Enhanced crack closure performance of microbial mortar through nitrate reduction

Microbial self-healing of concrete has been widely investigated, yet the suggested microbial pathways are limited to ureolysis and the aerobic oxidation of carbon sources. Each of these pathways has certain environment and process related drawbacks which arise a need for an alternative pathway to proceed further. This study presents the NO3- reduction as an alternative microbial self-healing strategy. In the tests, we used previously described NO3- reducing bacteria, and two different porous protective carriers. The highest crack width healed by the bacteria was 370 +/- 20 mu m in 28 days and 480 +/- 16 mu m in 56 days. Water tightness regain up to 85% was achieved at the end of 56 days for 465 +/- 21 mu m crack width. Precipitates were identified as forms of CaCO3 and were abundant in microbial specimens particularly on the inner crack surface. The findings evidence the potential of the NOT reduction pathway for development of microbial self-healing concrete. (C) 2016 Elsevier Ltd. All rights reserved.