Concrete Mixes
Concrete Mixes & Batch Ratios
For Different Applications
The basic techniques that will enable you to cast a foundation or slab are relatively straightforward. The secret to success lies largely in the correct concrete mixes and quantities being mixed together in the concrete mixes you use. Although the principles of mixing concrete and mortar are simple, this can be backbreaking work, especially if you decide to mix the concrete by hand yourself
If there is a reasonably large quantity of concrete to be used, it is advisable to hire a concrete mixer. Whether you are mixing by hand or in a concrete mixer, you will have to measure materials accurately to ensure you achieve concrete of consistent quality.
Batching Generally, materials for smaller jobs are batched by volume. Recommended ratios will enable you to get concrete mixes to match the function for which it is intended, or the strength of the concrete required.
One 50 kg sack of cement has a volume of 33 litres (0,033 m3)**. A builders’ wheelbarrow, filled level to the top, has a volume of 65 litres (0.065 m3, which is almost double the volume of a sack). When batching by volume, it is safe to assume that one wheelbarrow load is equivalent to two sacks of cement. Since sand bulks in volume when it is damp, the mix ratio table (below) is based on the use of damp bulked sand.
If you are measuring dry sand, reduce the quantity of each batch by 20–25 percent. You will also need to add more water to compensate for the lack of water in the sand. The recommended ratios are based on the use of either 19 mm or 13,2 mm commercial crushed concrete stone. Stone does not bulk in volume when it gets wet and so no correction is necessary.
** Note: m3 = cubic meter
Large Batches of Concrete Mixes
15 Mpa This is a low-strength concrete mix and is suitable for house foundations that are not reinforced, and for boundary walls and freestanding retaining walls.
25 Mpa This is a medium-strength concrete and is suitable for reinforced foundations, light-duty house floors, patio slabs, footpaths, steps, driveways and garage floors.
30 Mpa This is a high-strength concrete and is suitable for suspended structural beams, pre-cast beams and flagstones, heavy-duty workshop floors and suspended reinforced floors.
Small Batches of Concrete Mixes
You can use containers such as buckets, drums or tins. It is important that the same size container is used for all materials in a batch.
Moving and placing the concrete
Concrete Mixer
Note the reinforcing and the plastic waterproofing underlay.
Ready-Mixed Concrete
If you have large quantities of concrete to place, it is much more convenient to order it ready mixed. It is then mixed in a factory environment, according to your specifications. You must just ensure that workers are on site to place the concrete as soon as it is poured from the truck.
Hi there,
We are preparing to extend a house and according to the quotation, I was suppose to building sand 10 cubic meter and at cashbuild they gave me 1 cubic meter sand. What is the difference?
Your best bet is to contact a ready-mix concrete company and ask them to do the estimates for you. They will be able to give you a pretty instant reply.
Nathi, unfortunately we cannot make recommendations. Make sure whoever you approach is registered with the NHBRC.
which contractor that can build us concrete house with its required insulation
Hi, building a double storey house my ground floor is 210 sqm was advice to use 25mpa spec needed 19mm 70:30 mix 42.5mpa all in is 35cu just need to know how many ton (single truck) will a use and my first floor is 183sqm all in 36cu, please help just need to know how many trunks will i use?
Hi Lungelo, as much as we would like to help you it sounds like this is an assignment, and it is our policy not to do homework for students. You will have to do the calculations yourself. Good luck with your studies 😀
I forgot: I look forward to hearing from you. Thank you for your gracious time.
Good day. I’m a Quantity Surveying student who would like the estimated:
1) cement, sand, stone and water quantities for a 5000l trial mix of 30MPa concrete, with cement type CEM 1 42.5; and
2) cement, sand and water quantities for a 1l grout mixture to be used in CFA piles
Hi Sakinah, I have added a table at the end of this story with concrete mix proportions in ratios. I hope this helps.
hye.may i know the correct cement ratio with strength 30Mpa at 28 days? please help me.
