On the nature of structural disorder in calcium silicate hydrates with a calcium/silicon ratio similar to tobermorite

• Published in: Cement and concrete research Vol. 52; pp. 31 - 37
• Main Authors: Grangeon, Sylvain, Claret, Francis, Lerouge, Catherine, Warmont, Fabienne, Sato, Tsutomu, Anraku, Sohtaro, Numako, Chiya, Linard, Yannick, Lanson, Bruno
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.10.2013; Elsevier
• Subjects: ABSORPTION SPECTROSCOPY; Analysis of cement phases and constituents; Applied sciences; Buildings. Public works; CALCIUM; Calcium silicate hydrate; CALCIUM SILICATES; Calcium–silicate–hydrate (C[sbnd]S[sbnd]H); Cement concrete constituents; Cements; Crystal structure; ELECTRON MICROPROBE ANALYSIS; Electron probes; Engineering Sciences; Exact sciences and technology; FINE STRUCTURE; HYDRATES; Hydration; LAYERS; Materials; MATERIALS SCIENCE; Minerals; Nanocrystals; NANOSCIENCE AND NANOTECHNOLOGY; NANOSTRUCTURES; POWDERS; Properties of anhydrous and hydrated cement, test methods; Ribbons; SILICON; SIMULATION; Spectroscopy; STACKING FAULTS; TEM; TRANSMISSION ELECTRON MICROSCOPY; X-RAY DIFFRACTION; X-RAY SPECTROSCOPY; X-rays; X-ray diffraction; Spectroscopy; Calcium–silicate–hydrate (CSH); TEM; Crystal structure; X-ray diffraction(B); Experimental study; X ray diffraction; Disorder; Spectroscopy(B); Crystal structure(B); CSH phase; Spectrometry; Transmission electron microscopy; TEM(B); Cement paste; Tobermorite; Calcium―silicate―hydrate (C―S―H)(B); Crystal morphology; Comparative study; Structural analysis
• ISSN: 0008-8846; 1873-3948
• DOI: 10.1016/j.cemconres.2013.05.007

Four calcium silicate hydrates (CSH) with structural calcium/silicon (Ca/Si) ratios ranging from 0.82±0.02 to 0.87±0.02 were synthesized at room temperature, 50, 80, and 110°C. Their structure was elucidated by collating information from electron probe micro-analysis, transmission electron microscopy, extended X-ray absorption fine structure spectroscopy, and powder X-ray diffraction (XRD). A modeling approach specific to defective minerals was used because sample turbostratism prevented analysis using usual XRD refinement techniques (e.g. Rietveld analysis). It is shown that CSH with Ca/Si ratio of ~0.8 are structurally similar to nano-crystalline turbostratic tobermorite, a naturally occurring mineral. Their structure thus consists of sheets of calcium atoms in 7-fold coordination, covered by ribbons of silicon tetrahedra with a dreierketten (wollastonite-like) organization. In these silicate ribbons, 0.42 Si per bridging tetrahedron are missing. Random stacking faults occur systematically between successive layers (turbostratic stacking). Layer-to-layer distance is equal to 11.34Å. Crystallites have a mean size of 10nm in the a–b plane, and a mean number of 2.6–2.9 layers stacked coherently along the c* axis.