Influence of dispersants and dispersion on properties of nanosilica modified cement-based materials

Abstract Properties of cement pastes containing nanosilica (NS) dispersed with seven different dispersants were evaluated. The dispersants used were anionic surfactants, sodium dodecyl sulfate (SDS) and polycarboxylate ether (PCE) based superplasticizer, and two groups of non-ionic surfactants, Tweens (T20, T40) and Tritons (TX114, TX100, TX405). The degree of NS dispersions in de-ionized water and cement pore solutions with ultrasonication and dispersants were quantified based on their average hydrodynamic particle size (Z-avg.) and zeta potential obtained from dynamic light scattering (DLS) measurements. The properties of cement-NS pastes assessed were flowability, heat of hydration, and compressive strength. The results showed that except for PCE, all surfactants reduced the flow of cement paste at a given dosage, and therefore, they were subsequently used along with PCE to achieve adequate flow. The combination of PCE and another surfactant accelerated cement-NS hydration. There were strong correlations between the Z-avg. value of cement-NS suspensions made with non-ionic surfactants and the strength and total heat of hydration of the corresponding cement-NS pastes. Surfactant TX405 provided the cement-NS paste significantly high increment in strength (33%, 41%, and 54% at 1, 3, and 28-day, respectively). SEM and TGA results revealed that enhanced nucleation of CSH fibrils and higher gel-space ratio in TX405-cement-NS paste might be responsible for the strength improvement.