| Summary: | 博士 === 中華大學 === 土木工程學系 === 105 === This dissertation investigates the application of calcium sulfate composite coating in the fireproofing, heat insulation and sound insulation of building materials. The high crystallinity calcium sulfate whiskers were produced from the waste water by using microwave-assisted (MA) method. The as-prepared CaSO4 whiskers are of one-dimensional structure, and their aspect ratio is approximately 40. The construction applications of CaSO4 whiskers prepared by the MA method can be divided into three parts. The first part is to explore its flame retardancy using thermogravimetric analyzer, differential scanning thermal analyzer, direct combustion test at different temperatures (i.e., 150, 570, and 1100°C). Experimental results reveal that the addition of calcium sulphate whiskers not only improves flame retardancy but also lowers the ignition temperature of architectural coatings. The heat transfer is hindered by passage of the calcium sulfate coating until the endothermic reaction (i.e., the phase change of gypsum dehydration (CaSO4•2H2O) and β-hemihydrate calcium sulfate). The content of calcium sulphate whisker is a decreasing function of the burnt ratio on the calcium silicate substrate (including pyrolysis and carbonization). Accordingly, the calcium sulfate whisker can be regarded as an additive to improve the fire resistance of architectural coatings. In the second part, the calcium sulfate whisker are mixed with binder and coated on different substrates, including concrete columns, stainless steel and calcium silicate plates for thermal insulation measurement. Experimental results show that adding calcium sulfate whisker is capable of enhancing the thermal insulation resistance and preventing thermal transfer from heat source. The temperature difference between the heat source and the treated sample can reach as high as 13°C, showing superior thermal insulation effect. The enhanced performance can be attributed to the fact that the CaSO4 whiskers possess an endothermic nature and a high melting temperature (i.e., 1460°C). In the third part, we report an enhanced soundproof performance of polyvinyl acetate (PVA)-based coating by adding high-aspect-ratio calcium sulfate whiskers. This work uses an anechoic termination method to analyze the sound transmission loss (TL) of PVA-based coatings. The TL of CaSO4/PVA composite coating shows an increased trend with the amount of CaSO4 whiskers within the frequency region of 400‒3600 Hz. The improved TL can be attributed to the fact that an air pocket contained in the CaSO4 stacking layer, imparting the reflection and refraction during the sound wave transmission in the composite coating. The energy of incident sound wave is weakened by consecutive reflection, scattering, refraction and diffraction of sound wave in the CaSO4/PVA composite coating. Since the CaSO4 whiskers are synthesized from industrial wastewater by the MA method, the CaSO4/PVA composite coating can serve as eco-environmental decoration materials due to its excellent soundproof performance.
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