C4AF Reactivity—Chemistry and Hydration of Industrial Cement

The study described in this paper involved a close examination of one of the least-researched cement phases, 4CaO•Al(2)O(3)•Fe(2)O(3) (C(4)AF or ferrite). The two ferrite materials used in this program were: (1) extracted from an industrial clinker free of 3CaO•Al(2)O(3) (C(3)A or aluminate); and (2) a laboratory-synthesized C(4)AF compound. Both ferrite materials were initially characterized using optical microscopy, x-ray diffraction (XRD), and Raman spectroscopy. The hydration kinetics and reactivity of both materials were studied with a calorimetric technique. Similar to aluminate, ferrite also demonstrated a strong early hydration rate. An adequate amount of sulfate (SO(3)) was needed to regulate the ferrite hydration rate. Based on this work, an equivalent aluminate content, C(3)A(eq), is proposed. The hydration of C(3)A(eq) needs to be properly controlled with the appropriate amount of sulfate. The concept, based on equivalent aluminate content for cement sulfate optimization, ensures proper early hydration behavior from both C(3)A and C(4)AF and avoids potential cement-admixture incompatibility probems, especially for the cements containing little or no C(3)A content.