(257a) Synthesis and Characterization of Nano-Ettringite for Nano-Engineering of Cementitious Composites

The use of nanomaterials in modifying cementitious binders has gained tremendous attention in recent decades. Various nano-sized anhydrous inorganics, e.g. nano-silica, nano-titania, nano-limestone, and nano-clay etc., have been studied and shown to impact positive effects on both the fresh and mature state properties of cement composites. To the best of our knowledge, no studies have been conducted to investigate the use of nano-sized cement hydration products (e.g., nano-ettringite) in Portland cement or calcium sulfoaluminate binders. Ettringite is one of the first phases produced during the hydration of Portland cement, and it is the principal phase in hydrated calcium sulfoaluminate cements. It plays a vital role in controlling the early-age property of cementitious systems. Controlling the rate of ettringite precipitation can allow builders to regulate the hydration and physico-mechanical properties of cementitious binders according to their requirements.

This study aims at the synthesis of nano-sized ettringite for use in nano-engineering of concrete binders. A chemical precipitation method was studied with focus to understand the effects of various process parameters like addition of surfactants, stirring speed, and reaction time on the nucleation and growth of ettringite nanocrystals. Synthesized ettringites were characterized by dynamic light scattering (DLS), powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and infrared spectroscopy techniques. Results show that ettringite nano-rods readily nucleate and start growing within the first 30 minutes of mixing stoichiometry proportions of calcium hydroxide and aluminum sulfate precursor solutions. Although, the addition of surfactant and stirring parameters were observed to influence the size of synthesized ettringite nanoparticles, the reaction time clearly plays a dominant role in determining the size of the synthesized ettringite.