Ciria Report 108 Concrete Pressure On Formwork [upd] Jun 2026

Formwork is a crucial component in the construction industry, particularly in the building of concrete structures. The temporary structure is used to hold and shape concrete until it sets and gains sufficient strength. One of the primary concerns with formwork is the pressure exerted by the concrete on the formwork, which can lead to deformation, instability, or even collapse. CIRIA (Construction Industry Research and Information Association) Report 108, titled "Concrete Pressure on Formwork," provides a comprehensive guide on the subject. This report aims to summarize and expand on the key findings and recommendations of CIRIA Report 108.

The type of cement and the inclusion of admixtures (like plasticizers or retarders) heavily influence the stiffening rate and the resulting pressure envelope. 3. The CIRIA 108 Calculation Framework

This article provides a comprehensive overview of CIRIA Report 108, its governing principles, application, and comparison with modern alternatives for vibrated concrete. 1. Introduction to CIRIA Report 108

Before diving into the formula, it is vital to understand the physical principles that CIRIA 108 codifies.

To determine the design pressure, the engineer calculates two distinct limits: Where is the density of the concrete and ciria report 108 concrete pressure on formwork

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Confined space allows aggregate interlocking to absorb more vertical load.

Before the release of CIRIA Report 108, formwork design often relied on simplified hydrostatic assumptions or outdated empirical formulas. These older methods frequently overestimated pressure, leading to over-designed, expensive formwork, or underestimated it, resulting in dangerous blowouts.

The maximum lateral pressure exerted by concrete is not uniform. Initially, when fresh concrete is poured, it behaves like a heavy liquid, creating (P = ρ gh). However, as concrete sets and begins to gain shear strength, it stops acting as a liquid, and the lateral pressure stops increasing, even if the concrete level rises higher. Key Factors Affecting Pressure Formwork is a crucial component in the construction

The composition of the concrete drastically alters its behavior:

For decades, has stood as the definitive industry standard for calculating these pressures. Published by the Construction Industry Research and Information Association (CIRIA) in 1985, this document revolutionized formwork design by replacing overly conservative empirical formulas with a rational, multi-variable approach that accurately reflects real-world construction practices. The Evolution of Formwork Pressure Calculation

Ensure workers do not insert poker vibrators too deeply into previously placed, partially set layers of concrete, as this re-fluidizes the mix and spikes lateral pressure.

Note: The formula specifically assumes "normal" vibrated concrete and requires adjustments for special mixes like SCC, which act more fluidly. 5. Comparison with Other Standards (ACI 347 & DIN 18218) partially set layers of concrete

CIRIA Report 108 outlines a reliable, empirical method to calculate the maximum lateral pressure ( Pmaxcap P sub m a x end-sub

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Comprehensive Guide to CIRIA Report 108: Concrete Pressure on Formwork

vary depending on the specific tables and charts provided within the report document, adjusting for the concrete temperature and the presence of slag or ash.)