The relationship between compressive strength and temperature of concrete blocks under temperature dependent strain rate 10-5/s is analyzed, as shown in Figure 4.
It can be seen from the above diagram that the strength of concrete decreases with the increase of test temperature. The concrete strength decreased slightly before 300 degrees Celsius, or even a small increase. After 300 degrees, it decreased sharply and showed a certain fluctuation.
At 100 C, the compressive strength of concrete is slightly reduced, which is mainly the evaporation and loss of free water, the internal formation of capillary cracks in the specimen, and the stress concentration after loading, so the strength decreases slightly.
At 300 C, the dehydration of hydrated calcium silicate makes the cement slurry begin to shrink, while a large number of water vapor and gas emanate, which causes the concrete structure to expand and the crack pores lead to the reduction of concrete compressive strength by .
At 500, the compressive strength of concrete dropped to 60% of normal temperature. At this time, the water and hydration products of the internal structure of concrete have almost disappeared, and cracks and pores develop further. The decomposition of calcium hydroxide produces endothermic reaction, further enlargement of pores, and the destruction of concrete macroscopically.
At 700 C, the unhydrated cement particles and quartz particles in the cement were crystallized, which caused the concrete to expand sharply. The chemical reaction produced by the chemical reaction was partly molten at high temperature, and the strength was lost after cooling. The strength of ordinary concrete at about 700 degrees is about 30% of normal temperature.