Abstract
Concrete is a mixture of cement, water, sand and other aggregates in adequate proportions. Its high tensile strength and ability to withstand a vast range of environmental changes makes it the first choice for construction material. One of the major problems associated with concrete is its permeability because penetration of gases and/or liquids from the surrounding environment into the concrete, followed by physical and/or chemical reactions within its internal structure/s leads to irreversible damages. Although cement has autonomous capacity to heal, however cracks <0.2mm width can only self-heal. Biomineralization is one of the best ecofriendly techniques to tackle the problem of cracks in concrete structures. Biologically induced self-healing is beneficial in addressing all the drawbacks of concrete matrix. The most promising technology for producing crack resistant/highly self healing concrete in near future seems to be “BacillaFilla”: genetically modified version of Bacillus subtilis, is a “custom –designed” bacteria to embed deep into the cracks in concrete where they produce a mix of calcium carbonate and a special bacteria glue that hardens to the same strength as of the surrounding concrete. DOI: http://dx.doi.org/10.3126/ijasbt.v1i3.8582 Int J Appl Sci Biotechnol, Vol. 1(3) 2013 : 85-89
Highlights
Concrete is today’s material of choice for construction world-wide because of its strength and cost effectiveness
Since concrete is composed of aggregates of various sizes connected with hydration products generated by mixing cement and water, cracks in concrete can occur at any stage of the service life due to volume instabilities such as autogenous shrinkage and/or drying shrinkage
The calcium carbonate production by bacteria is generally regarded as “induced” as the type of mineral produced is largely dependent on the environmental conditions and no specialized structures or specific molecular mechanism are thought to be involved (Rivadeneyra et al, 1994)
Summary
Concrete is today’s material of choice for construction world-wide because of its strength and cost effectiveness. Micro cracks (width smaller than 0.2 mm) do not affect strength properties of concrete structures directly but they contribute to material porosity and permeability which leads to ingression of aggressive chemicals such as chlorides, sulfates and acids that results in concrete matrix degradation and premature corrosion of the embedded iron reinforcement hampering the structures durability in the long term (Jonkers and Schlangen, 2008). Carbon dioxide consumption by photosynthetic microorganisms shifts the equilibrium resulting in increase in pH (eqn 5) (Ariyanti et al, 2011) When this reaction occurs in the presence of calcium ion in the system, calcium carbonate is produced as described at chemical reaction in eqn.. When this reaction occurs in the presence of calcium ion in the system, calcium carbonate is produced as described at chemical reaction in eqn.6 Another pathway uses sulphur reducing bacteria (SRB).
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