title: Structural characterization of magnesium silicate hydrate: towards the design of eco-sustainable cements.
abstract: Magnesium-based cement is one of the most interesting eco-sustainable alternatives to standard cementitious binders. The reasons for the interest towards this material are twofold: (i) its production process, using magnesium silicates, brine or seawater, dramatically reduces CO2 emissions with respect to Portland cement production, and (ii) it is very well suited to applications in radioactive waste encapsulation. In spite of its potential, assessment of the structural properties of its binder phase (magnesium silicate hydrate or M-S-H) is far from complete, especially because of its amorphous character. In this work, a comprehensive structural characterization of M-S-H was obtained using a multi-technique approach, including a detailed solid-state NMR investigation and, in particular, for the first time, quantitative (29)Si solid-state NMR data. M-S-H was prepared through room-temperature hydration of highly reactive MgO and silica fume and was monitored for 28 days. The results clearly evidenced the presence in M-S-H of "chrysotile-like" and "talc-like" sub-nanometric domains, which are approximately in a 1 : 1 molar ratio after long-time hydration. Both these kinds of domains have a high degree of condensation, corresponding to the presence of a small amount of silanols in the tetrahedral sheets. The decisive improvement obtained in the knowledge of M-S-H structure paves the way for tailoring the macroscopic properties of eco-sustainable cements by means of a bottom-up approach.
authors.affiliation: Department of Chemistry "Ugo Schiff" & CSGI, University of Florence, Sesto Fiorentino 50019, Florence, Italy. francesca.ridi@unifi.it.
authors.forename: M
authors.initials: M
authors.lastname: Tonelli
authors.affiliation: Istituto di Chimica dei Composti OrganoMetallici, Consiglio Nazionale delle Ricerche - CNR U.O.S. di Pisa, Pisa 56124, Italy. silvia.borsacchi@pi.iccom.cnr.it.
authors.forename: F
authors.initials: F
authors.lastname: Martini
authors.affiliation: Istituto di Chimica dei Composti OrganoMetallici, Consiglio Nazionale delle Ricerche - CNR U.O.S. di Pisa, Pisa 56124, Italy. silvia.borsacchi@pi.iccom.cnr.it.
authors.forename: L
authors.initials: L
authors.lastname: Calucci
authors.affiliation: Department of Chemistry "Ugo Schiff" & CSGI, University of Florence, Sesto Fiorentino 50019, Florence, Italy. francesca.ridi@unifi.it.
authors.forename: E
authors.initials: E
authors.lastname: Fratini
authors.affiliation: Department of Chemistry and Industrial Chemistry, University of Pisa, Pisa 56124, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Geppi
authors.affiliation: Department of Chemistry "Ugo Schiff" & CSGI, University of Florence, Sesto Fiorentino 50019, Florence, Italy. francesca.ridi@unifi.it.
authors.forename: F
authors.initials: F
authors.lastname: Ridi
authors.affiliation: Istituto di Chimica dei Composti OrganoMetallici, Consiglio Nazionale delle Ricerche - CNR U.O.S. di Pisa, Pisa 56124, Italy. silvia.borsacchi@pi.iccom.cnr.it.
authors.forename: S
authors.initials: S
authors.lastname: Borsacchi
authors.affiliation: Department of Chemistry "Ugo Schiff" & CSGI, University of Florence, Sesto Fiorentino 50019, Florence, Italy. francesca.ridi@unifi.it.
authors.forename: P
authors.initials: P
authors.lastname: Baglioni