Preferred orientation of calcium aluminosilicate hydrate induced by confined compression

• Published in: Cement and concrete research 2018-11, Vol.113, p.186-196
• Main Authors: Geng, Guoqing, Vasin, Roman Nikolayevich, Li, Jiaqi, Qomi, Mohammad Javad Abdolhosseini, Yan, Jinyuan, Wenk, Hans-Rudolf, Monteiro, Paulo J.M.
• Format: Article
• Language: English
• Subjects: Aluminosilicates; Calcium; Calcium aluminosilicate hydrate; Calcium aluminum silicates; Calcium silicate hydrate; Cement; Deformation mechanisms; Deviatoric stress; Distribution functions; Elastic moduli; Fiber orientation; Gaussian distribution; High pressure X-ray diffraction; Nanocrystals; Nanostructured materials; Preferred orientation; Pressure; Texture; Texture formation
• ISSN: 0008-8846; 1873-3948
• DOI: 10.1016/j.cemconres.2018.09.002

The existing macroscale models of the calcium (alumino)silicate hydrate (C-(A-)S-H), the main binder of concrete, assume that the nanocrystallites maintain random orientation under any loading conditions. However, using synchrotron-radiation-based XRD, we report the development of preferred orientation of nanocrystalline C-A-S-H, from random at ambient pressure to strongly oriented under uniaxial compression with lateral confinement. The c-axes of the nanocrystals tend to align with the primary load. This preferred orientation is preserved after removing of external loading. The texture, quantified using a standard Gaussian fiber orientation distribution function (ODF), was used to calculate the averaged bulk elastic tensor of oriented C-(A-)S-H. It changes from isotropic (without texture) to transversely isotropic (with texture). Our results provide direct evidence of the reorientation of nanocrystalline C-(A-)S-H as a mesoscale mechanism to the irreversible deformation of cement-based material. The implications of these results for modeling the mechanical property of C-(A-)S-H at the macroscale are discussed.