Variation of microbial self-healing performance of cementitious composites with their biogranule content

Abstract

Existing studies on microbial self-healing concrete often employed an arbitrary approach to the initial amount of healing agents, leading to significant performance variations. The amount of bacteria becomes a crucial parameter affecting the overall cost of the material. Therefore, assessing the effect of initial bacteria content on microbial self-healing performances is essential. This study presents the variation of self-healing performances of biomortars with initial bacteria content ranging from 0.05 % to 2.50 % (0.07 %–3.20 % biogranule) w/w cement. All biomortars outperformed the crack healing performance of abiotic control specimens. The net contribution of microbial healing (MH‾net) was determined by analysing autogenous healing and microbial healing periods separately. The variations in initial bacteria content did not significantly affect MH‾net which could reach up to 125 μm in 2-weeks of water immersion. The minimum effective bacteria dosage in the form of biogranules for developing microbial self-healing concrete was determined as 0.05 % bacteria w/w cement with an overall crack healing limit of 300 μm. Microbial healing of cracks up to 300 μm crack width led to 50–80 % higher water tightness regain compared to the autogenously healed specimens. The purity of CaCO3 minerals sealing the cracks decreased with the increasing initial bacteria content of the biomortars. Overall, the initial bacteria content did not significantly affect the microbial self-healing performance in the tested dosage range. At the minimum effective bacteria dosage, consistent self-healing of cracks up to 300 μm became possible at the expense of approximately 20 % increase in the overall cost of the material.