| 要約: | Fire is known to cause spalling in concrete structures. Fire resistance of concrete structural elements are often predicted based on the assumption that spalling does not occur. This assumption is often not satisfied in real fire test. Researches show that spalling is more susceptible in high strength concrete, silica fume blended cement concrete and concrete of low water/cement ratio. Such quantifications are not always valid. The fundamental cause of spalling is still not addressed. Hence, this research uses the microstructure of hardened cement paste as the foundation for analysing the occurrence of spalling. Material models relating non-evaporable moisture loss and porosity subjected to elevated temperature were developed as they were identified as parameters that influence significantly on gas pressure build up in concrete. Experimental data on mass loss and volume of pores measurements performed on specimens of different water/cement ratio and degree of hydration subjected to different temperatures were used to develop the material models that are applicable to hardened cement paste. An analytical model on heat and mass transfer based on microstructure model was also developed to solve temperature, mass of vapour and gas pressure distributions within heated hardened cement paste.
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