Relationship between Fluidity of Cement Paste with Fluoride Ion and Type of Superplasticizer

Abstract

Fluoride ions decrease the fluidity of cement paste containing superplasticizer. This paper discusses the fluidity decrease from the influence of fluoride on the solid and liquid phases in cement paste, and investigates the difference between allylether-type and methacrylate-type polycarboxylate-based superplasticizers in cement paste containing fluoride ions. Regarding the solid phase, addition of fluoride ions generates fine particles, resulting in adsorption of superplasticizer on the fine particles. Regarding the liquid phase, addition of fluoride ions decreased Ca²⁺ concentration and increased SO₄^2- concentration; i.e., the adsorption hindrance. Allylether-type superplasticizers preferentially adsorb on the fine particles even with the adsorption hindrance; i.e., they are susceptible to the preferential adsorption. Methacrylate-type superplasticizers were less susceptible, but adsorption was hindered by the adsorption hindrance. When water-cement ratio increased, Ca²⁺ concentration increased and SO₄^2- was diluted, resulting in weak adsorption hindrance. Because of these concentration changes, methacrylate-type superplasticizers showed the preferential adsorption at high water-cement ratio.