Ciria Report 108 Concrete Pressure On Formwork «Windows»

For decades, engineers and contractors have relied on a single, authoritative document to navigate this risk:

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. ciria report 108 concrete pressure on formwork

Consider "horizontal layering" (pouring in lifts of 1-2 meters with a 30-minute delay between lifts). This allows lower layers to set, drastically reducing pressure on the bottom tie-rods. For decades, engineers and contractors have relied on

Order a penetration resistance test (ASTM C403 / BS EN 480-2) on your specific mix at the expected site temperature. This allows lower layers to set, drastically reducing

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.

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.