Abstract: This paper examines the compressive strength and water absorption properties of bacterial concrete by influence of bacteria isolated from three different places. The samples were isolated from cement, urea go down and dry activated sludge dumped soils. These bacteria was used in the concentration (0, 106, cells/ml) for making the bacterial concrete mixtures. The experimental investigation was carried out to evaluate the influence of bacteria on the compressive strength and water absorption at the age of 7, 14, 28 days. Under the influence of isolated bacteria, the compressive strength of concrete at the age of 7, 14, 28 days showed an increase of about 27.54%, 22.9%, and 15.7% as compared to control concrete. Similarly, Water absorption rate also showed decreased to 3.1 %, 3.8 % water by its weight which is less than the control concrete (CC) 4.2%. The use of bacteria will was to precipitate CaCO3 in their micro-environment by conversion of urea into ammonium and carbonate. The bacterial degradation of urea locally increases the pH and promotes the microbial deposition of carbonate as Calcium carbonate in a calcium rich environment. Thus, “Bacteria Calcite Precipitation” [BCP] phenomenon improved the strength by precipitating the calcium inside the bacterial concrete.
Porous materials are widely used for construction purposes. Even if concrete and mortar are usually covered in building, they are often exposed to environmental impacts like salt crystallization, freeze-thaw and carbonation or acid in rain water decrease the initial strength and durability of the concrete. This leads to deterioration of the concrete. After some decades, due to porous concrete may often carbonation. Carbon dioxide in the air can cause corrosion of embedded steel through a process known as carbonation. In this process, carbon dioxide gas dissolves in the pore water to form carbonic acid, which in turn reacts with the hydroxides in the pore solution which are alkaline. Once these hydroxides are consumed, the pH of the pore solution will fall to a level (< 9) where corrosion of the steel can occur. Corrosion due to carbonation is most common when the concrete more porous.
This present study deals with bacteria to fill porous in concrete and improve the compressive strength and increase the durability of the concrete. In this paper to evaluate the most important concrete parameters such as compressive strength, water absorption test. The effect of bacteria isolated from three different soil bacteria cell concentration (106, cells/ml) of bacteria were used.
2. Literature review
The compressive strength increase and reduce the permeability in concrete to add bacteria. This “bacteria calcite precipitation” [BCP] improved the permeability of the concrete, thus improving its durability, strength and deduct pores. The natural environment, chemical CaCO3 precipitation (Ca2++ CO32-? CaCO3?) is accompanied by biological processes, both of which often occur simultaneously or sequentially. This microbiologically induced calcium carbonate precipitation (MICCP) comprises of a series of complex biochemical reactions (Stocks-Fischer et al ). It is generally accepted that the durability of concrete is related to the characteristics of its pore structure [Khan 2003] . The permeability of the concrete is depending 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. The deterioration of concrete structures usually involves movement of aggressive gases and/or liquids from the surrounding environment into the concrete followed by physical and/or chemical reactions within its internal structure, possibly leading to irreversible damage [Claisse et al. 1997]. Recently, microbiologically induced calcium carbonate precipitation (MICCP) resulting from metabolic activities of some specific microorganisms in concrete to improve the overall behaviour of concrete has begun to attract interest of researchers. Previous studies with aerobic microorganism (Bacillus pasteurii and Pseudomonas aeruginosa) showed a significant improvement (about 18%) in compressive strength of cement mortar [Ramakrishnan et al. 1998; Ramachandran et al. 2001][4-5].Previous research has shown that Bacillus sphaericus bacteria are able to precipitate calcium carbonate on their cell constituents and in their micro-environment by conversion of urea in to ammonium and carbonate. The bacterial degradation of urea locally increases the pH and promotes the microbial deposition of calcium carbonate in a calcium rich environment [Wang J.Y., Van Tittelboom K., De Belie N.M.,Verstraete W. .
3.Materials and method
3.1 Isolation of bacteria
The samples were isolated from cement, urea go down and dry activated sludge dumped soils. The samples were serially diluted and plated on Nutrient agar at 37ºC for 24 hours as shown in figure 1.The isolates were microbiologically characterized by morphological and biochemically study. The colonies were added in nutrient broth which is incubated at 37ºC and placed in orbital shaker for 120 rpm is maintained and mother inoculum prepared. 
3.2. The ingredients required for preparation of growth culture
Peptone : 5 g/lt.
Veg extract : 1.50 g/lt.
Yeast extract : 1.59 g/lt.
Sodium Chloride : 5.00 g/lt.
3.3 Ordinary Portland cement
Ordinary Portland cement was used. It was tested as per Indian Specifications IS: 8112-1989 . Its physical and chemical properties are shown in Tables 2 and 3.
3.4 Sand and coarse aggregate
Locally available clean well-graded natural rivers and with a 4.75-mm maximum size as fine aggregates and coarse aggregate with 12.5 mm and 20mm nominal size was used. They were tested as per Indian Standard Specifications IS: 383-1970 . Their physical properties are given in Table 4.
Water is an important ingredient of concrete as it actively participates in chemical reactions with cement. Clean potable water was used for the preparation of concrete mixture. Prepared bacterial cultures (NB) add in to water.
Proportioning of concrete mixture consists of determination of the respective ingredients necessary to produce concrete having adequate workability, strength and durability for the particular strength and for various exposure conditions. The mix proportions for the controlled concrete of M20 grades were arrived from the trial mixes as per Indian standard (IS: 10262 – 2009) specifications and found to be 1: 1.8:2.8 (w/c = 0.50) respectively . These mixtures were used throughout the study. The details of mix proportions are given in Table 5 for M20 and control concrete mixtures, respectively.
