Role of layered double hydroxides in setting, hydration degree, microstructure and compressive strength of cement paste

The effects of calcined Mg-Al-CO3 LDH on setting time, hydration degree, microstructure as well as compressive strength of cement pastes were explored. Furthermore, the role of LDH in cement system has been revealed by characterizing the component and structural changes of LDH. The experimental results show that LDH is physically and chemically active in cement paste. 1-3% calcined LDH accelerates the hardening process and improve the setting of cement to some extent. LDH incorporation leads to the slight increasing in non evaporable water content, and the increasing ratio is less than 1% at each curing age. The hydration heat for LDH blended specimens are less than that of control cement because of the dilution effect. LDH accelerates the hydration reaction to some extent even though it is not a dramatic change. LDH has refine effect on pore structure of cement paste and the addition level of LDH should be no less than 2%. Cement pastes with LDH exhibits increased compressive strength regardless of curing time, and the increase rate at 28 days is lower than that obtained at early ages. Fulfillment of structure regeneration of calcined LDH in cement paste environment was also been revealed.