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Ciria Report 108 Concrete Pressure On Formwork -

The Gold Standard: An In-Depth Look at CIRIA Report 108 and Concrete Formwork Pressure

In the world of civil engineering and construction, few documents have achieved the status of a "silent standard" quite like CIRIA Report 108: Concrete Pressure on Formwork. Published in 1985 by the Construction Industry Research and Information Association (CIRIA), this report revolutionized how engineers calculate the lateral pressure exerted by fresh concrete on vertical formwork.

Formwork rigidity: Less rigid formwork can deform under pressure and attract greater loads; specify minimum stiffness or tie spacing to limit deflections and redistribution. ciria report 108 concrete pressure on formwork

CIRIA Report 108 (1985) provides a standard, non-hydrostatic method for calculating lateral concrete pressure on vertical formwork by accounting for placement rate, temperature, and concrete mix design. The model determines the maximum pressure based on either full hydrostatic pressure or a formula covering the "arch effect," which is widely recognized in standards like BS 5975. For more information, visit the official CIRIA R108 overview Concrete pressure on formwork (R108) - CIRIA The Gold Standard: An In-Depth Look at CIRIA

The theoretical maximum pressure concrete can exert is full hydrostatic pressure. This assumes the fresh concrete behaves exactly like a liquid; as the concrete is poured, the pressure increases linearly with depth ($P = \rho g h$). While safe, this approach is incredibly conservative. Designing formwork to withstand liquid pressure for a 10-meter pour requires heavy, expensive, and cumbersome falsework. Rate of placement (R) – Vertical rise speed

  1. Rate of placement (R) – Vertical rise speed of concrete in the form (m/h). Faster rates mean less time for stiffening, hence higher pressure.
  2. Temperature (T) – Affects cement hydration and setting. Cold concrete retains fluidity longer, increasing pressure.
  3. Concrete mix design – Slump, cement type, water-cement ratio, and use of superplasticizers or retarders.
  4. Formwork geometry – Height, width, and stiffness of the forms.
  5. Vibration – Internal or external vibration temporarily liquefies concrete, increasing local pressure.

Conclusion: Why CIRIA 108 Remains Indispensable

Nearly 40 years after its publication, CIRIA Report 108 "Concrete Pressure on Formwork" remains the gold standard for rational formwork design. It shifted the industry from fearful over-design to intelligent, risk-aware engineering.

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.

Reduction with time/setting: As concrete stiffens, lateral pressure decreases. The rate of reduction depends on mix chemistry, temperature, and admixtures (notably accelerators or retarders).