Application of Artificial Functional Aggregates Encapsulated Bacteria for Self-Healing of Cement Mortars

Abstract

In a bacteria-based self-healing concrete system, it is generally necessary to protect the bacteria from the harsh conditions of high alkalinity inside the concrete and limited physical space due to the on-going hydration of cement. The artificial functional aggregates (AFA) were developed as the protective carrier of bacteria in this paper. Self-healing capability of mortars containing AFA encapsulated bacteria was investigated. Moreover, crack-healing products were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG) and scanning electron microscope (SEM) with an energy dispersive spectrometer (EDS). The results showed that AFA encapsulated bacteria effectively promoted self-healing of cracks. Compared with control mortars, the effects of surface crack healing, internal crack healing, water tightness regain, and mechanical performance recovery of mortars with AFA encapsulated bacteria were significantly improved. Healing products in specimens with AFA encapsulated bacteria were observed, including CaCO3, C-S-H gel, hydromagnesite, and ettringite. Among them, the main healing product was CaCO3, which was not only formed on the walls of shallow cracks, but also largely deposited on the walls of deep cracks. Self-healing of mortars with AFA encapsulated bacteria can be attributed to the combined effects of chemically derived calcium carbonate, microbially induced calcium carbonate, on-going hydration of unhydrated cement particles, and pozzolanic activity reaction of the slag from AFA.