"What concrete do I need?" sounds like a simple question. Under the European standard EN 206, the answer has two parts: how strong the concrete must be, and what environment it must survive.
Part 1: strength class
The strength class is written like C25/30:
- 25 = characteristic strength in MPa measured on cylinders
- 30 = the same measured on 150 mm cubes
- Both at 28 days
| Class | Typical uses (always as specified by the engineer) |
|---|---|
| C16/20 | Blinding, non-structural fill |
| C20/25 | Lightly loaded, protected elements |
| C25/30 | Common for housing slabs, beams and columns |
| C30/37 | More demanding structures and exposures |
| C35/45 and above | Severe exposure, high loads, precast |
Part 2: exposure class (durability)
Strength alone does not guarantee a long life. The exposure class describes what attacks the concrete:
| Class | Meaning | Cyprus examples |
|---|---|---|
| XC1–XC4 | Corrosion caused by carbonation | Indoor elements (XC1), foundations (XC2), sheltered external (XC3), exposed to rain cycles (XC4) |
| XS1 | Airborne sea salt | Buildings near the coast |
| XS2 / XS3 | Submerged / tidal and splash zone | Harbours, sea walls |
| XA | Chemically aggressive ground | Some soils and industrial sites |
| XF | Freeze-thaw | Mainly high altitude, Troodos |
Each exposure class comes with limits on the maximum water/cement ratio, minimum cement content and a recommended minimum strength class. For example, EN 206's recommended values put XC3/XC4 and XS1 at around C30/37 and XS2/XS3 at C35/45. Always check the values in the Cypriot national provisions and the engineer's specification.
Why coastal Cyprus is different
Much of the Cypriot population and tourism sits within a few kilometres of the sea. Airborne chlorides reach the steel in concrete faster when the mix is porous or the cover is thin. Rusting steel expands and spalls the concrete. This is why balconies and frames near the sea often fail first.
The fix is at the design stage: the right exposure class, a low water/cement ratio, enough cover to the reinforcement and proper curing.
Three practical tips
- Order by full specification, not just "C25": strength, exposure class, maximum aggregate size and consistence (slump class).
- Do not add water on site. It moves the mix out of its exposure limits.
- Test it. Cube tests at 28 days confirm the strength you paid for.
If you are not sure what your project needs, our engineers can help you read the specification.
Frequently asked questions
What does C30/37 mean?
C30/37 means a characteristic compressive strength of 30 MPa on cylinders and 37 MPa on 150 mm cubes at 28 days.
Do I need special concrete near the sea?
Often yes. Airborne sea salt puts structures near the coast in a chloride exposure class (XS), which typically calls for a higher strength class, lower water/cement ratio and more cover to the reinforcement.
Who decides the concrete class?
The structural engineer specifies it on the drawings, based on structural needs and the exposure class of each element.
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