Research on the preparation of reversibly thermochromic cement based materials at normal temperature

In this paper, reversibly thermochromic cement at normal temperature was prepared by adding reversibly thermochromic microcapsules in white Portland cement. The research results showed that the color of the reversibly thermochromic cement added with a kind of blue reversibly thermochromic microcapsule with 30 °C switching temperature (B30, in which B is for the blue color, 30 is for the switching temperature, and the similar way is used in the following of the paper) could be changed reversibly from blue at lower temperature to white at higher temperature, and the switching temperature was about 42 °C. When added with a kind of red reversibly thermochromic microcapsule with 30 °C switching temperature (R30) or a kind of green reversibly thermochromic microcapsule with 30 °C switching temperature (G30), the color could be reversibly changed from red or green to white, and the switching temperature was about 58 °C. The kind of red reversibly thermochromic microcapsule could thus meet the needs of warm tone in winter and cool tone in summer in buildings. When the thermochromic microcapsule B30 was added in white Portland cement, the water content of the standard consistence of cement slurry increased by about 13%, and the mechanical properties, such as flexural strength and compressive strength, decreased by 20%–40%, but the setting time and the soundness of cement were not affected. All the research results indicate that the prepared material could meet the demand for creation of thermally comfortable environment of buildings. Through changing the solvent, the thermochromic microcapsule R5, G5 and B5 etc. were prepared further. Then by mixed 10% R5, G5 and B5 with white Portland cement, the switching temperatures could be lowered down to 26 °C, 26 °C and 17 °C respectively. The thermal effect of improved reversibly thermochromic cement based material (white cement mixed with 10% black microcapsule, and its switching temperature was about 24 °C) showed that it could warm buildings in winter and avoid buildings over-heated in summer.