Study on micro structure and composition distribution of concrete surface zone based on fractal theory and XCT technology

Abstract

Based on the fractal theory, the fractal dimension model of coarse aggregate gradation in concrete was proposed, and the fractal dimension of coarse aggregate gradation in concrete was calculated based on the measured data. The variations of the micro structure, composition distribution and porosity to paste ratio of concrete surface layer were investigated by the methods of X-ray computed tomography (XCT) and profile grinding technology (PGT). Moreover, the content variations of coarse aggregate and paste with depth in concrete surface were also studied. The results show that the coarse aggregate content in concrete surface layer increases but the porosity decreases with increase of depth from concrete surface. Finally, they all tend to be a constant when the depth is larger than a certain value. The porosity to paste ratio of concrete surface decreases with increase of concrete strength. The major composition is cement paste within 0.1 mm of concrete surface, which turns into mortar within 0.1 mm ~ 0.4 mm. The volume fractal dimension of coarse aggregate and the fractal dimension of coarse aggregate gradation in concrete is about 1.35 and 2.68, respectively.