Ciria Report 108 Concrete Pressure On Formwork -

The method can be extrapolated to conditions outside existing practice, but designers should exercise caution.

. This explicitly penalizes cold-weather pours by escalating the design pressure.

The temperature of the concrete mix at the time of placing (measured in °C). Higher temperatures accelerate the chemical hydration process, causing the concrete to stiffen faster and reducing the duration of maximum pressure. Conversely, cold weather retards setting times, keeping the concrete fluid longer and increasing lateral forces. Characteristics of the Mix

R 108 remains the foundational technical report detailing the calculation methodology. CIRIA C660 is a more modern publication that addresses the specific challenges of Self-Compacting Concrete (SCC) and updates the guidance for modern binder systems, but it essentially builds upon the fundamental physics established in R 108. For day-to-day structural calculations, most engineers refer back to the formulas and coefficient tables of R 108, while using C660 for edge-case scenarios involving highly fluid mixes. ciria report 108 concrete pressure on formwork

Before Report 108, engineers relied heavily on hydrostatic assumptions or early formulas that failed to account for modern concrete technology, such as chemical admixtures and high-frequency vibration. Overestimating pressure leads to over-engineered, expensive formwork. Underestimating it leads to catastrophic formwork bursts, safety hazards, and financial loss. Core Philosophy

P_max = 1.2 × 24 × 2 × 2 = 115.2 kN/m²

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. The method can be extrapolated to conditions outside

CIRIA 108 introduced a comprehensive, semi-empirical design method. It accounts for the complex chemical and physical changes that concrete undergoes during placing and setting. By accurately predicting maximum lateral pressure, the report allows temporary works designers to optimize ties, shores, and walers without compromising safety. Core Mechanics of Concrete Pressure

Prevent over-designing formwork, which inflates material and labor costs.

The geometry of the formwork profoundly affects how pressure dissipates through friction against the form faces. CIRIA 108 distinguishes between two primary conditions: The temperature of the concrete mix at the

Core concept: Fresh concrete behaves partly like a fluid when newly placed, so it exerts lateral pressure on formwork. The pressure magnitude depends on concrete properties, placement rate, consolidation (vibration), temperature, and time-dependent setting.

CIRIA Report 108, titled “Concrete Pressure on Formwork,” is a widely cited guidance document that synthesizes research and practice on the lateral pressures exerted by fresh (plastic) concrete against formwork during casting. Its primary aim is to help engineers, formwork designers and site teams predict and safely design formwork systems for vertical and inclined concrete elements.