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The beneficial effect of microbially induced carbonate precipitation on building materials has been gradually disclosed in the last decade. After the first applications of on historical stones, promising results were obtained with the respect of improved durability. An extensive study then followed on the application of this environmentally friendly and compatible material on a currently widely used construction material, concrete. This review is focused on the discussion of the impact of the two main applications, bacterial surface treatment and bacteria based crack repair, on concrete durability. Special attention was paid to the choice of suitable bacteria and the metabolic pathway aiming at their functionality in concrete environment. Interactions between bacterial cells and cementitious matrix were also elaborated. Furthermore, recommendations to improve the effectiveness of bacterial treatment are provided. Limitations of current studies, updated applications and future application perspectives are shortly outlined.

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Bacterial induced carbonate mineralization has been demonstrated as a new potential method for restoration of limestones in historic buildings and monuments. We claim here the formation of calcium carbonate was controlled by extracellular polymeric substances (EPS) isolated from Bacillus pasteurii. The process of crystallization nucleation was accelerated in the presence of cells and inhibited in the presence of EPS. The CaCO 3 film deposited on cement paste surface was about 100 µm after 7 d treatment. The results of various restoring methods showed that higher decrease of water absorption of cement paste was gained in brushing application in the presence of agar, which could maintain urease with high activity in long term compared to spraying method. The coefficient of capillary suction of cement paste treated with brushing method was reduced by 90%. Mixed media consisted of sands, urea, Ca 2＋ and concentrated biomass, was injected into artificial cracks of cement paste followed by continual nutrient supplement, and CaCO 3 particles were precipitated gradually between sands particles which were combined with cement matrix. The results showed that the compressive strength of recovered specimens was restored to 84%, which demonstrated that this kind of bio-restoration method is effective in repairing surface defects of cement-based materials.

Durability problems in concrete can often be linked to a high permeability, which is either caused by a high matrix permeability or the presence of cracks. Therefore, treatments that reduce the permeability of the matrix, or that close the crack from ingress of aggressive agents carried by water or air, would substantially enhance the service life of a concrete structure. Several chemical products are currently in use for consolidation and crack repair, but a new technique that has been the focus of much research efforts over the last decade is the bacteria-based calcium carbonate precipitation. This technique is now slowly making its way towards practical applications. The principles of the technique, the important influential parameters and the recent advances related to its use for consolidation, surface protection, external crack repair, and self-healing of cracks in concrete are discussed in this article. Also the wider applicability for mechanical strengthening and consolidation of natural stone and soils is shortly treated

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