Title: C4AF Reactivity—Chemistry and Hydration of Industrial Cement

Author(s): Hugh Wang, Delia De Leon, and Hamid Farzam

Publication: Materials Journal

Volume: 111

Issue: 2

Appears on pages(s): 201-210

Keywords: aluminate; cement; clinker; equivalent C3A; ferrite; reactivity

DOI: 10.14359/51686504

Date: 3/1/2014

Abstract:
The study described in this paper involved a close examination of one of the least-researched cement phases, 4CaO•Al2O3•Fe2O3 (C4AF or ferrite). The two ferrite materials used in this program were: (1) extracted from an industrial clinker free of 3CaO•Al2O3 (C3A or aluminate); and (2) a laboratory-synthesized C4AF compound. Both ferrite materials were initially characterized using optical microscopy, x-ray diffraction (XRD), and Raman spectros¬copy. 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 (SO3) was needed to regulate the ferrite hydra¬tion rate. Based on this work, an equivalent aluminate content, C3Aeq, is proposed. The hydration of C3Aeq needs to be properly controlled with the appropriate amount of sulfate. The concept, based on equivalent aluminate content for cement sulfate optimi¬zation, ensures proper early hydration behavior from both C3A and C4AF and avoids potential cement-admixture incompatibility prob¬lems, especially for the cements containing little or no C3A content.