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Hi Lloyd,

I would say a good mix to use by volume would be 1 part cement / 2.5 parts sand / 3 parts coarse aggregate. The coarse aggregate being graded from 20mm to 5mm in size. For 1 cubic meter, this would equate to approximately, 350kg cement, 875kg sand, 1050kg coarse aggregate (20-5mm) and 180 litres of water. So for 0.15 of a cubic metre you would need 52.5kg cement, 131.25kg sand, 157.50kg aggregate (20-5mm size) and 27 litres of water. Cement usually comes in 25kg bags these days so it should be OK to use 2 x 25kg bags (50kg) for a 0.15m3 batch. Try not to make the mix any wetter than is needed to ensure full compaction as this will reduce the strength. You may need to add a little more or a little less water from the target 27 litres. This mix should achieve a strength of about 30 MPa / 4000 psi. Best regards, Les