The development of cement formulations alternative to the traditional Portland (CaO-based) cement is currently object of great interest in the field of building materials research both with the aim of reducing the environmental impact associated with the CO2 emissions [1] and in view of solving specific needs required for particular applications, such as that of radioactive waste encapsulation [2-4]. In this field, low-pH cements are researched in order to overcome the problems related to the high alkalinity of Portland cement pore solution, which can cause the corrosion of the radioactive wastes and the degradation of the clayey materials used for waste storage [3,4]. One of the most promising alternative is rapresented by MgO-based cements, which, beside developing pH values lower than those typical of Portland cements [5], also respond to the eco-suistainability requirement of reducing CO2 emissions. Indeed, abundant natural sources, as for example the magnesium silicates present in the Earth Crust, can be employed to derive reactive periclase (MgO), used as starting material in these formulations [5]. MgO-based cements can be obtained from the hydration of MgO in the presence of silica sources, which leads to the formation of a binder phase called Magnesium Silicate Hydrate (MSH) analogous to the binder phase Calcium Silicate Hydrate (CSH), formed in CaO-based cements. Even if the interest in MgO-based cements is growing, as demonstrated by the large number of papers recently appeared in the literature [3-8], a full comprehension of their properties, such as 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, whose mechanical properties are still inferior to those of traditional Portland cements. In this work novel MgO-based cements obtained by hydration of a 1:1 molar mixture of MgO and silica fumes (MgO/SiO2) and mixed-formulations containing different amounts of MgO/SiO2 and Portland cement were developed. The muti-scale structural properties and hydration kinetcs of the prepared systems were investigated in detail by means of solid-state NMR spectroscopy (SSNMR) and Fast Field Cycling (FFC) relaxometry, which already proved to be very powerful for the study of cements [9-11], with the support of complementary techniques such as X-Ray Diffraction (XRD), thermogravimetry (TGA), IR spectroscopy, Scanning Electron Microscopy (SEM) and calorimetric techniques. The nature and the structure at the sub-nanometric scale of the formed hydrated phases, as well as their formation kinetics, were investigated on samples liophilized at different times of hydration by means of high-resolution SSNMR experiments for the observation of 1H, 29Si and 27Al nuclei. In particular, mono- and bi-dimensional 29Si MAS experiments allowed the different silicon sites, Q1, Q2 and Q3, characterized by different connectivity to -OSi, -OH, -OMg or -OCa groups, to be identified and quantified. In the case of mixed systems, it was also possible to distinguish between MSH and CSH domains, and to study their properties and relative amounts as a function of composition and hydration times.The state of water in the pastes and the evolution of the porous structure with hydration time, a property that is strongly related to the final mechanical properties of a cementitious material, were investigated directly on the cement pastes by means of 1H T1 Fast Field Cycling relaxometry and the measurements of 1H T2 relaxation times at low magnetic fields (proton Larmor frequency of 20 MHz) [10]. This work was financially supported by MIUR (FIR2013 Project RBFR132WSM). References [1] R. J. Flatt, N. Roussel, C. R. Cheeseman, J. Eur. Ceram. Soc. 32 (2012) 2787-2798. [2] A. Dauzeres, P. Le Bescop, P. Sardini, C. Cau Dit Coumes, Cem. Concr. Res. 40 (2010) 1327-1340. [3] A. Dauzeres, G. Achiedo, D. Nied, E. Bernard, S. Alahrache, B. Lothenbach, Cem. Concr. Res. 79 (2016) 137-150. [4] S. A. Walling, H. Kinoshita, S. A. Bernal, N. C. Collier, J. L. Provis, Dalton Trans. 44 (2015) 8126-8137. [5] M. Tonelli, F. Martini, L. Calucci, E. Fratini, M. Geppi, F. Ridi, S. Borsacchi, P. Baglioni, Dalton Trans 45 (2016) 3294-3304. [6] B. Lothenbach, D. Nied, E. L'Hôpital, G. Achiedo, A. Dauzères, Cem. Concr. Res. 77 (2015) 60-68. [7] C. Roosz, S. Grangeon, P. Blanc, V. Montouillout, B. Lothenbach, P. Henocq, E. Giffaut, P. Vieillard, S. Gaboreau, Cem. Concr. Res. 73 (2015) 228-237. [8] D. Nied, K. Enemark-Rasmussen, E. L'Hopital, J. Skibsted, B. Lothenbach, Cem. Concr. Res. 79 (2016) 323-332. [9] A. Rawal, B.J. Smith, G.L. Athens, C.L. Edwards, L. Roberts, V. Gupta, B.F. Chmelka, J. Am. Chem. Soc. 132 (2010) 7321-7337. [10] V. Bortolotti, L. Brizi, R. J. S. Brown, P. Fantazzini, M. Mariani, Langmuir 30 (2014) 10871-10877. [11] F. Barberon, J.P. Korb, D. Petit, V. Morin, E. Bermejo, Phys. Rev. Lett., 90 (2003) 116103-1-116103-4.
A multidisciplinary approach for the multi-scale structural study of eco-compatible MgO/CaO-based cements
S Borsacchi;F Martini;M Geppi;L Calucci
2016
Abstract
The development of cement formulations alternative to the traditional Portland (CaO-based) cement is currently object of great interest in the field of building materials research both with the aim of reducing the environmental impact associated with the CO2 emissions [1] and in view of solving specific needs required for particular applications, such as that of radioactive waste encapsulation [2-4]. In this field, low-pH cements are researched in order to overcome the problems related to the high alkalinity of Portland cement pore solution, which can cause the corrosion of the radioactive wastes and the degradation of the clayey materials used for waste storage [3,4]. One of the most promising alternative is rapresented by MgO-based cements, which, beside developing pH values lower than those typical of Portland cements [5], also respond to the eco-suistainability requirement of reducing CO2 emissions. Indeed, abundant natural sources, as for example the magnesium silicates present in the Earth Crust, can be employed to derive reactive periclase (MgO), used as starting material in these formulations [5]. MgO-based cements can be obtained from the hydration of MgO in the presence of silica sources, which leads to the formation of a binder phase called Magnesium Silicate Hydrate (MSH) analogous to the binder phase Calcium Silicate Hydrate (CSH), formed in CaO-based cements. Even if the interest in MgO-based cements is growing, as demonstrated by the large number of papers recently appeared in the literature [3-8], a full comprehension of their properties, such as 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, whose mechanical properties are still inferior to those of traditional Portland cements. In this work novel MgO-based cements obtained by hydration of a 1:1 molar mixture of MgO and silica fumes (MgO/SiO2) and mixed-formulations containing different amounts of MgO/SiO2 and Portland cement were developed. The muti-scale structural properties and hydration kinetcs of the prepared systems were investigated in detail by means of solid-state NMR spectroscopy (SSNMR) and Fast Field Cycling (FFC) relaxometry, which already proved to be very powerful for the study of cements [9-11], with the support of complementary techniques such as X-Ray Diffraction (XRD), thermogravimetry (TGA), IR spectroscopy, Scanning Electron Microscopy (SEM) and calorimetric techniques. The nature and the structure at the sub-nanometric scale of the formed hydrated phases, as well as their formation kinetics, were investigated on samples liophilized at different times of hydration by means of high-resolution SSNMR experiments for the observation of 1H, 29Si and 27Al nuclei. In particular, mono- and bi-dimensional 29Si MAS experiments allowed the different silicon sites, Q1, Q2 and Q3, characterized by different connectivity to -OSi, -OH, -OMg or -OCa groups, to be identified and quantified. In the case of mixed systems, it was also possible to distinguish between MSH and CSH domains, and to study their properties and relative amounts as a function of composition and hydration times.The state of water in the pastes and the evolution of the porous structure with hydration time, a property that is strongly related to the final mechanical properties of a cementitious material, were investigated directly on the cement pastes by means of 1H T1 Fast Field Cycling relaxometry and the measurements of 1H T2 relaxation times at low magnetic fields (proton Larmor frequency of 20 MHz) [10]. This work was financially supported by MIUR (FIR2013 Project RBFR132WSM). References [1] R. J. Flatt, N. Roussel, C. R. Cheeseman, J. Eur. Ceram. Soc. 32 (2012) 2787-2798. [2] A. Dauzeres, P. Le Bescop, P. Sardini, C. Cau Dit Coumes, Cem. Concr. Res. 40 (2010) 1327-1340. [3] A. Dauzeres, G. Achiedo, D. Nied, E. Bernard, S. Alahrache, B. Lothenbach, Cem. Concr. Res. 79 (2016) 137-150. [4] S. A. Walling, H. Kinoshita, S. A. Bernal, N. C. Collier, J. L. Provis, Dalton Trans. 44 (2015) 8126-8137. [5] M. Tonelli, F. Martini, L. Calucci, E. Fratini, M. Geppi, F. Ridi, S. Borsacchi, P. Baglioni, Dalton Trans 45 (2016) 3294-3304. [6] B. Lothenbach, D. Nied, E. L'Hôpital, G. Achiedo, A. Dauzères, Cem. Concr. Res. 77 (2015) 60-68. [7] C. Roosz, S. Grangeon, P. Blanc, V. Montouillout, B. Lothenbach, P. Henocq, E. Giffaut, P. Vieillard, S. Gaboreau, Cem. Concr. Res. 73 (2015) 228-237. [8] D. Nied, K. Enemark-Rasmussen, E. L'Hopital, J. Skibsted, B. Lothenbach, Cem. Concr. Res. 79 (2016) 323-332. [9] A. Rawal, B.J. Smith, G.L. Athens, C.L. Edwards, L. Roberts, V. Gupta, B.F. Chmelka, J. Am. Chem. Soc. 132 (2010) 7321-7337. [10] V. Bortolotti, L. Brizi, R. J. S. Brown, P. Fantazzini, M. Mariani, Langmuir 30 (2014) 10871-10877. [11] F. Barberon, J.P. Korb, D. Petit, V. Morin, E. Bermejo, Phys. Rev. Lett., 90 (2003) 116103-1-116103-4.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