Hi Nanda,
I am also a little confused, because concrete strength is measured in Mpa (after 28 days). Have a look at the table on this page that gives the range mostly used in ordinary construction today: concrete-mixes-by-weight If you have a unique structure that requires a special concrete mix then you will have to consult a structural engineer who will draw up the specifications for you.
hi , I am a little confuse , in relation of mixing of concrete , I need a 4500psi strength , what are the mix I should used
Hi Steve,
I agree it looks confusing, if you have a look at the first illustration on his page it says below the wheelbarrows that for 1 cubic meter of 15Mpa concrete mix .75 cubic meters sand and .75 cubic meters stone with 5 1/2 bags cement. So for your premix you must take into account the volume shrinkage when the sand fills the cavities between the stone. So .75 plus .75 will not end up as 1.5 cubic meters of mix but closer to 1 cubic meter then you must add your cement which will further fill the smaller cavities between the sand and stone. The shrinkage will be greater with a bigger stone size and coarser sand as well. Water is not taken into account as this will evaporate and the mix will shrink to its final volume. The Cement and Concrete Institute do say under “Estimating shrinkage. Because of the number and complexity of factors , estimating is, at best imperfect.” So with this in mind rather add a bit more cement to the mix and make it stronger rather than weaker.
I thought I had my foundation mix clear in my mind (house extension) but now my supplier has suggested pre-mixed sand and stone – they claim it is a 50 /50 mix by volume. This is great as it saves much-needed storage space but the question begs – how much cement /m3 of the mixed sand/stone for a 15Mpa mix?
I learnt on this page that ,75m3 of each + 5.5 bags of cement (plus water) only makes 1m3 of concrete, so it is obviously not a simple matter.
Thank you
Melvin there are examples on this page. BTW in SA we normally use crushed stone rather than gravel. Also when you use the kind of ratio you are quoting this is based on mixing by volume – i.e. using the same sized container for each dry material – and it is only suitable for small projects. If using a builder’s wheelbarrow, you can assume that two sacks of cement (50 kg x 2) = one wheelbarrow load of either sand or stone. Low strength concrete could be mixed in the ratio of 1:4:4 and would be 10-15 MPa at 28 days. Medium strength might be 1:3.5:3.5 = about 25 MPa. High strength 1:2:3 = no more than 40 MPa. But it really isn’t a reliable method and shouldn’t be used for major construction e.g. a house.
Brian one generally adds just enough water to ensure a pliable mix with good consistence. It depends largely on the size of the crushed stone used, but if 19 mm is used (which is common), plus an average quality sand, and a CEM 1-type cement (a common rather than masonry cement) – no admixture and measured to a slump of 75 mm then you will need on average, 210 litres per cubic metre of concrete. Ref: Fundamentals of Concrete by Brian Addis
Lameck I am not sure. Here is a link to a table that gives proportions for Grade 7 concrete – but I cannot guarantee its accuracy. Hope it helps.
It sounds to me as if you are a student? If so you really should be doing your own research and not asking other people to do it for you! However, the slump test is a measure of the consistence of fresh concrete – and it is the distance through which the top of the concrete moves down during the standard slump test according to SANS specifications. The flow test is only suitable for highly workable concrete that has a slump that is greater than 150 mm. It is also done according to SANS specs, using similar equipment to that used for slump tests. The flow test gives an accurate measurement of the workability of the concrete and an indication of its cohesiveness.
hi, may I know the correct mixed ratio for concrete grade “7”
Thank you – makes sense
Hi Steve,
Yes it does seem confusing. The measurements are correct on average, the reason for the loss of volume is mainly the empty spaces between the stone that get filled with the sand and cement. The cement also fills the small gaps in the sand as well. So it would appear that the amount “shrinks” when you add the amounts together. The Cement Institute Handbook has a 15MPa mix by volume as: 1:4:4 – 1 sack cement – 130 liters sand – 130 liters stone; vielding approx 190 liters of concrete which does not add up until you take the filling of the gaps into account. I hope this solves the problem. 😀
From the table above, one bag of cement plus 0.75m3 of sand and 0.75m3 of stone makes 1m3 of concrete? The sand and stone alone total to 1.5m3, plus the cement must be close on 1.7 m3 ignoring the water?
please i want to know the specific difference between the slump test and the flow test in concrete mixes.
I don’t see any mention regarding the water quantity needed: Is it merely a case of ensuring it is “runny” for warehouse floors? Mpa30 recommended mix.
can you know the compressive strength of a given concrete mix ratio (e.g. 1:1.5:3), what are the needed data for Cement, Sand & Gravel for us to know the compresive strength??? thanks