Bacterial wollastonite concrete for sustainable high performance construction

This study explores the mechanical, microstructural, and non-destructive properties of concrete incorporating microbial consortia, specifically ureolytic and non-ureolytic variants, at concentrations of 10⁹ and 10⁵ cells/ml across water-to-binder (w/b) ratios of 0.45, 0.4, and 0.35. Wollastonite was introduced as a mineral additive at substitution levels of 5%, 10%, and 15%, with performance declining beyond the optimal substitution threshold. After 28 days of curing, specimens with a higher consortium concentration (10⁹ cells/ml) exhibited compressive strength enhancements of 27.20%, 23%, and 22.31% for 5%, 10%, and 15% wollastonite incorporation, respectively, compared to the control. In contrast, the lower consortium concentration (10⁵ cells/ml) resulted in compressive strength improvements of 41.45%, 39.35%, and 31.07% for the corresponding substitution levels, indicating the efficacy of the lower consortium to develop strength properties at a younger age. Flexural strength followed a similar trend, with increases of 25%, 16.15%, and 25%, respectively. Notably, the lower consortium concentration (10⁵ cells/ml) provided superior mechanical performance compared to the higher concentration (10⁹ cells/ml) due to the lower cell density and biofilm formation. Non-destructive evaluations, including Ultrasonic Pulse Velocity (UPV > 4.5 km/sec) and rebound number above 40, confirmed the enhanced quality of the concrete. Regression analysis exhibited strong correlations (R² values) between compressive strength, flexural strength, split tensile strength, UPV, and rebound number. Microstructural analyses employing SEM-EDS, XRD, and FTIR spectroscopy remarked significant calcite deposition, leading to matrix densification and improved durability. The embodied energy evaluation significantly underscores the inclusion of wollastonite, a low-energy and low-emission calcium silicate mineral, significantly enhancing eco-efficiency by partially replacing cement. At the same time, the bacterial consortium promotes self-healing and durability with minimal environmental impact. These findings highlight the potential of microbial-wollastonite-based concrete as a sustainable and high-performance material for modern construction applications.