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.
Rearrange the formula: R_max = P_allowed / (1.2 × D × E) If your formwork is rated for 80 kN/m², you solve for R to determine the maximum trucks per hour. ciria report 108 concrete pressure on formwork
Introduction In the world of concrete construction, few elements are as critical—and as often misunderstood—as lateral pressure on vertical formwork. Over-pour a wall or misjudge the setting rate of a column, and the result is a blowout: thousands of dollars in wasted material, potential worker injury, and crippled project timelines. Research (including later CIRIA updates) shows that for
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? Introduction In the world of concrete construction, few
Have a ready-mix engineer track the concrete temperature. If the truck arrives cooler than expected, recalculate P_max immediately. Case Study: The Heathrow Terminal 5 Pours When constructing the massive diaphragm walls for Heathrow Terminal 5 (London), engineers faced pours up to 15 meters deep. Ordinary hydrostatic assumptions would have required 200 kN/m² formwork—impractical and expensive.
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.
Lateral pressure is a function of setting time and rate of pour , not just height.
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