Effect of alkalis on the mineral formation and properties of alite-sulfoaluminate cement

Abstract

This work studied the effects of alkalis on the mineral formation of alite-sulfoaluminate cement clinker and the properties of its cement, using limestone, fly ash, clay and gypsum as raw materials. The results indicated that minor amount of alkalis can improve the burnability of raw mixtures and accelerate the absorption of free lime. Excess amounts of sodium oxide (Na 2 O) or potassium oxide (K 2 O) (about 1 . 2%) were found to be adverse to the formation of C 4 A 3 S: The alkali distributes mostly in the interstitial phase, much less in belite crystal and then only traces in alite crystal. When the amount of alkali is about 1 . 2%, Na 2 O benefits the formation of C 3 S and can increase the early strength of cement. K 2 O, on the other hand, decreases the amount of formation of C 3 S and lowers the various age strengths of the cement. Adding alkalis prolongs the cement setting time.Notation C 3 S 3CaO . SiO 2 C 2 S 2CaO . SiO 2 C 4 A 3 S 4CaO . 3Al 2 O 3 . SO 3 CA

Influence of Alkalis on the Phase Development of Belite-Sulfoaluminate Clinkers

“…The amount of C 4 A 3 Ś is dependent on the amount of SO 3 [19]. Namely, due to the high amount of Na 2 O and K 2 O, alkali sulfates begin to form, leading to a decrease in the amount of SO 3 available for C 4 A 3 Ś formation [12,19]. This phenomenon is observed in the samples with the incorporation of K 2 O. KŚ and K 2 CŚ 3 were determined in these samples.…”

“…The amount of C 4 A 3 Ś is dependent on the amount of SO 3 [19]. Namely, due to the high amount of Na 2 O and K 2 O, alkali sulfates begin to form, leading to a decrease in the amount of SO 3 available for C 4 A 3 Ś formation [12,19].…”

“…The content of alkalis in raw meals is also increasing due to industrial by-products and/or wastes, which have increasingly replaced raw materials for clinker production in recent years [7,[14][15][16]. Alkalis affect the mineral composition, shape, and size of the phases [15,[17][18][19] and consequently the hydration rate [20]. Numerous papers addressed the effect of alkalis on the phase composition of Portland clinker and the properties of Portland cement.…”

“…The hydration kinetics of BCSA clinkers is influenced by both the major and minor phases [7]. In the case of alkali incorporation in alitesulfoalumiante cement clinkers, the amount of C 4 A 3 Ś is decreased [19], and in clinkers with a high amount of sulfoaluminate phase, the grains become rounded [24], while the size of the mostly rounded belite grains was reduced in belite-rich clinkers [17]. Potassium and sodium are most commonly incorporated into the crystal lattice of C 4 A 3 Ś, less so into the crystal lattice of C 2 S and C 4 AF [25].…”

Editorial

“…The mix of different types of fly ashes together with silica fume gives reasonable compressive strength without the need for cement clinker. j 'Effect of alkalis on the mineral formation and properties of alite-sulfoaluminate cement' (Liu et al, 2013). This paper also addresses the effects on mineral formation of alitesulfoaluminate cement clinker and its properties using limestone, fly ash, clay and gypsum as raw materials.…”