3.1.4 Site-mixed concrete
Site-mixed concrete shall be designed and mixed to ensure sufficient strength and durability.
Concrete should be mixed using an appropriate method to achieve the required strength and durability. Except for very small quantities, a mechanical mixer should be used. Where hand mixing, add an extra 10% of cement to the quantities shown in Tables 2 and 3.
Table 1: Guidance for site-mixed concrete
The information below applies to cement strength class 32.5 and 20mm maximum aggregate size. Where cement strength class 42.5 or higher is used, the cement weight should be decreased by 10%.
Table 2: Mix proportions by weight
| Standardised prescribed mix | Consistence class (slump in mm) | Cement (kg) | Fine aggregate (kg) | Coarse aggregate (kg) |
|---|---|---|---|---|
| ST1 | S1 (10-40) | 230 | 770 | 1,155 |
| ST2 | S2 (50-90) | 265 | 760 | 1,135 |
| ST2 | S3 (100-150) | 285 | 735 | 1,105 |
| ST2 | S4 (160-210) | 300 | 815 | 990 |
| ST3 | S2 (50-90) | 295 | 745 | 1,120 |
| ST4 | S2 (50-90) | 330 | 735* | 1,100 |
| ST5 | S2 (50-90) | 375 | 720* | 1,080 |
* Fine aggregate grading to be grades CP or MP only of BS EN 12620.
Table 3: Mix proportions by volume using a maximum 20mm aggregate size
| Cement strength class | Standardised prescribed mix | Consistence class (slump in mm) | Number of (25kg) bags of cement | Fine aggregate (litres) | Coarse aggregate (litres) |
|---|---|---|---|---|---|
| 32.5 | ST1 | S1 (10-40) | 1 | 50 | 80 |
| ST2 | S2 (50-90) | 1 | 45 | 65 | |
| ST2 | S3 (100-150) | 1 | 45* | 55 | |
| ST2 | S4 (160-210) | 1 | 45* | 50 | |
| ST3 | S2 (50-90) | 1 | 40 | 55 | |
| 42.5 or higher | ST1 | S1 (10-40) | 1 | 60 | 90 |
| ST2 | S2 (50-90) | 1 | 50 | 75 | |
| ST2 | S3 (100-150) | 1 | 50* | 65 | |
| ST2 | S4 (160-210) | 1 | 45* | 60 | |
| ST3 | S2 (50-90) | 1 | 45 | 65 |
*Fine aggregate grading to be grades CP or MP only to BS EN 12620.
Last updated: 2nd January 2025