Evaluation of effects of multi-varied atmospheric curing conditions on compressive strength of bacterial (bacillus subtilis) cement mortar

Addition of calcite-producing bacteria is a relatively new technique used globally to produce self-healing concrete/cement mortar as well as to increase compressive strength and durability. Due to different atmospheric conditions around the world, the performance of these bacteria will vary due to different curing conditions. In this study, the effects of different atmospheric curing conditions on the compressive strength of bio cement mortar (BCM) are examined. The atmospheric conditions (curing) are varied by combining different temperature and relative humidity, and wind speed and sunlight exposure time. The microorganism used is Bacillus subtilis, and it is added to concrete mortar through direct mixing. The concentration of the bacteria solution is 10⁹ cells/ml and two volumes of 30 ml and 50 ml are applied. Two control specimens - water-cured bio cement mortar (BC) and water-cured cement mortar (NC), are made to serve as baselines for comparison and evaluation of the effects of the curing conditions. The results showed that increased temperature, relative humidity and wind speed increased the compressive strength of BCM. However, increased sunlight exposure time decreased the compressive strength. The results indicated that atmospheric conditions influence the performance of bacteria in BCM. The BCMs had higher 7 and 28 days compressive strength than the control sample (water-cured cement mortar). The minimum and maximum 7 day increments were 53.7% and 120.6% respectively, while the 44.9% and 130.6% respectively were the 28 day. The results show that calcite-producing bacteria improves the compressive strength of cement mortar, however, the environmental curing conditions of the produced BCM will influence the calcite-producing ability of the bacteria.