基于破损分区理论和CT数重建混凝土数值模型

Reconstruction of concrete numerical model based on damage zoning theory and CT number

为了建立能真实反映混凝土试样内部细观结构的数值模型,分析大体积混凝土的损伤演化特性,利用便携式动力加载设备结合医用Marconi M8000螺旋CT扫描仪进行混凝土单轴压缩CT扫描试验,获得单轴压缩条件下混凝土试样的CT扫描图像。基于破损分区理论,提出了确定阈值的概率统计法,并将混凝土CT扫描图像分为骨料区、硬化水泥石区和孔洞裂纹区。进而基于CT扫描图中每个分辨单元的坐标,建立结构随机型数值混凝土模型,并对单轴静力压缩和拉伸条件下混凝土的损伤演化特性进行数值模拟。研究结果表明:结构随机型数值混凝土模型的细观结构与混凝土试样非常接近,该模型中骨料与砂浆的黏结界面厚度仅为0.04 mm左右,与真实混凝土试样的界面厚度(10~50μm)非常接近;在单轴拉、压应力状态下,混凝土细观裂纹均在强度相对薄弱的初始缺陷处开始萌生,随着应力的增加,裂纹绕着骨料并随强度较弱的界面扩展贯通,界面的强弱在很大程度上决定了混凝土的强度;在单轴压应力状态下,混凝土试样中裂纹较多且大多呈剪切裂纹,而在单轴拉应力状态下初始试样的起裂点较多,有多条裂纹同时发展,但随着应力水平的提高,试样中最终只产生1条与加载方向近乎垂直的主裂纹;无论是在单轴压缩还是单轴拉伸应力状态下,由于加载速度较慢,试样中裂纹扩展均不穿越骨料。

In order to establish a numerical model which truly reflect the internal mesoscopic structure of concrete specimen, and study the damage evolution characteristics of mass concrete, the uniaxial compression CT scanning test of concrete was carried out based on portable power load equipment combined with medical Marconi M8000 spiral CT. CT images of concrete samples under uniaxial compression were obtained. Based on the damage partition theory, a probability statistics method to determine the threshold was proposed, and the CT scan images of concrete were divided into aggregate area, hardened cement area and crack area. Based on the coordinates of each resolution unit in the CT scan, a structural random numerical concrete model was established, and the damage evolution characteristics of concrete under uniaxial static compression and tension were studied. The results show that the mesoscopic structure of structural random numerical concrete model is very close to the mesoscopic structure of concrete samples, and the interface thickness between aggregate and mortar in this model is only about 0.04 mm, which is very close to the interface thickness of real concrete samples(10 to 50 μm). In the condition of uniaxial tension and compressive stress, concrete microscopic cracks start to initiate at the initial defect with relatively weak strength, with the increase of stress, cracks expand and connect around the interface with relatively weak strength of aggregate, and the strength of the interface largely determines the strength of concrete. In the condition of uniaxial compressive stress, there are more cracks in the concrete samples and most of them are shear cracks. In the condition of uniaxial tensile stress, there are more crack initiation points in the samples at the beginning, and several cracks developed simultaneously, and however, with the increase of the stress level, only one major crack nearly perpendicular to the loading direction is finally generated in the sample. Under uniaxial compression or uniaxial tensile stress, due to the slow loading speed, the crack growth in the sample does not pass through the aggregate. 2 tabs, 9 figs, 22 refs.