Abstract:Concrete is the most widely used construction material in civil engineering. But plain concrete is a brittle material and has little resistance to cracking. The cracking in concrete promotes deterioration such as the corrosion of reinforcing rebar, therefore, repair in filling the crack is often carried out. Recently, repair methods using bio-based materials associated with microbial metabolic processes leading to precipitation of calcium carbonate have been intensively studied. In this study, influencing factors on the precipitation rate depending on the constituents of bio-based material comprising yeast, glucose and calcium acetate mixed in tris buffer solution was examined for improving the rate of initial reactions. In addition, effect of temperature change on the amount of calcium carbonate precipitation was also investigated. The precipitates were identified by X-ray diffraction. It was shown that the increase of temperature lead to a change on calcium carbonate precipitation and caused the pH decrease under 7.0.

This research examined differences in the concentration of Tris buffer solution on calcium carbonate precipitation in biobased repair materials. Four concentrations of Tris buffer solution were chosen based on previous research with initial pH 8.0 and 9.0. Initial experiments demonstrated that the concentration and pH of Tris buffer solution had an influence on the amount of precipitation of calcium carbonate. X-Ray Diffraction (XRD) analysis elucidated the morphological and structural differences of the calcium carbonate crystal, including calcite and vaterite. They are the prominent forms of CaCO 3 detected based on results obtained by according to FT-IR analysis. The result further explains the effectiveness of Tris buffer concentration.

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The use of bio-based material for repairing concrete is a relatively new method. Therefore, more results from simulated real-condition experiments are needed before being applied on a practical scale. In the recent past, several studies have been conducted on the improvement of bio-based repair materials. In this study, the bio-based material involving yeast, glucose, and calcium acetate mixed in a Tris buffer solution showed the potential to develop a microbial process leading to the precipitation of calcium carbonate. We investigated the factors affecting the precipitation rate of the calcium carbonate of bio-based materials for repairing leakage in the concrete specimens. Based on a series of experiments involving temperature, the type of dry yeast, and the concentration of the Tris buffer solution, the composition of bio-based materials with the highest precipitation rate of calcium carbonate was selected. The selected mixture could be applied to repair leakage of concrete until the cracks are sealed entirely.

The applicability of bio-based materials for concrete repair has been studied. This technique employs yeast, glucose and calcium acetate mixed in Tris buffer solution. The microbial metabolic process leads to precipitation of calcium carbonate. First, this study investigated the applicability of bio-based repair materials to small-scale concrete specimens. On this research, water permeability test was carried out to evaluate the effectiveness of the selected mixtures for sealing cracks in the concrete specimens. As the result of permeability tests carried out using specimens with crack width of 0.6 mm, water leakage through crack was observed to be negligible after 216 hours by continuous pouring method using bio-based repair materials. Also, this study showed the initial flow rate for the specimens with the same crack width does not influence crack sealing time. Furthermore, the precipitation of the calcium carbonate from the bio-based materials was analyzed by Fourier-Transformed Infra-Red spectroscopy (FT-IR) and then examined by X-ray Diffraction (XRD) for mineral identification formed through the microbial metabolic process.