Quantitative Microstructural and Experimental Assessment of Bacterial Self-Healing Concrete Using Vacuum-Impregnated Lightweight Aggregates

Abstract Bacterial concrete has been proposed as a potential approach to address sustainability challenges in concrete, primarily through its self-healing capabilities that may extend service life and reduce long-term maintenance needs. This study investigated the influence of different precursors and bacteria on the performance of self-healing concrete. Two different minerals (calcium lactate and sodium lactate at 75 mM / L ) were used as precursors with and without Bacillus pseudofirmus bacterial spores (at 10 8 cells / mL ) to prepare concrete specimens containing impregnated coarse lightweight aggregate. This approach quantifies the effects of precursor type and bacterial incorporation on healing efficiency and strength recovery, establishing clear links between chemical composition and performance outcomes. The compressive strength, crack healing efficiency, flexural strength, and strength recovery were evaluated for each mix type. The NaLac + Bac mix exhibited the highest self-healing efficiency (79% bottom faces, 69% side faces) and flexural strength recovery (18%) after 28 days without compromising compressive strength. MANOVA and violin plots showed significant differences between mix types with and without bacteria. The results indicated that a combination of sodium lactate and bacteria had the highest self-healing efficiency and flexural strength recovery. Scanning Electron Microscopy (SEM) revealed the morphology of calcite crystal healing products, whereas Energy Dispersive X-ray Spectroscopy (EDS) analysis confirmed the role of bacteria in promoting the formation of calcium-rich healing products, with Ca content increasing from 25% to 57% in the bacteria-containing mixes. Additionally, principal component analysis (PCA) correlated EDS elemental data with crack area reduction, confirming that calcium enrichment in bacteria-containing mixes corresponds to improved healing performance.