Synergies on rheology and structural build-up of fresh cement pastes with nanoclays, nanosilica and viscosity modifying admixtures

Abstract

Nanoclays, nanosilica and viscosity modifying admixtures can be used to tune rheological properties of cement pastes, in order to fulfill the requirements for non-conventional cast-in-place techniques. An experimental study on cement paste rheology was carried out to evaluate their combined effects on fluid cement pastes’ properties. A reference paste with cement blended with limestone filler and a low water to binder ratio was designed. A high range water reducing admixture (HRWRA), three types of viscosity modifying admixtures (VMA), and five nanocomponents (nanosilica and four different nanoclays) were added. Flowability, initial rheological properties and structural build-up of cement pastes were assessed with mini-cone slump test and dynamic shear rheometer test (DSR). The synergies between nanoclays, nanosilica and VMAs were evaluated. It was observed that an adequate combination of admixtures and nanoclays reduced the amount of HRWRA required to achieve target flowability, regarding the same components uncombined. The type and amount of VMAs and nanocomponents also produced changes on yield stress, viscosity and structural build-up. Their effect on structural build-up of fresh paste was related to reversible and non-reversible mechanisms, comparing the reduction of spread diameter of fresh samples stirred and left at rest over time measured with the mini-cone.