Blog · Materials
What types of cement are there?
Every bag of cement has product information on the back, but many people assume there are only two kinds: the more expensive waterproof bag and the cheaper paper bag that spoils when wet. There are actually five main types, each with its own grades and classes.
The five main types
Cement is classed from CEM I to CEM V. Only CEM I and CEM II are used for general construction, so those are the two that matter here.
- CEM I
- 100% Portland cement, often called Ordinary Portland Cement (OPC).
- CEM II
- Portland cement diluted with fly ash, limestone, slag, or a combination, up to a maximum of 35%.
Strength grades
CEM I and CEM II each come in three grades, named after the strength the cement reaches after 28 days: 32.5, 42.5 and 52.5 MPa.
Strength gain classes
| Letter | Meaning |
|---|---|
| R | Early (rapid) strength gain |
| N | Normal strength gain |
| L or S | Low or slow strength gain |
| A / B | CEM II only: A is diluted by less than 20%, B by 21–35% |
| V, S, L, M | CEM II additive: fly ash, slag, limestone, or M for more than one |
Reading the bag
CEM II/A-L 32,5R
And an MPa? A megapascal is a million pascals. One MPa is roughly the pressure of a 100-tonne mass pressing on a single square metre, which is a lot.
What we use
Our cement comes from Hanson or Heidelberg Materials and is CEM I 52.5N: pure Portland cement, at the top strength grade, with normal strength gain.
A cheaper CEM II looks like a saving, but you need more of it to reach the same strength. Our C10 (GEN1) mix uses 180 kg of CEM I 52.5N per cubic metre and our C40 uses 300 kg; with CEM II, both would need more.
Our mixes are trialled in a laboratory, where samples are cured, crushed and tested for performance.
- We use CEM I 52.5N, the top strength grade, rather than the cheapest option.
- Each type has grades, and each grade gains strength at its own rate.
- CEM II can contain up to 35% added material.
- Cement in a paper bag is easily spoiled by moisture.