Working Mechanism of Poly-Beta-Naphthalene Sulfonate and Polycarboxylate Superplasticizer Types from Point of Cement Paste Characteristics
K. Yamada, S. Ogawa, and S. Hanehara
Appears on pages(s):
adsorption; superplasticizer, surface (specific)
Working mechanism of a poly-beta-naphthalene sulfonate (NS) and polycarboxylate (PC) superplasticizer (SP) types was studied from the point of solution chemistry and initial hydration of cement. Test results showed that the dispersing characteristics of SP can be represented by two parameters, which are the critical dosage (CD) and dispersing ability (DA). When used at lower dosage than CD, SP did not affect the fluidity of paste. However, beyond CD value, the fluidity of paste showed a linear increase with SP dosage. DA is defined as the fluidity increment per unit of SP dosage. CD is closely related to the initial hydration heat, which corresponds to the surface area of initial hydrates. For NS type, CD is affected by the absorption ratio of NS into initial hydrates. The absorption amount is decreased by increasing the sulfate ion concentration supplied from the alkaline sulfate in cement or by delaying the addition of NS. In the case of PC, the absorption amount was negligible. DA of PC value is related to the sulfate ion concentration. SP adsorption on hydrates is in equilibrium state with SP concentration in solution phase. Furthermore, sulfate ion and SP showed a competitive adsorption on hydrates. More sulfate ion in solution phase changes the adsorption equilibrium of SP to a low adsorbed state. The decrease of adsorption amount of SP decreases the paste fluidity.