Improvements in the sustainability and durability of building materials depend on understanding interfacial properties of various mineral phases at the nanometer scale. Such understanding is often a challenge for current instrumentation, which is why we introduce a force field for atomistic simulations that provides excellent agreement with available experimental data, including X-ray structures, cleavage energies, elastic moduli, and IR spectra (INTERFACE force field). Using this model and measurements, we analyze nanoscale interfaces of tricalcium silicate (C3S), the major constituent of cement clinker. An extensive set of possible cleavage planes of the non-hydrated mineral shows cleavage energies in a range of 1300 to 1600 mJ/m2 consistent with the observation of faceted crystallites with an aspect ratio near one. Using pure and hydroxylated surface models that represent the first step in the hydration reaction, we examined the adsorption mechanism of several organic amines and alcohols at different temperatures. Strong attraction between -20 and -50 kcal/mol is found as a result of complexation of superficial calcium ions, electrostatic interactions, and hydrogen bonds on the ionic surface. Agglomeration of cleaved C3S surfaces in the absence of organic molecules was found to recover less than half the original cleavage energy (~450 mJ/m2) associated with reduced Coulomb interactions between reconstructed surfaces. Additional adsorption of organic compounds below monolayer coverage reduced the attraction between even surfaces to less than 5% of the original cleavage energy (~50 mJ/m2) related to their action as spacers between cleaved surfaces and mitigation of local electric fields. Computed agglomeration energies for a series of adsorbed organic compounds correlate with the reduction in surface forces in the form of measured grinding efficiencies.

Nanoscale interfaces of tricalcium silicate and organic dispersants in cement: Agglomeration and initial hydration

246th National Meeting (2013)

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