Superplasticizer adsorption on synthetic ettringite

J. Plank, C. Hirsch

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

26 Scopus citations

Abstract

The mode of action of polycondensate and polycarboxylate based superplasti-cizers is still under investigation. Major unresolved aspects are whether superplasticiz-ers adsorb to a higher extent on specific hydrate phases and whether superplasticizers are not only adsorbed, but also absorbed (e.g. intercalated). Ettringite, portlandite and gypsum are important mineral phases present during early hydration of cement. In this study, the interaction of different superplasticizers with these pure mineral phases is investigated. Naphthalene and melamine based poly-condensates and methacrylic acid/methacrylate ester based polycarboxylate superplasticizers were synthesized and used in the experiments. Ettringite was synthesized in suspension as well as from solution. Superplasticizers were added either at the beginning of ettringite crystallization or to a slurry of synthetic ettringite. Superplasticizer adsorption, quantity and morphology of ettringite formed were determined for each case. The influence of superplasticizer chemical structure on adsorption behaviour was found to be similar for cement and ettringite. SPs showing high adsorption on cement also show high adsorption on ettringite, and vice versa. The adsorption of polycarboxylate SPs on cement increases with increasing C3A/C4AF content. Polycondensate adsorption is generally high and increases little with increasing C3A/C4AF content. In the case of ettringite, polycondensate adsorption is significantly higher when the superplasticizer is added early in the ettringite crystallization process whereas polycarboxylate adsorption is not affected by early or delayed addition. Crystal size of ettringite is reduced in the presence of superplasticizer. The effect is particularly strong from polycondensates. Similar experiments carried out with portlandite and gypsum showed no significant adsorption of superplasticizer. It is concluded that ettringite is a sink for superplasticizer in cement. In the XRD patterns, no evidence for absorption (intercalation) of superplasticizers into the ettringite crystal structure was found.

Original languageEnglish
Title of host publication7th CANMET/ACI International Conference on Superplasticizers and Other Chemical Admixtures in Concrete
EditorsV.M. Malhotra
PublisherAmerican Concrete Institute
Pages283-297
Number of pages15
ISBN (Electronic)9780870311277
StatePublished - 1 Sep 2003
Externally publishedYes
Event2003 7th CANMET/ACI International Conference on Superplasticizers and Other Chemical Admixtures in Concrete - Berlin, Germany
Duration: 20 Oct 200323 Oct 2003

Publication series

NameAmerican Concrete Institute, ACI Special Publication
VolumeSP-217
ISSN (Print)0193-2527

Conference

Conference2003 7th CANMET/ACI International Conference on Superplasticizers and Other Chemical Admixtures in Concrete
Country/TerritoryGermany
CityBerlin
Period20/10/0323/10/03

Keywords

  • Adsorption
  • Ettringite
  • Polycarboxylate
  • Polycondensate
  • Polymer structure
  • Superplasticizer

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