Concrete mixes
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Concrete Mixes

Concrete Mixes & Batch Ratios

For Different Applications

workers mixing concrete


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.

15mpa mix graphic
To make 1 cubic metre of 15 Mpa concrete you will need to mix 5 1/2 bags of cement with 0,75 cubic metres of sand and 0,75 cubic metres of stone.

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.

Concrete_Big_Batches_Barrows25mpa-s
To make 1 cubic metre of 25 Mpa concrete you will need to mix 7 bags of cement with 0,70 cubic metres of sand and 0,70 cubic metres of stone.

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.

30Mpa mix
To make 1 cubic metre of 30 Mpa concrete you will need to mix 10 bags of cement with 0,65 cubic metres of sand and 0,65 cubic metres of stone.

 

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.

concrete batches with buckets graphic

Moving and placing the concrete

Time limits
The time that elapses between the start of mixing a batch and when that batch is placed and compacted should ideally not exceed 45 minutes. If concrete is not placed immediately after batching, cover it with plastic sheets or wet sacking so that it does not dry out in the sun or wind.
Concrete not placed and compacted within this time, or which has stiffened to a degree that its workability (consistency) cannot be restored fully by turning it over a couple of times with spades, should be discarded. This is because the hydration process would be in an advanced stage and retempering of the concrete will weaken it.
Moving the concrete
The concrete can be moved in buckets or wheelbarrows. If it is jolted too much, the stone will settle at the bottom. If this happens, remix the concrete before placing it. Do not let the concrete stand so long that it stiffens before it is placed.
Retempering
The concrete mix should be used within a maximum of two hours of being mixed and must never be retempered by mixing in additional water, as this reduces the resultant strength of the mix.

Concrete Mixer

 
concrete mixer
A concrete mixer has been used to mix the concrete, and wheelbarrows are used to place it.
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.

concrete truck delivery
Here a batch of concrete is mixed off-site and delivered and placed into the pre-dug foundation trenches.

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115 Comments

  1. Hi Karl, I have just checked the links from the books and they are all working fine. For the Concrete and Mortar Handbook and the Energy Efficient EBooks you will be directed to my book site howtobooks.co.za with a secure PayFast payment gateway. The Owner Building book is sold for me by Loot. Thanks for the support. Janek

  2. Hi how do i download this e book do i need a lot of data and how do i pay the money in thanks karl

  3. Julian you also need to know how wide the foundation is. You then multiply the length by the width and then by the depth/thickness and get your cubic meters then work out the quantities you need for that many cubic meters.

  5. How much concrete mix and how many bags cement

  6. How do I measure how much concrete mix is needed to lay are 300mm thick foundation 15m long

  9. Hi
    We want to make our own concrete kitchen countertops, but are battling to find info on the ratio of the mix we should use for this.
    Websites from other countries indicate that one can buy special cement for this purpose. Is this available in SA as well.
    Also do you have any advise on the best stain to use for this kind of project.

  11. I want to throw a white cement and fine crusher mix on a bathroom floor, which I want to polish. What mix do I need

  12. For what you are wanting to do and to make it a safe structure I would advise asking a structural engineer to assist you, if the structure were to collapse and someone was hurt then you would be liable and you would have no insurance cover either.

  13. Lisa Wilson says:

    Hi. I am building a diy pizza oven.
    I want to build a small rectangular slab which will be suspended, but supported on all 4 sides. The slab total size is 1200 x 1200. I want to sit the slab on top of blocks on all 4 sides. The overlap will be approx 170mm on each side.
    This is to be the cooking floor of the oven. I need to know what ratio is best and how thick the slab should be. I have mesh to put inside the slab as extra support.
    i purchased bags of concrete mix from the local hardware store. When I opened the bag, the ratio of cement looks very low to the sand. I have since bought seperate bags of sand and grey stone. I will need to purchase more cement.
    The medium/strong ratio as above looks good. But how much of each will I need for the slab size needed?
    The pockets of stone and sand come in 40kg bags. Not sure of the cement.

    thanks

  14. Hi,

    What proportion of cement, crush sand, fibres and chemical will be required to make a concrete mix design of M60 grade?

  16. Mohammed Abdul Razzak says:

    Can any one assist me to know the proportion for 20MPA Concrete Design Mix

  17. Raghavarao says:

    1 m3 contrete (manual) mixing howmany bags (50 kgs) cement
    MT Sand
    cft 20 mm metal required

  19. kelvin musonda says:

    Hi, how many bags of cement, stones tonnes and sand tonnes do i need to do a slab of 50 cubic meters.

    Regards
    Kelvin

  20. Please have a look at our post for mixes here: concrete-mixes-by-weight There are no hard and fast rules for water quantities most builders do it by eye and feel so long as it is not too dry or too wet. The professionals and readymix suppliers will do slump tests on batches to assess the correct mixture for specific applications and will depend on the materials used and the consistency required.

  21. Mohammad Shahidul Islam says:

    I want to know about water quantity with the mix ratio for 25 mpa strength

  23. DAVID MBEWE says:

    Hi
    I need an hand book Article or any Text book that will Educate me on different concrete mixes and morta mixes.
    I need to learn more to be able to implement better

  24. Hi Dumisani, If you look at the amount of sand delivered then times that by 10 then that will be what 10 cubic meters will be. BTW 10 cubic meters is a lot of sand.

  25. Hi Bernard, I have uploaded a file for you to download on our downloads page, just scroll down to “Concreting & Blockmaking”. This an AfriSam brochure that gives you all you need to know for your project. Basically they say that as a rough guide, using an aggregate cement ratio of 8:1 by loose volumes, three and a half bags of cement and a cubic metre of aggregate will be enough to make about 400 standard bricks. There are other factors that they talk about and you should read the whole paper first before starting. Good luck!