5. Preparation of Specimens
The concrete mixtures were prepared in a hand mixer for about 15 min. In order to maintain a constant slump value at about 80±20 mm. Concrete mixture proportions are shown in Table 5. The cement content was taken in this study 383Kg/m3, and the entire experiment W/C ratio is 0.5. All the test specimens were casted in steel moulds. The inside of the moulds was applied with oil to facilitate the easy removal of specimens. First the materials cement, quarry dust, fine aggregate, and coarse aggregate were weighed exactly, cement and sand were mixed first. Then coarse aggregate is added and thoroughly mixed. A bacterial solution was prepared by adding the required dosage of cell concentration to required quantity of water and mixed well. At this stage this bacterial solution was added to the concrete was then placed in the mould in three layers of equal thickness and a table vibrator was employed to compact the concrete in the mould. These 100 x 100 x 100 mm size of the specimens were used to determine strength properties of concrete. The all specimens have been kept in the moulds for 24 h at room temperature of 20°C. After remolded, the specimens were placed into a water curing tank full of saturated water at 20±2°C till testing times for standard curing.
6. Experimental Programs
6.1 Compressive strength test
The present study uses 100 mm × 100 mm × 100 mm concrete cubes were cast by using M20 grade concrete. Specimens with and without bacteria tested. After 24 h the specimens was removed from the mould and subjected to water curing for 7, 14 and 28 days. After the curing period before testing, the specimen was dried. Hydraulic Digital compression testing machine was used with a capacity of 2000KN and the pace rate of 2.5 KN/sec as show in figure.2. 
6.2. Water absorption test
The water absorption by immersion is determined according to the Belgian Standard NBN B15-215 Principally and the test setup as show in figure.3. The test consists of two major steps: saturating the specimens followed by drying. First the concrete specimens are immersed in water until the change in mass during 24 hours is less than 0.1%. The obtained saturated mass is called Ws. Afterwards, the specimens are dried in a ventilated oven at a temperature of 105±5°C until the difference in mass during 24 hours is less than 0.1% and the dry mass is called Wd. 
Water absorption = ((WS – WD)/ WD) * 100 in %
Ws- Saturated weight (kg)
Wd- Oven dried weight (kg)
7. Results and Discussion
7.1 Compressive strength test
Influence of isolated bacteria thus improves the compressive strength of concrete shown in Fig. 4. It is evident that compressive strength of bacterial concrete increased as compare to control concrete. Maximum increase in compressive strengths was achieved at CSB for all bacterial concretes. The improvement in compressive strength by bacteria is probably due to deposition of CaCO3 on the microorganism cell surfaces and within the pores of, which plug the pores within the binder matrix. The results from the study showed that due to inclusion of bacteria in concrete, compressive strength was improved which would in turn increase the overall durability performance of the concrete. The increase in compressive strengths is mainly due to filling of the pores inside the concrete with microbiologically induced calcium carbonate precipitation.
7.2. Water absorption test
The influence of bacteria on the water absorption of bacterial concrete shown in Fig. 5.The absorption of water by any material determines the amount of voids present in it. Hence the water absorption test has become vital in assessing the microstructure of concrete cubes indirectly. The above Figure.5 shows the water absorption characteristic of three bacterial concrete mixes with control concrete. The bacterial concrete at 28 days was absorbed CSB, USB, ASB 3.1 %, 3.8 %, 3.2 % water by its weight which is less than the control concrete (CC) 4.7%. similarly the age 14 days was absorbed CSB, USB, ASB 5.3 %, 4.6 %, 5.8 % water by its weight which is less than the control concrete (CC) 7.8 % and Also at 7 days was absorbed CSB, USB, ASB 7.6 %, 8.4 %, 7 % water by its weight which is less than the control concrete (CC) 4.7%. Hence the bacterial concrete has low water absorption characteristic due to “Bacteria Calcite Precipitation”.
The following conclusions have been drawn based on the experimental investigations carried out on concrete mixtures with and without bacteria.
– Bacteria plays a significant role in increasing the compressive strength of bacterial concrete by Cement soil Bacteria 23.75, Urea soil Bacteria 21.99 %, Activated Sludge Bacteria 15.24%.
– Water absorption also decreases Control concrete, Cement soil Bacteria 4.7%, Urea soil Bacteria 3.1 %, Activated Sludge Bacteria 3.2%.due to the calcium carbonate precipitation inside the concrete.
– The increase in compressive strength is mainly due to consolidation of the pores inside the bacterial induced calcium carbonate precipitation.
– We conclude that concrete-immobilized spores of such bacteria may be able to seal pours by formation Bacteria Calcite Precipitation. Hence the application of bacteria will improve the strength and durability of cement concrete therefore it appears promising field in near future.
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Arivusudar Nagarajan was born in Krishnagiri, Tamil Nadu, India, in 1984. He received the M.E.degree in Structural engineering from Government College of engineering, Salem, Tamil Nadu respectively. In 2006 he joined the Construction building materials business units in Pan India & Aboard (Cement, Ready mix concrete, Construction chemicals Divisions), His Presently working in Parex construction Chemicals as Regional Sales Manager–Project (South). Arivusudar Nagarajan is a fellow of the Institution of Engineers (India), National ready mixed concrete association, His Research and consultant activities have included various studies in ,Optimization of concrete materials ,Recycle waste materials & Acted Troubleshooter for many reputed construction company and Ready mix concrete industry , He has authored book & Journals – Study on flexural capacity of Built-up I Section with trapezoidal web.
J.Aruna He received the B.E. degree in Civil engineering. In 2009 he joined the Civil Construction Business unit (Dwell Housing systems , Eco Friendly & Green building concepts ) His Presently working in Raju Eco- Friendly housing system as General Manager, His Research and consultant activities have included various studies in, Optimization of Building materials, Recycle waste materials into building materials & Acted Troubleshooter for many reputed construction company.