Mechanisms Affecting Viscosity of Cement Paste Made with Microfines of Manufactured Sand

Viscosity of cement-based materials incorporating manufactured sand is affected by the content and physical properties of the microfines in the sand. However, some of the mechanisms affecting the viscosity remain unclear. This paper investigates the effect of microfine type and content on the apparent viscosity (ηapp) and residual viscosity in/near pseudo-Newtonian regime (ηrespse−New) of cement pastes. Limestone (LS), slate (ST), and tuff (TF) microfines with different specific surface areas were investigated. Test results showed that, by deducting the greater contribution of yield stress to ηapp when using finer microfines, the increase of ηrespse−New at a given PCE dosage was mainly associated with the lower average PCE coverage onto powder particles that intensified local fluid shearing. However, despite the additional PCE demand that reduced the local fluid shearing to maintain a fixed mini-slump flow, the ηrespse−New can increase by adding TF and LS, while decreased by using ST, given their discrepant effects on enhancing and reducing particle friction contacts, respectively. Specifically, particle friction contacts were correlated to the solid volume fraction, particle packing density, and flow index of Herschel-Bulkley model, with local fluid shearing related to the mean particle size and PCE coverage. A qualitative approach relating the local fluid shearing, interstitial fluid viscosity, and particle friction contacts was developed to describe the ηrespse−New, given the hydrodynamic and contact interactions between powder particles. The model yielded good estimation for cement pastes made with different types and additions of microfines.