SELF-HEALING CONCRETE WITH EMBEDDED MICROBIAL PHOTOCATALYTIC CAPSULES FOR STRUCTURAL LONGEVITY AND CARBON SEQUESTRATION

Abstract

The flexibility and longevity of reinforced concrete structures are essential issues in civil engineering, especially in regions where there is a tendency for microcracking, carbonation, and the accumulation of pollutants (such as industrial,|oil, coastal and other facilities). This paper describes a new self-healing concrete with embedded microbial photocatalytic capsules to independently and in situ repair cracks, improve mechanical properties, and sequester atmospheric CO₂and oxidatively degrade noxious surface contaminants. The capsules proposed are a hybrid bio-photocatalytic composite consisting of Bacillus subtilis spores encapsulated in a silica-based shell that has been modified with nano-titania (TiO₂ ) photocatalysts designed to remain stable in high-alkaline cementitious matrices. Once the cracks form, the moisture permeation accelerates the microbial activation process as it rushes into the cracks, precipitating calcium carbonate and plugging them. In contrast, the photocatalytic effect under natural sunlight reduces both the mineralisation of the CO₂ and the decay of nitrogen oxides (NO⁎) and volatile organic compounds (VOCs) on the bare concrete floor. Based on M40 grade concrete specimens incorporating 5%, 10%, and 15% volume-based capsules, experimental assessments were conducted to evaluate both accelerated crack formation and environmental protection. Mechanical strength gain indicated that the compressive strengths increased by up to 24.5 per cent compared to control samples, and many of the healing efficiencies showed more than 91 per cent in the first 21 days. The CO₂ capturing activity was 0.42 g/m2/day with 37.6 per cent pollutant degradation efficiency, averaging under normal daylight exposure. The microstructural studies through SEM and XRD showed that the cracks were all bridged and product deposited in crystalline form as CaCO₃ with a photocatalytic surface of TiO₂. Microbial photocatalytic capsules in concrete achieve multifunctionality, attempting to extend their service life, minimise maintenance outlays, and satisfy carbon-neutral infrastructure requirements. The study provides a framework for the wide-scale application of self-sustaining concrete materials suited to the environment, thereby meeting global sustainability and climate resilience targets, which may overhaul concrete building construction towards high-performance and low-maintenance civil infrastructure.