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Formation of nanocrystalline tobermorite in calcium silicate binders with low C/S ratio

2018; Elsevier BV; Volume: 152; Linguagem: Inglês

10.1016/j.actamat.2018.04.006

1873-2453

Patrizia Paradiso, Rodrigo Lino Santos, Ricardo Bayão Horta, José N. Canongia Lopes, P.J. Ferreira, R. Colaço,

Recycling and utilization of industrial and municipal waste in materials production

Pastes of calcium silicate binders with low CaO/SiO2 (C/S) ratio with an overall C/S molar ratio of 1.1 were produced by mixing these materials with water or with an aqueous solution of Na2SiO3. Both types of pastes (non-activated and Na2SiO3 activated) were analysed using X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM). The observations show that the hydration process of this novel type of cements results in the formation of tobermorite nanocrystals embedded in the amorphous calcium-silicate-hydrate (C-S-H) matrix, both in the case of water and of water + Na2SiO3 hydration. Selected area electron diffraction (SAED) patterns obtained in the HR-TEM observations enabled a full characterization of the tobermorite crystalline structure (type, unit cell, space group, lattice angles and parameters). Molecular dynamics (MD) simulations of the identified tobermorite structure were performed at various temperatures, showing its viability and thereby supporting the experimental results. To the best of the authors' knowledge, this report is the first to describe the spontaneous formation of crystalline tobermorite in the form of nanodomains dispersed in the C-S-H phase upon the hydration of calcium-silicate binders.