Concrete is the most widely used construction material of the world and maintaining concrete structures from premature deterioration is proving to be a great challenge. Early age formation of micro-cracking in concrete structure severely affects the serviceability leading to high cost of maintenance. Apart from conventional methods of repairing cracks with sealants or treating the concrete with adhesive chemicals to prevent the cracks from widening, a microbial crack-healing approach has shown promising results. The unique feature of the microbial system is that it enables self-healing of concrete. The effectiveness of microbially induced calcium carbonate precipitation (MICCP) in improving durability of cementitious building materials, restoration of stone monuments and soil bioclogging is discussed. Main emphasis has been laid on the potential of bacteria-based crack repair in concrete structure and the applications of different bacterial treatments to self-healing cracks. Furthermore, recommendations to employ the MICCP technology at commercial scale and reduction in the cost of application are provided in this review.

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Ordinary portland cement (OPC) is conventionally used as primary binder to produce concrete. The amount of carbon dioxide released during the manufacture of OPC and the extent of energy required to produce OPC are the matters of environmental concern in view of global warming and the poor availability of power. Fly-ash, abundantly available byproduct of coal fired thermal power stations is posing great environmental problems through its disposal. Fly ash with combination of alkalis like sodium hydroxide and sodium silicate can produce binding material depending upon the characteristics of these ingredients. The possibility of eco-friendly use of locally available fly-ash with commercially available alkalis in the development of effective binder; and the effect of various parameters on the compressive strength of geo-polymer concrete is explored in the present paper. The laboratory investigations under ambient and oven dry curing conditions suggested that locally available low calcium fly-ash is suitable for development of geo-polymer concrete; and the compressive strength of geo-polymer concrete is a function of mass ratio of alkaline liquid to fly-ash, mass ratio of sodium silicate to sodium hydroxide and molar concentration of sodium hydroxide.

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Microbial-induced carbonate precipitation (MICP) has a potential to improve the durability properties and remediate cracks in concrete. In the present study, the main emphasis is placed upon replacing the expensive laboratory nutrient broth (NB) with corn steep liquor (CSL), an industrial by-product, as an alternate nutrient medium during biocementation. The influence of organic nutrients (carbon and nitrogen content) of CSL and NB on the chemical and structural properties of concrete structures is studied. It has been observed that cement-setting properties were unaffected by CSL organic content, while NB medium influenced it. Carbon and nitrogen content in concrete structures was significantly lower in CSL-treated specimens than in NB-treated specimens. Decreased permeability and increased compressive strength were reported when NB is replaced with CSL in bacteria-treated specimens. The present study results suggest that CSL can be used as a replacement growth medium for MICP technology at commercial scale.