Papers by Author: Gang Hua Pan

Abstract: The aggregate occupies most of the volume of the concrete; it significantly affects the diffusion of CO₂ in the concrete. In this study, we adopted the accelerated carbonation test to investigate the effect of the aggregate content and paste thickness on the carbonation resistance of cement-based materials. Results showed that for the mortar specimens, 44% was the critical percolation sand volume. Within the critical volume, the dilution and tortuosity effects were in the dominant position; while over the critical volume, the interfacial transition zone (ITZ) and percolation effects were in the dominant position. For the concrete specimens, the paste thickness had good correlation with the concrete carbonation depth: the paste thickness increased and the carbonation depth showed a decrease tend; otherwise, the paste thickness decrease and the carbonation depth showed an increase tend.

Abstract: In this study three-dimensional X-ray computed tomography (X-ray CT) is used to investigate the testing results differences of cement paste and mortar before and after drying. It can be found that the mean gray values of paste and mortar before drying are bigger than after drying, and the impact of drying on cement paste is more serious than mortar. In addition, the porosity of non-drying cement paste and mortar is 1.10% and 0.43%, while that of drying cement paste and mortar is 1.55% and 0.70%, respectively. So, the porosity of paste and mortar markedly increases after drying process. The numbers of pores of paste and mortar sharply increase after drying process in particular between 0.01mm3 and 0.1mm3. The impact of drying on smaller pores is more serious than bigger pores.

Abstract: Cement asphalt mortar is a key part of flexible adjusting layer in slab ballastless track structure. In this paper, new materials of epoxy asphalt cement mortar (EACM) was prepared with epoxy and chemically modified asphalt emulsionwhich showed excellent in terms of durability and weather resistance. This paper through changing the proportions of the eopxy-asphalt cement ration studies the relationship among fluidity, compressive strength, and elastic modulus of EACM and cement asphalt mortar (CAM) use chemical modification of asphalt emulsion and normal asphalt emulsion. The results showed that chemically modified epoxy asphalt emulsion cement mortar turned out to be relatively better in compressive strength, frost resistance and weather ability compared with CAM. The chemical reaction mechanism of epoxy asphalt emulsion were investigated by the means of environmental scanning electron microscope (ESEM) method.

Abstract: Environmental Scanning Electron Microscope (ESEM) and Energy Dispersive X-ray Spectroscopy (EDS) were used to in situ observation microstructure character changes of hardened cement paste due to carbonation. Three types water-to-cement ratio of 0.53, 0.35 and 0.23 were research. When w/c=0.53, Carbonation enlarged the cracks, and some calcium carbonate spots appear on the calcium hydroxide crystals. When w/c=0.35, less cracks appear, and some white flocculent calcium carbonated appear on the calcium hydroxide crystals than above w/c=0.53 cement paste. When w/c=0.23, the microstructure character before and after carbonation have distinct changes, and some cracks become small or disappeared. Unhydrated cement clinkers continue to hydrate reactions and there are many white SiO₂•nH₂O (silica gel) after C-S-H gel carbonation in cement paste matrix.

Abstract: X-ray computed tomography (XCT), a non-destructive test, was used to study three dimensional (3D) meso-defect volume distribution changes of cement paste due to carbonation. The 3D meso-defect volume from 0.02mm3 ~5mm3 before and after carbonation was analyzed through add-on modules of 3D defect analysis. The experimental results show that the meso-defect volume fraction before and after carbonation are 0.7685% and 2.44%, respectively. After carbonation, the smaller defect increased significantly than the bigger defect.