Bio-inspired self-healing cementitious mortar using Bacillus subtilis immobilized on nano-/micro-additives

• Published in: Journal of intelligent material systems and structures Vol. 30; no. 1; pp. 3 - 15
• Main Authors: Khushnood, Rao Arsalan, ud din, Siraj, Shaheen, Nafeesa, Ahmad, Sajjad, Zarrar, Filza
• Format: Journal Article
• Language: English
• Published: London, England SAGE Publications 01-01-2019
• Subjects: compressive strength; Bacillus subtilis; iron oxide particles; siliceous sand; limestone particles; calcium lactate; self-healing; bio-inspired
• ISSN: 1045-389X; 1530-8138
• DOI: 10.1177/1045389X18806401

Bio-inspired self-healing strategies are much innovative and potentially viable for the production of healable cement mortar matrix. The present research explores the feasibility of gram-positive “Bacillus subtilis” microorganisms in the effective healing of nano-/micro-scale-induced structural and non-structural cracks. The main concern related to the survival of such microorganisms in cementitious environment has been successfully addressed by devising proficient immobilization scheme coherently. The investigated immobilizing media includes iron oxide nano-sized particles, micro-sized limestone particles, and milli-sized siliceous sand. The effect of induced B. subtilis microorganisms immobilized on nano-micro-additives was analyzed by the quantification of average compressive resistance of specimens (ASTM C109) and healing evaluation. The healing process was mechanically gauged by compressive strength regain of pre-cracked specimens after the healing period of 28 days. The pre-cracking load was affixed at 80% of ultimate compressive stress “
f
′
c
” while the age of pre-cracking was kept variable as 3, 7, 14, and 28 days to precisely correlate healing effectiveness as the function of cracking period. The healing mechanism was further explored by examining the healed micro-crack using field emission scanning electron micrographs, energy dispersive x-ray spectrographs, and thermogravimetry. The results revealed that B. subtilis microorganisms contribute extremely well in the improvement of compressive strength and efficient healing process of pre-cracked cement mortar formulations. The iron oxide nano-sized particles were found to be the most effective immobilizer for preserving B. subtilis microbes till the generation of cracks followed by siliceous sand and limestone particles. The micro-graphical and chemical investigations endorsed the mechanical measurements by evidencing calcite precipitation in the induced nano-/micro-cracks as a result of microbial activity.