三点抗折下纤维混凝土加载过程的体应变研究

The volume strain of fiber reinforced concrete with three points bending during loading

为提高混凝土的受拉性能,通常会在混凝土中添加纤维材料改善材料的力学性能.纤维混凝土在受外力荷载时,内部应变场非常复杂,现有技术很难对应变进行测量.采用X射线断层扫描(X-ray computed tomography,XCT)原位三点抗折实验,对纤维混凝土加载过程进行跟踪测试,用数字体积相关(digital volume correlation,DVC)计算不同纤维质量分数的试样在不同加载阶段材料内部的体应变.结果表明,在混凝土中加入纤维能较好地改善混凝土的断裂性能,明显减少裂缝的长度、宽度和体积.通过XCT结合DVC的方法得到不同纤维质量分数试样在不同加载阶段的体应变演化,发现试样破坏时,断裂面外仍然存在着不可忽略的变形耗能.通过体应变的分析可以得到试样受载后的内部变形响应.

In order to improve the tensile properties of concrete,fiber materials are usually added into concrete to improve its mechanical properties.The internal strain fields in the external loaded fiber reinforced concrete are very complex,and it is still difficult to test them currently.In this paper,the X-ray microcomputed tomography(XCT)in situ three-point bending test is used to track the loading process of fiber mortar.The digital volume correlation(DVC)is used to calculate the internal volume strain and the internal strain field of mortar with different fiber contents at different loading stages.The results show that adding fiber into concrete can improve the fracture performance of concrete,and the length,width and volume of crack are obviously reduced.The volumetric strain evolution of samples with different fiber content at different loading stages can be obtained by combining XCT with DVC.There is still non-negligible deformation energy consumption outside the fracture surface when samples fail.The internal deformation response of the specimen under load can be obtained by volume strain analysis.