Effect of Immobilized Bacteria in Diatomaceous Earth and Reused Concrete Aggregate in Recovering Properties of Self-Healing Recycled Aggregate Concrete

Abstract

The development of microcracks in recycled aggregate concrete (RAC) directly impacts its durability; hence, these cracks need to be treated. The authors propose bacterial self-healing by introducing Bacillus megaterium strains into 50% and 100% RAC mixes to heal cracks in RAC on their own. A protective bacterial carrier is needed to protect the bacteria in the high-pH environment of concrete and in a dense microstructure so that the CaCO3 production capacity of the bacteria is not affected. For this purpose, diatomaceous earth (DE) and reused concrete aggregate (RCA) were investigated in this study as potential carriers for the immobilization of bacterial spores that heal cracks in RAC on their own. Filling of surface cracks, the self-healing ratio within concrete, recovery of compressive strength, and water impermeability were examined to test self-healing, and were compared with those of samples containing directly inserted bacteria. Cracks with a maximum width of 0.47, 0.50, and 0.55 mm were completely filled in the specimens containing directly inserted bacteria, immobilized bacteria in RCA, and immobilized bacteria in DE, respectively. Specimens containing bacteria immobilized in DE and RCA had better self-healing performance in terms of recovery of concrete properties and self-healing ratio within concrete than did specimens containing bacteria directly added. Additionally, specimens containing bacteria immobilized in DE exhibited better self-healing results in precracked specimens up to 56 days of age, whereas self-healing by bacteria immobilized in RCA was found to be more effective in precracked specimens at 120 days of age. Overall, it was concluded that DE and RCA can be used as carriers for bacterial immobilization in self-healing RAC, which would not only maintain the durability of RAC but also increase its service life. Biobased self-healing in recycled aggregate concrete offers practical applications in the construction industry. This innovative technology incorporates biobased materials such as bacteria and encapsulated healing agents into the concrete mix, allowing for autonomous healing of cracks and damage. The use of recycled aggregates further enhances the sustainability of the concrete, reducing the environmental impact. The self-healing mechanism operates by activating the bacteria and releasing the healing agents upon crack formation, which then react with the surrounding environment to seal the cracks. This self-healing capability extends the lifespan of concrete structures, reducing the need for costly repairs and maintenance. Additionally, the biobased nature of this approach aligns with sustainable development goals, promoting the use of renewable resources and reducing reliance on traditional repair methods that involve energy-intensive processes and nonrenewable materials. The practical application of biobased self-healing in recycled aggregate concrete demonstrates the potential for more-durable and eco-friendly construction practices.