Work out the cement, sand and aggregate (ballast) quantities for a concrete mix by volume and ratio.
We add a 54% allowance to the wet volume because dry materials compact when mixed with water. Cement is shown in 25 kg bags; sand and aggregate are shown in tonnes.
A 1:1.5:3 mix (one part cement, one and a half parts sand, three parts aggregate) gives a strong structural concrete suitable for footings and slabs.
Yes. Combine the sand and aggregate figures — ballast is simply pre-mixed sand and gravel. Use roughly four parts ballast to one part cement for a general mix.
For a 1:2:4 mix you need roughly 300 kg of cement (about 12 bags of 25 kg) per cubic metre.
A 1:2:4 mix (cement : sharp sand : aggregate) is a common general-purpose ratio. For stronger structural work a 1:1.5:3 mix is often used.
Roughly half the weight of the cement (a water-cement ratio around 0.5). Add it gradually — the mix should be workable but not sloppy.
Calculate how much concrete you need for slabs, footings, columns and walls in cubic yards or metres.
OpenCalculate the concrete volume and number of bags needed for strip, pad and pier footings.
OpenEstimate the total cost of concrete for a slab, footing or footpath from the volume and your price per cubic yard or metre.
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