Retarding admixtures extend the time before initial set. This effectively increases R/T ratio, raising pressure. The report suggests applying a temperature correction or using an "effective temperature" lower than the actual concrete temperature.

Studies comparing CIRIA 108 predictions with experimental measurements have shown reasonable agreement. One study found predictions underestimated actual pressures by 1-2% for some wall configurations and overestimated by up to 11% for others. For self-compacting concrete (SCC), maximum pressures were generally less than hydrostatic and also lower than CIRIA 108 predictions, suggesting the method is appropriately conservative for SCC.

Inform the site operations team of the maximum allowed filling speed ( ) calculated in the design.

Vibrated concrete vs. pumping vs. self-compacting concrete (SCC) affects initial pressure.

Wall height H = 2.0 m Density D = 24.5 kN/m³ Placement rate R = 2.0 m/hr Concrete temperature T = 20°C C₁ = 1.00 (wall) C₂ = 0.45 (OPC with retarder)

Standard CIRIA 108 was written before SCC became ubiquitous. SCC has much higher flowability and longer setting retention. Does CIRIA 108 still apply?

is the total pour height. This is the absolute physical limit of pressure).

is a factor, the equations balance the rate of rise, temperature effects, and blending coefficients to pinpoint the depth at which the concrete transitions from a fluid-like state to a self-supporting mass. Step 4: Apply Boundary Constraints The calculated Pmaxcap P sub m a x end-sub

The formula above does not apply infinitely. CIRIA 108 imposes two absolute limits:

Prevent catastrophic blowouts that endanger site workers.

Any unexpected changes in the concrete delivery (such as a sudden switch to a highly retarded mix) require a re-evaluation of the formwork capacity.

This article breaks down every aspect of CIRIA 108, explaining how to apply its formulas, why it outperforms older standards like ACI 347, and how to prevent formwork failure on your next pour.

): 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.

If formwork is designed for a pour rate of

CIRIA Report 108 remains highly influential, but standard bodies have adapted its data into updated codes: