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The present experimental investigation examines the influence of penetrating chlorides on the pore structure of structural concrete. For this purpose, the pore structure of concrete subjected to chloride penetration is compared with that of a similar concrete isolated from chlorides. To achieve the present objective, partially protected concrete slabs were exposed to chlorides for about two years by ponding with an aqueous solution of sodium chloride from the cast face. On completion of the exposure regime, the pore structure of concrete exposed to chlorides was compared with that of the adjacent concrete isolated from chloride intrusion. The concrete subjected to chloride intrusion showed a significant reduction in the number of coarser pores compared to the adjacent concrete isolated from chlorides. Various possibilities, such as degree of carbonation and degree of hydration were examined, step by step, to explain the observed modifications to the pore structure. It is shown that these results strongly suggest that the voluminous chloride-bearing compounds, such as Friedel's salt and calcium chloride, preferentially precipitate in the coarser pores, and thereby decrease the number of coarser pores. Although chloride contamination may thus result in some blocking of the pores in the cover concrete, it is unlikely to enhance the overall durability of the concrete. Further intrusion of chlorides may be hindered for a short time, but it cannot be prevented, and will continue in course of time.
National University of Singapore,
University of Sheffield,
Stock #: CCA10451J