Abstract
An optimized strategy for the enhancement of microbially induced calcium precipitation including spore viability ensurance, nutrient selection and O2 supply was developed. Firstly, an optimal yeast extract concentration of 5 g/L in sporulation medium was determined based on viable spore yield and spore viability. Furthermore, the effects of certain influential factors on microbial calcium precipitation process of H4 in the presence of oxygen releasing tablet (ORT) were evaluated. The results showed that CaO2 is preferable to other peroxides in improving the calcium precipitation by H4. H4 strain is able to precipitate a highly insoluble calcium at the CaO2 dosage range of 7.5–12.5 g/L, and the most suitable spore concentration is 6 × 108 spores/ml when the spore viability (viable spore ratio) is approximately 50%. Lactate is the best carbon source and nitrate is the best nitrogen source for aerobic incubation. This work has laid a foundation of ternary self-healing system containing bacteria, ORT, and nutrients, which will be promising for the self-healing of cracks deep inside the concrete structure.
Highlights
There has been growing interest in microbial self-healing process due to its potential in longlasting, efficient and environment-friendly crack repair of concrete [1,2]
We developed an integrated strategy for the enhancement of MICP including spore viability ensurance, nutrient selection and O2 supply
A bacterial strain H4, identified to be a type of Bacillus species with high calcium precipitation activity, was isolated from the sediment samples collected from a mangrove conservation area in Shenzhen Bay
Summary
There has been growing interest in microbial self-healing process due to its potential in longlasting, efficient and environment-friendly crack repair of concrete [1,2]. Self-healing of concrete cracks by bacteria is based on microbial-induced calcium carbonate (CaCO3 ) precipitation (MICP) [3,4,5]. Based on the biosynthetic pathway of carbonate, the mechanisms of MICP that have been applied in the self-healing concrete can be classified into several types, such as ureolysis, aerobic respiration, and anaerobic respiration [7]. Four different factors regulate MICP performance, which include: (i) concentration of soluble calcium, (ii) concentration of carbonate, (iii) pH, and (iv) availability of nucleation sites for the formation of calcium carbonate crystal [8]. The central issue in the microbial self-healing process is the calcium precipitating activity of bacteria [3,7]. Several strategies that have been applied by different investigators for enhancement of Materials 2017, 10, 116; doi:10.3390/ma10020116 www.mdpi.com/journal/materials
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