Ciria Report 108 Concrete Pressure On Formwork May 2026

In the 1970s and 80s, engineers realized the "fluid head" method was wasting millions on over-engineered formwork. Concrete stiffens as it hydrates. CIRIA 108 introduced the concept of "pressure relief" based on setting time.

CIRIA 108 is not for SCC (Self-Compacting Concrete). For SCC, assume full fluid pressure (( \rho gh )) until the HPC (High Performance Concrete) has a measured yield stress > 300 Pa.

Your turn: Do you still use the CIRIA 108 nomographs, or have you moved to pressure sensors and digital monitoring?

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Suggested Image for the Post: A graph showing "Lateral Pressure (kN/m²)" on the Y-axis vs "Height (m)" on the X-axis, with two lines:

Alt Text: Comparison graph of concrete pressure on formwork showing CIRIA 108 plateau vs hydrostatic pressure.

Understanding Concrete Pressure on Formwork: Insights from CIRIA Report 108 ciria report 108 concrete pressure on formwork

Formwork is a critical component in concrete construction, providing a mold for the concrete to take shape. However, the pressure exerted by the concrete on the formwork can be substantial, and if not properly understood and managed, it can lead to accidents, damage, and costly repairs. CIRIA Report 108, "Concrete pressure on formwork," provides valuable guidance on this critical aspect of concrete construction.

What is concrete pressure on formwork?

Concrete pressure on formwork refers to the lateral pressure exerted by the concrete on the formwork as it is placed and compacted. This pressure can vary depending on several factors, including:

Key findings from CIRIA Report 108

The report provides a comprehensive review of the factors influencing concrete pressure on formwork and offers practical guidance on how to:

Best practices for managing concrete pressure on formwork In the 1970s and 80s, engineers realized the

Based on the recommendations in CIRIA Report 108, here are some best practices for managing concrete pressure on formwork:

Conclusion

CIRIA Report 108 provides valuable insights into the complex topic of concrete pressure on formwork. By understanding the factors influencing concrete pressure and following best practices, construction professionals can ensure the safe and efficient construction of high-quality concrete structures. Whether you're a seasoned practitioner or a student, this report is an essential resource for anyone involved in concrete construction.

References: CIRIA Report 108: Concrete pressure on formwork. (Please check the publication details and availability)

Published in 1985, CIRIA Report 108 ( Concrete Pressure on Formwork

) provides a standardized method for calculating lateral pressure exerted by fresh concrete, accounting for variables like rate of rise and mixture design. It remains a primary reference in BS 5975:2019 for determining the maximum pressure ( cap P sub m a x end-sub Suggested Image for the Post: A graph showing

) on vertical formwork. Detailed information regarding the report can be found at Concrete pressure on formwork (R108) - CIRIA

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

Yes, but with caution. Research (including later CIRIA updates) shows that for SCC, the coefficient (1.2) is insufficient. SCC can maintain fluid-like behavior for longer, leading to near-hydrostatic pressures.

Updated guidance: When using SCC, many engineers use a modified CIRIA approach with a coefficient between 1.8 and 2.5, or simply default to full hydrostatic pressure (D x H) for formwork safety.

Wind load is external, but CIRIA 108 only covers internal concrete pressure. For tall, slender formwork, wind can add 0.5 to 1.0 kN/m² of suction, stacking on top of P_max.

No document is perfect. Critics note:

To address these, CIRIA issued subsequent guidance (e.g., C660 "Formwork Pressure"), but Report 108 remains the foundational reference.