The identification of eco-compatible cements is a relevant issue in the field of building materials research. Reactive magnesia cements, obtained through the hydration of highly reactive periclase (MgO) that, in the presence of a silica source, forms the M-S-H (magnesium silicate hydrate) binder phase, constitute one of the most promising emerging technologies for the reduction of CO2 emissions involved in the production of traditional CaO-based (Portland) cement. At present the production of MgO-based cements is active only in pilot plants; to plan an industrial scale-up it is crucial to characterize the reaction kinetics, the nature of the hydrated products and the micro/nano structure of the obtained phases. Although several studies on M-S-H phases appeared recently in the literature,1 a thorough investigation of these properties is still lacking.? In this study multinuclear NMR relaxometry and spectroscopy techniques, which revealed fundamental for the characterization of Portland cement pastes,2-5 were applied to obtain information on the dependence of M-S-H structural properties and hydration kinetics on hydration time. In particular, the status of water in pastes was investigated at different hydration times by analyzing 1H (and in some cases 2H) T1 relaxation times measured by FFC NMR relaxometry and 1H T2 relaxation times determined by low resolution experiments at 20 MHz. On the other hand, 29Si- and 1H-MAS Solid State NMR experiments were applied to pastes freeze-dried at different hydration times in order to investigate the connectivity and chemical coordination of Si sites and the presence of OH groups and structural water molecules. The obtained results were discussed also taking into account complementary data obtained by DSC, TGA, XRD and SEM measurements. This work was financially supported by MIUR (FIR2013 Project RBFR132WSM). References: [1] J. Szczerba et al. Thermochim. Acta 2013, 567, 57-64. F. Jin, A. Al-Tabbaa Thermochim. Acta, 2013, 566, 162-168. F. Jin, A. Al-Tabbaa Cem. Concr. Compos. 2014, 52, 27-33. Z. Li et al. Constr. Build. Mater. 2014, 61, 252-259; W. -S. Chiang et al. J. Mater. Chem. A 2014, 2, 12991-12998; T. Zhang et al. Cem. Concr. Res. 2014, 65, 8-14; S. A. Walling et al. Dalton Trans. 2015, 44, 8126-8137. [2] J. P. Korb C. R. Phys. 2010, 11, 192-203. [3] A. Valori, P. J. McDonald, K. L. Scrivener Cem. Concr. Res. 2013, 49 65-81. [4] V. Bortolotti et al. Langmuir 2014, 30, 10871-10877. [5] A. Rawal et al. J. Am. Chem. Soc. 2010, 132, 7321-7337.
Investigation of innovative eco-compatible cement pastes by NMR relaxometry and spectroscopy
Silvia Borsacchi;Marco Geppi;Lucia Calucci
2015
Abstract
The identification of eco-compatible cements is a relevant issue in the field of building materials research. Reactive magnesia cements, obtained through the hydration of highly reactive periclase (MgO) that, in the presence of a silica source, forms the M-S-H (magnesium silicate hydrate) binder phase, constitute one of the most promising emerging technologies for the reduction of CO2 emissions involved in the production of traditional CaO-based (Portland) cement. At present the production of MgO-based cements is active only in pilot plants; to plan an industrial scale-up it is crucial to characterize the reaction kinetics, the nature of the hydrated products and the micro/nano structure of the obtained phases. Although several studies on M-S-H phases appeared recently in the literature,1 a thorough investigation of these properties is still lacking.? In this study multinuclear NMR relaxometry and spectroscopy techniques, which revealed fundamental for the characterization of Portland cement pastes,2-5 were applied to obtain information on the dependence of M-S-H structural properties and hydration kinetics on hydration time. In particular, the status of water in pastes was investigated at different hydration times by analyzing 1H (and in some cases 2H) T1 relaxation times measured by FFC NMR relaxometry and 1H T2 relaxation times determined by low resolution experiments at 20 MHz. On the other hand, 29Si- and 1H-MAS Solid State NMR experiments were applied to pastes freeze-dried at different hydration times in order to investigate the connectivity and chemical coordination of Si sites and the presence of OH groups and structural water molecules. The obtained results were discussed also taking into account complementary data obtained by DSC, TGA, XRD and SEM measurements. This work was financially supported by MIUR (FIR2013 Project RBFR132WSM). References: [1] J. Szczerba et al. Thermochim. Acta 2013, 567, 57-64. F. Jin, A. Al-Tabbaa Thermochim. Acta, 2013, 566, 162-168. F. Jin, A. Al-Tabbaa Cem. Concr. Compos. 2014, 52, 27-33. Z. Li et al. Constr. Build. Mater. 2014, 61, 252-259; W. -S. Chiang et al. J. Mater. Chem. A 2014, 2, 12991-12998; T. Zhang et al. Cem. Concr. Res. 2014, 65, 8-14; S. A. Walling et al. Dalton Trans. 2015, 44, 8126-8137. [2] J. P. Korb C. R. Phys. 2010, 11, 192-203. [3] A. Valori, P. J. McDonald, K. L. Scrivener Cem. Concr. Res. 2013, 49 65-81. [4] V. Bortolotti et al. Langmuir 2014, 30, 10871-10877. [5] A. Rawal et al. J. Am. Chem. Soc. 2010, 132, 7321-7337.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
