The project aims at attaining high durability of concrete and gaining high strength of cement. We plan to make use of bacterial species which can hydrolyze the enzyme Urease efficiently to produce microbial concrete. Such bacterial are known to produce calcium which is useful in giving strength to cement.
We are working in 2 stages.
Stage 1: Here we check the effect of bacterial solution on cement mortar and along with that we check the effectiveness of the bacterial solution to fill the cracks in concrete by precipitation of calcium in the cracks. Stage 2: To prepare concrete using the cement and solution (bacterial) in optimum ratio and checking its effectiveness from strength and durability perspective.
Till now Stage 1 is partially over: We have made use of this bacterial solution(Emulsion: Bacillus culture+ nutrient broth+ sucrose+ urea+ calcium chloride+ antifungal agent(griseofulvin)to heal the existing cracks in the concrete walls. For achieving high 7 days we have made use of bacterial solution in some fixed proportion with water. The 7 days test was performed on 7/12/11 with 5%, 10%, and 15% of the bacterial solution with respective percentage of water. We have gained a significant percentage increase in the strength of the cubes made with bacterial solution with water versus those made with only water
Bacteria at work
Microbially induced calcite precipitation (MICP)
Microbially induced calcite precipitation (MICP) is known to be a natural phenomenon associated with a wide range of bacterial species such as Bacillus spp. provided the right conditions, namely, an alkaline environment rich in Ca2+ ions. Bacterially induced mineralization has recently emerged as a method for protecting and consolidating decayed construct materials. Calcite (CaCO3) is one of the most common and widespread minerals on the earth, constituting 4% by weight of the earth’s crust.
Calcite precipitation is a common phenomenon which forms natural rock and exists in environments such as marine water, fresh water, and soils. Microbial calcite precipitation can be induced by organisms involved in the nitrogen cycle, via the hydrolysis of urea by enzyme urease, which results in the production of carbonate ions in the presence of ammonium. Calcium carbonate is readily precipitated under these conditions, in the presence of calcium.
Microbial calcite precipitation comprises a series of complex biochemical reactions. During microbial urease activity, 1 mol of urea is hydrolyzed intracellularly to 1 mol of ammonia and 1 mol of carbonate, which spontaneously hydrolyzes to form additional 1 mol of ammonia and carbonic acid. Subsequently, these products equilibrate in water to form bicarbonate, 1 mol of ammonium and hydroxide ions which give rise to a pH increase and ions Ca2+ and CO32- present in the surrounding precipitate as CaCO3. Urea hydrolysis is the most easily controlled of the carbonate generating reactions, with the potential to produce high concentrations of carbonate within a short time.
Bacillus spp. was used in this study. The culture was grown in Nutrient broth-urea (NBU) medium containing peptone, sodium chloride, yeast extract, 2% urea and 25mM calcium chloride and incubated at room temperature on shaker condition (130 rpm). Calcium chloride acts as the source of calcium ions and urea as the source of carbonate ions.
* There is a rise in the compressive strength of the mortar cubes till 5 % bacterial solution. * The strength is reduced when the proportion of bacterial solution is increased up to 10 % and beyond. * The cubes with 15% bacterial solution shows 8 % decrease in strength. * The 1%, 2%, 3% cubes developed less cracks in comparison to control cubes. * The cubes when observed after testing , the control cubes had more number of empty pores.
* 3% cubes showed an increase in compressive strength of 36 % in comparison to control cubes.
* Reduction in empty pore space.(which prevent the ingress of water and other chemicals )
* Bacteria does not have any physical effect on the cement.
* Chemically inert.
* Bacterial solution can be prepared on a large scale .
* No skilled labour is required.
* Its production is economical.
* Microbial activity on the microstructure of bacteria modified mortar by S.Ghosh, M.Biswas, B.D. Chattopadhyay, S.Mandal. * Effect of calcifying bacteria on permeation properties of concrete structures by Dr. Varenyam Achal. * Work on BacillaFilla by New Castle University.
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