Role of Calcifying Bacteria on Durability Properties of Carbonated Cement Mortar

Abstract

Current concern about degradation of concrete, and ageing infrastructure, impose an unprecedented demand on construction industry, which requires sustainable technologies to meet society’s need in a cost effective manner. Microbial Concrete which is perfect blend between biology and engineering presents an highly efficient method to remediate, building and construction materials. Different research groups have proposed the ureolytic microbial calcium carbonate precipitation by different calcifying bacteria. Although urea hydrolysis presents a straight forward model for studying microbial CaCO3 precipitation but it also possess certain limitations. The large amount of ammonia released with large amount of nitric acid production can cause detrimental effect to the environment and produces pungent odours. Therefore, in the present study our aim was to develop an effective carbonation process in presence of microbes, based on Microbially induced calcium carbonate precipitation (MICCP) to enhance the durability properties of building materials and structures. The effect of initial carbonation curing of 7 days was examined on ordinary Portland cement (OPC) mortars. A bacterium Bacillus megaterium have been successfully used to optimize different parameters (pH ,Carbonic Anhydrase activity, CaCO3 precipitation) in presence of pure CO2, in in-vitro conditions, and to improve the durability properties of cement mortars ex-vitro. In in-vitro conditions, a particular conc. of CO2 i.e. 0.112g/L was optimized to induce maximum carbonate precipitation. For field study, bacterial mortar cubes of dimension 70.6 x 70.6 x 70.6 were subjected to bacterial culture and carbonation curing to see the enhancement in durability properties. The results indicated that microbial process involving ureolytic pathway increased the compressive strength by almost 36%, and Microbial process involving Carbonation curing increased compressive strength by 38% with reference to their respective controls. Bacterial deposition of a layer of calcite on the surface of specimens, and carbonate precipitates formed between cement and sand particles resulted in almost 3 times decrease in water absorption and permeability compared to control cubes without bacteria. It shows that bacterial carbonation can yield significant results in enhancing the durability of construction materials without the use of urea.