The Influence of Bleeding of Cement Suspensions on Their Rheological Properties

Abstract

Flowable concretes tend to segregate. The risk of segregation is particularly high when the concrete is vibrated during the compaction process. A well-known segregation phenomenon is the so-called “bleeding”. This is a rise of water to the surface of the freshly poured concrete due to the difference in density between the mixing water and the concrete’s denser solid components (aggregates, cement and additives). This type of segregation occurs particularly within the paste. The focus of this paper is, therefore, on the sedimentation behavior at the microscale of concrete and especially on the influence of this process on rheological properties of the cement paste. In addition to common bleeding tests of cement suspensions using standing cylinders, rheometric measurements were performed on the suspensions during the bleeding process. A measuring procedure was developed for the rheometric measurements of the sedimenting cement suspensions. The rheological properties of the investigated cement suspensions were determined at four specific measuring times and at four specific measuring heights (i.e., positions) each. With this method it could be shown that the cement suspensions are not homogeneous over their height and that bleeding has a great influence on the rheological properties of cement suspension.

Assessing the dimensional stability of alkali-activated calcined clays in the fresh state: a time-lapse X-ray imaging approach

“…A possible explanation is that when evaporation is allowed (drying regime), the net reduction of the water volume favours colloidal interactions, which was also the case of sample C3-20. Previous rheological measurements supported this hypothesis, showing that viscosities measured at different vertical positions within a given samples, in the presence of bleeding, varied, with viscosity being higher in the bottom parts of the sample where the occurrence of bleeding induced a local increase in the packing density [46]. Therefore, for sample C2 in unsealed conditions, particle interaction is favoured by evaporation and, apparently, the amount of shrinkage is mostly controlled by the degree of reactivity, with the sample reacting in the higher pH solution displaying a slightly lower amount of shrinkage.…”

“…It is therefore recommended that, for specific case studies, this approach is integrated with additional measurements aimed at providing a comprehensive view of the early age behaviour of the studied system. Given the importance of colloidal interaction in controlling early dimensional stability, rheological measurements may provide complementary information to underpin the envisaged mechanisms of shrinkage in the fresh state [48,46].…”

Effect of Structural Build-Up on Interlayer Bond Strength of 3D Printed Cement Mortars

“…In the extrusion process, the shearing of nozzle wall leads to the migration of particles and the formation of lubrication layer at the interface between the 3DPC and the wall of the nozzle, which leads to more water migration to the surface of the deposition layer, as shown in Figure 10 . The rheological properties of suspension significant influence the migration of particles and the formation of lubrication layer [ 42 ]. The cement paste with PCE polymer has a lower viscosity and yield stress than that with TS polymer, which is beneficial for the migration of particles and the formation of lubrication layer during extrusion.…”