Abstract
In the present work, squeeze flow techniques were used to investigate the influence of squeezing rates on the yield stress of mortars in fresh state. The tested samples were prepared under similar conditions of room temperature and atmospheric pressure. The fresh mortars were tested at three squeezing rates (20 and 200mm/s) 15 minutes after mixing. The results show that the material’s yield stress increases with the increasing of the squeeze velocity. This increase is evident at low tensile speeds and is not obvious at high tack velocity. Elongational viscosity values increased as a result of the gap reduction for all the tested samples. However, when the squeeze speed was high, the strain rate increased because of the high displacement rates, a significant reduction in the mortar’s elongational viscosity was observed compared with those obtained when the squeeze speed was low. Despite that this behavior is associated with fluid-solid phase separation, which occurs for low displacement rates, these viscosity values actually represent the behavior of the material in practical situations when submitted to different velocities. The increase in the displacement rate of one order of magnitude caused a reduction in the viscosity of one order of magnitude.
Highlights
The fresh state of a cement-based material, including mortar, corresponds to only a minor part of its lifetime, the behavior of the material within this frame has major consequences on its hardened properties
Elongational viscosity values increased as a result of gap reduction for all the tested samples
Despite the fact that this behavior is associated to fluid–solid phase separation which occurs for low displacement rates, these viscosity values represent the behavior of the material in practical situations when submitted to different velocities
Summary
The fresh state of a cement-based material, including mortar, corresponds to only a minor part of its lifetime, the behavior of the material within this frame has major consequences on its hardened properties. The currently applied methods for testing this kind of materials during the fresh state are simple but limited. The flow table (ASTMC1437, EN-1015-3) and dropping ball (BS-4551) methods investigate fresh mortar by using single point measurements [1]. These methods are unable to dissociate the contributions of the yield stress or of the viscosity on the resulting measurements. In order to overcome the limitations of the traditional methods, rotational rheometers have been used, in which the mortar’s rheological behavior and parameters such as yield stress and viscosity were determined in either shear stress or shear rate-controlled procedures [3, 4]. The technique is an important tool for controlling and developing cementitious material formulations, including mortar, especially for the simulation of mixing and pumping situations
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