Integrating Bacteria and Rubber Additives to Enhance Impact Resistance, Tensile Strength, and Self-Healing Capabilities of Concrete

Self-healing rubberized concrete (SHRC) represents an innovative approach to improving the durability, strength, and flexibility of concrete while addressing sustainability challenges. In this study, two bacterial strains, Rhizobium leguminosarum (RL) and Sporosarcina pasteurii (SP), were incorporated at 20% of the total water volume with three concentrations (108, 1010 and 1014 cells/mL), along with 15% recycled rubber as a partial sand replacement. The impact of these modifications on workability, mechanical performance, impact resistance, and crack healing was evaluated through slump tests, compressive and tensile strengths, impact resistance analysis, and microstructural studies using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The addition of rubber particles reduced workability and mechanical performance due to their porous nature and lower stiffness. However, incorporating bacterial cultures (RL + SP), particularly at concentrations of 1010 + 1010 cells/mL, significantly improved these properties. Indirect tensile strength increased by up to 99%, while compressive strength rose by 98.7% compared to rubber-only mixes. Impact resistance improved by 131.8% at the first crack and 123.1% at the ultimate crack under the same bacterial concentration. Enhanced microstructural characteristics, including reduced voids and extensive calcium carbonate precipitation, facilitated effective crack healing and improved durability. The combined effects of rubber and bacterial agents demonstrated superior self-healing capabilities, with complete crack closure observed within the rubberized concrete matrix. This study will describe previous related works on the mechanical behavior of rubberized concrete and compare the behavior of rubberized concrete containing rubber only to that containing two types of bacteria with rubber. These findings highlight the potential of SHRC to deliver sustainable, high-performance concrete with improved mechanical and durability characteristics through innovative self-healing and material recycling strategies. The findings suggest the possibility that bacterial therapy would be a more economical option than CFRP rehabilitation for cracked concrete members, which could be a suggestion for further study.