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高温下混凝土结构在消防射水扑救时的力学性能会严重恶化,特别是其抗拉强度的降低尤为显著。为了深入研究不同高温、不同冷却方式对混凝土材料的劈裂抗拉强度的影响,对工程中常用的强度等级为C35的商品混凝土试件进行300,600,800℃高温加热,并分别采用自然冷却和水冷却两种方式降温,观察分析试件的物理化学变化规律及其原因。再将试件静置3周以上,分别进行巴西圆盘劈裂试验。研究结果表明:水冷却和高温对混凝土试件物理化学特性及劈裂抗拉强度影响很大,而且随着温度升高这种影响比自然冷却时更为明显,主要表现在当加热温度超过300℃后,水冷却造成的拉伸强度下降程度明显大于自然冷却的试件。在试验研究结果基础上,建立了考虑冷却方式影响的三段式温度-冷却损伤演化方程,并确定出相应的特征参数。
Under high temperature, the mechanical properties of concrete structures will be seriously deteriorated in fire fighting water ejection, especially the reduction of tensile strength is particularly significant. In order to further study the effect of different high temperature and different cooling methods on the splitting tensile strength of concrete materials, commercial concrete specimens with C35 strength grade commonly used in the project were heated at high temperature of 300, 600 and 800 ℃, and were respectively cooled by natural and water cooling Ways to cool down, observation and analysis of physical and chemical changes in the specimen and its causes. The specimens were then allowed to stand for more than three weeks, respectively, for Brazil disc splitting test. The results show that water cooling and high temperature have a great influence on the physical and chemical properties and splitting tensile strength of concrete specimens, and the effect is more obvious than that of natural cooling as the temperature increases. The main effect is that when the heating temperature exceeds 300 ℃, the degree of decrease of tensile strength caused by water cooling is obviously greater than that of naturally cooled specimens. Based on the experimental results, a three-stage temperature-cooling damage evolution equation considering the influence of cooling mode is established, and the corresponding characteristic parameters are determined.