Title: Interaction of Superplasticizers with Clay-Bearing Aggregates

Author(s): A. A. Jeknavorian, L. Jardine, C. C. Ou, H. Koyata, and K. Folliard

Publication: Symposium Paper

Volume: 217

Issue:

Appears on pages(s): 143-160

Keywords: clay; high range water reducer; naphthalene sulfonate formaldehyde condensate (NSFC); polycarboxylates; smectite; sodium montmorillonite; superplasticizer

DOI: 10.14359/12911

Date: 9/1/2003

Abstract:
With the increased use of polycarboxylated-based comb-type polymers as highrange water reducers, more frequent opportunities exist to uncover unexpected interactions with the various materials used in cementitious mixtures. In this paper, attention is drawn to the increased dose-slump response of polycarboxylate-based comb-type superplasticizers versus naphthalene sulfonate formaldehyde condensates (NSFC) when swellable clays are present in certain aggregate sources. In the expanded state, these clays have been found to adsorb polycarboxylate-based superplasticizers, rendering this class of dispersants less effective in providing slump increase or water reduction. This effect is apparently not observed with NSFC. Among the approaches identified to mitigate the adsorption effects of expandable clay materials, a class of sacrificial agents has been found effective in restoring the expected dose-response of polycarboxylate superplasticizers. A model for the interaction of polycarboxylate comb-type polymers with an expandable clay as well as the lab performance of a clay modifying agent will be discussed.