Synchrotron Radiation Pair Distribution Function Analysis of Gels in Cements

Crystals

Ana Cuesta¹  Oriol Vallcorba¹  Miguel A.G. Aranda¹  Isabel Santacruz²  Jesus D. Zea-Garcia²  Diana Londono-Zuluaga²  Angeles G. De la Torre² 

[1] ALBA Synchrotron radiation facility, Carrer de la Llum 2-26, 08290 Cerdanyola del Vallès, Spain;Departamento de Química Inorgánica, Cristalografía y Mineralogía, Universidad de Málaga, 29071 Málaga, Spain;

关键词: Portland cement;    cementitious materials;    C-S-H gel;    amorphous phases;    total scattering;   

DOI  :  10.3390/cryst7100317

来源: DOAJ

【 摘 要 】

The analysis of atomic ordering in a nanocrystalline phase with small particle sizes, below 5 nm, is intrinsically complicated because of the lack of long-range order. Furthermore, the presence of additional crystalline phase(s) may exacerbate the problem, as is the case in cement pastes. Here, we use the synchrotron pair distribution function (PDF) chiefly to characterize the local atomic order of the nanocrystalline phases, gels, in cement pastes. We have used a multi r-range analysis approach, where the ~4–7 nm r-range allows determining the crystalline phase contents; the ~1–2.5 nm r-range is used to characterize the atomic ordering in the nanocrystalline component; and the ~0.2–1.0 nm r-range gives insights about additional amorphous components. Specifically, we have prepared four alite pastes with variable water contents, and the analyses showed that a defective tobermorite, Ca11Si9O28(OH)2.8.5H2O, gave the best fit. Furthermore, the PDF analyses suggest that the calcium silicate hydrate gel is composed of this tobermorite and amorphous calcium hydroxide. Finally, this approach has been used to study alternative cements. The hydration of monocalcium aluminate and ye’elimite pastes yield aluminum hydroxide gels. PDF analyses show that these gels are constituted of nanocrystalline gibbsite, and the particle size can be as small as 2.5 nm.

【 授权许可】

Unknown