Cement
Some people confuse concrete with cement, but cement is just the ‘glue’ which holds the other constituents of concrete, sand and gravel, together.
There are a range of different cements but these are the three you will most commonly come across:
General Purpose Cement
This is consistent, versatile and cost effective product which makes it a good choice for most building works.
It is suitable for Domestic concrete slabs, driveways and footpaths
Trivial Fact -You may hear standard cement referred to as Portland Cement – This is because the finished concrete has an appearance similar to stone quarried from Portland in England.
Sulphate Resisting Cement
Sulfate Resisting Cement is a blended cement designed to improve the performance of concrete where the risk of sulfate attack may be present.
It also provides improved durability for concrete, and the steel reinforcement, in most aggressive environments, such as seawater exposure.
It has an additional cost, but it is much better for:
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- Geothermal areas
- Soils containing sulphates
- Saline Areas
- Area that are frequently wet such as concrete swimming pools
Rapid Set Cement
Normally found in dry premixed concrete mixes.
This is a cement with various additives that speed up the reaction to give an initial hardening within 15 minutes.
Speeding up of the cement reaction time does lead to lower final strength.
This makes this product good for things like setting fence posts………… but NOT for significant structural applications.
Water Cement Ratio
One of the most important issues with cement is ensuring the ratio of water and cement is correct as this affects both the final strength and the durability. For instance:
- Water cement ratio 0.5 (10L water to 20kg cement) is needed for high strength 35MPa.
- Increasing the Water cement ratio to 1 (20L water to 20kg cement) will reduce the strength to 10MPa.
To ensure they don’t add too much water premix companies usually measure the water content in the sand and gravel piles and reduce the water content accordingly.
This means ading water to a premix lorry will affect the strength of the concrete
For more information see Concrete.