New Model Describing Distribution of Adsorbed Superplasticizer on the Surface of Hydrating Cement Grain
Johann Plank
Panagiotis Chatziagorastou
Christian Hirsch
Abstract：The adsorption behaviour of chemically different superplasticizers, such as melamine formaldehyde sulphite polycondensate(PMS), β-naphthalene sulfonate formaldehyde polycondensate(BNS) and polycarboxylate(PC), on early hydrating cement phases was studied. For this purpose, pure ettringite(AFt), monosulfate (AFm) and syngenite were prepared. The adsorbed amount and zeta potential of early hydration products were measured. It is found that zeta potential is the key factor determining the amount of superplasticizer absorbed. Synthetic ettringite precipitated from solution shows a highly positive zeta potential, hence it adsorbs great amount of negatively charged superplasticizer. Monosulfate has only a slightly positive zeta potential and adsorbs smaller amounts of superplasticizer. For syngenite, portlandite and gypsum, the zeta potential is around zero or negative. These phases do not adsorb superplasticizers.Consquently, a hydrating cement grain is best represented by a mosaic structure, with superplasticizer molecules mainly adsorbed on ettringite spots.
Keywords：cementsuperplasticizeradsorptionettringite(AFt)monosulfate (AFm)syngenitezeta potential
Publication Date：2007-01-01
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：7( 7-13 )