Synchrotron X-ray nanotomographic and spectromicroscopic study of the tricalcium aluminate hydration in the presence of gypsum

• Published in: Cement and concrete research Vol. 111
• Main Authors: Geng, Guoqing, Laboratory of Waste Management, Paul Scherrer Insitut, 5232 Villigen PSI, Myers, Rupert J., University of Edinburgh, School of Engineering, King's Buildings, Sanderson Building, Edinburgh EH9 3FB, Yu, Young-Sang, Shapiro, David A., Winarski, Robert, Levitz, Pierre E., Kilcoyne, David A.L., Monteiro, Paulo J.M., Material Science Division-Lawrence Berkeley National Laboratory, Berkeley, CA 94720
• Format: Journal Article
• Language: English
• Published: United States 15-09-2018
• Subjects: ALUMINATES; CALCIUM COMPOUNDS; CONCRETES; CRYSTALLOGRAPHY; DIFFUSION BARRIERS; DISSOLUTION; ENERGY DEPENDENCE; GYPSUM; HYDRATION; MATERIALS SCIENCE; MORPHOLOGY; PORTLAND CEMENT; RHEOLOGY; SIMULATION; SYNCHROTRON RADIATION
• ISSN: 0008-8846; 1873-3948
• DOI: 10.1016/J.CEMCONRES.2018.06.002

The rheology of modern Portland cement (PC) concrete critically depends on the correct dosage of gypsum (calcium sulfate hydrate) to control the hydration of the most reactive phase - tricalcium aluminate (C{sub 3}A). The underlying physio-chemical mechanism, however, remains unsolved mainly due to the lack of high-spatial-resolved and chemistry-sensitive characterization of the C{sub 3}A dissolution frontier. Here, we fill this gap by integrating synchrotron-radiation based crystallographic, photon-energy-dependent spectroscopic and high-resolution morphological studies of the C{sub 3}A hydration product layer. We propose that ettringite (6CaO·Al{sub 2}O{sub 3}·SO{sub 3}·32H{sub 2}O) is the only hydration product after the initial reaction period and before complete gypsum dissolution. We quantify the 2D and 3D morphology of the ettringite network, e.g. the packing density of ettringite at various surface locations and the surface dissolution heterogeneity. Our results show no trace of a rate-controlling diffusion barrier. We expect our work to have significant impact on modeling the kinetics and morphological evolution of PC hydration.