Abstract
The creation of cracks, which are the most common cause of structural failure, has a significant impact on the structure's strength and durability. As a result, effective repair and maintenance are vital and unavoidable for treating any of these issues. Self-healing mortar holds promising benefits for reducing the cost of repair as cracks are autonomously repaired without any human intervention. This study investigated the effect of bacteria type, bacteria content, bacteria concentration, and nutrient type on the properties of the self-healing mortar. Three types of bacteria, Bacillus sphaericus, Bacillus Megaterium, and Bacillus subtilis encapsulated in calcium alginate beads, were introduced into the mortar. Two concentrations of bacteria, 2× 108 and 2× 109 Colony Forming Units per milliliter, and different percentages of bacteria of cement weight were selected for the study. In addition, calcium lactate and calcium acetate were used at 0.5% of cement weight as nutrition for bacteria. Tests were performed for compressive strength, bending strength, SEM, EDX, and TGA/DTG. The results show a significant development in the mechanical behaviour of mortar, especially with Bacillus Megaterium using a 2.5% bacterial proportion with a concentration 2× 109 CFU/ml. This can be related to the filling of voids and cracks in microbial mortar by calcite, which was confirmed by SEM and EDX.
Highlights
Mortar is one of humanity's most widely used construction materials, and it is the main structure used in every country's infrastructure development [1,2,3]
This indicates that internal micro-cracks caused by loading have the ability to heal and the ability to restore the mechanical properties of mortar to their original state by using bacteria [36,45,46]
On another hand, using the FP bacteria, the recovery ratio of compressive strength of the reloaded cracked samples compared to the unloaded samples in mix M11 using 0.25% of bacteria FP is equal to 64.05%, 71.47%, and 81.02% at age of 28, 56, and 90 days respectively
Summary
Mortar is one of humanity's most widely used construction materials, and it is the main structure used in every country's infrastructure development [1,2,3]. Self-healing mortar produces calcium carbonate (limestone) biologically to seal pores in the mortar matrix or heal cracks on the surface of mortar structures [13,14] These microbial deposits may act as nucleation sites, enhancing early cement hydration and resulting in higher compressive and flexural strengths [15,16,17,18]. Achal et al developed a self-healing cement mortar with Bacillus Subtilis and reported that it increased the compressive strength of microbial remediation specimens by up to 40% They referred to the importance of using bacteria to improve the durability and self-healing ability of cracks in building structures [36]. This study ensures the use of ready-prepared powdered bacteria compared to traditional liquid solutions of bacteria that need preparation
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