开裂混凝土有效导热系数研究:三维模拟与试验验证

利用三维的细观数值模拟,研究了混凝土在单轴拉伸和压缩破坏过程中有效导热系数(ETC)的变化规律,并分别给出拉伸应变、压缩应变与ETC的定量关系。研究发现:(1)拉伸过程中,混凝土试件的ETC在塑性阶段显著下降(23%),但在软化阶段变化很小;(2)压缩过程中,混凝土试件的ETC在塑性强化阶段前期显著下降(30%),在塑性强化阶段后期趋于稳定,而在下降阶段又开始缓慢地减小;(3)骨料与砂浆间界面开裂所形成的界面热阻是导致混凝土ETC在塑性阶段急剧下降的主要原因;(4)开裂强化了混凝土导热性能的各向异性。随后,对单轴压缩破坏混凝土垂直于裂纹方向ETC(C-ETCV)进行了试验测量。数据表明:在单轴压缩过程塑性强化阶段前期,C-ETCV急剧下降20%~25%;在塑性强化阶段后期逐渐趋于稳定。随后利用模拟结果拟合确定了王家俊模型中的界面热阻因子,比较了王家俊模型与试验结果,两者比较吻合,证明了数值方法和王家俊模型的正确性。

Study of effective thermal conductivity of cracked concrete: three-dimensional simulation and experimental validation

A mesoscopic numerical method is proposed to investigate the effective thermal conductivity (ETC) of both tensile and compressive cracked concrete,and this method is applied to obtain the quantitative relationships between tensile or compressive strain and ETC, respectively. The main conclusions are drawn as follows:(a) for tensile dominated failure, concrete ETC decreases by 23% during plastic stage whereas a very slight linear decrease is found at complete failure;(b) for compressive dominated failure, ETC decreases by 30% during earlier plastic stage, and then becomes steady afterwards. In the softening stage,ETC linearly decreases with the increase of compressive strain;(c) it is the interfacial thermal resistance induced by the micro-cracks between aggregates and mortar rather than the macro-cracks that play the dominant role in this phenomenon;(d) concrete ETC shows more anisotropy when cracks appear. Then an experimental validation of compressive cracked concrete''s ETC vertical to cracks (C-ETCV) shows that C-ETCV decreases by 20%~25% at earlier plastic stage and then becomes steady at later plastic stage. The numerical results obtained simulations are used to determine the interfacial thermal resistance factor in Wang model. A good agreement between the data from simulation, Wang model and experiment indicates the correctness of this study.