On Formwork [cracked] — Ciria Report 108 Concrete Pressure

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.

): The vertical speed at which the formwork is filled (measured in meters per hour) is a primary driver of pressure. Faster placement rates mean a taller column of fluid concrete accumulates before the bottom layers begin to stiffen, resulting in higher peak pressures. Concrete Temperature (

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.

) for an existing formwork setup, maximizing productivity without risking structural integrity.

If you need help checking a specific formwork design, tell me your , rate of rise , concrete temperature , and mix type . I can walk you through the math to find your maximum design pressure. Share public link ciria report 108 concrete pressure on formwork

Use a simple plumb line mark on the formwork with a time log. Or use modern IoT sensors that trigger alarms if the pour rate exceeds your R_max.

Despite its clarity, CIRIA 108 is often misapplied. Here are the top five errors observed on job sites:

Retarding admixtures extend the time before initial set. This effectively increases R/T ratio, raising pressure. The report suggests applying a temperature correction or using an "effective temperature" lower than the actual concrete temperature.

Many global engineers compare CIRIA 108 to the American Concrete Institute’s ACI 347 (Guide to Formwork for Concrete). There are stark differences: In the world of concrete construction, few elements

Using the correct pressure values ensures formwork does not bulge or fail (blowout).

To safely and economically design formwork today:

The challenge for engineers was finding a reliable mathematical model that balanced safety (preventing formwork failure) with economy (not over-designing the formwork). This is where CIRIA Report 108 stepped in.

Internal vibration can locally increase pressure by 20–40% directly around the vibrator head. However, CIRIA 108 notes that proper vibration does not increase formwork pressure if the placement rate accounts for vibration-induced fluidization. The key is to avoid over-vibration, which can segregate concrete and cause blowouts. Faster placement rates mean a taller column of

This article provides a comprehensive overview of CIRIA 108, exploring its background, principles, and application in modern construction. 1. Introduction to CIRIA 108

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.

Based on the findings of CIRIA Report 108, the following recommendations and best practices are proposed: