Influence of thermal shock by brush cooling of concrete in fire situations

ABSTRACT In situations of abrupt temperature differences, as the residential fires, these structures must support the thermal chock. Thus, this is paper aims to assess the behavior of concrete exposed to high temperatures and subsequent abrupt cooling. For this we analyzed this effect on the characteristic resistences with fck of 25, 35 and 40MPa. The analyzies observed the resistence losses and the colorations of the concretes. The samples were submitted to the temperature of 300, 600, 900 and 1200°C for 90 minutes and tempered in freshwater. The strength were compared to the reference samples and to the theory to estimate the strength of the concrete exposed to abrupt cooling. The results show that concretes with Fck equal to 35 and 40MPa present lower strength when compared to the concrete with fck equal to 25MPa. On the other hand, at 900 and 1200°C, the percentage of strength lost is the same as 25MPa. However, at temperatures of 900 and 1200°C, the loss percentage is equal to the concrete with fck of 25MPa. That is, the higher the strength is, the higher the lost rate and the higher the incidence appearance of craks when heated and cooled.

摘要：在诸如住宅火灾这类骤变温差场景中，建筑结构需具备抵御热冲击的能力。为此，本研究旨在评估混凝土经高温作用后再遭遇骤冷的性能表现。本次试验针对抗压强度标准值（fck）分别为25MPa、35MPa及40MPa的混凝土，分析了该冷热交变工况对其特征强度的影响。试验中观测了混凝土的强度损失与外观色泽变化：将试样分别置于300℃、600℃、900℃及1200℃环境中保温90分钟，随后置于清水中进行骤冷处理。将试验测得的强度与基准试样强度及理论计算值进行对比，以推演骤冷工况下混凝土的强度变化规律。试验结果表明，抗压强度标准值为35MPa与40MPa的混凝土，其残余强度低于fck为25MPa的混凝土；当受热温度达到900℃与1200℃时，前两者的强度损失率与fck为25MPa的混凝土基本一致。换言之，混凝土的初始抗压强度越高，其经冷热交变后的强度损失率越高，且受热骤冷过程中裂缝的出现概率也越高。