1H fast field-cycling (FFC) NMR relaxometry was applied for the first time to monitor the state of water during the hydration reaction of MgO and silica that leads to the formation of magnesium silicate hydrate (M-S-H), the binder phase of innovative cements with promising applications in the containment of radioactive waste. To this aim, water proton longitudinal relaxation rates (R1= 1/T1) were measured in the Larmor frequency range between 10 kHz and 30 MHz at different hydration times ranging from 0.5 h to ∼4 months. The obtained R1versus frequency (NMRD) curves were analyzed considering fast exchange of water molecules between a hydration layer, where dynamics is affected by interactions with the surface of solids present in the reacting mixture, and a bulk phase. For the hydration layer, water molecules undergoing fast local molecular dynamics on the surface gave a constant contribution to R1throughout the investigated frequency range. On the contrary, water molecules undergoing slow dynamics on the surface gave a dispersion of R1and their motions were modeled as "reorientations mediated by translational displacements" in the length scale of a particle and of a cluster of particles, where particles are silica nanoparticles and/or M-S-H globules that form during hydration. The model parameters reflected the different typical steps of cement hydration, showing smooth trends in the induction and diffusion steps and sudden changes during the nucleation and growth period in which water is consumed and M-S-H forms.

Hydration of MgO-Based Cement: Water Dynamics by1H Fast Field-Cycling NMR Relaxometry

Martini, Francesca
Primo
;
Geppi, Marco;
2017

Abstract

1H fast field-cycling (FFC) NMR relaxometry was applied for the first time to monitor the state of water during the hydration reaction of MgO and silica that leads to the formation of magnesium silicate hydrate (M-S-H), the binder phase of innovative cements with promising applications in the containment of radioactive waste. To this aim, water proton longitudinal relaxation rates (R1= 1/T1) were measured in the Larmor frequency range between 10 kHz and 30 MHz at different hydration times ranging from 0.5 h to ∼4 months. The obtained R1versus frequency (NMRD) curves were analyzed considering fast exchange of water molecules between a hydration layer, where dynamics is affected by interactions with the surface of solids present in the reacting mixture, and a bulk phase. For the hydration layer, water molecules undergoing fast local molecular dynamics on the surface gave a constant contribution to R1throughout the investigated frequency range. On the contrary, water molecules undergoing slow dynamics on the surface gave a dispersion of R1and their motions were modeled as "reorientations mediated by translational displacements" in the length scale of a particle and of a cluster of particles, where particles are silica nanoparticles and/or M-S-H globules that form during hydration. The model parameters reflected the different typical steps of cement hydration, showing smooth trends in the induction and diffusion steps and sudden changes during the nucleation and growth period in which water is consumed and M-S-H forms.
Martini, Francesca; Borsacchi, Silvia; Geppi, Marco; Forte, Claudia; Calucci, Lucia
File in questo prodotto:
File Dimensione Formato  
2017-JPCC121-26851.pdf

accesso aperto

Descrizione: articolo principale
Tipologia: Versione finale editoriale
Licenza: Tutti i diritti riservati (All rights reserved)
Dimensione 2.02 MB
Formato Adobe PDF
2.02 MB Adobe PDF Visualizza/Apri

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11568/892947
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 8
  • ???jsp.display-item.citation.isi??? 8
social impact