The effects of early hydration reactivity of cement on the dispersing force of polycarboxylate type superplasticizer (PC) were investigated by using normal Portland cement (NPC) and belite-rich low heat Portland cement (LHC). Early hydration reactivities were controlled for both NPC and LHC by exposing them to an condition of 80%RH and 20°C. Regardless the differences in cement type and in early hydration reactivities of cements, the fluidity of PC-added paste was positively related to PC adsorption amount per BET specific surface area of the solid phase of the paste, AdPC/BET. The dispersing force of PC was determined by the amount of PC adsorbed on the unit surface area of the solid phase. In each cases of NPC or LHC, AdPC/BET corresponded to the variation of BET specific surface area of the solid phase of the paste, SSApc. The variation of SSApc was caused by the variation of cement early hydration reactivity. AdPC/BET was also affected by the sulfate ion concentration in the solution phase of the paste, because sulfate ions act as competitive adsorbates with PC. AdPC/BET for LHC was larger than AdPC/BET of NPC at the same SSApc because of the lower alkaline sulfate content of LHC.
