Influence of Pore Structure on Chloride Distribution in Surface Layer of Cement Paste under Cyclic Wet-Dry Condition

摘要

This research focuses on influence of pore structure on chloride distribution in surface layer of cement paste under cyclic wet-dry condition. The results of chloride distribution reveal that drying and wetting cycles can lead to a peak value of chloride content (C_(max)) occurring in surface layer of cement paste. C_(max) increases with the increase of W/C. While the depth ( ∆_x) at which C_(max) appears does not show a regular change. Moreover, C_(max) should be used to predict service life of concrete structures when C_(max) appears in the chloride profiles. For the influence of pore structure, there exists an obvious hyperbolic relationship between chloride diffusion coefficient (D), C_(max) and pore structure parameters. D and C_(max) increase with total porosity and the most probable pore diameter, decrease with tortuosity, and stabilize gradually. And the most probable pore diameter has the most significant impact on D and C_(max). In addition, XRD and SEM-EDS results indicate that the deposition of Friedel's salt results in the formation of more inkbottle shaped pores, which may cause the appearance of C_(max) under cyclic drying-wetting conditions due to hysteretic moisture effect.