Bacillus Subtilis as Self-Healing Agent in Cement Mortar:  Combined and the Separate Effect of Bacteria and Calcium  Lactate on Self-Healing Behavior in Cement Mortar

Sohail Muhammad; Humair Ahmed Siddiqui; Muhammad Ishaque Abro; Adil Usmani; Muhammad Amjad Anwar Malik

doi:10.22581/muet1982.2102.16

Sohail Muhammad Department of Materials Engineering, NED University of Engineering and Technology, Karachi, Sindh, Pakistan.
Humair Ahmed Siddiqui Department of Materials Engineering Faculty, NED UET, Karachi , Sindh, Pakistan. School of Engineering, Faculty of Science and Engineering, University of Waikato, Hamilton 3240, New Zealand.
Muhammad Ishaque Abro Department of Metallurgy and Materials Engineering, Mehran University of Engineering and Technology, Jamshoro, Sindh, Pakistan.
Adil Usmani Department of Materials Engineering, NED University of Engineering and Technology, Karachi, Sindh, Pakistan.
Muhammad Amjad Anwar Malik Department of Materials Engineering, NED University of Engineering and Technology, Karachi, Sindh, Pakistan.

DOI: https://doi.org/10.22581/muet1982.2102.16

Abstract

Cement mortar, which is one of the most useful materials for construction applications, can deteriorate its performance by developing cracks. In order to cope with this issue, the materialsâ€™ scientist came forward with a unique biogeochemical phenomenon in which cement mortar can selfheal its crack autonomously using calcium carbonate precipitating bacteria and their feed. In this research, it was intended to study the separate and combined effect of Bacillus Subtilis (bacteria) and Calcium Lactate (feed) on the properties of conventional mortar. Cement mortars were made using conventional method and cast in the form of cylinders. Four types of samples were taken. Sample-N contains only cement and sand, Sample-B was made by addition of bacteria Bacillus Subtilis with sand and cement, Sample-C contains Calcium Lactate which is usually used as feed for Bacteria while the last sample â€˜BCâ€™ have both Bacteria as well as Calcium Lactate. The samples were observed up to 44 days for their surface characteristics and compressive strength. The Sample-N and B did not show any remarkable change in their surface appearance with respect to curing time. Sample-C and BC did show the precipitation of CaCO3 but the Sample-C precipitation was stopped soon while for Sample-BC, the precipitation was continued for a longer time. The Sample-BC showed the highest compressive strength (approximately 17.57 MPa), followed by Sample-N (approximately 13.32 MPa), Sample-B (approximately 11.04 MPa) while Sample-C displayed lowest strength (approximately 2.75 MPa). This gives an idea that Calcium Lactate which acts as feed for bacteria has the negative effect on the strength if not consumed and converted into CaCO3.