British method of mix design

The British (DoE) method (BRE/DoE 1988, "Design of Normal Concrete Mixes") selects the mix from charts and tables; it is a wet-density method.

Steps

1. Target mean strength: $f_m = f_{ck} + k\,s$, with $k = 1.64$ (5% defectives) and $s$ = standard deviation (about 4-8 MPa, from site data).
2. w/c ratio: from Table 2, find the strength at w/c 0.5 for the cement type, aggregate type (crushed/uncrushed) and age; draw the curve through this point on Fig 1 and read the w/c for the target strength; check the maximum w/c from durability requirements and use the lower value.
3. Free-water content: from Table 3, for the slump (0-10, 10-30, 30-60, 60-180 mm) or Vebe time, the maximum size (10, 20, 40 mm) and the aggregate type. When the fine and coarse aggregates are of different types: $W = \frac{2}{3} W_f + \frac{1}{3} W_c$, where $W_f$ and $W_c$ are the water contents for the type of fine and coarse aggregate respectively.
4. Cement content = free water / (w/c); check the minimum and maximum limits.
5. Total aggregate content: from Fig 3, find the wet density of concrete for the free-water content and the aggregate SG; total aggregate = wet density - cement - water.
6. Fine aggregate proportion: from Fig 4, using the grading zone (% passing 600 micron), size, slump and w/c.
7. Fine and coarse aggregate masses: FA = proportion $\times$ total aggregate; CA = remainder; the coarse aggregate may be split into sizes.
8. Trial mix: adjust for slump and strength; correct for the moisture content at site.

 f_ck+ks -> w/c -> + water -> cement
                       |
   density chart -> total agg -> FA / CA