Rheo-viscoelastic behaviour of fresh cement-based materials: Cement paste, mortar and concrete

Abstract

The viscoelasticity of fresh fine cement-based material can be investigated by rheological means using dynamic shear rheometry, hence, the term rheo-viscoelasticity. However, readily available classical rheometers are limited to the study of paste due to the aggregate size associated with mortar and concrete. This study, therefore, sets out to experimentally investigate the rheo-viscoelastic behaviour of cement-based materials containing rheology modifiers, by progressively evaluating the viscoelasticity of cement paste-mortar-concrete. The tests carried out include strain sweep, shear rate sweep, creep and creep recovery, stress relaxation and three interval thixotropy test (3ITT). The results show a trend of improved linear viscoelastic properties of the control fresh cement-based materials due to progressive inclusion of aggregate (increasing volume fraction and size). However, the rheology modifiers widely varied this trend, tending to make it difficult to approximate the rheo-viscoelastic behaviour of mortar and concrete from that of the cement paste as generally suggested in literature. The increase in the coarse volume fraction improved the stability of the cement-based materials microstructure to varying shearing rates. The study suggests that the liquid phase has a role in improving the creep recovery and stress relaxation of the mixes. Furthermore, pseudo-strain hardening was observed for the cement-based materials and flocculation-driven structuration was found to be reduced for the cement paste due to the progressive inclusion of aggregates leaving hydration as the main driving source of concrete’s structuration.