约束条件下混凝土早期收缩开裂规律研究

发布时间：2018-05-20 01:38

本文选题：约束收缩 + 混凝土开裂　；参考：《哈尔滨工业大学》2014年硕士论文

【摘要】：随着混凝土应用范围的逐渐扩大，由于收缩开裂导致的耐久性问题也不断凸现出来。近年来国内外学者对混凝土的收缩开裂问题进行了大量研究，但大多数处于采用非约束状态评判和定性化研究阶段，因此开展约束状态下的混凝土收缩规律研究与裂缝监测具有重要意义。首先通过试验测试了混凝土1d～15d龄期的劈拉强度、立方体抗压强度和弹性模量等早期基本力学性能，得出了混凝土早期基本力学性能随龄期的发展规律曲线。其次基于毛细管理论，利用不同龄期钻取的平板约束条件下的混凝土试样，通过对试件进行化学结合水和孔结构试验，结合混凝土早期粘弹性模型，对混凝土约束条件下的早期收缩值进行了理论计算。再次利用光纤Bragg光栅传感器，测试了平板约束条件下混凝土在不同坍落度和风速条件下的早期收缩和开裂参数，研究了混凝土早期收缩开裂应力与实际劈拉应力的差异，得出混凝土开裂时的收缩应力仅为同龄期劈拉强度的75%，约束条件下的混凝土收缩开裂是内部应力累计造成的。同时将光纤Bragg光栅传感器实测的收缩值与理论计算值进行比较，发现采用理论计算的早期值要大于实测值，且两者的偏差较大，但在3d后两者的结果较为接近。最后通过利用光纤Bragg光栅传感器监测内钢环及混凝土环的应变，研究了圆环约束条件下混凝土环的早期收缩应力发展规律和开裂应力，结合混凝土的早期基本力学性能研究了约束条件下混凝土早期收缩开裂应力与实际劈拉应力的差异，发现混凝土开裂时的收缩应力比同龄期劈拉强度低40%左右；对比三种约束条件下混凝土早期收缩开裂表明，约束程度越大混凝土早期开裂龄期越短，开裂时的收缩应力也越小，但开裂时的应力水平反却高。
[Abstract]:With the gradual expansion of concrete application scope, the durability problem caused by shrinkage cracking is also emerging. In recent years, scholars at home and abroad have done a lot of research on shrinkage cracking of concrete, but most of them are in the stage of unconstrained state evaluation and qualitative research. Therefore, it is of great significance to study the shrinkage law and crack monitoring of concrete under constraint state. The early mechanical properties such as splitting tensile strength cube compressive strength and elastic modulus of concrete at 1d~15d age were tested and the development law curve of the early basic mechanical properties of concrete with age was obtained. Secondly, based on the capillary theory, the concrete samples with different ages are used to test the water and pore structure of the specimens, combined with the early viscoelastic model of concrete. The early shrinkage of concrete is calculated theoretically. Using fiber Bragg grating sensor, the early shrinkage and cracking parameters of concrete under different slump and wind speed are tested, and the difference between the early shrinkage cracking stress of concrete and the actual splitting tensile stress is studied. It is concluded that the shrinkage stress of concrete cracking is only 75% of the splitting tensile strength of the same age period, and the shrinkage cracking of concrete under constraint conditions is caused by the accumulative internal stress. At the same time, the measured shrinkage value of fiber Bragg grating sensor is compared with the theoretical calculation value. It is found that the early value of theoretical calculation is larger than the measured value, and the deviation between the two values is large, but after 3 days, the results of the two values are close. Finally, by using fiber Bragg grating sensor to monitor the strain of inner steel ring and concrete ring, the early shrinkage stress development and crack stress of concrete ring under circumscribed conditions are studied. Combined with the early mechanical properties of concrete, the difference between early shrinkage cracking stress and actual splitting tensile stress of concrete under confined conditions is studied. It is found that the shrinkage stress of concrete during cracking is about 40% lower than that of splitting tensile strength of the same age period. Compared with the early shrinkage cracking of concrete under three kinds of restraint conditions, the higher the degree of restraint is, the shorter the early cracking age is, the smaller the shrinkage stress is, but the higher the stress level is during cracking.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU528

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