装配式结构新老混凝土竖缝界面区孔隙率分布模型

装配式混凝土结构中存在大量新老混凝土连接界面，模板效应导致界面区水泥砂浆孔隙率相对增大，从而引起其力学及耐久性能的弱化。为定量描述界面区水泥砂浆孔隙率分布特征，制作了不同水灰比搭配的新老混凝土竖缝平整界面区试件。利用扫描电镜获取各试件距离界面不同位置处的灰度图像，并采用数字图像处理工具进行图像信息增强处理和二值化处理，从而获得孔隙像素占总像素的比值(即名义孔隙率),据此分析了新老混凝土竖缝平整界面区名义孔隙率的分布特征；基于名义孔隙率与真实孔隙率之间的稳定关系，建立了新老混凝土竖缝平整界面区孔隙率的分布模型；考虑凿毛区新老混凝土含量连续变化关系，建立了凿毛界面区孔隙率的分布模型。结果表明：名义孔隙率在界面处最大，向混凝土内部逐渐减小，最后趋于稳定，总体变化趋势具有高斯函数特征；随水灰比增大，从界面到内部各部位的名义孔隙率均呈现相对增大趋势，但不同水灰比混凝土各自界面区与内部稳定区的相对名义孔隙率却接近一致。

Porosity distribution model for interfacial zone of new and old concrete with vertical seam in prefabricated structures

There are a large number of new and old concrete interfaces in prefabricated concrete structures. The template effect causes the enlargement of cement mortar porosity in the interfacial zones, which weakens their mechanical properties and durability. In order to quantitatively describe the porosity distribution characteristics of cement mortar in interfacial zones, new and old concrete specimens with smooth vertical interfaces and different water cement ratios were prefabricated. Scanning electron microscopy (SEM) was used to obtain the gray images of each specimen at different positions from the interface. Digital image processing (DIP) tools were used for image information enhancement and binarization. Thus, the ratio of pore pixels to total pixels was obtained, namely nominal porosity. With test results, the distribution characteristics of nominal porosity in the interfacial zones of new and old concrete with smooth vertical interfaces were analyzed. On the basis of the stable relationship between nominal porosity and real porosity, a porosity distribution model was established for the interfacial zones of new and old concrete with smooth vertical interfaces. Furthermore, considering the continuous variation of new and old concrete contents in the chiseled section, the porosity distribution model of chiseled interfacial zone was established. Results show that the nominal porosity reached the maximum at the interface, then decreased gradually towards the interior of concrete, and finally tended to be stable. The overall variation trend could be characterized by Gaussian function. With the increase in water cement ratio, the nominal porosity of each position from interface to interior concrete presented a relatively increasing trend, but the relative nominal porosity from the interfacial zone to the interior stable zone was nearly the same for the concrete with different water cement ratios.