be prepared by adding spore forming bacteria in the concrete that are able to continuously precipitate calcite, this process of production of calcite precipitation is called Microbiologically Induced Calcite Precipitation (MICP) [1]. Microbial calcite precipitation is mainly due to ureolytic activity and carbonate biomineralization of bacteria. Under suitable conditions, most bacteria are capable of inducing carbonate precipitation. In addition, carbonate particles can also be produced by ion exchange through the cell membrane [2]. The basic principle for this process is that the microbial urease hydrolyzes urea to produce ammonia and carbon dioxide and the ammonia released in surrounding subsequently increases pH, leading to accumulation of insoluble calcium carbonate. Bacterial CaCO 3 formation through urea hydrolysis is known as Bacterial Calcite Precipitation [3]. Bacterial Cultures improves the strength of cement sand mortar [4] and crack repair on surfaces of Satinder Kaur khattra, Assistant professor, Civil Engineering Department, COAE&T, Punjab Agricultural University, Ludhiana-141004 Manisha Parmar , Department of Microbiology, College of Basic Sciences and Humanities, Punjab Agricultural University, Ludhiana-141004 Urmila Gupta Phutela, Professor, School of Energy Studies for Agriculture, COAE&T, Punjab Agricultural University, Ludhiana-141004 concrete structures [5, 6]. Bacterial Calcite Precipitation (BCP) is highly desirable because it is pollution free and natural. There are several applications of BCP; the most important is strength development. Bio concrete has many advantages over the ordinary concrete; it needs a much shorter time; it is suitable for in-situ process; raw material of bio cement are produced at a lower temperature and can be used as eco-construction material as it consumes less energy and less CO 2 [7]. Bacteria to be incorporated in concrete should be alkali resistant to endure the high pH of concrete. The “Bacterial Concrete” can be made by embedding bacteria in the concrete that are able to constantly precipitate calcite. Several bacteria have the ability to precipitate calcium carbonate. These bacteria can be found in soil, sand, natural minerals. The selection of the bacteria is depend on the survive capability of bacteria in the alkaline environment. Most of the microorganisms die in an environment with pH value of 10 or above [8]. The use of microbial concrete in Civil Engineering has become increasingly popular. From enhancement in durability of cementious materials to improvement in sand properties, from repair of limestone monuments, sealing of concrete cracks to highly durable bricks, microbial concrete has been successful in one and all. This technology also offers the advantage of being novel and eco- friendly. This special kind of concrete has multiple usage. With recent encouraging reports on compressive strength enhancements achieved in conventional concrete through Microbiologically Induced Calcium Carbonate Precipitation (MICCP). The present study was aimed at isolation and characterization of more efficient urease producing bacterial strains for improving the strength of cement concrete. II. MATERIALS AND METHODS 2.1 Isolation and purification of urease producing bacterial strain Ureolytic bacteria used in the present studies were isolated from various sources, like poultry dung compost, cowshed, milk sample, etc. Ureolytic bacteria were isolated by inoculating 1ml of serially diluted soil suspension on modified Urea agar (composition gl -1 : Potassium dihydrogen phosphate: 2.0; Glucose: 1.0; Peptone: 0.2; Sodium chloride: 5.0; Urea: 20.0; Phenol red: 0.012; Agar: 15.0; pH: 7) plates and incubating at 25+2 o c in dark [9]. Colonies that turn the agar red or pink were picked and streaked for isolation onto Urea agar plates. Further, colonies were picked and further streaked for purification. The cultures were maintained at refrigerated temperature on nutrient agar as by repeated sub-culturing fortnightly. 2.2 Cultural characteristics of Bacteria Cultural characteristics of all the isolates were studied on the basis of Gram’s staining [10] and colony Study of Strength Variation of Concrete Using Ureolytic Bacteria Satinder Kaur Khattra, Manisha Parmar, Urmila Gupta Phutela