Experimental Investigatn on Physio-Mechanical and Micro- Structural Properties of Bio-Based Self-Healing Concrete

Abstract

Concrete is the most versatile construction material, yet it is prone to cracking owing to environmental stress. As a result, cracks in concrete weaken its strength and durability. Cracks also require maintenance and repair, necessitating the use of additional materials and incurring repair costs. Self-healing concrete, which can automatically heal cracks as they occur, can help to avoid cracks. Unfortunately, the initial cost of self-healing concrete is higher than normal concrete due to the higher cost of nutrient and bacterial growth medium. In the current study, the workability, compressive strength, water absorption, self- healing ef iciency, microstructure, and environmental and economic aspects of conventional and self-healing concrete were investigated. To make self-healing concrete samples, ordinary portland cement, fine aggregate, coarse aggregate, water, calcium lactate, and Bacillus subtilis bacteria (9.84 x 10 6 and 4.56 x 10 8 cells/mL) were immediately mixed together. The results of the slump cone test showed that bacterial concrete is more workable than regular concrete. Moreover, all bacterial concrete samples outperformed conventional concrete samples in terms of strength and water absorption. At 28 days of curing, 9.84 x 10 6 cells/mL of bacterial concentration at a dosage of 20 mL showed the greatest improvement in strength and water absorption by 14.37% and 23.05%, respectively than conventional concrete. This could be because Bacillus subtilis bacteria precipitate calcite to fill voids and microcracks inside the concrete matrix. When a crack occurs, moisture and oxygen enter the concrete through the cracks, causing bacteria to awaken from dormancy and begin feeding on calcium lactate, precipitating calcite as a healing product. Based on the test results, crack width of less than 0.5 mm was healed completely after 14 days of curing. Furthermore, to lower the initial cost, calcium lactate was synthesized from waste eggshells and lactic acid. This can bring the price of bacterial concrete down to 1.742 times that of traditional concrete. In general, the current study emphasizes the use of bacterial self-healing concrete, which is eco-friendly, cost-ef ective, and makes concrete workable, strong, durable, and crack-healing without external human intervention.