Relevance of layered double hydroxides and their derived mixed oxides nanoparticles in the crystallization of cement hydration phases: A time-resolved study of the kinetic mechanism

Layered double hydroxides (LDH) are multifunctional additives capable of improving the microstructure of cementitious matrices. Thermal decomposition of LDH at 400 °C leads to the formation of nanocrystalline mixed oxides (MO), which can regenerate the layered structure upon contact with water, a phenomenon known as the memory effect. This regeneration accelerates cement paste consolidation, highlighting the potential of these materials for 3D printing applications. In this paper, time-resolved synchrotron radiation techniques (X-ray absorption spectroscopy and X-ray diffraction) were used to elucidate the mechanism of LDH structural regeneration in conjunction with the formation of cement hydration phases. The acceleration of the hydration process was confirmed by increased ettringite (AFt) formation, with a more pronounced effect for samples containing MO. This behavior indicates that the combination of the memory effect and the high specific surface area (SSA ≈ 37 m 2 g- 1 ) of the MO particles favors heterogeneous nucleation, contributing to the crystallization kinetics of AFt. The results reveal a direct correlation between the presence of nanoparticles and the structural and phase transformations during cement hydration. • In-situ studies carried out to elucidate the mechanism of structural regeneration of LDH in the cementitious environment. • The contribution of the memory effect and the surface area of additive in the cement hydration reactions was evaluated. • Time-resolved XAS and XRD results showed MO particles contribute to the formation of AFt phase and dissolution of gypsum. • EXAFS results allowed us to simultaneously detail the crystallization process of both LDH particles and cement reactions. • It was possible to correlate the effect of LDH and MO nanoparticles on the rheological behavior of cement.