Cement Content Explained
Cement content per cubic metre of concrete is set by two separate requirements — a strength-driven figure worked out from the water content and adopted water-cement ratio, and a durability-driven minimum set by the exposure class. The higher of the two applies.
How cement content is calculated
Once the water content and the adopted water-cement ratio are both known, cement content follows directly: cement = water ÷ w/c. This is the strength-driven cement content — the amount needed to hit the adopted w/c at the estimated water demand.
The exposure-class minimum
EN 206, via the applicable national annex, separately sets a minimum cement content for each exposure class, on top of whatever the strength calculation alone gives. This exists because durability depends on there being enough cement paste to fill voids and resist ingress, independent of the strength grade — a lean, low-cement mix can be durability-deficient even if it technically reaches its strength class. Where the exposure-class minimum is higher than the strength-driven figure, the higher (minimum) value is adopted. Check your national annex’s current exposure class tables for the minimum cement content that applies to your project.
Frequently asked questions
Can cement content ever be too high?
Yes — very high cement contents increase heat of hydration (raising cracking risk in mass sections) and cost, without necessarily improving performance further. Mix design aims for the cement content that satisfies both strength and the exposure-class minimum, not the maximum available.
Does a richer mix (more cement) always mean more durable concrete?
Not by itself — durability also depends on the water-cement ratio being controlled, proper curing, and adequate compaction. Cement content and w/c work together, not independently.
Where do I find the exact minimum cement content for my exposure class?
Check your national annex’s current exposure class tables for the minimum cement content that applies to your project.