۱- Introduction

۲- Materials and methods

۳- Results

۴- Discussion

۵- Conclusions

References

Abstract

Self-healing concrete based on calcium carbonate precipitation induced through bacterial activity has been investigated in recent years by teams around the world. For the first time, optimisation of the self-healing performance was considered in terms of the number of bacterial spores required, the concentration and composition of nutrients and precursors, and whether a two-component system was likely to efficiently produce self-healing in concrete. This information is required if efficient and cost-effective self-healing systems based on bacterial activity are to be implemented. For this research, coated expanded perlite was used to immobilise bacterial spores and encapsulate nutrients as two separate components for self-healing concrete. Self-healing capacity was evaluated by imaging and by initial surface absorption of water. The results indicated that healing could be achieved when coated expanded perlite containing self-healing agents was used as a 20% replacement of fine aggregate and if a suitable ratio of spores to calcium acetate was provided. This research is the first to show that self-healing is not simply a requirement of having sufficient healing compounds (e.g. calcium acetate) but that a minimal number of bacterial spores are also required to ensure that sufficient cells take part in the healing process.

Introduction

The effect of some water-borne ions (e.g. chlorides) on the durability of reinforced concrete is well documented, and cracked concrete has been shown to be more susceptible to permeation of these deleterious ions. Consequently, research is being undertaken in an attempt to develop concrete that can self-heal cracks; potentially reducing repair and maintenance costs on key infrastructure [1–۳]. One approach to autonomic self-healing is the utilization of microbiologically induced calcite precipitation (MICP). This approach utilises the metabolic activity of bacteria and biomineral precursors embedded within the concrete to form an inorganic compound as a healing material. This is usually calcium carbonate, typically in the form of calcite but sometimes as vaterite [4,5]. This healing material can precipitate in small cracks soon after they form and it has the potential to limit the permeation of water and dissolved ions. Thereby the life of concrete structures can be extended without the need for manual intervention; which can be both costly and dangerous, particularly for structures with poor access. While there have been a number of studies into the feasibility of using MICP for self-healing in concrete, there have not been studies on optimising the self-healing performance through consideration of the number of bacterial spores required, the concentration and composition of nutrients and precursors or whether a twocomponent system is likely to efficiently produce self-healing in concrete.