冷却方式和高温对混凝土劈裂抗拉强度影响

INFLUENCE OF DIFFERENT COOLING MODE AND HIGH TEMPERATURE ON CONCRETE SPLITTING TENSILE STRENGTH

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, mechanical properties of the concrete structure, especially the tensile strength, would be seriously deteriorated in fire fighting. In order to study the effect of different temperature and cooling mode on splitting tensile strength of concrete materials, the common commercial concrete C35 specimens were heated at high temperature, 300, 600, 800 ℃ respectively. Then, the rule and the cause of the physical and chemical change of these specimens were observed and analyzed with water cooling and natural cooling respectively. Finally keeping the specimens for more than 3 weeks, and the Brazilian disc splitting test was carried out. The result showed that the water cooling and high temperature greatly affected the physical and chemical feature of the concrete specimen also and their splitting tensile strength, and as the temperature increased, the effect of water cooling was more obvious than natural cooling. Mainly in the temperature of over 300 ℃ , the decline degree of the tensile strength of specimens caused by water cooling was obviously larger than natural cooling. Based on the test result, the temperature and cooling damage equation was constituted, and the corresponding feature parameter was determined.