Study on degradation of concrete characteristics in the high temperature environment

In nuclear power plant facilities, the concrete used as the foundations of high temperature equipment may be exposed to heat for long period, for example 30 years, due to thermal conduction from the equipment. Therefore, in order to evaluate the integrity of such foundations, it is necessary to investigate the change of physical properties of concrete itself when it is subjected to elevated temperature. For this purpose, the long term heating test on concrete for 1.5 years at maximum has been carried out. In this paper, the results of a series of such heating tests including that at high temperature for up to six months are reported, and the compressive strength and the modulus of elasticity under the influence of heat are discussed. The materials used and the mixing of concrete, the test items, the heating condition and exposure condition, the specimens, and the results of long term heating test, thermal cycle heating test, short term heating test, and weight change are described. The compressive strength was higher after heating than before heating in the long term heating and the thermal cycle tests. (K.I.)