Characterization of self-healing processes induced by calcium nitrate microcapsules in cement mortar

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The objective of this study was to evaluate the self-healing effectiveness of urea-formaldehyde microcapsules with calcium nitrate as a healing agent in cement mortar. Calcium nitrate was selected as a healing agent because of its ability to react with available unhydrated cement particles in crack surfaces contributing to the formation of new hydration products that may potentially heal the crack. Self-healing capability of cement mortar with different microcapsule contents was evaluated under dry and wet healing conditions. Cracks ranging from 27.0 to 386.5 μm on average were created by three-point bending and indirect tensile tests. Cracks were observed by light microscopy over a 28-day healing period. Analysis of captured images showed signs of healing in the form of small crystallike features on the edge of the cracks on water-cured specimens after 7 days of healing. Furthermore, an improvement in self-healing efficiency was reported in specimens with microcapsule contents of 0.85 and 1.0% compared to the control after 14 days of the healing period. Environmental scanning electron microscopy (ESEM) coupled with energy dispersive spectroscopy (EDS) was utilized to investigate the morphology and chemical nature of the healing products. Crystallike and gellike healing products were found with the majority being crystallike. Crystallike healing products were likely calcium carbonate in the form of calcite crystals, whereas gellike healing product's chemical nature was presumably calcium silicate hydrate (CSH).

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Journal of Materials in Civil Engineering

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