Similarities and differences of pumping conventional and self-compacting concrete

In Practice, Self-Compacting Concrete (SCC) is Considered as a Simple Extension of Conventional Vibrated Concrete (CVC) When Pumping is Concerned. the Same Equipment, Materials, Pumping Procedures and Guidelines Used for CVC Are Applied When Pumping SCC. on the Other Hand, It Has Been Clearly Shown that the Rheological Properties and the Mix Design of SCC Are Different Than CVC. Can the Same Pumping Principles Employed for CVC Be Applied for SCC? This Paper Compares the Some Published Results of Pumping of CVC with Those for SCC. a First Striking Difference between Pumping of CVC and SCC is the Flow Behaviour in the Pipes. the Flow of CVC is a Plug, Surrounded by a Lubricating Layer, While during the Flow of SCC, Part of the Concrete Volume itself is Sheared Inside the Pipe. as a Result, the Importance of Viscosity Increases in Case of SCC. Due to the Low Yield Stress of SCC, the Behaviour in Bends is Different, But Quite Complex to Study. Due to the Lower Content of Aggregate and Better Stability of SCC, as It is Less Prone to Internal Water Migration, Blocking is Estimated to Occur at Lower Frequency in Case of SCC. © RILEM 2010

Fresh concrete pumping arrest investigation for thixotropy by a CFD modelling apporach

Concrete pumping operations determine construction speed, finishing quality, durability and even structural integrity. When pumping operations cannot be continued, most problems occur due to complex time-dependent transformations. This causes significant industrial costs (e.g. material and delay). Since time-dependent aspects are currently not fully understood and cannot be predicted, a way to quantify time-dependent aspects is needed. Therefore, we make an attempt by numerical simulation by comparing thixotropic cases with different pumping arresting times. After an introduction to fresh concrete rheology and numerical modelling, ten representative thixotropy cases are analysed. Despite some unresolved numerical instabilities, the numerical framework allows to estimate pumping pressure peaks after resting time. The results evaluate a thixotropy model, which is generally applicable for less thixotropic SCC’s. It is clear that flow re-initiation after rest in concrete pumping is poorly understood. Numerical simulation could be one approach for further analysis and is potentially important for practice. Future work such as simulation of concrete mixers, pressure increase after pumping arrest, formwork pressure decay and leakage are therefore recommended

State of the Art on Prediction of Concrete Pumping

Large scale constructions needs to estimate a possibility for pumping concrete. In this paper, the state of the art on prediction of concrete pumping including analytical and experimental works is presented. The existing methods to measure the rheological properties of slip layer (or called lubricating layer) are first introduced. Second, based on the rheological properties of slip layer and parent concrete, models to predict concrete pumping (flow rate, pumping pressure, and pumpable distance) are explained. Third, influencing factors on concrete pumping are discussed with the test results of various concrete mixes. Finally, future need for research on concrete pumping is suggested.ope

Challenges in Rheological Characterization of Cement Pastes using a Parallel-Plates Geometry

Cement-based materials are characterized as complex suspensions that may experience a thixotropic behavior caused by physical and chemical phenomena. The characterization and understanding of the rheological properties of cement-based materials have become essential with the introduction of 3D printing in field of civil engineering. Therefore, there is a need to accurately measure such properties to obtain repeatable and consistent results. To measure the rheological properties, different geometries are available, such as vane, parallel-plates, or coaxial cylinders: These are the most used for cement-based materials. Although, there are no specific guidelines on how to select the appropriate geometry for the material that will be tested. Proper understanding of the advantages and disadvantages as well as the limitations of each geometry should be taken into account. Since parallel-plates is a common tool used to evaluate fresh cement-based materials, due to its simplicity, the small sample volume required and the variable gap that can simulate the distance between the aggregates. This paper discusses the major challenges and issues encountered when using parallel-plates geometry to measure the rheological properties of cement-based suspensions under shear. Some issues such as wall slip, sample spill, dryness, particles sedimentation, non-uniform shear rate applied, etc. can be prevented but the user should be aware of these problems

Correlation Between “Very Early” Age Fracture Performance and Evolution of Rheological Properties of High Performance Fiber Reinforced Cementitious Composites with Adapted Rheology

The tremendous advances in concrete technologies our society is witness of, do not only provide the construction industry with new advanced materials and processing/ manufacturing techniques, but also require the performance of cement based materials to be investigated not only in its structural service state, but also throughout its very early and early age life. Tailored successful placement and development of mechanical performance, even in the first hours of life, can affect the structural durability and discriminate about the successful accomplishment of the structural performance throughout the service life. In this paper reference is made to a High-Performance Fibre-Reinforced Cementitious Composite, formulated with adapted rheology to ease its placement and most of all to achieve a tailored alignment of the fibres through the casting flow. The development of tensile and shear fracture properties in the first hours (up to three) after the first contact between cement and water has been studied with an ad-hoc designed test set-up. The knowledge of such properties is of the utmost importance to foster the use of these kind of advanced cement based materials with adapted rheology in precast construction, where the design of transient situations, including demoulding and handling, may play a crucial role, also in the sight of optimizing the productivity. In a quality control framework, the development of tensile and shear fracture properties of the investigated materials in the considered time frame have been also correlated to the evolution of rheological properties, so far evaluated through a mini-slump flow tests