Solid State NMR Spectroscopy and 1H Relaxometry for a Multi-Scale Investigation of Innovative MgO-Based Cements

In the last years, MgO-based cementitious materials have attracted great interest because of the low CO2 emissions associated with their production and especially for applications requiring relatively "low" pH of the cement pore solution, such as nuclear waste containment [1]. The binder phase of MgO-based cements is magnesium silicate hydrate (M-S-H), the amorphous phase that forms from the reaction of MgO with a source of silica and water. Although the structure and nature of M-S-H have been investigated [2-3], a full comprehension of properties, such as the hydration kinetics, the nature of the hydrated products and their multi-scale structure and organization, is still lacking. The investigation of these properties, as well as the research for new formulations with improved performances, is fundamental to achieve the industrial breakout of these materials. In this work we have combined Solid State NMR spectroscopy (SSNMR) and 1H relaxometry to obtain a detailed multi-scale description of novel MgO-based cements prepared by hydration of MgO and fumed silica (SiO2) and of mixed formulations containing MgO/SiO2 and Portland cement. A 29Si SSNMR investigation on samples freeze-dried at different hydration times allowed us to obtain quantitative information on the nature and structure of the binder phases at the nanometric level, as well as on their formation kinetics [4]. The analysis of 1H T2 and 1H T1 obtained by means of Fast Field Cycling relaxometry on cement pastes during their hydration provided a description of the state of water and of the evolution of the solid phases [5]. Parole chiave: NMR, cements, nanoscale, structure, dynamics, water Riferimenti: [1] S.A. Walling and J. L. Provis Chem. Rev. 116, 4170-4204 (2016). [2] B. Lotenbach, D. Nied, E. L'Hôpital, G. Achiedo, and A. Dauzères Cem. Concr. Res. 77, 60-68 (2015). [3] M. Tonelli, F. Martini, L. Calucci, E. Fratini, M. Geppi, F. Ridi, S. Borsacchi, and P. Baglioni Dalton Trans. 45, 3294-3304 (2016). [4] F. Martini, M. Tonelli, M. Geppi, F. Ridi, S. Borsacchi, and L. Calucci Cem. Concr. Res. 2017 DOI: 10.1016/j.cemconres.2017.08.029. [5] F. Martini, S. Borsacchi, M. Geppi, M. Tonelli, F. Ridi, and L. Calucci Micropor. Mesopor. Mater. 2017 DOI: 10.1016/j.micromeso.2017.05.031. Ringraziamenti: MIUR (FIR2013 Project RBFR132WSM) is acknowledged for financial support.