Microstructure evolution of hydrated cement pastes

Abstract

We propose an original method based on both proton nuclear magnetic relaxation dispersion and high-resolution NMR spectra to investigate the microstructure of synthesized Ca3SiO5-hydrated cement paste. This method allows a clear assessment of the local proton chemical sites as well as the determination of dynamical information of moving proton species in pores. We show also how the microstructure evolves during and after completion of hydration in a range of length scales between 2 and 500 nm. In particular, we show how the pore size distribution of the cement paste reaches progressively a power-law characteristic of a surface-fractal distribution with a dimension Df = 2.6, which takes into account the hierarchical order in the material. Last, we study how this pore size distribution is modified during setting by varying either the water-to-cement ratio or addition of ultrafine particles. This shows that our method could be relevant to relate the mechanical properties to the microstructure of the material. This proposed NMR method is general enough for the characterization of microstructure of any porous media with reactive surface involving water confinement.

Model for the interpretation of nuclear magnetic resonance relaxometry of hydrated porous silicate materials

“…The water surface residency time is found to be about 2-5 orders of magnitude shorter than values that consistently emerge when the SL models of Korb and co-workers are fitted to experimental NMR relaxation rate data [2][3][4][5][6][7][8][9]. Furthermore, no MD simulation reveals large-scale surface diffusion of water prior to desorption.…”

“…Yet, a bulk water molecule diffuses a distance of about 0.4 µm in 13 µs, a distance which is much larger than typical pore thickness in cementitious materials where, despite uncertainty as to the morphology of mature C-S-H, most pores have sizes ranging from about 2 nm to 50 nm [7,13,14]. Furthermore, the fast-exchange model has limited application if τ s ≈ 10 µs.…”

Multi-scales nuclear spin relaxation of liquids in porous media

“…NMRD were also concerned with probing directly the dynamics of proton species at the pore surfaces and specific surface areas of cement-based materials [16]. Similar methods gave information about the microstructure time-evolution of hydrated cement pastes [17,18]. More recently, low field two-dimensional NMR relaxation studies: T 1 -T 2 [19] and T 2 -T 2 [20] evidence exchange of water between the connected micropores of white cement.…”

Nano-optimized Construction Materials by Nano-seeding and Crystallization Control

“…It also enables to study the pore size distribution over time. For instance, the fractal character of cement paste was clearly demonstrated with the power-law followed by the pore size distribution [Plassais, 2005]. New NMR techniques are certainly a high-performing tool in order to provide access to hydration processes at nano scale also in presence of admixtures [Rottstegge 2006].…”