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

Experimental study of formwork tightness as a function of rheological properties of SCC

Several studies relating formwork pressure to rheology exist, however the relationship between rheology and leakage through formwork joints remains to be investigated. In practice, standard documents are used to define formwork tightness requirements, typically using a qualitative approach. To try bridge this gap in knowledge, we developed a test set-up to study tightness of formwork joints under pressure as a function of varying rheological properties. Coupled with standard rheology tests, this new test set-up provides means of linking flow rate, formwork pressure, flow area, and the rheological properties. The study seeks to provide insight on measurable governing parameters and thus inform formwork tightness requirements in a more quantifiable manner. This paper presents a test set-up designed to study the flow of fresh paste through small openings. It highlights a preliminary study on the pressure-driven flow of limestone paste through a bottom orifice in a cylindrical container. While this new device may not be directly representative of the actual conditions in formwork, it provides a good base for a fundamental study that can then be extrapolated to a more representative test operation. Preliminary results show a linear relationship between the flow rate and the applied pressure. The results also show that increasing the flow area by a factor of 2.33 had a higher impact than an increase in yield stress and viscosity by a factor of 2.54 and 3.80 respectively. However, more tests need to be carried out to obtain clear trends

Critical Grain Size of Fine Aggregates in the View of the Rheology of Mortar

The aim of this research was to investigate the validity of the Krieger-Dougherty model as a quantitative model to predict the viscosity of mortar depending on various aggregate sizes. The Krieger-Dougherty model reportedly predicted the viscosity of a suspension, which includes cement-based materials. Concrete or mortar incorporates natural resources, such as sand and gravel, referred to as aggregates, which can make up as much as 80% of the mixture by volume. Cement paste is a suspending medium at fresh state and then becomes a binder to link the aggregate after its hydration. Both the viscosity of the suspending medium and the characteristics of the aggregates, therefore, control the viscosity of the cement-based materials. In this research, various sizes and gradations of fine aggregate samples were prepared. Workability and rheological properties were measured using fresh-state mortar samples and incorporating the various-sized fine aggregates. Yield stress and viscosity measurements were obtained by using a rheometer. Based on the packing density of each fine aggregate sample, the viscosity of the mortar was predicted with the Krieger-Dougherty model. In addition, further adjustments were made to determine the water absorption of fine aggregates and was transferred from successful experiment to simulation for more accurate prediction. It was also determined that both yield stress and viscosity increase when the fine aggregate mean size decreases throughout the mix. However, when the mean size of the fine aggregates is bigger than 0.7 mm, the yield stress is not affected by the size of the fine aggregate. Additionally, if aggregate grains get smaller up to 0.3 mm, their water absorption is critical to the rheological behavior

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

Rheological properties considering the effect of aggregates on concrete slump flow

Rheology of concrete allows us to understand the flow behavior of concrete and further extend the quantitative evaluation of its construction performance. The use of a concrete rheometer is promising for the purpose, but sometimes limited high associated cost and procedure complexity. This study proposes a simulation-based model that correlates the slump flow test results to a concrete's rheological properties, allowing quantitative evaluation through this simple method. The proposed model is based on single-fluid simulation using the volume-of-fluid method, with an extension to accommodate the partial segregation of coarse aggregates. Either the channel flow or the L-shaped panel filling of SCC is simulated using the rheological properties obtained by our model. Finally, the rheograph describing the self-compacting ability of SCC is updated