Magnesium Silicate Hydrate (M-S-H) is the binder phase of magnesium based cements, which are attracting interest as an eco-sustainable alternative to standard Portland cement. Indeed their production process, taking place from magnesium silicates, brine or seawater, dramatically reduces the CO2 emissions, and they are well suited to applications for radioactive waste encapsulation [1]. Due to the complete amorphous character, the assessment of the structural properties of M-S-H is still open [1,2]. In this study multinuclear NMR relaxometry and spectroscopy techniques, which revealed fundamental for the characterization of Portland cement [3], were applied to get insights into the silicate structural properties and water status in M-S-H obtained through room temperature hydration of highly reactive MgO and silica fume. In particular, the analysis of 1H and quantitative 29Si Solid State NMR experiments, together with results obtained from DSC, TGA, XRD and SEM measurements, carried out on M-S-H samples freeze-dried at precise times of hydration, allowed us to propose a detailed structural model of M-S-H. On the other hand, the status of water in pastes and the M-S-H surface to volume ratio were characterized and monitored at different hydration times by analyzing 1H (and in some cases 2H) T1 relaxation times, measured by Fast Field Cycling NMR relaxometry, and 1H T2 relaxation times. The multi-scale characterization of the structure of M-S-H here obtained can improve the comprehension of MgO-based cements and potentially contributes to tailoring the macroscopic properties from the modification at the nanoscale. References [1] Vlasopoulos, N., Process for producing cement binder compositions containing magnesium. WO/2012/028471, March 8, 2012; Dong, H., et al., Feasibility study of synthesizing MgO from local waste brine using aqueous ammonia. 14th International Congress on the Chemistry of Cement, Beijing, 2015. Vol. 1: p. 1-9; Zhang, T., et al., Magnesium-Silicate-Hydrate cements for encapsulating problematic aluminium containing wastes. J. Sustain. Cem.-Based Mater., 2012. 1: p. 34-45; Hwang, K. -Y., et al., MgO- based binder for treating contaminated sediments: characteristics of metal stabilization and mineral carbonation. CLEAN-Soil Air Water, 2014. 42: p. 355-363; Walling, S. A., et al., Structure and properties of binder gels formed in the system Mg(OH)2-SiO2-H2O for immobilisation of Magnox sludge. Dalton Trans., 2015. 44: p. 8126-8137. [2] Roosz, C., et al., Crystal structure of magnesium silicate hydrates (M-S-H): the relation with 2:1 Mg-Si phyllosilicates, Cem. Concr. Res., 2015. 73: p. 228-237; Li, Z. et al., Characterization of reaction products and reaction process of MgO-SiO2-H2O system at room temperature. Constr. Build. Mater., 2014. 61: p. 252-259. [3] Korb J. P. et al., Microstructure and texture of hydrated cement-based materials: a proton field cycling relaxometry approach, Cem. Concr. Res., 2007. 37: p. 295-302; Rawal, A., et al., Molecular silicate and aluminate species in anhydrous and hydrated Cements, J. Am. Chem. Soc., 2010. 132: p. 7321-7337.
LOOKING INSIDE MAGNESIUM SILICATE HYDRATE THROUGH 29SI SOLID STATE NMR AND 1H RELAXOMETRY: STRUCTURE AND WATER STATUS
Borsacchi S;Martini F;Calucci L;Geppi M;
2016
Abstract
Magnesium Silicate Hydrate (M-S-H) is the binder phase of magnesium based cements, which are attracting interest as an eco-sustainable alternative to standard Portland cement. Indeed their production process, taking place from magnesium silicates, brine or seawater, dramatically reduces the CO2 emissions, and they are well suited to applications for radioactive waste encapsulation [1]. Due to the complete amorphous character, the assessment of the structural properties of M-S-H is still open [1,2]. In this study multinuclear NMR relaxometry and spectroscopy techniques, which revealed fundamental for the characterization of Portland cement [3], were applied to get insights into the silicate structural properties and water status in M-S-H obtained through room temperature hydration of highly reactive MgO and silica fume. In particular, the analysis of 1H and quantitative 29Si Solid State NMR experiments, together with results obtained from DSC, TGA, XRD and SEM measurements, carried out on M-S-H samples freeze-dried at precise times of hydration, allowed us to propose a detailed structural model of M-S-H. On the other hand, the status of water in pastes and the M-S-H surface to volume ratio were characterized and monitored at different hydration times by analyzing 1H (and in some cases 2H) T1 relaxation times, measured by Fast Field Cycling NMR relaxometry, and 1H T2 relaxation times. The multi-scale characterization of the structure of M-S-H here obtained can improve the comprehension of MgO-based cements and potentially contributes to tailoring the macroscopic properties from the modification at the nanoscale. References [1] Vlasopoulos, N., Process for producing cement binder compositions containing magnesium. WO/2012/028471, March 8, 2012; Dong, H., et al., Feasibility study of synthesizing MgO from local waste brine using aqueous ammonia. 14th International Congress on the Chemistry of Cement, Beijing, 2015. Vol. 1: p. 1-9; Zhang, T., et al., Magnesium-Silicate-Hydrate cements for encapsulating problematic aluminium containing wastes. J. Sustain. Cem.-Based Mater., 2012. 1: p. 34-45; Hwang, K. -Y., et al., MgO- based binder for treating contaminated sediments: characteristics of metal stabilization and mineral carbonation. CLEAN-Soil Air Water, 2014. 42: p. 355-363; Walling, S. A., et al., Structure and properties of binder gels formed in the system Mg(OH)2-SiO2-H2O for immobilisation of Magnox sludge. Dalton Trans., 2015. 44: p. 8126-8137. [2] Roosz, C., et al., Crystal structure of magnesium silicate hydrates (M-S-H): the relation with 2:1 Mg-Si phyllosilicates, Cem. Concr. Res., 2015. 73: p. 228-237; Li, Z. et al., Characterization of reaction products and reaction process of MgO-SiO2-H2O system at room temperature. Constr. Build. Mater., 2014. 61: p. 252-259. [3] Korb J. P. et al., Microstructure and texture of hydrated cement-based materials: a proton field cycling relaxometry approach, Cem. Concr. Res., 2007. 37: p. 295-302; Rawal, A., et al., Molecular silicate and aluminate species in anhydrous and hydrated Cements, J. Am. Chem. Soc., 2010. 132: p. 7321-7337.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
