Increase of the reactivity of densified silica fume by sonication treatment

Five silica fumes from different manufacturers were subjected to ultrasonic treatment in order to decrease particle agglomeration and improve particle dispersion. The effectiveness of the sonication was observed as a reduction in particle size distribution of sonicated silica fume (SSF) compared to non-sonicated silica fume. SSF was added to Portland cement, and then the hydrated paste was analysed by thermogravimetric analyses (TGA/DTG) and scanning electron microscopy (SEM/EDX). The results were compared with those of control pastes made with untreated densified silica fume (DSF), as well as a reference cement paste of ordinary Portland cement (OPC). A maximum grade of de-agglomeration by the sonication was obtained, with a high volume of particles of diameter less than 1 μm. Images obtained by transmission electron microscopy (TEM) of the SSF showed sintered particles that could not be fragmented by the treatment. Micro-structural characterisation results showed an increase in the reactivity of the silica fume after the treatment.