Effect of nano MgAl-NO3 and MgAl-HCOO layered double hydroxides on early hydration kinetics and chloride binding in cement paste

Enhancing the durability of cement paste through the incorporation of appropriate additives represents a promising approach to improving the sustainability of cement production. In particular, the inclusion of layered double hydroxides (LDHs) in cementitious systems has been shown to enhance their corrosion resistance to Cl− and SO42− anions. However, LDHs, due to their anionic exchange capability, significantly affect the initial kinetics. In this work, two types of nanometric LDHs, MgAl-NO3 and MgAl-HCOO, were added to cement paste in different proportions (1, 3, and 5 wt% of the binder) to investigate early hydration kinetics and to quantitatively evaluate the effect of anion exchange on cement hydration products and clinker phase consumption by in situ X-Ray diffraction (XRD). In addition, the chloride binding capacity of selected LDHs was tested by means of XRD and thermogravimetric analyses. The results show that, in the early hydration stage, LDHs can capture SO42⁻ ions, thereby inhibiting early ettringite precipitation and enhancing the production of hydration products (portlandite) after the first 24 h. LDHs containing formate decrease the availability of Ca2⁺ in solution, thereby limiting the precipitation of calcium-rich phases, slowing down the dissolution of alite (C3S). Geochemical modelling supports these findings. Finally, both MgAl-NO3 and MgAl-HCOO improved the chloride binding capacity of the cement paste due to their excellent anion exchangeability.