Influence of temperature on the dispersibility of polycarboxylate type superplasticizer for highly fluid concrete

The recent polycarboxylate type superplasticizer (PC) for highly fluid concrete shows high dispersibility for cement and it is possible to make highly fluid concrete with good slump retention at 20 degreesC. However, at higher temperatures, the slump loss tends to increase. At lower temperatures, the fluidity is low just after mixing, and the fluidity tends to increase with time. The mechanism of the temperature dependence was investigated. In the experiments using normal Portland cement paste, the time variations of BET specific surface and sulfate ion concentrations 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 mixing water. The low dispersibility at lower temperature was attributed to the high sulfate ion concentration in mixing water. 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.