Ultrasonication effect of silica fume and colloidal nanosilica on cement pastes

ABSTRACT

The high performance cementitious materials can be produced using silica fume (SF) and nanosilica (NS). Due to the small size of their particles, these materials became agglomerate, reducing their reactivity potentials. Some researchers have studied methods of dispersing these particles as ultrasonicators and rotational mixers, but studies on these materials are still needed, especially on the effect of colloidal nanosilica ultrasonication. Thus, this article aimed to evaluate the effect of ultrasonication (use of high energy ultrasound) of silica fume and colloidal nanosilica on cement pastes. Five pastes were investigated, a reference with 100% Portland cement CP V-ARI, and other four replacing 2% and 10% of the Portland cement by colloidal nanosilica and silica fume, respectively, in their natural state and after ultrasonication. The tests of compressive strength, thermogravimetry analysis (TGA), infrared spectroscopy and mercury intrusion porosimetry (MIP) were performed on pastes. The results showed that the use of colloidal NS in substitution of Portland cement increased C-S-H production, pore refinement and compressive strength of the pastes, however the use of SF in its natural state increased the pore size and decreased the mechanical performance of the pastes due to the agglomeration of its particles. By ultrasonication of SF, there was higher C-S-H production, pore refinement and compressive strength when compared to SF paste without the ultrasonication process, proving the effectiveness of this method for the dispersion of these particles. Nevertheless, ultrasonication of colloidal nanosilica did not result in significant differences in the microstructure and mechanical performance of the pastes.

Keywords
Dispersion; compressive strength; thermogravimetric analysis (TGA); porosimetry (MIP)