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

The Core Principle: Why Concrete Isn’t Water

To understand CIRIA 108, you must abandon the "liquid assumption."

Core Purpose: To provide a reliable, empirical model for predicting maximum lateral pressure ( Pmaxcap P sub m a x end-sub ) to ensure safe and cost-effective formwork design.

Critical Factors That Influence R and E

The magic of CIRIA 108 lies in accurately capturing Rate (R) and Setting Time (E). Misjudging these is the primary cause of formwork failure.

Formwork Height

Report 108 distinguishes between the height of the formwork and the pressure envelope. In tall columns, the pressure might reach a maximum peak and then drop off near the bottom because the concrete there has set. In short walls, the pressure might be hydrostatic because the pour finishes before the concrete has time to stiffen.