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Improvement effect of a phase change material on microstructure of cement‐based materials at elevated temperatures

In this investigation, a phase change material with a melting temperature of about 450°C (PCM‐45) is prepared and applied to solve microstructure degradation problem of concrete matrix when exposed to temperatures more than 500°C. The morphology changes of PCM‐45 and the improvement effects of PCM‐45 on microstructure of cement matrix are investigated based on microstructure characteristics, ultrasonic pulse velocity of cement paste and compressive strengths of cement mortar with different dosages of PCM‐45 at 500, 600, 700, 800 and 900°C. The results show that morphology of PCM‐45 is changed, indicating that PCM‐45 transforms from solid to liquid phase and that the liquefied PCM‐45 can diffuse at elevated temperatures. When temperature returns to room temperature, the liquefied PCM‐45 becomes solidified, during which process the microstructure of cement matrix is improved. Therefore, compressive strength and ultrasonic pulse velocity of specimens with PCM‐45 are greatly increased compared to those of specimens without PCM‐45.