Measuring the distribution of sulfate phases in cement

Abstract

Sulfate is present as various phases in Portland cement and these phases have distinct effects on the hydration and hardening of cement-based materials. A set of sulfate phases, with dissolution behaviour to easily soluble sulfates and gypsum, could be studied as a whole. Two chemical extraction methods, the 50% ethanol method and the saturated soda method, are initially proposed and described to study the quantitative distribution of easily soluble sulfates and gypsum in Portland cements. The ethanol method proposed can selectively dissolve easily soluble sulfates in cements and clinkers in a 1·5–2·5 min extraction process; and is more efficient than 1·5–2·5 min water extraction. The determination of gypsum depends on completely extracting the gypsum in a 2 h extraction with saturated soda solution at 300:1 (ml:g) of liquid–solid ratio. The gypsum determined is an overall phase, which would include anhydrite, semihydrate, dihydrate and other calcium sulfate in Portland cements.