Ciria Report 108 Concrete Pressure On Formwork [top] May 2026

CIRIA Report 108 (1985) serves as a foundational technical guide for calculating lateral concrete pressure on formwork, offering methods based on concrete mix, placement rate, and temperature. While widely adopted for temporary works design and standards like BS 5975, the method has limitations with highly flowable or self-compacting concrete. For the full report, visit CIRIA Bookstore AI responses may include mistakes. Learn more Form pressure generated by fresh concrete

CIRIA Report 108 (1985) is a seminal guide for calculating lateral concrete pressure on vertical and inclined formwork, utilizing a trapezoidal pressure distribution model. It provides empirical formulas incorporating factors like mix composition, placement rate, and temperature, acting as a, reference for modern construction and formwork design. Read the full report details at www.sciencedirect.com

An empirical model to predict fresh concrete lateral pressure

CIRIA 108 vs. ACI 347 (The US Standard)

Many global engineers compare CIRIA 108 to the American Concrete Institute’s ACI 347 (Guide to Formwork for Concrete). There are stark differences: ciria report 108 concrete pressure on formwork

| Feature | CIRIA 108 (UK/Global) | ACI 347 (US) | | :--- | :--- | :--- | | Primary Variable | Setting time (E) and Rate (R) | Column size and pour rate | | Pressure Equation | P = 1.2 x D x R x E | P = D x (C1√R + C2) | | Minimum Value | 25 kN/m² | 30 kPa (624 psf) | | Best For | Walls, deep sections, controlled rates | Columns, moderate pours |

Verdict: ACI 347 uses empirical curves based on column size. CIRIA 108 is more scientific for walls and unusual geometries because it explicitly accounts for the concrete's hydration chemistry. For complex projects, many engineers run both and use the higher (safer) value.

The Famous CIRIA 108 Pressure Formula

The report’s most influential contribution is the formula for maximum lateral pressure (P_max) at the base of a vertical form: CIRIA Report 108 (1985) serves as a foundational

P_max = C1 × (R / T) + C2

Where:

  • P_max = maximum lateral pressure (kN/m²)
  • R = rate of placement (m/h)
  • T = concrete temperature (°C)
  • C1 and C2 = coefficients depending on concrete type, slump, and formwork characteristics (provided in tables within the report)

For typical structural concrete (slump 50–100 mm, without retarders), C1 ≈ 7.2 and C2 ≈ 18, giving: CIRIA 108 vs

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:

  • Rate R = 2 m/h
  • Temperature T = 20°C
  • P_max = 7.2 × (2/20) + 18 = 7.2 × 0.1 + 18 = 0.72 + 18 = 18.72 kN/m²

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.

Best Practices for Modern Formwork Design Using CIRIA 108

To safely and economically design formwork today:

  1. Always perform a site-specific CIRIA calculation. Never rely on rule-of-thumb multipliers.
  2. Measure concrete temperature at the point of placement. Use a digital thermometer.
  3. Monitor actual placement rate. Use laser or ultrasonic sensors on the form face.
  4. Apply a safety factor (typically 1.5 on calculated pressure) for formwork ties and panel bending.
  5. Consider using adjustable-rate pumps to slow placement when temperature drops overnight.
  6. For SCC (slump flow >650 mm), revert to 80% of hydrostatic as a conservative baseline.
  7. Document your calculations – CIRIA 108 is accepted by most building inspectors and third-party reviewers.