By using the test pieces of concrete of the same mixture design, the thermal conductivity and stress-strain relation are measured. Temperature range is from 100 to 800℃ with 100℃ steps.
Unloaded simple support beam under JIS heating curve is calculated with these data. Temperature and stress distribution in side are clarified. Decomposition of concrete is taken into account. This calculation supposes the homogeneous material property for concrete, and crack or explosion cannot be calculated.
Another experiment for explosion of gravel and concrete under intense heating are carried with preheated furnace at 800℃. Andesite, granite and chert are tested. Andesite is not damaged, granite cracked from crystal interfaces, most specimens of chert are not damaged but some specimens not homogeneous texture are exploded. Concrete specimens with above gravel are tested. Entrained air is extracted by vacuum pump and hardened under compression to minimize porosity. After heating small cracks are appeared for andesite, large cracks appeared for granite, and small surface explosion are observed for chert. They are similar for the test of gravel only. Next by using andesite, concrete specimens are made with ordinary method (porosity) and tested in wet state. Heating rate is set to 1000℃/30min. When the center of the specimen reaches to about 250℃, specimen exploded into small pieces. This phenomenon is reproducible for wet specimens, but does not occur for dried specimens. The reason can be considered as to vapor explosion. This phenomenon is not reported yet in literature.