低坍落度混凝土早龄期单轴直接拉伸试验研究

Experimental Study on Uniaxial Direct Tensile of Low Slump Concrete at Early Age

为了研究钢筋的存在对连续配筋混凝土路面(CRCP)早期开裂的影响,缓解连续配筋混凝土早期开裂的问题,为连续配筋混凝土路面设计提供依据,基于对轴向直接拉伸试验和间接拉伸试验试验难度和效果的区别,以及连续配筋混凝土路面在温缩和干缩作用下受力状态的符合程度,通过轴向直接拉伸模拟连续配筋混凝土路面早期开裂的过程,采用控制变量的试验方法对不同配筋率、不同配筋形式及不同龄期的钢筋混凝土试件在轴向拉力作用下的开裂性能进行试验分析。为探索钢筋和混凝土的应变以及裂缝的产生和发展的规律,基于传统直接拉伸试验,通过优化拉伸试件的形状与尺寸来提高轴向受力的符合程度,使用球铰支座固定试件避免试件偏心受压,利用高精度摄像与图片处理技术提高裂缝的发展过程中观测数据可靠度,采用位移控制模式对试件进行轴向拉伸并记录首次开裂以及裂缝发展过程中钢筋和混凝土应变数据。通过钢筋混凝土开裂过程的动态观测和试验数据分析,研究了在轴向受拉状态下连续配筋混凝土路面结构的力学性能,得出了首次开裂后不同配筋率的连续配筋混凝土的受力特点和引起配筋混凝土早期开裂的极限拉应力、应变的时变规律,并给出了相同配筋率下合理的配筋位置、配筋数量和钢筋的截面尺寸。

In order to study the influence of the existence of steel bars on the early cracking of CRCP,to reduce its early cracking,and to provide a basis for the design of CRCP,based on the difference of difficulty and effect between axial direct tensile test and indirect tensile test as well as the compliance of the stress states of CRCP under the action of temperature shrinkage and dry shrinkage,the early cracking process of CRCP is simulated by axial direct tension.The cracking performances of the RC specimens with different reinforcement ratios,different reinforcement types and different ages under the action of axial tension are analyzed by the test method of controlling variables.In order to explore the generation and the development rules of strain and crack of steel and concrete,based on the traditional direct tensile test,the shape and sizes of the tensile specimens are optimized to improve the compliance of the axial forces,the specimens are fixed by ball hinged supports to avoid eccentric compression,the reliability of the observation data during the crack propagation is improved by using high-precision camera and image processing technology,the specimens are axially stretched by displacement control mode,and the strain data of steel and concrete during the first cracking and crack propagation are recorded.Based on the dynamic observation of the RC cracking process and analysis of the experimental data,the mechanical properties of CRCP structure under axial tension are studied,the mechanical characteristics of continuous RC with different reinforcement ratios after the first cracking and the time-varying rules of ultimate tensile stress and strain that cause the early cracking of RC are obtained.The reasonable reinforcement locations,number of reinforcements and cross-sectional dimensions of steel bars for the same reinforcement ratio are given.