Interactions between fluoride ions and cement paste containing superplasticizer

Fluoride compounds are used as fluxes in the low-temperature calcination of cement. Elution of fluoride ions after calcination decreases the fluidity of cement paste containing superplasticizers, but the mechanism of fluidity decrease is unclear. Authors investigated the effects of fluoride on cemen...

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Bibliographic Details
Published in:Cement and concrete research 2017-01, Vol.91, p.33-38
Main Authors: Matsuzawa, Kazuki, Atarashi, Daiki, Miyauchi, Masahiro, Sakai, Etsuo
Format: Article
Language:English
Subjects:
ADSORPTION
ALUMINIUM OXIDES
Calcium fluoride
Calcium silicate hydrate
CALCIUM SILICATES
CALCIUM SULFATES
Cement
Cement manufacture (E)
Cement paste
Cement paste (D)
CEMENTS
Dispersion (A)
Elution
FINE PARTICLES
Fluoride (D)
Fluorides
Fluxes
High-range water reducers (D)
IONS
MATERIALS SCIENCE
Particle physics
PLASTICIZERS
Roasting
SILICA
Silicon dioxide
SILICON OXIDES
Specific surface
SPECIFIC SURFACE AREA
SULFONATES
Superplasticizers
Surface area
Surface chemistry
TEMPERATURE RANGE 0065-0273 K
TRANSMISSION ELECTRON MICROSCOPY
Tricalcium silicate
Viscosity
WATER
Yield strength
Yield stress
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Summary:Fluoride compounds are used as fluxes in the low-temperature calcination of cement. Elution of fluoride ions after calcination decreases the fluidity of cement paste containing superplasticizers, but the mechanism of fluidity decrease is unclear. Authors investigated the effects of fluoride on cement pastes containing superplasticizers and the fluidity decrease mechanism. KF addition to cement paste containing a polycarboxylate- or naphthalenesulfonate-based superplasticizer increased the yield stress, the amount of adsorbed superplasticizer, and the solid-phase specific surface area. KF addition increased the amount of adsorbed superplasticizer for alite paste but not for Ca3Al2O6-CaSO4 paste. Transmission electron microscopy found SiO2 fine particles after KF addition. In the absence of water, the increase in specific surface area with fluoride was larger in hydrated than in unhydrated cement. It is supposed that the fluidity decrease results from the preferential adsorption of superplasticizer on SiO2 particles generated by reactions between hydrated calcium silicate and fluoride ions.
ISSN:0008-8846
1873-3948
DOI:10.1016/j.cemconres.2016.10.006