Study On Retarding The Setting Of Alkali-Slag Cement

The reasons that cause the rapid setting of ASC were researched by means of DTA, XRD, SEM analyses and liquid composition of cement paste. The principal reasons, which cause the rapid setting of ASC, are due to a mass of CSH gel formation in hydration initial stages. Especially the formation of a mass of CSH gel between slag grains causes the rapid setting of ASC. On the base of having studied the reasons for the rapid setting of ASC, the new retarder that can effectively retard the setting of ASC had been developed. When the content of new retarder in ASC is between 3.5 and 5.0%, the initial setting time of ASC has prolonged to 2 hours or so, the final setting time has been about 3 hours. Not only does the setting time of cement become normal, but also the strength of early age and later age is higher than ASC without the retarder. The action mechanisms of the new retarder include three aspects. First, because the high electrovalence cations in the retarder prior to Ca2+ ions enter into silicic acid glue groups, SiO2 glue nucleus are not easy to react with Ca2+ ions, which decreases the amount of CSH gel between the slag grains. Second, the retarder makes silicic colloid particles produce much bigger positiveζ-potential, so the silicic colloid particles are hard to coagulation. Third, a mass of uniform, compact CSH gel that cover the entire surface of slag grains, also inhibits the slag from hydrating.