Use this imperial concrete calculator to determine how ready mix concrete is required for
laying a given area or volume of concrete. This will work for a slab or footing.
We also have an 'Metric' version of this calculator here.
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Desirable properties in a concrete mix
- Ensure the concrete mix is workable which allows correct placement and consolidation
- Ensure the optimum desired quality of the hardened concrete is met which improves resistance to
freezing and thawing, water tightness (low permeability) , wear resistance, and strength
- The quality of the concrete is dependant mainly on the water to cement ratio, so water requirements should
be minimised to reduce the cement requirement thereby reducing the overall cost
- The mix should be a stiff as possible
- Use the largest aggregate practicable
- Use the optimum ratio of fines to coarse aggregate
- A low water to cement ratio is the number one issue that affects concrete quality. Do not add too much
water
Components in concrete
- Portland Cement - the aggregate and sand is coated by a paste formed from the cement and water. This paste
then hardens and binds the fines (sand) and aggregate together
- Water - this is needed to chemically react with the cement and to make the concrete workable
- Aggregate - The fines are sand and gravel or crushed stone is the coarse aggregate (10, 20 & 40mm) in
most mixes
Admixtures in Concrete
- Accelerators - added to the concrete to reduce overall setting times and gain early strength. Calcium
chloride is the lower cost accelerator, however a non-chloride accelerator should be specified if reinforcing
has been used, to prevent corrosion of the steel
- Retarder - used in hot weather to delay setting. Also used for difficult jobs and specialist finishes. May
also act as a water reducer
- Fly Ash - improves workability, easier to finish and reduces the cement content
- Air Entrainment - improves the workability of the concrete as well as the durability