Effect of nanosilica particles on the rheological and mechanical properties of cement pastes using polyhydroxyl and polycarboxylate-based superplasticizers

Abstract

This study assesses the effect of both silica nanoparticles of different sizes and different types of superplasticizers on rheological properties and 28-day compressive strength of Portland cement pastes. The experimental program comprised the utilization of 36 and 264 nm sizes nanoparticles and the superplasticizers used were polyhydroxyl and polycarboxylate-based high-range water reducers. Subsequently, the nanoparticles and superplasticizers were added to cementing pastes on which rheology tests were performed under a controlled rate (CR) mode, in order to quantify the yield stress and the plastic viscosity according to the Binghamian rheological model. As a result, it was found a saturation range between 0.8 wt % and 1.2 wt % of the used polyhydroxyl and polycarboxylate-based superplasticizers, from which the reduction of the rheological properties of the pastes was not further modified. Also, pastes using a simultaneous addition of 0.5 wt % of 36 nm-size nanosilica and 0.6 wt % of polyhydroxyl superplasticizer further optimize both the rheological and mechanical properties of the control mixture, and the compressive strength of the pastes increased up to 9% for using this nanoparticle dosage. It was found that the coarser nanoparticles (264 nm) provide pastes with enhanced mechanical properties and better workability compared to the ones provided by the finer nanoparticles (36 nm). Finally, several practical equations were proposed for the prediction of the rheological properties of yield stress and plastic viscosity of Portland cement pastes based on the nanosilica and superplasticizer additions.