Influence of SiO2@CaAl-LDH core-shell nanocomposite on rheology and hydration of cement

Abstract

Nano-SiO2@ Layered double hydroxide (LDH) core-shell nanocomposite shows a promising application as high-efficiency chloride adsorbent in cement-based materials. However, its effect on rheology and hydration of cement is not yet known. In this study, the SiO2@CaAl- LDH core-shell nanocomposite by growing the LDH on nano-SiO2 surface was firstly created using in-situ co-precipitation method. The influence of as-synthesized nanocomposite on the rheology and hydration of cement was systematacially researched through contrasting experiments. Besides, microstructures of SiO2@LDH and its cement paste were characterized. The results show that the LDH with petal-like shape on the nano-SiO2 surface exhibits a higher specific area than pure nano-SiO2 and LDH alone. The addition of SiO2@CaAl-LDH core-shell material significantly shortens the initial and final setting time of cement and increases cement hydration heat generation rate and the total exothermic amount for 72 h. Contrary to the mixture of LDH, the additions of nano-SiO2 and SiO2@LDH increases the yield stress and plastic viscosity of cement paste. Compared to the additions of LDH and SiO2, the addition of SiO2@LDH more significantly enhances the strength of cement, of which the highest increasing level reaches 66 % at the early age of 1 d. In addition, SiO2@LDH exhibits the best refinement effect on the pore structure of cement because of the synergetic effect between the LDH and nano-SiO2.