The concrete's strength and properties of concrete's destruction in high temperature are largely influenced by temperature distribution of inside or moisture content. Furthermore, in case of high strength concrete, the possibility of the cross-sectional deficit called spalling is getting stronger according to the rate of surface moisture content. However, according to the existent researches, spalling dose not arise in the range of 3% or less of moisture content rate, even if intensity is high. And the cause can be considered that the influence of pore pressure which generates in concrete's inside becomes larger in the range of high moisture content rate. Therefore, the purpose of this research is to clarify the process of moisture movement and a change in internal pressure caused by changing in the microstructure under high temperature, by the method of changing the microstructure on the surface of concrete artificially and adjusting surface moisture content rate.
