This article breaks down every aspect of CIRIA 108, explaining how to apply its formulas, why it outperforms older standards like ACI 347, and how to prevent formwork failure on your next pour. Before CIRIA 108, engineers primarily relied on hydraulic pressure formulas, assuming that fresh concrete behaved like a liquid (Pressure = Density x Depth). While this approach (often called the "hydrostatic" model) is safe, it is wildly uneconomical. It assumes that until concrete hardens, every inch of height exerts full fluid pressure.
For decades, engineers and contractors have relied on a single, authoritative document to navigate this risk: ciria report 108 concrete pressure on formwork
ACI 347 uses empirical curves based on column size. CIRIA 108 is more scientific for walls and unusual geometries because it explicitly accounts for the concrete's hydration chemistry. For complex projects, many engineers run both and use the higher (safer) value. Special Cases: Self-Compacting Concrete (SCC) Standard CIRIA 108 was written before SCC became ubiquitous. SCC has much higher flowability and longer setting retention. Does CIRIA 108 still apply? This article breaks down every aspect of CIRIA
Applying CIRIA 108, they measured the setting time (E) of the site mix (a high-density concrete with PFA) at 3.5 hours and controlled the rate of rise (R) to 1.2 m/hour. The resulting P_max was just 120 kN/m². It assumes that until concrete hardens, every inch
In the late 1970s and early 1980s, CIRIA undertook a massive research project, observing real-world pours in walls, columns, and slipforms. The result, published in , provided empirical evidence that concrete stiffens (develops "shear strength") as it hydrates, thereby reducing peak pressure significantly below the hydrostatic maximum.