Chemo-mechanical characterization of hydrated calcium-hydrosilicates with coupled Raman- and nanoindentation measurements
Creators: name: Stemmermann, P.
name: Garbev, K.
name: Gasharova, B.
name: Beuchle, G.
name: Haist, M.
name: Divoux, T.
Publisher: name: Amsterdam [u.a.] : Elsevier Science
Year: 2020
Subjects: subject: Hydraulic calcium –hydrosilicate
subject: Nanoindentation
subject: Raman spectroscopy
subject: Aluminum compounds
subject: Calcium oxide
subject: Degrees of freedom (mechanics)
subject: Density (specific gravity)
subject: Hardening
subject: Hydrated lime
subject: Hydration
subject: Lime
subject: Portland cement
subject: Reaction kinetics
subject: Silicates
subject: Silicon
subject: Calcium silicate hydrate
subject: Homogeneous distribution
subject: Mechanical characterizations
subject: Mechano-chemical activation
subject: Nano-indentation measurements
subject: Nanoscale mechanical properties
subject: Ordinary Portland cement
subject: Water to cement (binder) ratios
subject: Calcium silicate
subject: calcium
subject: chemical composition
subject: hydration
subject: nanoparticle
subject: nanotechnology
subject: silicate
subject: Dewey Decimal Classification::500 | Naturwissenschaften::550 | Geowissenschaften

description: Celitement is a new type of cement that is based on hydraulic calcium-hydrosilicate (hCHS). It is produced by mechanochemical activation of Calcium-Silicate-Hydrates (C-S-H) in a grinding process. Due to the lack of typical clinker minerals, its CaO/SiO2 (C/S) ratio can be minimized from above 3 (as in Ordinary Portland Cement) down to 1, which significantly reduces the amount of CO2 released during processing. The reaction kinetics of hCHS differs from that of classical clinker phases due to the presence of highly reactive silicate species, which involve silanol groups instead of pure calcium silicates and aluminates and aluminoferrites. In contrast to Portland cement, no calcium hydroxide is formed during hydration, which otherwise regulates the Ca concentration. Without the buffering role of Ca(OH)2 the concentration of the dissolved species c(Ca2+) and c(SiO4 4−) and the corresponding pH must be controlled to ensure a reproducible reaction. Pure hCHS reacts isochemically with water, resulting in a C-S-H phase with the same chemical composition as a single hydration product, with a homogeneous distribution of the main elements Ca and Si throughout the sample. Here we study via nanoindentation tests, the mechanical properties of two different types of hardened pastes made out of Celitement (C/S = 1.28), with varying amounts of hCHS and variable water to cement ratio. We couple nanoindentation grids with Raman mappings to link the nanoscale mechanical properties to individual microstructural components, yielding in-depth insight into the mechanics of the mineralogical phases constituting the hardened cement paste. We show that we can identify in hardened Celitement paste both fresh C-S-H with varying density, and C-S-H from the raw material using their specific Raman spectra, while simultaneously measuring their mechanical properties. Albeit not suitable for phase identification, supplemental EDX measurements provide valuable information about the distribution of alkalis, thus further helping to understand the reaction pattern of hCHS. © 2020 The Authors