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Measuring Yield Stress to Correlate Slump of Concrete and Cement Paste
Concrete is the most widely used man-made material (measured by tonnage made) in the world. One of the most important characteristics of these materials is the so-called workability. The workability is the ability of a fresh (plastic) concrete mix to fill a given form/mold properly with the desired work (vibration) and without reducing the concrete's quality. Workability depends amongst others on water content, aggregate (shape and size distribution), cementitious content and age (level of hydration) and can be modified by adding chemical admixtures, like superplasticizer or rasing water content. However, excessive water leads to increased bleeding (build-up of surface water) and/or segregation of aggregates (when the cement and aggregates start to separate), with the resulting concrete having reduced quality. Workability can be measured by the "concrete slump test", a simplistic measure of the plasticity of a fresh batch of concrete following ASTM C 143 or EN 12350-2 test standards. Slump is normally measured by filling an "Abrams cone" with a sample from a fresh batch of concrete. The cone is placed with the wide end down onto a level, non-absorptive surface. It is then filled in three layers of equal volume, with each layer being tamped with a steel rod to consolidate the layer. When the cone is carefully lifted off, the enclosed material slumps a certain amount, owing to gravity. However, it was shown in the past that determining the yield stress rheologically is a fast and easy method to correlate slump. As soft foods like concrete are often difficult to work with when using conventional plate/plate or concentric cylinder geometries on rotational rheometers because of the possible wall slip and excessive sample disruption during loading into narrow gaps vane geometries are recommended here. When a vane rotor is fully immersed in the sample, the yield stress itself can then be calculated according to Boger: [formula] (1). With T being the Torque and K the vane parameter that depends on the height (H) and the diameter (D) of the paddle according to: [formula] (2).
Measuring Yield Stress to Correlate Slump of Concrete and Cement Paste
Concrete is the most widely used man-made material (measured by tonnage made) in the world. One of the most important characteristics of these materials is the so-called workability. The workability is the ability of a fresh (plastic) concrete mix to fill a given form/mold properly with the desired work (vibration) and without reducing the concrete's quality. Workability depends amongst others on water content, aggregate (shape and size distribution), cementitious content and age (level of hydration) and can be modified by adding chemical admixtures, like superplasticizer or rasing water content. However, excessive water leads to increased bleeding (build-up of surface water) and/or segregation of aggregates (when the cement and aggregates start to separate), with the resulting concrete having reduced quality. Workability can be measured by the "concrete slump test", a simplistic measure of the plasticity of a fresh batch of concrete following ASTM C 143 or EN 12350-2 test standards. Slump is normally measured by filling an "Abrams cone" with a sample from a fresh batch of concrete. The cone is placed with the wide end down onto a level, non-absorptive surface. It is then filled in three layers of equal volume, with each layer being tamped with a steel rod to consolidate the layer. When the cone is carefully lifted off, the enclosed material slumps a certain amount, owing to gravity. However, it was shown in the past that determining the yield stress rheologically is a fast and easy method to correlate slump. As soft foods like concrete are often difficult to work with when using conventional plate/plate or concentric cylinder geometries on rotational rheometers because of the possible wall slip and excessive sample disruption during loading into narrow gaps vane geometries are recommended here. When a vane rotor is fully immersed in the sample, the yield stress itself can then be calculated according to Boger: [formula] (1). With T being the Torque and K the vane parameter that depends on the height (H) and the diameter (D) of the paddle according to: [formula] (2).
Measuring Yield Stress to Correlate Slump of Concrete and Cement Paste
Plog, Jan P. (author)
2014
3 Seiten, Bilder, Tabellen, 6 Quellen
Conference paper
English
Zementpaste , Kunststoff , Oberflächenwasser , Zement , Stahl , Wassergehalt , Größenverteilung , Hydratation , Entmischung , Plastizität , Tonnage , Prüfnorm , Fließspannung , Beimengung , Superplastifizierer , Wandgleiten , Rheometer , Rotor , Zylindergeometrie
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