开裂混凝土有效导热系数研究:三维模拟与试验验证

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

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。

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 quantita-tive relationships between tensile or compressive strain and ETC, respectively. The main conclusions aredrawn as follows：（a） for tensile dominated failure, concrete ETC decreases by 23% during plastic stagewhereas 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 softeningstage,ETC linearly decreases with the increase of compressive strain;（c） it is the interfacial thermal resis-tance induced by the micro-cracks between aggregates and mortar rather than the macro-cracks that playthe dominant role in this phenomenon;（d） concrete ETC shows more anisotropy when cracks appear. Thenan experimental validation of compressive cracked concrete’s ETC vertical to cracks（C-ETCV） shows thatC-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 inWang model. A good agreement between the data from simulation, Wang model and experiment indicatesthe correctness of this study.