Production of non-axenic ureolytic spores for self-healing concrete applications

The bin-based self-healing concrete market demands an inexpensive bin-agent. The use of axenic ureolytic spore cultures has been demonstrated to be efficient but too expensive, due to an operational expense (OPEX) cost of about 500 (sic)/kg of bio-agent. A new selection process to obtain a powderous material containing an efficient ureolytic microbial community (Cyclic EnRiched Ureolytic Powder or CERUP) has been developed. Ureolytic activity, calcium carbonate precipitation capability and the effects in concrete were evaluated at production scales of 5 L and 50 L The non-axenic culture obtained following this new selective process, at both 5 L and 50 L scales, proved to be as good as the benchmark Bacillus sphaericus both in urea hydrolysis (20 g urea/L in 24 h) and calcium carbonate precipitation (0.3 g CaCO3/g VS.h). Plain incorporation of CERUP in concrete was found to be efficient at levels of 0.5% and 1% of the cement weight. Furthermore, a brief economical evaluation was performed to verify the economic feasibility of this product. Only OPEX costs were considered since capital expense (CAPEX) costs are directly related to the dimensions of scale and thus not possible to estimate at this stage of the research. The OPEX cost per unit of CERUP is about 40 times lower than the OPEX cost of a B. sphaericus axenic culture. However, even with such decrease in cost, the production of bacterial spores to incorporate in concrete is too expensive. (C) 2015 Elsevier Ltd. All rights reserved.