Title:
Cement Characteristics Affecting the Performance of (3-Naphthalene Sulfonate Superplasticizer
Author(s):
Y Nakajima, T. Goto, and K. Yamada
Publication:
Symposium Paper
Volume:
217
Issue:
Appears on pages(s):
311-326
Keywords:
adsorption equilibrium; alkali sulfate; 0-naphthalene sulfonate superplasticizer (PNS); calcium sulfate; fluidity; free lime; incompatibility; Langmuir; modeling; sulfate ions
DOI:
10.14359/12922
Date:
9/1/2003
Abstract:
The performance of 3-naphthalene sulfonate superplasticizer (PNS) is known to be affected by various cement characteristics e.g. the kind of calcium sulfate, the amount of alkali sulfates and free lime, and the phase composition of the clinker especially the amount of C3A. In this study, the affecting mechanisms of these characteristics are explained by a unified model. In the model proposed, the fluidity is assumed to be determined by the adsorbed amount of PNS per unit surface area of hydrates (Ad/Hy) only. Ad/Hy is affected by the S042- concentration in the solution phase of the cement paste if PNS and So42- are in Langmuir type competitive adsorption equilibrium. Of course, the surface area of hydrates also influences fluidity by changing the Ad/Hy ratio. There has been an unsolved problem for the working mechanism of PNS, which is the quantitative discrimination between the absorption into initial hydrates and adsorption onto hydrates. The only PNS adsorbed on hydrates is expected to work as a dispersant. This problem can be avoided by using the proposed model. This model can also take into account the effect of S042 concentration just after mixing affecting the absorption behavior of PNS during initial hydration. This model predicts the performance of PNS only, by two parameters, S042concentration and surface area of hydrates. Based on the model, all cement characteristics relating the So42- concentration and surface area of hydrates are understood to be quite important for the performance of PNS. The well-known cement characteristics mentioned above can be attributed to changes in S042- concentration and surface area of hydrates.