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

Abstract

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 nanomicro-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 0 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.

Isolation of alkaliphilic calcifying bacteria and their feasibility for enhanced CaCO3 precipitation in bio‐based cementitious composites

“…Similarly, 9%, 7% and 2% increment was recorded in the case of C. amylolyticum (3A), C. imtechense (4F) and C. efficiens (1E) respectively. The strength improvement mechanism is associated with the pore refinement via calcite precipitation (Khushnood, et al, 2018). In vitro results of calcite precipitation (Fig.…”

“…The Bacillus species have been reported with maximum of 25.93% increase in compressive strength of cementitious mortar (Ghatiya and Pendharkar, 2017). Bacillus species are extensively researched in self-healing concrete; however, isolated strains in the recent studies have not been reported yet (Khushnood et al, 2018;Khushnood et al, 2019;Shaheen et al, 2019). Arthrobacter specie is also reported as 8.9% strength increase in cementitious mortar (Park et al, 2010).…”

“…At present, coherent self-healing concrete system via intrusion of calcifying microbes is designed to impart self-remediated mechanisms to avoid external repairs (Stocks-Fischer et al, 1999;Ramakrishnan et al, 2001;Chaurasia et al, 2014). Moreover, the intrusion of microbes enhances the mechanical strength of the concrete matrix against abrasion hence improving the structural health of the system (Khushnood et al, 2018). However, the repairing efficiency by MICP depends upon bacterial strain, precipitation pathway, pH, temperature, relative humidity, dissolved inorganic carbon and nutrients availability (Shaheen et al, 2019).…”

Self-repairing polyethylene fiber-reinforced-concrete with bacillus subtilis bacteria a review

“…Adopting bacteria with spores that activated in the water and oxygen is essential. Another solution is to apply protection immobilized thorough various carrier compounds as silica gel, polyurethane (PU) [118], graphite-nano-platelets (GNP), melamine based microcapsules [119], hydrogel [49], diatomaceous earth [120], light-weightaggregate (LWA) as expanded clay particles Liapor [121][122][123] and immobilized on nano-/micro-additives [124]. ii) Most organisms did not survive in a pH value above 10.…”

Effect and Mechanism of Encapsulation-Based Spores on Self-Healing Concrete at Different Curing Ages

“…Therefore, a variety of materials are used as carriers to encapsulate microorganisms, such as polyurethane, ,, hydrogel, − microcapsule, − and other organic polymer materials. Moreover, graphite nanoplatelets (GNPs), iron oxide nanosized particles (IONPs), silica gel, , expanded clay particles, ,, expanded perlite (EP) particles, , ceramsite, calcium sulfo-aluminate cement, recycled aggregate, aerated concrete granules, lightweight aggregates (LWAs), ,, diatomaceous earth (DE), and many other inorganic materials are used as carriers. These carriers can protect microorganisms from the complex environment inside the concrete to a certain extent, prolong the survival time of microorganisms, and improve the self-healing efficiency of concrete cracks in later ages.…”