Real-time high-resolution X-ray imaging and nuclear magnetic resonance study of the hydration of pure and Na-doped C3A in the presence of sulfates
AuthorsKirchheim, A. P.
Dal Molin, Denise Carpena Coitinho
Fischer, Peter J.
Emwas, Abdul-Hamid M.
Provis, John L.
Monteiro, Paulo José Meleragno
KAUST DepartmentImaging and Characterization Core Lab
Advanced Nanofabrication, Imaging and Characterization Core Lab
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AbstractThis study details the differences in real-time hydration between pure tricalcium aluminate (cubic C3A or 3CaO·Al2O 3) and Na-doped tricalcium aluminate (orthorhombic C3A or Na2Ca8Al6O18), in aqueous solutions containing sulfate ions. Pure phases were synthesized in the laboratory to develop an independent benchmark for the reactions, meaning that their reactions during hydration in a simulated early age cement pore solution (saturated with respect to gypsum and lime) were able to be isolated. Because the rate of this reaction is extremely rapid, most microscopy methods are not adequate to study the early phases of the reactions in the early stages. Here, a high-resolution full-field soft X-ray imaging technique operating in the X-ray water window, combined with solution analysis by 27Al nuclear magnetic resonance (NMR) spectroscopy, was used to capture information regarding the mechanism of C3A hydration during the early stages. There are differences in the hydration mechanism between the two types of C3A, which are also dependent on the concentration of sulfate ions in the solution. The reactions with cubic C3A (pure) seem to be more influenced by higher concentrations of sulfate ions, forming smaller ettringite needles at a slower pace than the orthorhombic C3A (Na-doped) sample. The rate of release of aluminate species into the solution phase is also accelerated by Na doping. © 2011 American Chemical Society.
SponsorsA.P.K. acknowledge the financial support of CAPES, CNPq of The Brazilian Ministry of Education, and FAPERGS (Rio Grande do Sul Foundation to Support Research) and is grateful to Dong-Hyun Kim and Anne Sakdinawat (Center for X-ray Optics) for their assistance in acquiring the X-ray images. This publication was based on work supported in part by Award No. KUS-11-004021, made by King Abdullah University of Science and Technology (KAUST). The operation of the microscope is supported by the Director, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, of the U.S. Department of Energy under Contract No. DE-AC02-05-CH11231. The participation of John Provis in this work was supported by the Banksia Foundation, Australia, through the awarding of the Brian Robinson Fellowship, as well as by the Australian Research Council.
PublisherAmerican Chemical Society (ACS)