Ettringite Strengthening at High Pressures Induced by the Densification of the Hydrogen Bond Network

Abstract

Ettringite is a rare mineral with high-water content, more than half of its weight, and a relevant secondary product in Portland cement. Using density functional theory, we simulate the crystal structure and properties of ettringite under pressure. Our calculations predict a change in slope for all the lattice parameters versus pressure at about 2.5 GPa. Above such pressure, the elastic properties show a drastic increase of nearly 80% in the bulk modulus. This finding is explained in terms of a concurrent amorphization and densification of the hydrogen bond network. At low pressures, ettringite can be compressed substantially without significant repulsion in the hydrogen bond network. At high pressures, the hydrogen bonds become stiff, and their contribution to the total repulsion is then important. These changes are also supported by the evolution on the electronic density of ettringite with pressure.

Mechanical properties of ettringite and thaumasite—DFT and experimental study

“…The experimental elastic constants of ettringite obtained by Brillouin spectroscopy were discussed in detail in the work by Speziale et al [4]. Our DFTcalculated elastic constants and corresponding moduli are presented in Table 2 together with the previously published data of ettringite obtained by using empirical force fields, particularly ReaxFF [17,18], and at the DFT level [39]. Our calculated elastic constants are in a very good agreement with the experimental ones (see Fig.…”

“…4). Our DFT calculated values of K, G, E and ν show a slightly better agreement with the experiment [4] than those obtained by Manzano et al (2012) [39], who also used the PBE functional in the DFT calculations. The difference between our results and those by Manzano et al can be attributed to the different basis sets used in the two studies.…”

“…The difference between our results and those by Manzano et al can be attributed to the different basis sets used in the two studies. In our calculations we applied the delocalized plane wave basis set with high energy cut-off of 600 eV, which allows very high accuracy, whereas in the work by Manzano et al [39] the localized DZP (double zeta polarization) atomic basis set was used [40].…”

Pressure‐induced anomalous behavior of thaumasite crystal

“…The columnar component of [Ca 3 Si(OH) 6 ·(H 2 O) 12 ] 4+ became significantly incompressible after 2.32 GPa, eventually leading to the nonlinear pressure behavior of the unit cell volume. This type of complicated bi‐linear pressure response has been reported in ettringite and hemicarboaluminate, and it has been explained by the layer in the crystals and the densification of the hydrogen bond network in the layer of ettringite . In the case of thaumasite, a similar nonlinear pressure response was observed, but the mechanism behind the response might have been more complicated, since the nonlinear behavior of the lattice parameters occurred at different pressure levels.…”

Advances in understanding hydration of Portland cement

“…First-principles calculations were used to study tobermorite [139], jennite, [137] tricalcium aluminate [140], ettringite [141], and monocarboaluminate hydrates [136].…”