Search

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. [ABSTRACT FROM AUTHOR]

The ureolytic bacteria and nutrients were immobilized in the artificial functional carrier (AFC) and the self-healing cement mortar, based on the AFC-encapsulated bacteria, was prepared for this paper. The crack self-healing effect of mortars with and without bacteria under different exposure environments (standard curing, dry–wet cycle curing, and water curing) was investigated by the visual observation of surface and internal cracks, water permeability tests, and mechanical performance recovery. In addition, the internal healing products of the cracks were observed using the metallographic microscope. The results show that the mortar specimens containing ureolytic bacteria immobilized in artificial functional carrier have a higher crack area repair ratio, and better water tightness regain and recovery ratio of flexural strength compared with the control mortars under the same exposure environment. The self-healing effect of mortar cracks with and without bacteria is obviously affected by the exposure environments. The self-healing effect of the cracks are the best when the mortar specimens are cured in water, followed by dry–wet cycle curing, and the self-healing effect of the cracks is the worst in standard curing, indicating that the presence of water is necessary for crack self-healing. The mortar specimens with bacteria generate more repair products in the surface and interior of the cracks to greatly improve the self-repair ability of the specimens, which promotes the recovery of water tightness and mechanical performance. [ABSTRACT FROM AUTHOR]

The autogenous healing potential of cement-based materials is affected by multiple factors, such as mix composition, crack width, pre-cracking age and external environmental conditions. In this study, the effects of curing conditions and supplementary cementitious materials (SCMs) on autogenous self-healing of early age cracks in cement mortar were investigated. Three curing conditions, i.e., standard curing, wet–dry cycles and incubated in water, and two SCMs, i.e., fly ash (FA) and blast furnace slag (BFS) with various contents (cement replacement ratio at 0%, 20%, and 40%) were examined. A single early age crack (pre-cracking age of 3 days) with a width of 200~300 μm was generated in cylindrical mortar specimens. Autogenous crack self-healing efficiency of mortar specimens was evaluated by performing a visual observation and a water permeability test. Moreover, microstructure analysis (XRD, SEM and TG/DTG) was utilized to characterize the healing products. The results indicated that the presence of water was essential for the autogenous self-healing of early age cracks in cement mortar. The efficiency of self-healing cracks was highest in specimens incubated in water. However, no significant self-healing occurred in specimens exposed to standard curing. For wet–dry cycles, a longer healing time was needed to obtain good self-healing compared to samples incubated in water. SCMs type and content significantly affected the autogenous self-healing ability of early age cracks. The self-healing efficiency of early age cracks decreased with increases in FA and BFS content. BFS mortars exhibited greater recovery in relation to water penetration resistance compared to the reference and FA mortars. Almost the same regain of water tightness and a lower crack-healing ratio after healing of 28 days in FA mortars were observed compared to the reference. The major healing product in the surface cracks of specimens with and without SCMs was micron-sized calcite crystals with a typical rhombohedral morphology. [ABSTRACT FROM AUTHOR]

• The functional aggregates were developed for self-healing cement-based materials. • The functional aggregates improved the self-healing efficiency of mortars. • More calcium carbonate formed inside the crack in mortars with functional aggregates. • The major healing product in the crack mouth was calcite. Cracking seriously affects the functionality and durability of the concrete structure. Therefore, the development of robust self-healing concrete is important to extend the service life of the structure. In this study, artificial functional aggregates with fly ash, silica fume, metakaolin, limestone powder and sodium carbonate powder were designed and prepared by the powder granulation technology to promote the self-healing efficiency of concrete. Mortar specimens with artificial functional aggregates which partially replaced the sand were prepared to verify the feasibility of the approach. Crack self-healing efficiency was evaluated by visual observation and the water ingress test. In addition, healing products formed in the crack were analyzed with XRD, TG and SEM, respectively. Experimental results indicated that the artificial functional aggregates were well combined with the mortar matrix and could be intersected by cracking. The addition of artificial functional aggregates improved the self-healing capacity of mortar specimens. Mortar specimens with artificial functional aggregates exhibited higher closure ratio of surface crack and better regain of water tightness compared with the control specimens. The maximum crack width that can be healed was about 0.47 mm in the mortar specimen with artificial functional aggregates. Microstructure investigation showed that the major healing products in the crack mouth were calcite precipitations which firstly deposited on both walls of the crack and then gradually overlapped together to become denser and denser with the extension of healing time. More calcium carbonate precipitations were observed in internal crack of mortars with artificial functional aggregates compared to the control mortar due to the effective supply of carbonate ions from the artificial functional aggregates. Typical hydration product C-S-H gel was also detected by SEM observation in the internal crack wall. [ABSTRACT FROM AUTHOR]