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Chloride diffusuion is regarded as the dominant chloride transport process in concrete and the main cause of the corrosion of steel in concrete structures exposed to chloride-rich environments. Surface biodeposition can be applied to both new and existing concrete structures to restrain this deterioration. To gain comprehensive overview to the protective mechanism of surface biodeposition, a theoretical study of chloride diffusion through surface-biodeposited concrete is required. This paper proposes a physical model for surface biodeposited concrete, and develops a theoretical model to predict chloride diffusion of surface-biodeposited concrete structures. The model describes movement and retention of moisture and chloride by means of balance equations and diffusion laws. The influences of biodeposition and substrate properties on chloride diffusion are studied by a finite difference model. Results indicate that chloride diffusion is controlled by both the biodeposition and the substrate.

A remediation technique of cracked concrete by bacterial mediated carbronate deposition i.e. bio-deposition is discussed. Bio-deposition is a technique that comes from a broader category of biomineralization. The aim of this study was to investigate the plugging of artificially cracked concrete using bacteria Sporosarcina pasteurii and combined with sand as a filling material in artificially made cuts in concrete specimens which was cured in urea and Ca2+ medium and to research the effects on the compressive strength and flexural load of healing of concrete specimens by bio-deposition. The remediation efficacy of cracks in concrete was studied through compressive strength test and flexural failure test. Experimental results show that bio-deposition is able to make the improvement in concrete compressive strength and flexural load. The technique can be used to improve the compressive strength and flexural load of cracked concrete specimens and the remediation of cracks.

Bio-deposition has led to the exploration of remediation and improvement technique in the field of cementitious materials. The aim of this study was to investigate the effects of bio-deposited carbonate on parameters affecting concrete properties and the effects of bio-deposition on the durability of concrete specimens. The remediation efficacy of cracks in concrete was studied through compressive strength test and flexural failure test. Water absorption and the resistance towards carbonation of concrete were analyzed by water absorptivity test and concrete accelerated carbonation test, respectively. Experimental results show that bio-deposition is able to make the improvement in concrete compressive strength and the remediation of cracks. Bacterial deposition of calcite on the surface of the concrete specimens results in a decrease of capillary water uptake and carbonation rate constant, and an increase in resistance towards degradation processes.

To gain an insight into the protective mechanism of surface biodeposition, a theoretical study of carbon dioxide diffusion through surface-biodeposited concrete is required. The present paper proposes a physical model for surface biodeposition and the concept of water-percolated porosity, and develops a theoretical model to predict carbonation of surface-biodeposited concrete structures. The model describes movement and retention of heat, moisture and carbon dioxide by means of balance equations and diffusion laws. The influences of biodeposition and substrate properties on carbon dioxide diffusion are studied by a finite difference model. Results indicate that carbon dioxide diffusion is controlled by both the biodeposition and the substrate. Biodeposition can significantly reduce carbon dioxide concentration at the concrete surface, but this interfacial concentration increases with time.

Biodeposition treatment had been proposed as alternative techniques for improvement in the durability of concrete structures. Laboratory experiments were conducted by bacterially mediated carbonate precipitation on the surface and subsurface of specimens of concrete. Some properties of specimens and crystal, such as the crystal phase, morphology and growth of the crystal deposited on specimens, water penetration, the resistance towards carbonation of concrete and so on, were analyzed by XRD, SEM, water absorptivity test and concrete accelerated carbonation test. Some efficiencies of biodeposition treatment for were investigated by experiment. Results show that the mineral crystal deposits uniformly on the surface and subsurface of specimens, phases of crystal are calcite and vaterite. Biodeposition effectively reduces capillary water uptake and leading to carbonation rate constant decreased by 25~40%. Bacterially mediated carbonate mineralization can be an ecological and novel alternative for improvement in the durability of concrete structures.

Microbial carbonate precipitation had been proposed as alternative technique for improvement in concrete materials. Laboratory experiments were conducted by bacterially mediated carbonate deposition on the surface and subsurface of concrete specimens. The crystal phase, morphology and growth of the crystal deposited on specimens as well as the efficiency of bonding and protection were analyzed by means of X-ray diffraction (XRD), scanning electron microscope (SEM), and ultrasonic test. Water absorption and the resistance of carbonation of concrete were analyzed by water absorptivity test and concrete accelerated carbonation test, respectively. Results show that phases of crystal are calcite and vaterite. The crystals are deposited uniformly on the surface of specimens. Biodeposotion effectively reduces capillary water uptake and carbonation rate constant.