Ciria Report 108 Concrete Pressure On Formwork Jun 2026

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The absolute upper limit of concrete pressure is its hydrostatic envelope. This is calculated using the density of the concrete and the total height of the pour:

Explicitly restrict external form vibrators or deep poker revibration if the design relies on early concrete stiffening.

The report accounts for cement type, the inclusion of fly ash (PFA) or ground granulated blast-furnace slag (GGBS), and the use of chemical admixtures like retarders or superplasticizers. Admixtures that delay setting increase the duration of hydrostatic pressure.

To understand CIRIA 108, you must abandon the "liquid assumption." ciria report 108 concrete pressure on formwork

Do you need a using the CIRIA equations?

) generated during this transient fluid state. Accurate prediction prevents two catastrophic outcomes:

CIRIA 108 defines the as a value between two extremes:

Concrete lateral pressure does not increase infinitely with depth. Because the bottom layers begin to stiffen while the top layers are still being poured, the pressure distribution profile transitions from hydrostatic to a uniform rigid block. You can use this as a LinkedIn article,

Using empirical formulas derived from testing, designers calculate the peak pressure based on the placement rate ( ), concrete temperature ( ), and the coefficients C1cap C sub 1 C2cap C sub 2 . The fundamental equation takes the form:

). The design pressure used for the formwork is always . 4. Evolution of the Standard: From 108 to C766

The design pressure is taken as the of two calculated values: the fluid pressure (Dh) versus the pressure given by the formula above.

Internal vibrators liquefy concrete to remove air pockets. If a worker drops a vibrator too deeply into concrete that has already begun to set, they will re-liquefy it, instantly spiking the lateral pressure back to full hydrostatic levels. The report accounts for cement type, the inclusion

The CIRIA 108 methodology identifies several critical variables that influence how much pressure fresh concrete exerts: Rate of Concrete Rise (

Pmax=C1Rcap P sub m a x end-sub equals cap C sub 1 the square root of cap R end-root (Where C1cap C sub 1

The report recommends a for vertical formwork, as opposed to a full hydrostatic triangle:

Design Pressure = 24.5 × [1.00√2.0 + 0.45×1.00√(2.0 – 1.00√2.0)] = 24.5 × [1.414 + 0.45√(2.0 – 1.414)] = 24.5 × [1.414 + 0.45√0.586] = 24.5 × [1.414 + 0.45×0.765] = 24.5 × [1.414 + 0.344] = 24.5 × 1.758