Light-responsive algal-bacterial symbiosis for crack self-healing in cement mortar: evidence of surface-to-depth healing mismatch

초록

Aerobic bacterial healing of microcracks in concrete is often constrained by an insufficient oxygen supply inside cracks, which limits the repair of deeper crack regions. To address this issue, a light-responsive algal-bacterial symbiotic self-healing cementitious system was developed by immobilizing bacillus pseudofirmus (BP) spores and spirulina platensis (SP) cells in porous ceramsite, and the effects of optical density (OD)-based algal dosage at a fixed BP inoculation level were systematically investigated under different lighting regimes. The results showed that the ABS-8 group achieved the best overall healing performance when the BP spore suspension was fixed at OD600 = 0.6 and the SP algal suspension was adjusted to OD560 = 0.8. Artificial lighting reduced the time required for complete surface crack closure from 28 d to 14 d and increased the maximum healable crack width from 456 mu m to 565 mu m. However, the crack depth reduction achieved at 28 d under artificial lighting was 20.4 mm, which was lower than the 24.6 mm obtained under natural lighting, indicating that accelerated surface closure did not synchronously enhance deep crack repair and internal continuity recovery. Microstructural analyses revealed that calcite was the dominant crystalline phase in all the healed products. Therefore, the differences in self-healing performance were not governed by phase transformation but mainly by the spatial continuity and crystallization quality of CaCO3 deposited within the crack volume. These findings provide new mechanistic insights and design guidance for the coordinated optimization of lighting regimes and OD-based algal dosages in light-responsive self-healing systems.

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