Sugar-coated expanded perlite as a bacterial carrier for crack-healing concrete applications

Microbial-induced carbonate precipitation (MICP) can realize self-diagnosis and self-healing of concrete to reduce the maintenance costs and extend the lifetime of concrete structures. However, the self-healing capacity of the cracks is below par using existing self-healing methods. Thus, adopting the sugar-coating method to immobilize bacteria and nutrients was proposed in this paper. The effect of expanded perlite (EP) wrapped with various materials as bacterial carrier and nutrient carrier on the crack-healing capacity of concrete has been investigated. The results indicated that after EP particles were coated, the numerical tube pressure was increased, and the water absorption was reduced. Wrapping materials can effectively reduce the breakage rate of the EP particles and resist the invasion of water in the process of mixing with concrete. The EP particles after wrapping process were found to enhance the healing capacity of concrete cracks. In particular, the crack-healing of concrete peaked when EP particles immobilized with bacterial spores were wrapped with a low-alkaline material (potassium magnesium phosphate cement). This result was also validated by the water permeability experiments. After 28 d of crack-healing, the maximum value of the completely healed crack width was 1.24 mm. EP is a low-cost material; thus, it can be used as a bacterial carrier for large-scale self-healing concrete applications. (C) 2019 Elsevier Ltd. All rights reserved.