Ciria Report 108 Concrete Pressure On Formwork -

Pmax=C2KHcap P sub m a x end-sub equals cap C sub 2 cap K the square root of cap H end-root (Where C2cap C sub 2 relates to the form geometry, is a temperature/blending factor, and is the total fluid height).

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 enforces a baseline minimum pressure to account for localized surges during bucket discharging, pump pressure pulses, and accidental over-vibration. Practical Comparison: CIRIA 108 vs. Other Standards Feature / Parameter CIRIA Report 108 ACI 347 (American Standard) BS EN 1993 / DIN 18218 (Eurocode aligned) Primary Region United Kingdom and Commonwealth North America / International Concrete Technology Adaptation ciria report 108 concrete pressure on formwork

Friction between the concrete and the internal faces of the formwork transfers a portion of the vertical load directly to the forms, reducing the lateral thrust at the base.

): Temperature directly dictates the hydration rate of cement. Higher temperatures accelerate the chemical reaction, causing the concrete to stiffen and set faster, which reduces the duration and magnitude of the fluid pressure. Conversely, cold weather prolongs the liquid state, increasing the load on formwork. Concrete Density ( Pmax=C2KHcap P sub m a x end-sub equals

Formwork rigidity: Less rigid formwork can deform under pressure and attract greater loads; specify minimum stiffness or tie spacing to limit deflections and redistribution.

The report provides a table for selecting $C_2$ based on the type of cement or blend and the use (or absence) of admixtures, with values ranging from 0.30 to 0.60. The six key categories are: Other Standards Feature / Parameter CIRIA Report 108

Rough form liners (e.g., plywood) and stiff formwork can reduce measured pressure compared to smooth steel forms. CIRIA 108 provides reduction factors but recommends caution—friction effects are unreliable.

For pours where the concrete begins to set before the full height is reached, CIRIA 108 provides an empirical formula to calculate the true maximum lateral pressure:

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.