ECO-SUSTAINABLE CEMENTS: UNRAVELING THE STRUCTURE OF MAGNESIUM SILICATE HYDRATE

MgO-based cements are recently attracting a noticeable interest as eco-sustainable alternative to traditional Portland cements, thanks to the much lower CO2 emissions associated with their production process [1]. Magnesium Silicate Hydrate (MSH), the binder phase of these innovative cements, arising from the hydration of MgO and a silica source, is a complex amorphous phase, with a micro- and nano-structure still relatively unknown [2, 3]. In this work we present the results of the first extensive characterization of the structural properties of MSH, obtained by means of multinuclear Solid State NMR and 1H relaxometry techniques. In particular, 1H and quantitative 29Si mono- and bi- dimensional Solid State NMR experiments, carried out on MSH samples freeze-dried at precise times of hydration, allowed us to obtain detailed structural information at the nanoscale, identifying, quantifying and characterizing two different kinds of phyllosilicate-like domains present. On the other hand, 1H T1, obtained by Fast Field Cycling technique, shed light on the the status of water in pastes at different hydration times and on the evolution of the surface to volume ratio of the material. The NMR results, together with those obtained from thermal, X-ray diffraction and SEM analyses allowed a detailed multi-scale characterization of the structural features of MSH to be obtained, which can improve the comprehension of MgO-based cements and contribute to tailoring the macroscopic properties from the modification at the nanoscale. This work was performed with the financial support of Ministero dell"Istruzione, Università e Ricerca scientifica MIUR (FIR2013 Project). References [1] E. M. Gartner, D.E. Macphee Cem. Concr. Res. 41, 736-749 (2011) [2] Z. Li, T. Zhang, J. Hu, Y. Tang, Y. Niu, J. Wei, Q.Yu Constr. Build. Mater. 61, 252-259 (2014) [3] S. A. Walling, H. Kinoshita, S. A. Bernal, N. C. Collier, L. J. Provis Dalton Trans 44, 8126-8137 (2015)