Self-healing of early-age cracks in cement mortars with artificial functional aggregates

Abstract

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.