浅谈混凝土抗压强度随温度的变化

分析了温度应变速率10-5/s下混凝土砌块抗压强度与温度的关系，如图4所示。

从上述图中可以看出，混凝土强度随试验温度的升高而降低。混凝土强度在300℃之前略有下降，甚至略有增加。300度后急剧下降，出现一定的波动。

在100℃时，混凝土的抗压强度略有下降，主要是自由水的蒸发和损失、试样内部毛细裂缝的内部形成以及加载后的应力集中，强度略有下降。

在300℃时，水化硅酸钙脱水使水泥浆开始收缩，大量水蒸气和气体散发，使混凝土结构膨胀，裂缝孔导致混凝土抗压强度降低（8）。

在500℃时，混凝土抗压强度降至正常温度的60%。此时，混凝土内部结构的水和水化产物几乎消失，裂缝和孔隙进一步发展。氢氧化钙分解产生吸热反应，进一步扩大孔隙，宏观破坏混凝土。

在700℃时，水泥中的未水化水泥颗粒和石英颗粒结晶，使混凝土急剧膨胀。化学反应所产生的化学反应在高温下部分熔融，冷却后失去了强度。普通混凝土在700度左右的强度约为正常温度的30%。

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 [8].

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.

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