The aim of this study is to investigate the effect of water migration from cracks into the bulk paste on autogenous self-healing. Nuclear magnetic resonance (NMR) technique was utilized to monitor water migration from cracks into the bulk paste during the process of autogenous self-healing. NMR results show that initially the water in the crack migrates into the bulk paste and the water content of the bulk paste increases significantly. However, after 5-h autogenous self-healing, the amount of non-chemically bound water in the bulk paste (adjacent to the crack surfaces) determined by NMR decreased instead. It indicates that some of the water coming from the crack was used for additional hydration of unhydrated cement particles in the bulk paste (during the process of autogenous self-healing). Before this study, in term of autogenous self-healing only the recoveries that related to the filling of cracks were concerned. The observation and quantification of densification of cement paste adjacent to the crack surfaces provides a new insight into autogenous self-healing.

In this research, self-healing due to further hydration of unhydrated cement particles is taken as an example for investigating the effects of capsules on the self-healing efficiency and mechanical properties of cementitious materials. The efficiency of supply of water by using capsules as a function of capsule dosages and sizes was determined numerically. By knowing the amount of water supplied via capsules, the efficiency of self-healing due to further hydration of unhydrated cement was quantified. In addition, the impact of capsules on mechanical properties was investigated numerically. The amount of released water increases with the dosage of capsules at different slops as the size of capsules varies. Concerning the best efficiency of self-healing, the optimizing size of capsules is 6.5 mm for capsule dosages of 3%, 5%, and 7%, respectively. Both elastic modulus and tensile strength of cementitious materials decrease with the increase of capsule. The decreasing tendency of tensile strength is larger than that of elastic modulus. However, it was found that the increase of positive effect (the capacity of inducing self-healing) of capsules is larger than that of negative effects (decreasing mechanical properties) when the dosage of capsules increases.