Effects of chloride Ion binding on microstructure of cement pastes

The corrosion of steel caused by chloride ions is considered to be the main durability problem of reinforced concrete structures. This paper investigates the total chloride ion content, free chloride concentration in expressed pore solution, Friedel's salt content, and porosity of portland cement (PC) and PC/fly ash (FA) combination pastes after 7 days of water curing followed by 28 or 150 days immersion in water or 0.3, 0.7, 1.0, and 2.0 mol=L sodiumchloride solutions. Results showed that the chloride ion binding capacities of the pastes increased with increase of free chloride ion concentration. The relationship between bound and free chloride ion contents could be described by Langmuir's equation. The addition of fly ash decreased the bound chloride content and showed negative influences on Friedel's salt formation due to low activity. Porosity of cement paste decreased as the concentration of soaking chloride ion increased, and was inversely proportional to the amount of Friedel's salt formed