Investigating a new method to assess the self-healing performance of hardened cement pastes containing supplementary cementitious materials and crystalline admixtures

The autogenous healing of cementitious materials allows for the self-healing of cracks in concrete structures. It is known to be caused by (a) further hydration occurring when water penetrating the crack reacts with the unreacted binder on the crack face and (b) calcite precipitation resulting from the reaction between Ca2+ diffused from the cement paste and CO32− in penetrated water. Herein, isothermal calorimetry was used to analyze the further hydration of unreacted binder in hardened pastes containing ordinary Portland cement (OPC), supplementary cementitious materials, and crystalline admixtures. The amount of heat produced decreased with increasing sample age because of the reduction in the unreacted binder amount. Long-term further hydration in samples containing ground granulated blast-furnace slag and silica fume caused them to show increased heat production compared to OPC. However, no particular difference in comparison to OPC was detected for samples containing fly ash. When calcium sulfoaluminate was used as an expansion agent, heat production increased for a material age of 7 days and decreased after 28 days (compared to the case of OPC). Finally, self-healing products were analyzed by scanning electron microscopy with energy dispersive spectrometry. The results showed that the products contained calcite and an amorphous material regardless of the binder, while ettringite was observed to form in calcium sulfoaluminate and crystalline admixtures containing samples.