Diana Londono-Zuluaga

Multiscale understanding of tricalcium silicate hydration reactions

Tricalcium silicate, the main constituent of Portland cement, hydrates to produce crystalline calcium hydroxide and calcium-silicate-hydrates (C-S-H) nanocrystalline gel. This hydration reaction is poorly understood at the nanoscale. The understanding of atomic arrangement in nanocrystalline phases is intrinsically complicated and this challenge is exacerbated by the presence of additional crystalline phase(s). Here, we use calorimetry and synchrotron X-ray powder diffraction to quantitatively follow tricalcium silicate hydration process: i) its dissolution, ii) portlandite crystallization and iii) C-S-H gel precipitation. Chiefly, synchrotron pair distribution function (PDF) allows to identify a defective clinotobermorite, Ca11Si9O28(OH)2.8.5H2O, as the nanocrystalline component of C-S-H. Furthermore, PDF analysis also indicates that C-S-H gel contains monolayer calcium hydroxide which is stretched as recently predicted by first principles calculations. These outcomes, plus additional laboratory characterization, yielded a multiscale picture for C-S-H nanocomposite gel which explains the observed densities and Ca/Si atomic ratios at the nano- and meso- scales.

Understanding cement hydration by pair distribution function and Rietveld analyses

There are many commercially important multiphase materials which contain amorphous/nanocrystalline phases, such as cement pastes, porcelains, or pharmaceutical compounds. The analysis of amorphous/nanocrystalline phase(s) within cement matrices that contain high amounts of crystalline phase(s) is very challenging. Synchrotron techniques can be very useful to characterize such complex samples [1]. Here, we report measurements of total scattering data quantitatively analyzed by Pair Distribution Function (PDF) and Rietveld methodologies to determine nanocrystalline and microcrystalline phase contents. Furthermore, laboratory techniques (laboratory powder diffraction using internal standard, thermal analysis, and magic-angle-spinning nuclear magnetic resonance) were also used to complement the sample characterization.