Self-healing of surface cracks in mortars with expansive additive and crystalline additive

This research studies the self-healing potential of cement-based materials incorporating calcium sulfoaluminate based expansive additive (CSA) and crystalline additive (CA). Mortar specimens were used throughout the study. At the age of 28 days, specimens were pre-cracked to introduce a surface crack width of between 100 and 400 μm. Thereafter, the specimens were submerged in water to create a self-healing process. The experimental results indicated that the mixtures with CSA and CA showed favorable surface crack closing ability. The optimal mix design was found to be a ternary blend of Portland cement, 10 wt.% CSA and 1.5 wt.% CA, by which a surface crack width up to about 400 μm was completely closed, and the rate of water passing was dropped to zero within 28 days. It was hypothesized that the amount of leached Ca2+ from the matrix plays an important role on the precipitation of calcium carbonate which is the major healing product. The analyses showed that those specimens with CSA/CA additions released more Ca2+ than that control specimen. Moreover, those specimens with additives had higher pH value which would favor calcium carbonate precipitation.