Influence of colloidal nanosilica on ultrafine cement hydration: Physicochemical and microstructural characterization

The influence of colloidal nanosilica addition on an ultrafine cement have been studied in terms of physicomechanical and microstructure properties. Primarily, experiments were carried out to produce an ultrafine cement (UF) with a Blaine specific surface area greater than 10.500 cm2/g. Nanosilica was added in amounts of 2% and 4% on UF cement basis. All cements were tested for initial and final setting times, consistency of standard paste, flow of normal mortar and compressive strengths after 1, 2, 7 and 28 days. The hydration products were determined by X-ray diffraction analysis and by Fourier transform infrared spectroscopy, at 1, 2, 7 and 28 days. The microstructure of the hardened cement pastes and their morphological characteristics were examined by scanning electron microscopy, whereas porosity and pore size distribution were evaluated by mercury intrusion porosimetry.

► Colloidal nanosilica addition in ultrafine cement (≈10.700 cm2/g) did not lead to immediate mechanical gain.
► At 28 days an increase of 11 MPa was observed.
► More packed and refined microstructure was observed.
► Total porosity and average pore diameter were decreased leading to a denser microstructure.