Abstract
The recent polycarboxylate type superplasticizer (PC) shows high dispersibility for cement and it is possible to make highly fluid concrete with good slump retention at 20℃. However, at higher temperatures, tile slump loss tends to increase. At lower temperatures, the fluidity is low just after mixing, and the fluidity tends to increase with time.
In this paper, the mechanism of the temperature dependence of PC as mentioned above was investigated. In the experiments using normal Portland cement paste, the time variations of BET specific surface of cement paste and sulfate ion concentrations in liquid phase of cement paste were evaluated. The time variation of the dispersibility is thought to be explained by the combination of surface area change of cement paste and sulfate ion concentration change in solution phase. The low dispersibility at lower temperature just after mixing was attributed to the high sulfate ion concentration in solution phase. The fluidity gain at lower temperatures was attributed to the slower hydration speed and the larger decrease of sulfate ion concentration. The larger fluidity loss at high temperatures was attributed to the higher reaction rate of cement.
