Calcium sulfoaluminate cement and supplementary cementitious materials-containing binders in self-healing systems

Creation of more durable concrete is one pathway to achieving improved sustainability and carbon footprint over a concrete structure's life. Microbially induced calcite precipitation has been shown to densify concrete microstructure and fill cracks, reducing moisture transport. One challenge associated with the longevity of bacterial-concrete systems is the high pH environment of the cement paste. Herein, two approaches to address this challenge were investigated: (i) sustainable binder systems, such as calcium sulfoaluminate (CSA) cement and fly ash substitutions of ordinary portland cement (OPC), which lead to lower pH systems, and (ii) non-axenic bacterial cultures, which may facilitate growth of more alkaline-resistant bacteria. Mechanical properties, water absorption, self-healing ability, and survivability of the bacterial systems were tracked, finding that incorporation of non-axenic bacteria did not result in increased bacteria survivability compared to axenic bacteria. However, both bacteria healed cracks <0.35 mm and similarly improved absorption. Of the binders tested, OPC-fly ash and CSA cement mixtures led to increased sustainability, higher cell viability, and better improvements to microstructure and crack healing over time compared to OPC.