A General and Scalable Formulation of Pure CaAl-Layered Double Hydroxide via an Organic/Water Solution Route

Abstract

CaAl-layered double hydroxide (CaAl-LDH) has recently been proposed as potential concrete hardening accelerators, because of the similarity in the AFm phase (a family of hydrated calcium aluminate phases) that occurs in hydrated cement. The applications of the promising materials require synthesis routes to be capable of producing large-scale, byproduct-free, and easy-to-handle CaAl-LDH. Herein, we report a general and scalable synthesis of pure CaAl-LDH via an organic/water solution. The possibility of the formation of CaAl-LDH is addressed in terms of the prevention of ethanol from the generation of CaCO3 byproduct. The morphology and crystallinity of CaAl-LDH are tuned by varying different pH value, ethanol/water volumetric content, crystallization time, and temperature. A proper synthesis condition (for example, an ethanol/water volume ratio of 4:1, a pH value of 10.5–11.5, an aging time of 24 h, and a crystallization temperature of 70 °C) are optimized, and further readily scaled up, by a factor of up to 20, with respect to the initial starting materials. Our results of pure CaAl-LDH in different organic/water solutions may open up a means to produce promising concrete hardening accelerators in large amounts.