Ciria Report 108 Concrete Pressure On Formwork __link__

Review: CIRIA Report 108 – Concrete Pressure on Formwork

Author: P.J. Clear
Publisher: Construction Industry Research and Information Association (CIRIA)
Year: 1990 (Reprinted with minor amendments 1995)

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.

2. The "CIRIA Bypass" If you have a slow-setting retarder (common in summer), CIRIA 108 allows for zero pressure relief. Your formwork ties must be designed for full fluid head. ciria report 108 concrete pressure on formwork

Practical Implementation on Site

How do you turn CIRIA 108 into actionable formwork design?

Crucially, the report places a "cap" on pressure. Even if the rate of rise is high, the pressure will not increase indefinitely. It levels off once the concrete at the bottom has stiffened enough to support the load of the concrete above it. Review: CIRIA Report 108 – Concrete Pressure on

B. The "Formwork Pressure" vs. "Hydrostatic" Distinction One of the most valuable sections explains the phenomenon of particle interference. As concrete stiffens, the aggregate particles begin to arch, transferring load to the sides of the formwork via friction, thereby reducing the pressure on the lower layers. R108 quantifies this reduction, leading to more economical formwork designs compared to assuming full liquid head.

• From the top down to a certain height (the point of setting): Pressure increases hydrostatically.
• Below that height (the stiffened zone): Pressure remains constant (at the maximum value) down to the base of the form.

Appendices

The determining factor is internal friction, which the report links directly to the rate of rise (R) and the initial setting time (E) of the concrete.