108 Concrete Pressure On Formwork [portable]: Ciria Report

Pressure=min(Hydrostatic,Pmax)Pressure equals min of open paren Hydrostatic comma cap P sub max end-sub close paren Case B: Columns (Width ≤ 2m)

). If the calculated empirical pressure is greater than the hydrostatic pressure, the hydrostatic value is used as the design maximum.

Have a ready-mix engineer track the concrete temperature. If the truck arrives cooler than expected, recalculate P_max immediately.

Generally taken as 25 kN/m³ for reinforced concrete. ciria report 108 concrete pressure on formwork

): A variable determined by cement type and the presence of admixtures. It represents the time required for the concrete to cease behaving as a fluid.

, to account for impact forces during skip or pump discharge. Comparisons with Other Standards (ACI 347 & BS 5975) Metric / Feature CIRIA Report 108 ACI 347 (American Standard) BS 5975 (UK Code of Practice)

Although newer guidelines for specialized concretes exist, remains an indispensable, robust, and industry-standard reference for calculating concrete pressure on formwork. By carefully applying its formulas for wall and column pressure, designers can achieve the balance between safety, efficiency, and economy in structural concrete construction. If the truck arrives cooler than expected, recalculate

Before Report 108, formwork designers relied on empirical rules-of-thumb or overly conservative hydrostatic pressure models. The hydrostatic assumption—that fresh concrete behaves exactly like a liquid (pressure = density × height)—led to massively over-engineered (and expensive) formwork. Conversely, simplified rules like "pressure = 1.5 × height" often proved unsafe for high-slump, fast-pouring conditions.

Don't rely on lab data. Take a trowel to the concrete in the jump form. If it isn't green (setting), you are still at maximum pressure.

is the total height of the pour. This assumes the concrete acts as a perfect liquid for its entire depth. It represents the time required for the concrete

Lower temperatures delay setting (longer liquid phase), resulting in higher pressures.

Lower values indicate mixes that stiffen quickly (reducing pressure), while higher values indicate mixes with prolonged workability.

If formwork is designed for a pour rate of