Eco-compatible MgO-based cements represent one of the most promising alternative to the traditional CaO-based ones, allowing a strong reduction of CO2 emissions involved in the production process. Indeed, the hydration of reactive periclase (MgO) in the presence of a source of silica gives rise to a binder phase, known as Magnesium Silicate Hydrate (MSH), analogous to the CSH (Calcium Silicate Hydrate) phase present in traditional cements. However the mechanical properties achieved so far are still inferior to those of CaO-based cements, and the research for new formulations with improved performances is necessary in order for a diffusion on industrial scale to take place. To this aim precious information can arise from the study of the multi-scale structural properties of these systems, as well as of the formation process of the binder phases, whose nature is still not well understood. This work presents a solid-state NMR (SSNMR) and relaxometric study of eco- compatible cements obtained by hydration of mixtures of MgO, traditional Portland cement and silica fumes. Both SSNMR and relaxometry already proved to be very powerful techniques for the study of cements [1-4]. Here, the nature and the structure of the spieces formed at different times of hydration were investigated on freeze-dried samples by means a multinuclear SSNMR aprroach, based on the observation of 1H, 29Si and 27Al. In particular, mono- and bi-dimensional 29Si experiments allowed to identify the presence of both CSH and MSH domains, and to study their properties and relative composition also as a function of hydration time. On the other hand, the measurement of 1H T1"s by means of Fast Field Cycling (FFC) relaxometry was used to obtain information on the status of water in the cement pastes, as well as on the evolution of the porous structure. This work was financially supported by MIUR (FIR2013 Project RBFR132WSM). References [1] A. Rawal, B.J. Smith, G.L. Athens, C.L. Edwards, L. Roberts, V. Gupta, and B.F. Chmelka J. Am. Chem. Soc. 132, 7321-7337 (2010) [2] F. Barberon, J.P. Korb, D. Petit, V. Morin, E. Bermejo Phys. Rev. Lett. 90, 116103-1-116103-4 (2003) [3] C. Roosz, S. Grangeon, P. Blanc, V. Montouillout, B. Lothenbach, P. Henocq, E. Giffaut, P. Vieillard, and S. Gaboreau Cement Concrete Res. 73, 228-237 (2015) [4] S.A. Walling, H. Kinoshita, S.A. Bernal, N.C. Colliera, and J.L. Provis Dalton Trans. 44, 8126-8137 (2015)
MULTI-SCALE STRUCTURAL INVESTIGATION OF INNOVATIVE MgO/CaO BASED CEMENTS
L Calucci;M Geppi;S Borsacchi
2015
Abstract
Eco-compatible MgO-based cements represent one of the most promising alternative to the traditional CaO-based ones, allowing a strong reduction of CO2 emissions involved in the production process. Indeed, the hydration of reactive periclase (MgO) in the presence of a source of silica gives rise to a binder phase, known as Magnesium Silicate Hydrate (MSH), analogous to the CSH (Calcium Silicate Hydrate) phase present in traditional cements. However the mechanical properties achieved so far are still inferior to those of CaO-based cements, and the research for new formulations with improved performances is necessary in order for a diffusion on industrial scale to take place. To this aim precious information can arise from the study of the multi-scale structural properties of these systems, as well as of the formation process of the binder phases, whose nature is still not well understood. This work presents a solid-state NMR (SSNMR) and relaxometric study of eco- compatible cements obtained by hydration of mixtures of MgO, traditional Portland cement and silica fumes. Both SSNMR and relaxometry already proved to be very powerful techniques for the study of cements [1-4]. Here, the nature and the structure of the spieces formed at different times of hydration were investigated on freeze-dried samples by means a multinuclear SSNMR aprroach, based on the observation of 1H, 29Si and 27Al. In particular, mono- and bi-dimensional 29Si experiments allowed to identify the presence of both CSH and MSH domains, and to study their properties and relative composition also as a function of hydration time. On the other hand, the measurement of 1H T1"s by means of Fast Field Cycling (FFC) relaxometry was used to obtain information on the status of water in the cement pastes, as well as on the evolution of the porous structure. This work was financially supported by MIUR (FIR2013 Project RBFR132WSM). References [1] A. Rawal, B.J. Smith, G.L. Athens, C.L. Edwards, L. Roberts, V. Gupta, and B.F. Chmelka J. Am. Chem. Soc. 132, 7321-7337 (2010) [2] F. Barberon, J.P. Korb, D. Petit, V. Morin, E. Bermejo Phys. Rev. Lett. 90, 116103-1-116103-4 (2003) [3] C. Roosz, S. Grangeon, P. Blanc, V. Montouillout, B. Lothenbach, P. Henocq, E. Giffaut, P. Vieillard, and S. Gaboreau Cement Concrete Res. 73, 228-237 (2015) [4] S.A. Walling, H. Kinoshita, S.A. Bernal, N.C. Colliera, and J.L. Provis Dalton Trans. 44, 8126-8137 (2015)I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
