Abstract The composition of the aqueous phase significantly influences the rheology and hydration of fresh cement paste in the presence of PCE superplasticizer. In addition, the molecular structure of PCE has a decisive role on its performance in cementitious materials. It is found that the charge density of the backbone has a minimal effect on the interparticle force, and the length of the side chain plays a more significant role in determining the interparticle force. In addition, the dosage of PCE affects both the strength and the decay length of the interparticle force. In the PCE-free sample, the higher ionic strength of the aqueous phase contributes to a higher yield stress. The effect is thought to be caused by the different influences of the cations and PCE interactions. Calcium seems to support the polymer adsorption and potassium seems to affect the depletion forces. The yield stress increases with resting time when high dosages of PCE are used in pore solutions, although the surface becomes more negatively charged. The adsorbed PCE at rest tends to bridge the particles rather than disperse them. The experimental results suggest that the polymer and the ion can form complexes in the liquid phase, leading to size changes. This would increase the depletion forces and an increased bridging effect between the particles at rest, thus affecting the rheological properties.
Abstract Numerous factors influence the dynamics of material flow. When pumping multiphase granular suspensions, such as concrete, through complex piping systems, many questions remain unanswered. This research, conducted as part of the Priority Program SPP 2005 Opus Fluidum Futurum—Rheology of Reactive, Multiscale, Multiphase Construction Materials, funded by the German Research Foundation (DFG), aims to deepen our understanding of flow dynamics and particle mechanics under nonlinear flow conditions. The primary objective is to characterize flow-induced particle migration (FIPM) and the formation of a lubrication layer by analyzing concrete composition and its rheological properties. These factors play a crucial role in determining the flow behavior of multiphase granular suspensions and their impact on pump pressure. While existing studies have provided insights into the behavior of complex suspensions in generic flow conditions, their behavior in intricate geometries remains largely unexplored. This project employs both experimental and numerical approaches to investigate additional effects arising from streamline curvature and particle phase mass inertia. Through innovative experimental methods, significant insights have been gained into particle behavior within dense, opaque, enclosed moving systems. These findings contribute to the development and validation of models that qualitatively and quantitatively describe the flow behavior of multiphase granular suspensions in complex geometries, such as pipelines. Such knowledge is essential for predicting flow dynamics, assessing pressure loss, and preventing blockages during pumping. It also has broader applications in modern technologies, including 3D printing and energy-efficient pumping systems.
Abstract In recent years, there has been a growing interest in digital construction techniques such as 3D printing with concrete by layered extrusion. While this method offers various benefits, it also imposes high requirements regarding the rheological characteristics of printable materials. With the abandonment of traditional formwork, it becomes crucial for printable mortars and concretes to swiftly adapt their consistency to each stage of the process. Accordingly, material behavior can shift by several orders of magnitude within a short period of time, posing significant challenges for both mix design and test methodology to assess the rheological behavior of fresh concrete. Attention must especially be paid to the static parameters, and their evolution over time, as they are used to define the buildability of 3D printable materials. This research addresses the structural build-up of cementitious materials in their fresh state. One goal is to develop and refine a methodology that allows the characterization of a wide range of materials, as well as their modeling. The research focusses on high-potential test methods, with particular emphasis on rotational rheometry and penetration tests. The methodology developed is further utilized to explore the mechanisms behind the influence of aggregate properties and fiber addition on the rheological behavior and process-related parameters of fresh concrete in the context of 3D printing. The findings are utilized to propose models capable of predicting the material behavior during printing processes and preventing failure. Finally, this research facilitates a rheology-based approach to mix design.
Abstract A key requirement onto the concrete properties is that during the placement process the fresh concrete needs to completely fill the formwork while staying homogeneous. Whereas substantial research onto the flow and sedimentation behavior of fresh concrete has been presented regarding highly flowable self-compacting concretes, research regarding these properties on ordinary, vibrated concretes has been missing. In the presented research thus the sedimentation behavior of ordinary concrete as well as model systems was investigated. Here it could be shown, that even concretes which are seen as stable show significant changes in their homogeneity due to vibration compaction and that these local variations in aggregate content and particle size distribution have pronounced influence on the local rheological properties of the mix. The results could be closly linked to the nanoscopic particle inventory. Further, a novel measurement technique for the rheological properties of fresh concrete was developed which relies on the inverse analysis of the flow behavior of the concrete during the discharge process of a mixing truck. Using so-called Computer Vision Methods, video images of the concrete flow process can be used to derive rheological parameters such as the yield stress of the plastic viscosity.
Abstract New technologies in the concrete industry like 3D printing, complex construction projects, or simulations, require very accurate measurements of the flow behavior, i.e., stress dependency on local shear rate and shear history. Unfortunately, most commercial systems, often called concrete viscometers, only feature relative measurements or compute pseudo-absolute values from complex flow fields which cannot be described analytically. The assumptions are usually of good quality but carry the risk of producing misleading results. Therefore, a new concrete rheometer, the Adaptive Coaxial Concrete Rheometer (ACCR), was built to measure absolute values comparable to commercial small-scale rheometers. The experimental setup of the rheometer and the necessary theory are described in detail, including some specific features to fulfill the requirements of ISO 3219 for coaxial rheometers. The important gap correction for serrated measuring systems to inhibit wall slip is explained, and examples are given for rotational plate-plate and coaxial systems. The calibration and validation measurements are presented to demonstrate the high accuracy of the ACCR and the good comparability for different flow behaviors. Then, a practical study of the flow behavior for an industrial Self Compacting Concrete (SCC) concrete is presented and discussed. Finally, the yield stress of the SCC was investigated using classical extrapolation methods and compared to an optical method using the ACCR.
