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Mixing Concrete
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Specifications for Ordinary Concrete

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This page gives the technical information on the requirements for aggregates used in the preparation of concrete taken from BS882, and the recommendations for prescribed mixes. For a more general overview of the uses of concretes for bedding, haunching and as sub-bases, see the Mortars and Concrete page.

The information on this page is widely used by concrete suppliers in making up their mixes, but has to be backed up with a strict testing procedure to verify compliance. However, it does offer a good guide to the basic 'recipes' used in the large-scale production of concretes.

Aggregates are classed as Fine or Coarse and variable proportions of each are mixed with a quantity of cement and water to give a concrete. The first two tables give the grading limits for fine and coarse aggregates, while the third table gives the prescribed mixes for ordinary concretes (no additives) and finallym, the free water:cement ratio.

The VERY approximate quantities of materials used to generate 1m³ of a ST4 or C20 (1:2:4) equivalent concrete are.....

  • Ordinary Portland cement (OPC) - 350 kg
  • Fine aggregate (sand) - 700 kg
  • Coarse Aggregate (gravel) - 1100 kg
  • Water - 190 kg (190 litres)

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Fine Aggregates
Grading of Fine Aggregate
Percentage by mass passing B.S sieve
Sieve Size Overall
Limits		 Additional Limits for Grading
C M F
10.00 mm 100 - - -
5.00 mm 89 -100 - - -
2.36 mm 60 -100 60 - 100 65 - 100 80 -100
1.18 mm 30 -100 30 - 90 45 - 100 70 -100
600 µm 15 -100 15 - 54 25 - 80 55 -100
300 µm 5 -70 5 - 40 5 - 48 5 - 70
150 µm 0 - 15 - - -
Fine aggregate grading limits - from BS 882

 

Coarse Aggregates
Grading of Coarse Aggregate
Percentage by mass passing B.S sieve
Sieve
size
(mm)		 Graded Aggregate Single-sized Aggregate
40-5mm 20-5mm 14-5mm 40mm 20mm 14mm 10mm
50 100 - - 100 - - -
37.5 90-100 100 - 85-100 100 - -
20 35-70 90-100 100 0-25 85-100 100 -
14 - - 90-100 - - 85-100 100
10 40-75 30-60 50-85 0-5 0-25 0-50 85-100
5 0-5 0-10 0-10 - 0-5 0-10 0-25
2.36 - - - - - - 0-5
Coarse aggregate grading limits - from BS 882

 

Prescribed Mixes for Ordinary Structural Concrete

Weight of cement and total dry aggregate in kg to produce approximately one cubic metre of fully compacted concrete together with the percentage by weight of fine aggregate in total aggregates. The restrictions in the types of cement and aggregates that may be used are given in 6.1.2 C.P. 110. Admixtures may not be used in ordinary structural concrete.

Grade of
Concrete		 Max Size of
Aggregate
(mm)		   40   20   14   10
Workability Medium High Medium High Medium High Medium High
Slump
(mm)		 50-100 100-150 25-75 75-125 10-50 50-100 10-25 25-50
                 
7.5
(1:3:6)		 Cement (Kg)   180 200   210 230   - -   - -
Total Agg. (Kg) 1950 1850 1900 1800 - - - -
Fine Agg. (%) 30-45 30-45 35-50 35-50 - - - -
                 
10 Cement (Kg)   210 230   240 260   - -   - -
Total Agg. (kg) 1900 1850 1850 1800 - - - -
Fine Agg. (%) 30-45 30-45 35-50 35-50 - - - -
                 
15 Cement (kg)   250 270   280 310   - -   - -
Total Agg. (kg) 1850 1800 1800 1750 - - - -
Fine Agg. (%) 30-45 30-45 35-50 35-50 - - - -
                 
20
(1:2:4)		 Cement (kg)   300 320   320 350   340 380   360 410
Total Agg. (kg) 1850 1750 1800 1750 1750 1700 1750 1650
Zone 1 (%) 35 40 40 45 45 50 50 55
Zone 2 (%) 30 35 35 40 40 45 45 50
Zone 3 (%) 30 30 30 35 35 40 40 45
                 
25
(1:1½:3)		 Cement (kg)   340 360   360 390   380 420   400 450
Total Agg. (kg) 1800 1750 1750 1700 1700 1650 1700 1600
Zone 1 (%) 35 40 40 45 45 50 50 55
Zone 2 (%) 30 35 35 40 40 45 45 50
Zone 3 (%) 30 30 30 35 35 40 40 45
                 
30
(1:1:2)		 Cement (kg)   370 390   400 430   430 470   460 510
Total Agg. (kg) 1750 1700 1700 1650 1700 1600 1650 1550
Zone 1 (%) 35 40 40 45 45 50 50 55
Zone 2 (%) 30 35 35 40 40 45 45 50
Zone 3 (%) 30 30 30 35 35 40 40 45

 

Free water:cement ratio
Exposure Max free
water/cement ratio
Mild 0.65
Moderate 0.55
Severe 0.45
This table gives the maximum amount of water that should be added to a concrete, determined by planned usage and cement content.
Note this is maximum water content; oftentimes, less water than suggested by this table will be used, as a concrete with a lower slump will be required.
 
So, from the prescribed mix table above, we can see that a C20 concrete using a 14mm coarse aggregate with a slump of less than 50mm has a cement content of 340Kg. Assuming moderate exposure is anticipated, the free water:cement ratio of 0.55 gives us.....
340Kg × 0.55 = 187Kg
......and, as water very conveniently has a specific density of 1Kg per litre, 187 litres would be the maximum permissable amount of watre to be added to a 1 cubic metre mix.

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