高温后混凝土断裂性能研究

Residual Fracture Behaviors of Concrete Subjected to Elevated Temperatures

基于双K断裂韧度准则,对高温后混凝土Ⅰ型断裂性能进行试验研究,得到了历经65,120,200,300,350,400,450,500,600℃高温后混凝土试件的烧失量w.采用楔入劈拉法测得高温后试件荷载-裂缝开口位移(p-CMOD)全曲线,并据此计算出相应温度下混凝土试件的起裂韧度Kini、失稳韧度Kic、断裂能GF以及特征长度值lch.结果表明:随着受火温度的上升,Kini单调下降,而Kic,GF变化趋势为"保持不变—上升—下降";lch随温度的变化规律与Kic和GF随温度的变化规律一致,说明三者均可以作为高温后混凝土的延性指标.

Based on the double-K criterion, the residual Mode-I fracture behaviors of concrete subjected to elevated temperatures were investigated. The test specimens were molded according to ＂Norm for fracture test of hydraulic concrete＂（DL/T 5332--2005） which were exposed to temperature varying from 65 ℃ to 600 ℃. The mass losses of all the specimens were recorded. The wedge splitting method was employed to obtain the p（load）-CMOD（crack mouth opening displacement） curves of post-fire specimens from which the initial fracture toughness Kini, the critical fracture toughness Kic and the fracture energy GF were calculated. It was demonstrated that the Kini decreases monotonously with increasing temperature; however the Kic and GF sustain a hole-increase-decrease tendency with temperature. Furthermore, the characteristic length as a brittleness parameter was also calculated and there exists a same tendency with Kic and GF, which meant that these three parameters are similar as the index of brittleness for post-fire concrete.