CONCRETE COVER TO REINFORCEMENT

What this calculator checks

The calculator determines the concrete cover to the reinforcement, \(c_{nom}\), according to EN 1992-1-1 §4.4.1 — the distance from the concrete face to the nearest reinforcing bar. It is the first dimension to fix on any reinforced-concrete element, because from it follows the effective depth \(d = h - c_{nom} - \phi/2\), which enters every resistance check.

The base expression (4.1):

\(c_{nom} = c_{min} + \Delta c_{dev}\)

where \(\Delta c_{dev}\) is the execution tolerance (recommended value 10 mm), and \(c_{min}\) is the minimum cover (4.2):

\(c_{min} = \max\left\{ c_{min,b} \; ; \; c_{min,dur} + \Delta c_{dur,\gamma} - \Delta c_{dur,st} - \Delta c_{dur,add} \; ; \; 10 \text{ mm} \right\}\)

The two requirements

The minimum cover satisfies two conditions at once, and the larger governs:

• Bond (\(c_{min,b}\)) — the concrete must surround the bar by at least its diameter, so the force transfers through bond (Table 4.2).
• Durability (\(c_{min,dur}\)) — the concrete must protect the steel from corrosion over the design life. It depends on the exposure class (Table 4.1: XC for carbonation, XD/XS for chlorides, etc.) and the structural class (Table 4.3N), adjusted for design life, concrete class and quality control.

Casting against the ground

When concrete is cast directly on the ground, without formwork, the surface is irregular and the cover must be increased:

• against prepared ground (blinding concrete): \(c_{nom} \ge 40\) mm
• directly on the ground: \(c_{nom} \ge 75\) mm

The calculator applies these minima when you select the casting mode, typical for foundations.

Input data

• Exposure class — the code from Table 4.1 (XC1…XA3).
• Design working life — 50 or 100 years; 100 years raises the structural class.
• Concrete class — a stronger concrete lowers the durability cover required.
• Bar diameter — enters the bond requirement.
• Casting mode — formed or against the ground.

Assumptions and limitations

• The values are the recommended ones (NDP) from the default National Annex of EN 1992-1-1; the local National Annex may differ.
• It covers reinforcement for reinforced concrete (Table 4.4N). Prestressing steel (Table 4.5N) is not treated.
• Fire resistance requirements (EN 1992-1-2), which may impose larger covers, are not treated.

Related calculations

• Reinforced section — uses the \(d = h - c_{nom} - \phi/2\) resulting here
• Crack-width verification — the cover enters the crack width directly
• Punching shear — for the effective depth of the slab
• Isolated footing — where casting against the ground is the rule