Time-dependent viscous behaviour of shear-thinning/shear-thickening cement pastes

Abstract

According to what is extensively and logically assumed, a better anti-thixotropic behaviour than thixotropy was expected for shear-thickening cement pastes. However, the shear-thickening Portland and volcanic cement pastes studied here showed apparent thixotropic behaviour when step-up tests were performed. This unexpected result was tentatively justified assuming that, just at the beginning of the step-stress, virtually instantaneous particle aggregation (for step-up tests) and disaggregation (for step-down tests) take place. In other words, the existence of fast jamming or unblocking mechanisms developed by shear-thickening cement pastes was hypothesised. Then, it was supposed that the initial reorganisation of cement particles was followed by a progressive erosion of the jammed state (step-up) or progressive aggregation of the unblocking state (step-down) due to the constant action of shear stress. These ideas were used to model an empirical equation for the dependence of viscosity on shear stress, which can be used for cement applications.