# Influence of Bacillus subtilis-Instigated Calcite Precipitation on Damage Progression and Ionic Transport

## TL;DR

This study explores how Bacillus subtilis bacteria improve concrete durability by changing its mechanical behavior and reducing ion transport.

## Contribution

The study reveals that Bacillus subtilis alters concrete's damage progression and transport resistance through calcite precipitation.

## Key findings

- Concrete with Bacillus subtilis shows a shift from brittle to quasi-ductile behavior with improved strain capacity.
- Chloride ion penetration and capillary sorptivity decrease by up to 57% and 60%, respectively.
- X-ray diffraction confirms microbial-induced calcite formation, reducing crack-assisted transport.

## Abstract

Bacteria-based self-healing concrete is extensively shown to improve strength and durability; yet, the mechanistic relationship among microbial activity, damage progression, and transport resistance is still ambiguous. This study examines the interrelated mechanical and transport properties of concrete that incorporates Bacillus subtilis by directly substituting mixing water. Concrete mixtures with 0%, 5%, and 10% bacterial solution were assessed for compressive strength, complete stress–strain response, split tensile strength, flexural toughness, fast chloride ion penetration, and capillary sorptivity. X-ray diffraction was employed for microstructural validation. Results indicate a dose-dependent shift from brittle to quasi-ductile behavior, marked by augmented strain capacity, postponed crack localization, and improved post-cracking energy absorption. The mechanical alterations resulted in substantial decreases in chloride ion penetrability (up to 57%) and capillary sorptivity (up to 60%), signifying a drop in crack-assisted transport. X-ray diffraction verified the production of calcite resulting from microbial-induced calcium carbonate precipitation. The results indicate that the improvement in durability of bacterial concrete is attributable not only to pore filling but also to altered damage mechanisms that diminish the connectedness of transport channels, underscoring the potential of Bacillus subtilis as a bio-admixture for resilient structural concrete.