Plastic deformation mechanism of calcium-silicate hydrates determined by deviatoric-stress Raman spectroscopy. (August 2021)

• Record Type: Journal Article
• Authors: Gardner, David W.; Li, Jiaqi; Kunz, Martin; Zhu, Chenhui; Monteiro, Paulo J.M.; Maboudian, Roya; Carraro, Carlo
• Is Part Of: Cement and concrete research. Volume 146(2021)
• Publication Date: 2021-08
• Subjects: Calcium-silicate-hydrate -- Small-angle X-ray scattering -- Spectroscopy -- Creep -- Carbonation; Cement -- Periodicals; Cement -- Research -- Periodicals; Concrete -- Periodicals; Concrete -- Research -- Periodicals; Ciment -- Périodiques; Béton -- Périodiques; Cement; Concrete; Periodicals; 620.135
• DOI: 10.1016/j.cemconres.2021.106476
• Languages: English
• ISSNs: 0008-8846

Abstract

Abstract: Creep of the cement matrix affects the structural stability of concrete. In Portland cements, the creep is largely controlled by the binding phase calcium-(aluminum-)silicate-hydrate, or C-(A-)S-H. This phase has a lamellar structure and under deviatoric stress aligns its c -axis with the principal stress. However, the limiting resistance to this reorientation is unknown at the nanocrystalline level. Small-angle X-ray scattering shows that the lamellae thickness decreases under 100's MPa deviatoric stress. Deviatoric stress Raman spectroscopy shows that there are two ways that this break-up can occur. If the material's silicate chains are cross-linked, then strain in SiO bonds does not increase above certain stresses, indicating a relaxation adjacent to the SiO bond. If the chains are not cross-linked, then the silicate chains are broken up by rastering against each other, introducing defects. These results show that the plastic deformation of C-(A-)S-H is relevant for Portland cement creep. Graphical abstract: Deviatoric-stress Raman spectroscopy shows how the structure of cement hydrates affects the way they plastically deform. Unlabelled Image Highlights: C-(A-)S-H samples under stress were characterized at the bond and grain level. Small angle scattering showed that 720 MPa reduced grain thickness by 30%. In-situ Raman showed that cross-linked C-A-S-H slips along its intralayer. However, in-situ Raman showed that C-S-H slips along the interlayer. In-situ Raman also showed a growth in CaCO3, indicating fracture in both samples.