Effect of blast furnace slag on self-healing of microcracks in cementitious materials

The physico-chemical process of self-healing in blast furnace slag cement paste was investigated in this paper. With a high slag content i.e., 66% in cement paste and saturated Ca(OH)2 solution as activator, it was found that the reaction products formed in cracks are composed of Csingle bondSsingle bondH, ettringite, hydrogarnet and OH–hydrotalcite. The fraction of Csingle bondSsingle bondH in the reaction products is much larger than the other minerals. Large amount of ettringite formed in cracks indicates the leaching of SO42 − ions from the bulk paste and consequently the recrystallization. Self-healing proceeds fast within 50 h and then slows down. According to thermodynamic modeling, when the newly formed reaction products are carbonated, the filling fraction of crack increases first and then decreases. Low soluble minerals such as silica gel, gibbsite and calcite are formed. Compared to Portland cement paste, the potential of self-healing in slag cement paste is higher when the percentage of slag is high.