Formwork - Ciria Report 108 Concrete Pressure On

Although published decades ago, CIRIA Report 108 remains a landmark in formwork engineering. It shifted the industry from conservative guesswork to rational, measured pressure prediction. Today, it is often used alongside more recent standards and computational modeling, but its empirical core—linking rate of pour, temperature, and pressure—is still taught and applied worldwide.

In summary: CIRIA Report 108 provides engineers with a reliable, temperature- and rate-based method to calculate lateral concrete pressure on formwork, balancing safety with material efficiency. For any concrete pour requiring designed formwork, understanding this report is a fundamental skill.

CIRIA Report 108 (1985) serves as the UK industry-standard guide for calculating lateral concrete pressure on formwork, utilizing a semi-empirical formula that accounts for placement rate, concrete density, and temperature. The report distinguishes between wall and column pressures and covers the impact of modern admixtures, though it may be conservative for highly flowable self-compacting concrete. The report is available through the CIRIA bookstore. Concrete pressure on formwork (R108) - CIRIA

This is the speed at which the concrete level climbs vertically inside the formwork. It is NOT the same as the pump output.

Actionable tip: Control R by limiting concrete delivery trucks or adjusting pump speed.

CIRIA Report 108 is a classic example of industry research that successfully transferred into daily practice. While it requires careful application when dealing with modern, highly fluid concrete mixes (like SCC), it remains the "go-to" document for standard concrete pours.

It is written with the authority of research but the pragmatism of the construction site. For any engineer designing vertical formwork, R108 remains an indispensable tool, serving as a sanity check against more complex modern standards. ciria report 108 concrete pressure on formwork

Rating: 4.5/5 (Deducted 0.5 only due to the need for supplementary guidance on modern admixtures).

CIRIA Report 108, "Concrete pressure on formwork," serves as a foundational guide for calculating the lateral pressure exerted by fresh concrete on temporary formwork structures, accounting for variables like rate of rise, temperature, and mix composition. It provides specific formulas to determine maximum pressure ( Pmaxcap P sub m a x end-sub

) and design coefficients for walls and columns to prevent formwork failures. For more details, visit CIRIA. Construction and Building Materials

CIRIA Report 108 (1985) provides a standard, non-hydrostatic method for calculating lateral concrete pressure on vertical formwork by accounting for placement rate, temperature, and concrete mix design. The model determines the maximum pressure based on either full hydrostatic pressure or a formula covering the "arch effect," which is widely recognized in standards like BS 5975. For more information, visit the official CIRIA R108 overview Concrete pressure on formwork (R108) - CIRIA

CIRIA Report 108 (1985) establishes the standard UK methodology for calculating lateral concrete pressure on vertical formwork, utilizing factors like placement rate, temperature, and mix composition to determine maximum pressure. Referenced in BS 5975:2019, the report addresses both hydrostatic and reduced pressure scenarios to optimize formwork design. Purchase the report at the CIRIA Official Bookshop. Concrete pressure on formwork - BS5975:2019 - Prontubeam

Published in 1985, CIRIA Report 108 ( Concrete Pressure on Formwork Although published decades ago, CIRIA Report 108 remains

) provides a standardized method for calculating lateral pressure exerted by fresh concrete, accounting for variables like rate of rise and mixture design. It remains a primary reference in BS 5975:2019 for determining the maximum pressure ( cap P sub m a x end-sub

) on vertical formwork. Detailed information regarding the report can be found at Concrete pressure on formwork (R108) - CIRIA

Published in 1985, CIRIA Report 108 (R108) serves as a primary industry standard for calculating the lateral pressure of fresh concrete on formwork. The report provides an empirical formula to determine maximum pressure based on variables like concrete density, rate of rise, and temperature, which remains relevant for ensuring safe, cost-effective formwork design. For full details, visit CIRIA. Concrete pressure on formwork (R108) - CIRIA

To appreciate CIRIA Report 108, one must compare it to other major standards:

| Aspect | CIRIA 108 | ACI 347 (USA) | EN 12812 (Europe) | |-------------|----------------|--------------------|-------------------------| | Base formula | P_max = C1*(R/T) + C2 | P_max = C_w × C_c × (7.2 + 785R/(T+17.8)) | P_max = F + (R/(T+1)) × K | | Temperature | Explicit (°C) | Explicit (°C) | Explicit (°C) | | Slump influence | Coefficients for 0–50mm, 50–100mm, >100mm | C_c factor (0.5 to 1.2) | Built into K factor | | Rate limit | No strict cap, but pressure limited to hydrostatic | R ≤ 2.1 m/h for formula; above that, hydrostatic | R limited based on form class | | Minimum pressure | Yes (C2 term) | Yes (7.2 factor) | Yes (F term) |

CIRIA 108 is often considered more flexible for low- to moderate-rate pours, while EN 12812 is more prescriptive for safety-critical applications. Many formwork manufacturers now produce load tables that directly reference CIRIA 108, Class 1 or 2 loading. In summary: CIRIA Report 108 provides engineers with

Before Report 108, formwork designers relied on empirical rules-of-thumb or overly conservative hydrostatic pressure models. The hydrostatic assumption—that fresh concrete behaves exactly like a liquid (pressure = density × height)—led to massively over-engineered (and expensive) formwork. Conversely, simplified rules like "pressure = 1.5 × height" often proved unsafe for high-slump, fast-pouring conditions.

Recognizing this gap, CIRIA initiated a research program in the late 1970s, led by A.C. Hargreaves and others, to measure actual lateral pressures during real-world pours. The result was CIRIA Report 108 (1985), which provided:

The report became an instant reference for structural engineers, formwork suppliers, and concrete contractors worldwide.

This is often the most contentious variable on site. If a crane is pumping concrete rapidly, $R$ is high, leading to high calculated pressure. If the pour is slow (perhaps delayed by a pump blockage), $R$ drops, and pressure drops.

Higher slump (e.g., self-consolidating concrete) increases fluidity and delays stiffening. CIRIA 108 recommends adjusting the coefficient C1 upward for slump >120 mm. For SCC (slump flow >600 mm), many designers conservatively revert to hydrostatic pressure.