Performance of Phosphazene-Containing Polymer-Strengthened Concrete after Exposure to High Temperatures

The strength properties of concrete strengthened with a polymer including phosphazene after exposure to high temperatures is investigated in this study. The Taguchi ${\mathrm{L}}_{25}$ ($5^5$) method was used to reduce the number of experiments and to find the parameters affecting the experimental results. Percentage of phosphazene in the monomer (0%, 1%, 2%, 3%, and 4%), curing period (28, 60, 90, 180, and 365 days), cement content (300, 350, 400, 450, and $500\mathrm{kg}/{\mathrm{m}}^3$), and high temperature (20°C, 200°C, 400°C, 600°C, and 800°C) were chosen as experimental parameters. For the experiments, $100\times 100\times 100\mathrm{mm}$ cubes were prepared. The specimens were removed from water after the end of predetermined curing times and dried at $105\pm 5°\mathrm{C}$. Then, they were exposed to temperatures of 200°C, 400°C, 600°C, and 800°C. The next step was impregnation of the samples with a vinyl acetate monomer containing phosphazene for a 24-h period under atmospheric conditions. The polymerization of specimens was conducted at 60°C for 4 h. The compressive strength, ultrasonic pulse velocity, and changes in weight were determined for the specimens. Furthermore, X-ray powder diffraction (XRD), energy dispersive X-ray (EDX), and scanning electron microscope (SEM) image analyses of specimens were carried out. The findings showed that the best results were found from specimens with low cement content and 3% polymer containing phosphazene. Therefore, this study has found that polymer containing phosphazene can strengthen buildings exposed to high temperatures.