Formwork is a critical component in concrete construction, providing a mold for the concrete to take shape. However, the pressure exerted by the concrete on the formwork can be substantial, and if not properly understood and managed, it can lead to accidents, damage, and costly repairs. CIRIA Report 108, "Concrete pressure on formwork," provides valuable guidance on this critical aspect of concrete construction.
remains the definitive industry standard for calculating the lateral pressure exerted by fresh concrete on temporary structures. Published by the Construction Industry Research and Information Association (CIRIA) in 1985, this document revolutionized formwork design by replacing oversimplified empirical formulas with a comprehensive, scientifically validated methodology. Accurate calculation of concrete pressure is critical for structural safety, cost optimization, and quality control on construction sites. The Evolution of Formwork Pressure Calculation
While highly versatile, CIRIA Report 108 is an empirical framework developed under specific criteria. Designers must be aware of its boundaries:
Confined space allows aggregate interlocking to absorb more vertical load.
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Design recommendations (practical guidance)
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Report 108 identifies that fresh concrete does not behave as a true fluid for very long. Instead, it transitions from a liquid-like state to a semi-rigid solid as it sets. The maximum lateral pressure ( Pmaxcap P sub m a x end-sub ) depends on several interlocking variables: Rate of Vertical Rise (
Introduced precise mathematical limits based on rising rate ( 5. Modern Status: From 108 to Guide CS030 Formwork is a critical component in concrete construction,
Formwork rigidity: Less rigid formwork can deform under pressure and attract greater loads; specify minimum stiffness or tie spacing to limit deflections and redistribution.
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) based on factors such as concrete weight density, rate of rise, and temperature, is recognized within BS 5975:2019. For detailed information and to acquire the report, visit CIRIA .
The report generally considers a maximum pressure envelope that starts as hydrostatic for the first 1-2 meters and then tapers or stays constant depending on the rate of rise. 3.2. Setting Time and Temperature remains the definitive industry standard for calculating the
The formula assumes standard internal poker vibration restricted to the top 1 to 2 meters of the freshly placed layer. Deep, continuous revibration of lower layers breaks early crystallization, rendering the formula invalid and driving pressures toward full hydrostatic limits.
Freshly poured concrete behaves initially as a heavy liquid, exerting hydrostatic pressure against vertical forms. As time passes, the concrete undergoes hydration, loses workability, and begins to set, transitioning from a fluid to a self-supporting solid.
): Use the empirical formula incorporating the rate of rise ( ), temperature ( ), section geometry ( ), and the cement blending factor ( The coefficient
When concrete is poured into a mold, it initially behaves like a dense fluid, exerting hydrostatic pressure against the vertical faces of the formwork. As time passes, the concrete undergoes a chemical hydration process, loses workability, and begins to stiffen into a self-supporting solid.