--- title: "British method of mix design" subject: "Concrete Technology and Masonry Structure" chapter: 3 key: "semester_5/concrete_technology_and_masonry_structure:british-method-mix-design" source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/british-method-mix-design site: BCT Engineering --- # British method of mix design Concrete Technology and Masonry Structure · Chapter 3: Mix design of concrete and property of green concrete - Asked in: 2066 Bhadra (old course), 5 marks - Video: [British DoE (Department of Environment) Method of Mix Design](https://www.youtube.com/watch?v=NnAAEeIJgkc) — Ceylara Academy - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/british-method-mix-design - Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-3 ## Question Describe the step by step process of mix design of concrete by using the British method. ## Short answer DoE method: target mean strength fm = fck + 1.64 s. Determine w/c from strength charts and durability limits. Free water content from tables by slump, max size, aggregate type (uncrushed/crushed). Cement content = water / w/c. Total aggregate = wet density – cement – water. Fine aggregate proportion from grading zone and slump charts. Adjust with trial mix and moisture corrections. ## Answer 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. ```text f_ck+ks -> w/c -> + water -> cement | density chart -> total agg -> FA / CA ``` ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. In the British method, target mean strength is A. fck - 1.64 s B. fck + 4 C. fck D. fck + 1.64 s Answer: D. fm = fck + k s with k = 1.64 for 5% defectives. (Key point: Target strength) 2. When the w/c from the strength curve and the durability maximum differ, the w/c used is A. the lower B. the higher C. the average D. always 0.5 Answer: A. The lower value satisfies both strength and durability. (Key point: w/c choice) 3. Free water for mixed uncrushed and crushed aggregate is A. Wf/2 + Wc/2 B. 2/3 Wf + 1/3 Wc C. 1/3 Wf + 2/3 Wc D. Wf + Wc Answer: B. W = 2/3 Wf + 1/3 Wc per the answer. (Key point: Mixed aggregate water) 4. Total aggregate content is found as A. cement x w/c B. water / w/c C. wet density - cement - water D. volume of CA x bulk density Answer: C. The wet density from Fig 3 minus cement and free water gives total aggregate. 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