Rice Husk as a Bio-carrier for Bacillus paramycoides: Enhancing the Mechanical Performance and Self-Healing Capacity of Concrete

This study investigates the enhancement of the mechanical performance and self-healing capacity of concrete using Bacillus paramycoides cells immobilized on raw rice husk (RH) as a bacterial carrier. Raw rice husk, a naturally porous lignocellulosic agricultural by-product, was selected to provide a favorable microenvironment for bacterial survival and biomineralization within the cementitious matrix. Mortar and concrete specimens containing 1% and 3% RH, with and without bacterial immobilization, were prepared and evaluated for workability and compressive, splitting tensile, and flexural strengths after 7, 28, 56, and 90 days of curing. The crack-healing performance of the bio-treated specimens was assessed through surface observations, while SEM/EDX analyses were performed to examine the microstructural characteristics of the healing products. The bio-treated mixtures exhibited enhanced crack-healing performance compared with the corresponding control mixtures. SEM/EDX analysis provided evidence of calcium-rich carbonate precipitates associated with microbially induced calcium carbonate precipitation (MICP) within the healed microcracks. Although bacterial immobilization did not increase the 90-day compressive strength beyond that of the control concrete, it significantly mitigated the strength reduction associated with incorporating raw rice husk and improved the mechanical performance compared with the corresponding RH mixtures without bacteria. Improvements in the splitting tensile and flexural strengths were also observed, which may be associated with crack filling and matrix densification resulting from biomineralization. Among the investigated mixtures, concrete containing 1% RH with immobilized bacterial cells exhibited the most balanced performance in terms of workability, mechanical properties, and crack-healing behavior. Overall, the results demonstrate that raw rice husk-immobilized Bacillus paramycoides represents a promising bio-based system for enhancing the mechanical performance and bio-healing capacity of concrete. By utilizing raw rice husk as a bacterial immobilization carrier, the proposed approach promotes the beneficial utilization of agricultural waste and has the potential to contribute to the development of more durable cementitious materials.