Use of Fly Ash, Blast Furnace Slag, and Chemical Gypsum for the Synthesis of Calcium Sulfoaluminate-Based Cements


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Title: Use of Fly Ash, Blast Furnace Slag, and Chemical Gypsum for the Synthesis of Calcium Sulfoaluminate-Based Cements

Author(s): G. Belz, J. Beretka, M. Marroccoli, L. Santoro, N. Sherman, and G. L. Valenti

Publication: Special Publication

Volume: 153


Appears on pages(s): 513-530

Keywords: blast furnace slag; calcium sulfoaluminates; cements; ettringite; compressive strength; C AF; expansion; fly ash; high-early-strength cements; hydration; shrinkage; supersulfated cement; wastes; Materials Research

Date: 6/1/1995

Presents a study on high-early-strength cements based on calcium sulfoaluminate, C 4A 3S. These cements can be produced at temperatures about 300 C lower than normal portland cement and can also be synthesized using industrial process wastes and byproducts, such as fly ash, blast furnace slag, chemical gypsums, and other waste materials containing reactive sulfate and alumina. Cements designed to contain C 4A 3S, Beta-C 2S, and CS or C 4A 3S, calcium sulfosilicate, C 5S 2S, and CS have been synthesized using (a) pure analytical reagent (AR) calcium carbonate or commercial limestone as the source of CaO; (b) fly ash, blast furnace slag, bauxite, clay, or alumina as the source of Al 2O 3 and SiO 2; and (c) natural gypsum, phosphogypsum, or desulfogypsum as the source of sulfate. Ettringite, C 6AS 3H 32, generated by the hydration of C 4A 3S and CS is responsible for the high early strength of these cements. The hydration of the silicate phase and the presence of C 5S 2S contribute to ultimate strength. These ettringite-containing cements do not expand and, in fact, have dimensional stabilities similar to portland cement. In these types of cements, durability problems may arise from the poor resistance of ettringite to carbonation. Due to the higher resistance to carbonation of another calcium sulfoaluminate hydrate, monosulfate (C 4ASH 12), the investigation has been extended to a composition which included brownmillerite, C 4AF, whose presence promotes the conversion of ettringite to monosulfate during hydration.