Adsorption of Superplasticizer Admixtures on Alkali-activated Slag Pastes

Alkali-activated slag (AAS) binders are obtained by a manufacturing process less energy-intensive than ordinary Portland cement (OPC) and involve lower greenhouse gas emissions. These alkaline cements allow the production of high mechanical strength and durable concretes. In this paper, the adsorption of different superplasticizer admixtures (naphthalene-based, melamine-based, and a vinyl copolymer) on the slag particles in AAS pastes using alkaline solutions with different pH values have been studied in detail. The effect of the superplasticizers on the yield stress and plastic viscosity of the AAS and OPC pastes were also evaluated. The results obtained show that the adsorption of the superplasticizers on AAS pastes is independent of the pH of the alkaline solutions used and lower than on OPC pastes. However, the effect of the admixtures on the rheological parameters depends directly on the type and dosage of the superplasticizer as well as of the binder used and, in the case of the AAS, on the pH of the alkaline activator solution. In 11.7-pH NaOH-AAS pastes dosages of the superplasticizers required to attain similar reduction in the yield stress are ten-fold lower than for Portland cement. In this case the superplasticizers studied show a fluidizing effect considerably higher in 11.7-pH NaOH-AAS pastes than in OPC pastes. In 13.6-pH NaOH-AAS pastes, the only admixture observed to affect rheological parameters is the naphthalene-based admixture due to its higher chemical stability in such extremely alkaline media.


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  • Accession Number: 01141926
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Oct 19 2009 6:57PM