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Frequently Asked Questions
What is CEM I?
Essentially pure clinker cement.
Only a very small allowance for other constituents.
It is the reference cement.
Other types are described against it.
Portland cement usually means this.
Why is it the fastest?
Because clinker does the early work.
There is more of it than in any blend.
So strength arrives sooner.
Early-age performance is its advantage.
Final strength is matched by others.
Where is that useful?
Precast production turning moulds around.
Work that must be struck or loaded early.
Cold-weather concreting, where reactions slow.
And high-strength mix designs.
Anywhere the programme is tight.
Why is it hot?
Hydration releases heat as it proceeds.
More clinker means more heat, faster.
Speed and heat come from one reaction.
They cannot be separated.
It is inherent to the cement.
Why is heat a problem?
The heat has nowhere to escape to.
The core runs far hotter than the surface.
The cooler surface restrains the core.
Thermal cracking follows days later.
It cannot be repaired afterwards.
So what suits a large pour?
A lower-heat blended cement.
CEM III especially, or a CEM II blend.
The heat is released more slowly.
Peak core temperature is lower.
The strongest cement is the wrong tool.
What about carbon?
It is the highest of any cement here.
Clinker manufacture releases the carbon dioxide.
More clinker means more of it.
On a carbon target this matters most.
Specifying it by habit works against you.