EFFECTS OF BLAST FURNACE SLAG AND WATER REDUCING ADMIXTURES ON THE DETERMINATION OF CHLORIDE CONTENT OF PORTLAND CEMENT PASTES

摘要

Knowing the free and total chloride amounts in hydrated cement materials is essential for service life of prediction, particularly in the case of reinforced concrete structures. Many factors can influence the free and bound chloride in Portland cement based material: a) CaO/Al_2O_3 ratio, b) pH solution changed by cement type, and c) sulfonated plasticizers and superplasticizers. This paper aims to analyze the influence of blast furnace slag and water reducing admixtures in the determination of chloride contents of cement pastes. Cement pastes containing different contents of blast furnace slag and fixed concentrations of admixtures (polycarboxylate and lignosulfonate basis) were produced with known chloride amounts. Free and total chlorides were determined by potentiometry using ion-selective electrode. The chloride binding capacity was only noticeable for cement type I (without blast furnace slag) and for lower amount of chloride added (0.1% by mass of binder). The free chloride content drastically increased for additions of chlorides higher than 0.1% by mass of binder, which indicated that the binding chloride capacity reached its saturation amount. The presence of blast furnace slag significantly affected the relative errors for total chloride determinations as well as the presence of polycarboxylate.