受火温度和时间对喷水冷却后混凝土剩余抗压强度的影响

Influences of fire temperature and time on concrete residual compressive strength after water cooling

通过对不同受火温度和时间喷水冷却后混凝土试块剩余抗压强度的试验研究,得到高温后混凝土试块的受压破坏特征和混凝土剩余抗压强度与受火温度和受火时间的耦合关系。研究结果表明:随着受火温度的升高和受火时间的增加,喷水冷却后混凝土剩余抗压强度整体上呈逐步降低的趋势;但在受火温度较低(θ≤500℃)或受火时间t较短(t≤100 min)时,混凝土剩余抗压强度反而有所上升,分析其原因为在较低受火温度或较短受火时间作用时,适当的高温促进了混凝土内部未水化的水泥熟料进一步水化完全,此时高温对混凝土强度的有利作用大于其分解、变形不协调等不利作用。试验建立高温后混凝土剩余抗压强度与受火温度和受火时间的计算公式,并根据抗压强度的损失比例大小对火灾的大小进行评价,将火灾分为大火((θ20)tφ>110 000)、中火(90 000<(θ20)tφ≤110 000)和小火((θ20)tφ≤90 000)3种类型。

The concrete residtial compressive strength after different temperature and time by water cooling was experimentally researched. The compression failure characteristics and relationship between the concrete residual compressive strength and fire temperature and time were obtained. The experiment results show that with the increase of the fire temperature and time, concrete residual compressive strength tended to decrease generally, but when the temperature was low （θ≤500℃） or time was short （t≤ 100 min）, the concrete residual compressive strength increased on the contrary. The reasons were considered as that appropriate temperature inside concrete could promote cement hydration reaction which could increase the strength. According to the experiment results, the formula for strength and fire temperature-time after water cooling was built. Considering the proportion of the compressive strength loss, assessment of fire was proposed, which included big fire （（θ-20）.t.φ〉 110 000）, middle fire （90 000〈（θ-20）.t.φ≤ 110 000） and small fire （（θ-20）.t.φ≤〈90 000）.