Self-Healing Performance of Nanosilica-Modified Engineered Cementitious Composites Exposed to High Temperatures

This study investigated the self-healing performance of nanosilica-modified engineered cementitious composites (ECCs) exposed to high temperatures. Nanosilica (NS) was used in 0%, 0.25%, 0.50%, and 0.75% proportions of cementitious materials by mass in the mixtures. NS-modified ECC cylindrical samples ($\mathrm{Ø}100\times 200\mathrm{mm}$) were produced and cured at $23°\mathrm{C}\pm 2°\mathrm{C}$ for 28 days. Then, these samples were exposed to $20°\mathrm{C}\pm 2°\mathrm{C}$, 100°C, 200°C, 300°C, 400°C, 500°C, 600°C, 700°C, and 800°C temperatures. After the samples were cooled at room temperature, microcracks were formed in the ECC samples, but the samples exposed to higher than 400°C were dispersed when the crack was formed. The wetting–drying cycles were applied for the self-healing of cracked samples. Lastly, the splitting tensile strength, ultrasonic pulse velocity, and chloride ion permeability of the NS-modified ECC samples were determined. Scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX), X-ray diffraction analysis (XRD), and Fourier transform infrared spectroscopy (FTIR) analyses were also performed to examine the microstructure of NS-modified ECC samples. This study found that all samples were self-healed within 15 days, and the highest splitting tensile strength recovery rate was obtained from 0.75 NS-modified ECC samples with 107.44%.