混凝土水力劈裂试验研究

Experimental research on hydraulic fracture of concrete

本文采用改进后的楔形劈拉试验密封装置进行了有(无)水压作用下的混凝土(水力)劈拉试验。设计的密封装置通过特制的夹具、硅胶板来实现密封水的作用,以承受施加在混凝土试件预制缝的外部水压力。试验表明,本文设计的密封装置对混凝土试件断裂参数的影响相对较小。根据预埋在裂缝尖端水压力传感器记录的数据,拟合并总结出混凝土试件缝面水压力在不同阶段的分布情况及一般规律。试验结果表明,不论是慢速加载还是快速加载,当水稳定进入裂缝时,缝面水压分布曲线主要由直线段和抛物线段两部分组成;慢速张开情况下裂缝口的水有足够的时间流入裂缝内,快速张开时缝内水的运动明显有滞后性。当慢速与快速加载作用达到相同的裂缝张开宽度时,慢速加载时缝面水压力是快速张开情况下的2~3倍。外水压对混凝土楔形劈拉失稳荷载影响较大,随着外水压的增大,试件的失稳荷载明显减小;快速加载下,失稳荷载比慢速加载时要有所增大。水力劈裂试件的扩展裂缝形状比较平直,而无水压作用时,试件劈裂扩展裂缝形状则有较多的曲折。

A series of wedge-splitting experiments on concrete specimens are conducted with a developed sealing device. This sealing device employs silicon plates and specially designed clamps to apply the water pressure within the crack instead of the use of adhesive. The experimental results without water pressure in- dicate that the sealing device has a minimal effect on the fracture parameters of concrete. According to the pressure data recorded by the pre-set transducers, the water pressure distributions along the crack under fast and slow loading are obtained. The internal water pressure consists of a constant curve and a parabolic curve when the crack length is larger than the critical crack length in both fast and slow loading condi- tions. The water within the crack has sufficient time to enter the crack when subjected to a slow split load- ing, and the water pressure during slow loading is over twice that of the fast loadings when reaching the same CMOD. The external water pressure has a great influence on the concrete crack propagation. With the increasing of the external water pressure, the critical loading decreases obviously. Moreover, the crack prop- agated in a tortuous shape in dry tests, while under hydraulic loading, the crack propagated in a straight manner.