Modification of recycled concrete aggregate by calcium carbonate biodeposition

A growing demand for raw materials leads to danger of premature depletion of the natural sources. An alternative is to use by-products, provided their quality is improved. The paper presents surface modification of recycled aggregate concrete using biodeposition involving a method employing Sporosarcina pasteurii (Bacillus pasteurii) bacteria. It was possible to obtain reduction in water absorption of aggregate, the effect was more visible in case of finer fractions and for aggregates originating from inferior quality concrete. Calcium chloride was used for precipitation of calcium carbonate, while culture medium consisting of beef extract, peptone and urea was used for cultivation of microorganisms. In addition, whey, ecologically dangerous by-product from dairy industry was found to be effective as a culture medium. Presence of calcium carbonate crystals covering aggregate grains was confirmed by observations under scanning electron microscope. In the perspective, the proposed method, upon appropriate improvements, seems worthwhile due to ecological and technological reasons.

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► Calcium carbonate biodeposition method contributed to decrease in water absorption of recycled concrete aggregate.
► Better efficiency was obtained for finer aggregate fraction and in the case of aggregate of lower quality.
► Efficiency of calcium chloride and whey as culture media was confirmed.
► Observations under SEM showed covering aggregate grains with calcium carbonate.