Effectiveness of expanded clay as a bacteria carrier for self-healing concrete

Sanghyun Han,Eun Kyung Choi,Woojun Park,Namhyun Chung,Chongku Yi

doi:10.1186/s13765-019-0426-4

Abstract

Cracking of concrete over time, is a natural phenomenon. Longer service life of concrete structures is desirable. Self-healing concrete using bacteria, which could form CaCO3 crystals for crack sealing, has promised benefits to reduce cost for concrete maintenance, because cracks could be autonomously repaired without human intervention. However, because of harsh concrete internal environment render the effectiveness depending on the bacteria viability within concrete. In this study, expanded clay (EC) was used as a carrier, to protect bacteria (Lysinibacillus boronitolerans YS11) from the harsh environment during the process. Existence of bacteria inside EC was observed using electron microscopy. When exposed to bacterial solution of 1.0 × 109 cells/mL, bacterial density within EC reached approximately 0.82 × 107 cells/g of dry EC. Extent of bacterial viability within EC, submerged to solution containing 1.0 × 108 cells/mL, was 53.6% of free bacteria solution containing 1.0 × 107 cells/mL, as measured with fluorescein diacetate assay. When rate of calcium carbonate formation was measured with Ca2+ disappearance, rates were comparable between bacteria within EC (submerged to bacterial solution containing 1.0 × 108 cells/mL) and free bacteria (1.0 × 107 cells/mL). This finding indicates that bacteria with EC is very active for generation of CaCO3 within EC. All experimental results suggest that EC may be an adequate bacteria carrier for self-healing concrete.

Highlights

Concrete is a construction material that cannot be replaced, with other modern technologies yet
Because of high pH inside concrete, shear forces by mixing, and shrinkage during concrete drying, bacterial viability is very limited for appropriate healing ability of self-healing concrete
Bacteria Lysinibacillus boronitolerans YS11 was isolated from rhizosphere soil of Miscanthus sacchariflorus using biomineralization-inducing B4 medium, which is often used for screening of possible calcium carbonate precipitating bacteria [8]

Summary

Introduction

Concrete is a construction material that cannot be replaced, with other modern technologies yet. Concrete is irreplaceable construction material in terms of availability, versatility, and economy. Cracks in concrete shorten the life of concrete [1, 2]. The importance and necessity of self-healing concrete has been emphasized [3, 4]. In bacterial-based self-healing concrete, calcium carbonate (CaCO3) produced by bacteria heals the crack [5–7]. Because of high pH inside concrete, shear forces by mixing, and shrinkage during concrete drying, bacterial viability is very limited for appropriate healing ability of self-healing concrete. To solve such problems, various carriers have been studied to protect bacteria [8–10]

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Results