Influence of specimen geometries and drying conditions on concrete cracking in restrained elliptical ring tests
Influence of specimen geometries and drying conditions on concrete cracking in restrained elliptical ring tests
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DOI：
10.1016/j.conbuildmat.2019.02.118
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发表时间：
2019-05-20
影响因子：
7.4
通讯作者：
Zhao, Xiaoyu
中科院分区：
文献类型：
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作者：
Dong, Wei;Yuan, Wenyan;Zhao, Xiaoyu
约束收缩椭圆环试验已被确立为评估混凝土早期开裂潜力的有效方法，因为椭圆环可以提供比圆形环更高程度的约束。本研究以不同厚度之钢筋约束混凝土圆环及椭圆形圆环，分别进行顶面、底面干燥及外圆周干燥试验。通过比较不同几何条件和干燥条件下混凝土开裂龄期，揭示了环几何形状、约束钢环厚度和干燥条件对混凝土环开裂过程的影响。此外，通过引入虚拟温度场来模拟混凝土的收缩效应，对圆环和椭圆圆环的断裂机理进行了数值分析。结果表明，无论是圆环还是椭圆环，增加钢环厚度都能提高约束程度，从而缩短开裂龄期。然而，改进对于圆环更显著。上下表面干燥和外圆周表面干燥的断裂过程完全不同：外圆周表面干燥时，裂纹从外表面萌生，向内表面扩展;对于从顶面和底面干燥，裂缝在混凝土环的内圆周处沿高度方向部分沿着开始，并沿径向沿着逐步扩展，直至裂纹扩展遍及整个环壁。在这两种情况下，由混凝土的不均匀收缩引起的自约束和来自内部钢环的外部约束贡献了裂缝扩展的驱动效应。一般来说，与圆环相比，椭圆环具有提供更高程度约束的优点。因此，椭圆环试验法可作为传统圆环试验法的补充，用于评定具有较高抗裂性的混凝土的开裂倾向。(C)2019爱思唯尔有限公司版权所有。
The restrained shrinkage elliptical ring test has been established as an efficient method for assessing the cracking potential of concrete at early ages because an elliptical ring can provide a higher degree of restraint compared with a circular one. In this study, a series of circular and elliptical concrete rings restrained by steel rings with various thicknesses were tested under top & bottom surfaces drying or outer circumferential surface drying. By comparing concrete cracking age under different geometrical and drying conditions, the effects of ring geometry, restraining steel ring thickness and drying condition on the cracking process in concrete rings were revealed. Furthermore, numerical analyses were conducted to investigate the fracture mechanism for circular and elliptical rings by applying a fictitious temperature field to simulate the shrinkage effect of concrete. It is found that the increase of steel ring thickness can enhance the degree of restraint, therefore shorten the cracking age for both circular and elliptical rings. However, the improvement is more significant for circular rings. The fracture processes under the two drying conditions, i.e. top & bottom surfaces drying and outer circumferential surface drying are completely different: for drying from outer circumferential surface, the crack initiates at the outer surface and propagates towards the inner surface; for drying from top & bottom surfaces, the crack initiates partially along the height direction at the inner circumference of a concrete ring, and propagates along the radial direction, step by step, until the crack propagates throughout the whole ring wall. In both cases, the self-restraint caused by the non-uniform shrinkage of concrete and the external restraint from the inner steel ring contribute the driving effects for crack propagation. In general, compared with circular rings, the elliptical rings demonstrate the advantage of providing a higher degree of restraint. The elliptical ring test method can, therefore, supplement the traditional circular ring test method for assessing cracking tendency of concrete with higher cracking resistance. (C) 2019 Elsevier Ltd. All rights reserved.