Fresh concrete pressure

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Course of the fresh concrete pressure

The fresh concrete pressure or formwork pressure is generally referred to as the load component of the fresh concrete that acts perpendicularly on the surface of the formwork . Shear stresses can also occur due to friction between the fresh concrete and the formwork surface.

During and after installation in the formwork, the fresh concrete still needs a supporting effect until it has sufficient dimensional stability. This means that the formwork must absorb the fresh concrete pressure in the period from the start of the concrete installation until it has sufficient inherent stability.

Influencing variables and course of the fresh concrete pressure

The fresh concrete pressure is influenced by a large number of parameters. The material properties of the fresh concrete and in particular the concrete weight, the concrete consistency and the setting behavior have a major effect on the size of the concrete pressure, the latter being influenced in particular by the type of cement , the concrete admixtures and the fresh concrete temperature.

In addition to the purely material-related influencing factors, there are effects from the concreting process and the formwork construction. Particular mention should be made of the rate of rise of the concrete, the type and intensity of compaction, the tightness of the formlining, the reinforcement routing, the formwork inclination and the formwork height or the height of the concreting section.

In the area of ​​the vibrator , the fresh concrete pressure behaves quasi-hydrostatically, assuming a concrete weight for normal concrete of approx. 25 KN / m³. With increasing concreting height, the fresh concrete pressure also increases (see picture). As a result of the stiffening and solidification of the fresh concrete (caused by structure formation from chemical and physical processes, in particular the hydration of the cement) and as a result of the friction between the fresh concrete and the formwork surface or reinforcement (silo effect), the increase in fresh concrete pressure is reduced. After reaching the maximum value of the fresh concrete pressure, there is a continuous drop in pressure. If the concrete reaches its inherent stability (approx. End of solidification), support by the formwork is no longer necessary. However, due to the deformation of concrete and formwork, there is usually still an impressed compressive stress in the system.

Technical regulations

The following documents should be mentioned as essential specifications issued by national standardization institutes or technical-scientific associations with regard to the loading of formwork by fresh concrete:

  • ACI 347-04: Guide to Formwork for Concrete. American Concrete Institute, 2004.
  • CIB-CEB-FIP 27-98-83: Manuel de Technologie “Coffrage”, 1977.
  • CIRIA Report No. 108: Concrete Pressure on Formwork. Construction Industry Research and Information Association, London, 1985.
  • DIN 18218: 2010-01 Fresh concrete pressure on vertical formwork (Pressure of Fresh Concrete on Vertical Formwork). Beuth publishing house. 2010.
  • IS 14687: 1999: Guidelines for falsework for concrete Structures, New Delhi, 1999.
  • JGJ 162-2008: Technical code for safety of forms in construction, People's Republic of China, 2008.
  • NF P93-350: Equipment de Chantier - Branches industrialisées pour ouvrages en béton. 1995.
  • TGL 33421/01: Concrete construction, shuttering method, standing shuttering, 1977.

In Germany, DIN 18218: 2010-01 must be used for the dimensioning of vertical formwork. In addition to the calculation approaches for conventional vibrated concrete, this also contains regulations for highly flowable concretes, such as B. self-compacting concrete.

Individual evidence

  1. ^ Proske, Tilo; Khayat, Kamal; Omran, Ahmed; Leitzbach, Olaf: Form Pressure Generated by Fresh Concrete - A review about practice in formwork design. Materials and Structures, RILEM Publications, July, 2014 (47): 1099-1113.
  2. ↑ DIN 18218: 2010-01 Fresh concrete pressure on vertical formwork (Pressure of Fresh Concrete on Vertical Formwork). Beuth publishing house. 2010.
  3. ↑ Specht, Manfred (1973): The load on formwork and armor by fresh concrete. Werner-Verlag, Düsseldorf, 1973.
  4. ↑ Specht, Manfred (1973): The load on formwork and armor by fresh concrete. Werner-Verlag, Düsseldorf, 1973.
  5. ↑ Proske, Tilo: Fresh concrete pressure when using self-compacting concrete - A realistic model for determining the effects on formwork and scaffolding, dissertation (Formwork Pressure using Self-Compacting Concrete, PhD Thesis), Technische Universität Darmstadt, 2007.
  6. ^ Graubner, Carl-Alexander; Boska, Erik; Motzko, Christoph; Proske, Tilo: Formwork loading from high-performance concrete with a flowable consistency, calculation model and practical implementation. In: Zeitschrift Bauingenieur, 04/2009, Springer VDI Verlag 2009: 163-171.
  7. ^ Proske, Tilo; Khayat, Kamal; Omran, Ahmed; Leitzbach, Olaf: Form Pressure Generated by Fresh Concrete - A review about practice in formwork design. Materials and Structures, RILEM Publications, July, 2014 (47): 1099-1113.
  8. ↑ DIN 18218: 2010-01 Fresh concrete pressure on vertical formwork (Pressure of Fresh Concrete on Vertical Formwork). Beuth publishing house. 2010.