Bio-enhanced lightweight concrete: self-healing and mechanical performance

This study evaluated bacterial modification of lightweight expanded clay aggregate (LECA) using Bacillus pasteurii and Bacillus subtilis , and the subsequent performance of B. subtilis -treated structural lightweight concrete. Aggregate treatment reduced LECA water absorption by up to 51.9 and increased dry mass by 1.5–2.0%. SEM showed localized deposits on bacteria-treated LECA and at concrete crack/interface regions, including partial filling of an approximately 2 μm crack in the matched healed bacterial specimen. XRD established calcite-compatible intensity in clinker-free LECA and supported an increased calcite contribution in the matched S9/S8 concrete pair, although calcite/alite overlap prevented unique carbonate quantification and vaterite/aragonite could neither be confirmed nor excluded. For undamaged compression, bacterial concrete was 6–10% above the strength-reduced control, with the maximum at 14 days. After 21 days of healing, bacterial concrete reached 24.94 MPa in compression and 3.24 MPa in flexure, respectively 23 and 35% above the corresponding healed bacteria-free specimens. The bacterial mixture also increased air content from 2.0 to 5.5 and slump from 10–13 to 13–16 cm, while fresh density decreased from 1550 to 1450 kg/m 3 . The results support short-term bacteria-associated mineral deposition and mechanical recovery, while air control and longer-term durability remain necessary for practical validation.