Influence of pore structure and moisture distribution on chloride “maximum phenomenon” in surface layer of specimens exposed to cyclic drying-wetting condition

Influence of Pore Structure on Chloride Penetration in Cement Pastes Subject to Wetting-Drying Cycles

“…However, the chloride profile is very complicated under cyclic wet-dry environments. Instead of chloride decreasing monotonously with distance from the exposed surface increasing, a chloride concentration peak (as shown in Figure 1 [1]) was first discovered in 1993 [2,3] and was reported in other studies [4][5][6][7][8] successively. According to the recent researches [1,9,10], the chloride concentration peak is induced by the coupling effect of moisture hysteresis caused by alternate wet-dry and bound chloride releasing due to carbonation.…”

“…Noted that the "free" and "total" chloride measured by the above method is actually water-soluble and acid-soluble chloride separately, which is deemed as free and total chloride in this research. Besides, a high-precision numerical controlled milling machine was used to grind powder layer by layer automatically [25], and its grinding thickness is 0.5 mm with error controlled within 0.04 mm [8], which highly improves the accuracy of chloride distribution along with depth.…”

“…e water absorption porosity (P c ) was tested through the vacuum saturating method. e detailed operations were listed in reference [8]. By converting the mass difference between complete dry and full saturation of specimens into volume, the volume of capillary pores, that is, P c , can be obtained with equation (2).…”

“…It is caused by the fact that moisture evaporation is easier after total porosity, the most probable pore size, and water absorption porosity increase, leading to the decrease of S mean . Moreover, since the saturation of matrix is closely related to its absorption capacity, that is, the lower that former is, the greater the latter is [8,32], more salt solution will be absorbed into the matrix in the following wetting and M mean will be promoted consequently. Figure 9 presents the relation between total porosity and D eff and D app .…”

“…erefore, chloride penetration will be accelerated. Furthermore, Neithalath [39][40][41] discovered that water absorption porosity is closely related to connectivity, as portrayed by equation (8). It is obvious that they two are linearly correlated.…”