Modeling of Creep Properties of concrete at Early Ages

在这项研究中，进行了以下试验和数值分析，以研究混凝土早期的徐变特性，并检验其建模所需的基本因素。混凝土被认为是由砂浆和粗骨料组成的复合材料。那么，砂浆就是由于蠕变而变形的部分。为此，对早期砂浆试件进行了单轴压缩蠕变试验。在试验中测量了干燥蠕变应变和基本蠕变应变。装载时年龄不到24小时。选取砂浆龄期、应力强度比和水灰比作为影响因素，根据试验结果评价了它们对砂浆徐变应变的影响。在测试中，环境温度和湿度在计算机控制的舱内保持恒定(20ﾟC，70%RH)。研究了处理混凝土徐变过程中大的统计离散性的建模方法。有效的…通过将实际设计公式作为本构模型的一部分进行数值模拟，证实了概率模型的概念更适用于具有较大统计变化的力学性能的建模。为了研究粗骨料的尺寸和空间分布对混凝土徐变和收缩的影响，基于有限元方法建立了一种称为混凝土单元的复杂单元。在这种情况下，混凝土被模拟为由砂浆和粗集料组成的复合材料，在粗集料的结构层次上。通过对混凝土变形行为的各种数值模拟，证实了混凝土单元概念在混凝土内部结构数值分析中的有效性，在此基础上进行的混凝土试件徐变试验和对实际结构混凝土徐变的研究可视为本研究的延伸。较少

In this study, the following experiment and numerical analysis were conducted to investigate the creep property of concrete at early ages and to examine the basic factors necessary for its modeling.1. Concrete is considered as a composite material made up of mortar and coarse aggregates. Then, mortar is the part which deforms due to creep. Therefore, uniaxial creep tests in compression were conducted for mortar specimens at early ages. The drying creep strain and the basic creep strain were measured in those tests. The age at loading was less than 24 hours. Choosing age of mortar, ratio of stress to strength, and water-cement ratio as the influencing factors, their influence on creep strain of mortar was estimated from the test results. In the test, surrounding temperature and humidity were kept constant (20ﾟC, 70% RH) in a computer-controlled chamber.2. The method of modeling to deal with the large statistical scatter involved in the creep of concrete was investigated. The effectivene … More ss of the concept of a probabilistic model to the modeling of the mechanical property with a large statistical variation was confirmed through numerical simulations using a practical design formula as a part of the constitutive model.3. A kind of complex element called concrete element based on the finite element method was developed to investigate the influence of the size and the spatial distribution of coarse aggregates on the creep and shrinkage of concrete. in this case, concrete is modeled as a composite material made up of mortar and coarse aggregates in the structural level of coarse aggregates. The effectiveness of the concept of a concrete element to the numerical analysis of such an internal structure of concrete was confirmed through various numerical simulations on the deformational behavior of concrete.The creep test for concrete specimens based on this basic study and the investigation of the creep of concrete of actual structures may be considered as the extension of the present study. Less