Application of perlite as encapsulation carrier for bacteria in the self-healing concrete

Crack formation is commonly observed on concrete structures. Although the cracks slightly affect the mechanical properties of concrete constructions, the ingress of aggressive ions, gasses and liquids through the cracks may reduce the durability of concrete. In order to enhance the autogenous healing capacity of concrete, specific healing agents was introduced to the concrete matrix. Microbially induced calcite precipitation (MICP) is the biological process through which micro-organisms exert calcite or calcium-bearing minerals. In this study, the bacteria-based self-healing agents were encapsulated in lightweight aggregates (expanded perlite) which act as carriers and protectors for bio-agents and replace part of the regular concrete fine aggregates. Bacteria and nutrients consisting of calcium acetate and yeast extract were encapsulated separately. While cracks occur, the two-component bio-agents are released from particles by ingressive water through cracks, and subsequently bacterially precipitated calcite results in closure of micro cracks. This study aims at determining the potential of perlite working as the suitable carrier for bio-agents. The study focuses on investigating the recovery of liquid tightness of cracked concrete specimen through water permeability test, physical closure of cracks and decrease of crack depth by using optical microscope. Results of experiment showed the bacterial concrete specimens with cracks-wide up to 0.4 mm has been completely healed after 5 to 6 months healing in wet-dry cycle. But other control specimens only showed partial healing of cracks in the same healing regime. Bio-specimens showed higher degree of crack repairing along depth. However, split sections of cracks along depth showed that despite complete surface crack closure was observed on some bio-specimens, none of specimens showed complete healing along depth. We therefore concluded bacteria shows potential for particularly increasing crack-healing capacity of concrete construction and perlite works effectively in terms of protecting bacteria in the self-healing process.