Uniaxial stress increases layer stacking disorder in calcium silicate hydrates with low calcium content. (1st March 2023)

• Record Type: Journal Article
• Authors: Gardner, David W.; Li, Jiaqi; Kunz, Martin; Liao, Wei-Chih; Zhu, Chenhui; Carraro, Carlo; Monteiro, Paulo J.M.; Maboudian, Roya
• Is Part Of: Acta materialia. Volume 246(2023)
• Publication Date: 2023-03-01
• Subjects: X-ray diffraction -- Creep -- Crystal plasticity -- Cement -- Preferred orientation; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2023.118726
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: The long-term stress response of concrete is controlled by the intergrain and intragrain interactions of calcium-silicate-hydrates (C-S-H), nanocrystalline forms of tobermorites. To investigate both types of interactions, we examined the deviatoric stress response of 11 Å tobermorite powder with X-ray diffraction, finding that its layer stacking (i.e., sliding) disorder significantly increases. A similar experiment was performed on nanocrystalline C-S-H powders before and after applying a 360 MPa uniaxial stress. Layer stacking disorder (in the form of intragrain deformation) increases when there is low water content and when the basal spacing is large. We also find that grains with a smaller thickness-to-diameter aspect ratio are first to develop preferred orientation (in the form of intergrain sliding), facilitated by gel water. These findings show that intragrain deformations in C-S-H can occur at relatively low stresses and provide insights into the creep mechanism of C-S-H. Graphical abstract: Image, graphical abstract Description: X-ray diffraction on calcium-silicate-hydrate compacts shows that the compaction mechanism depends on the porosity of the C-S-H grains. When porosity is high and there is sufficient gel water, then grains with lowest thickness-to-diameter aspect ratio will align first. If the porosity is low or the basal spacing is ≥11.5 Å, then intragrain layer stacking disorder will be present.