Self-healing bacterial mortar with calcium lactate and improved properties

Building Materials

The advancing technologies of self-healing concrete focus on reversing and repairing the micro-cracks that form in concrete at early ages, increasing the durability of the structure. The utilization of the metabolic properties of bacteria in bacteria-based self-healing mortar has yielded promising results in the reduction of cracks. Two species of bacteria Bacillus sphaericus (BS), Bacillus pasteurii (BP) were used in this study and patched at a ratio of cement weight in addition to Calcium Lactate being added as nutrition of bacteria. Setting time test was performed to measure the effect of bacteria on fresh mortar properties. The bacterial mixtures were compared to control mix to study their behavior under the influence of permeability test, compressive strength test, flexural strength test, sulfate resistance test and acid resistance test. Also, the restoration of bacterial mixes was tested. Furthermore, advanced technique were employed to evaluate the influence of bacteria addition, e.g. Scanning Electron Microscope (SEM). The cell concentration of Bacillus sphaericus (BS) and Bacillus pasteurii (BP) of all bacterial mortar mixes were counted. The bacteria nutrition acts as accelerator of cement pastes for initial setting time for all bacterial mortar compared to control mortar, while acts as a retarder of cement pastes for final setting time for all bacterial mortar compared to the control samples. Rate of water Absorption decreased with time and became nearly impermeable for BS60 and BP60 at the age of 120 days. Compressive strength of BS60 at 120 days age increased by 124 % compared to the control specimens. Flexural strength value of BS30 at the age of 120 days increased by 168 % compared to control mortar. Results showed that BP60 had a high ability to resist salts and acids. SEM proved that the bacterial mortar had less voids than that of control mortar. Microbial Induced Calcite Precipitation (MICP) is responsible for filling up the pores in mortar and hence decreased the rate of water absorption and the capillary permeability coefficient, while increasing the compressive and flexural strength for bacterial mortar.