Self-healing performance of nanosilica-doped concrete based on microbial mineralisation

The effects of different dosages of expanded perlite (as a carrier for bacteria) and nanosilica on the strength and self-healing properties of cement mortar were investigated. The strengths of specimens at different curing ages were tested using a pressure testing machine. Additionally, pre-cracks were formed in specimens and the cracks and healing products were observed by electron microscopy, scanning electron microscopy and X-ray diffraction to validate the experimental results. The results showed that the self-healing agents agglomerated at the cracks and triggered a metabolic reaction, thus resulting in the formation of numerous calcium carbonate precipitates that sealed the cracks and therefore significantly improved the self-healing of the cement mortar. Nanosilica facilitates the hydration reaction of cement and undergoes a pozzolanic reaction with calcium hydroxide; this reaction consumes calcium hydroxide and generates hydrated calcium silicate to fill pores. Consequently, the incorporation of an appropriate amount of nanosilica effectively enhanced the strength of the cement mortar. Simultaneously incorporating self-healing agents and nanosilica at suitable dosages provides a new approach for optimising both the mechanical properties and self-healing performance of concrete.