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

According with what is extensively and logically assumed, anti-thixotropic behavior better than thixotropy was expected for shear-thickening cement pastes. However, shear-thickening Portland and Volcanic cement pastes here studied showed apparent thixotropic behavior 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 hypothesized. Then, it was supposed that the initial reorganization 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 viscosity dependence on shear stress, which can be used for cement applications.