Ciria Report 108 Concrete Pressure On Formwork 🎉

In the world of construction, few forces are as misunderstood—or as dangerous—as fresh concrete pressure on formwork. Every year, projects face blowouts, bulging forms, and even catastrophic failures because engineers and contractors underestimate the liquid-like pressure exerted by newly placed concrete. For decades, the industry struggled with inconsistent guidelines until a groundbreaking document changed everything: CIRIA Report 108, "Concrete Pressure on Formwork."

Published by the Construction Industry Research and Information Association (CIRIA), Report 108 remains the gold standard for calculating lateral pressure exerted by fresh concrete on vertical and inclined formwork systems. Despite being originally released in the 1980s (with updates in subsequent years), its principles continue to inform modern design codes, including ACI 347 and EN 12812.

This article provides a comprehensive breakdown of CIRIA Report 108—its history, key formulas, practical applications, and why it remains indispensable for safety and efficiency in concrete placement.

The report doesn't give one number; it gives a maximum pressure (( P_max )) based on the slower of two rates:

The key takeaway: Temperature is a variable, not a constant.

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

The report’s most influential contribution is the formula for maximum lateral pressure (P_max) at the base of a vertical form:

P_max = C1 × (R / T) + C2

Where:

For typical structural concrete (slump 50–100 mm, without retarders), C1 ≈ 7.2 and C2 ≈ 18, giving:

P_max = 7.2 × (R / T) + 18

Importantly, the report states that pressure never exceeds the full hydrostatic head (ρgh ≈ 24 × height in kN/m²), and it sets a minimum pressure for low rates or high temperatures.

Example calculation:

If the form height is 3 m, full hydrostatic would be 72 kN/m². The CIRIA method allows a far lighter formwork system, saving material and labor.

The core of the report is the design pressure formula. For internal vibration (the standard method of compaction), the design pressure $P_max$ is given by: ciria report 108 concrete pressure on formwork

$$P_max = C_1 \sqrtR + C_2 \sqrtH + C_3$$

However, in practice, designers usually utilize the simplified charts derived from the report's regression analysis. The standard CIRIA equation is often presented as:

$$P = D \left[ C_1 \sqrtR + C_2 K \sqrtH \right]$$

Where:

Slipforms have their own rules. CIRIA 108’s static formulas do not directly apply to continuously moving formwork (use CIRIA 59 or equivalent instead).

Most engineers memorize the rule of thumb: Pressure is 110 kN/m² or ( 2.4 \times R ), whichever is lower. But the report details five distinct concrete types (ST1 to ST5) and their rheology.

For modern mix designs (high workability, superplasticizers): Be careful. CIRIA 108 assumes "vibration" limited to 1.5m below the top. If you over-vibrate or use self-compacting concrete (SCC), the pressure reverts to full hydrostatic. In the world of construction, few forces are

CIRIA Report 108, titled “Concrete Pressure on Formwork,” is a widely cited guidance document that synthesizes research and practice on the lateral pressures exerted by fresh (plastic) concrete against formwork during casting. Its primary aim is to help engineers, formwork designers and site teams predict and safely design formwork systems for vertical and inclined concrete elements.

Key points

Pressure characteristics and influencing factors

Design recommendations (practical guidance)

Typical practical procedure (condensed)

Limitations and application notes

Further action

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