CNR ExploRA

Poster, 2016, ENG

Traditional Portland cement and MgO-based cement: a promising combination?

Tonelli, M., Ridi, F., Borsacchi, S., Martini, F., Calucci, L., Fratini, E., Geppi, M., Baglioni, P.

ICCOM-CNR; Università di Pisa; Università di Firenze

Cement formulations based on reactive periclase (MgO) [1,2] constitute a promising emerging technology toward eco-sustainable binders, with reduced CO2 emissions as compared to the traditional CaO-based cements, which have been demonstrated useful in the field of radioactive waste containment. [3] The aim of the present study was the investigation of the hydration reaction and on the microstructure development of pastes prepared by mixing Portland cement and MgO/SiO2 blend. Different percentages of CaO- and MgO-based binders were evaluated to explore the possibility of preparing pastes that could in principle combine the optimal mechanical properties of calcium based cement with the ecological features of MgO-based cement. The hydration kinetics of the mixtures were investigated by means of Differential Scanning Calorimetry. Concurrently, the pastes were characterized by means of a multi-scale approach and the formation of hydrated phases was studied by Thermogravimetric Analysis, Fourier Transform IR spectroscopy and X-ray Diffraction. The structural properties of all samples were investigated by solid state 29Si-NMR. Finally, the morphology of the pastes has been studied by means of Scanning Electron Microscopy. The results showed that in the mixed pastes both calcium silicate hydrate (C-S-H) and M-S-H binder gel phases form, but, as evidenced in Fig.1, their domains remain segregate in different regions. Moreover, interestingly, the kinetics of hydration in the mixed samples is dominated by MgO/SiO2 hydration in the first period, while the diffusional stage is mostly dependent on the Portland cement presence. Acknowledgements: CSGI and FIR2013 (Project RBFR132WSM) for financial support. References [1] Lothenbach, B., et al., Magnesium and calcium silicate hydrates, Cement and Concrete Research, 2015. 77: p 60-68 [2] Chiang, W.-S., et al., Multiscale structure of calcium and magnesium silicate hydrate gels, Journal of Material Chemistry A, 2014. 2: p 12991-12998 [3] 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 (17), 8126- 8137.

4th International Workshop on Mechanisms and Modelling of waste/cement interactions, Murten, Switzerland, 22-25/05/2016