Autogenous self-healing of cement with expansive minerals-II: Impact of age and the role of optimised expansive minerals in healing performance

This part of the study presents the optimisation of expansive minerals mix proportions and establishes a quantitative and qualitative correlation between self-healing and the cracking age of cementitious materials. The hydration degree of cementitious materials is considered as a quantitative measure of age and the corresponding healing performance was analysed to establish an age-healing relation. Healing performances were assessed in terms of load recovery, crack sealing efficiency and gas permeability. The microstructure of materials was investigated using XRD, TGA and SEM-EDX. The self-healing performance of particular cement mixes shows linearly increasing correlation with the reduction of hydration degree. However, cement mixes containing expansive mineral result in higher healing performance than mixes containing only Portland cement (PC). This observation was confirmed for all cracking ages. Blends containing only PC showed healing materials that were mostly calcite and portlandite, while the optimised use of expansive minerals produced denser healing materials with C-S-H, and complex Ca, Mg, Si, Al combined hydrated and carbonated products in addition to calcite and portlandite. The results further suggest that the proportions of calcite, portlandite and ettringite in healing compounds have an increasing trend with the age of hardened cementitious materials.