---
title: "Principles of mix design; factors not in DOE"
subject: "Concrete Technology and Masonry Structure"
chapter: 3
key: "semester_5/concrete_technology_and_masonry_structure:mix-design-principles-doe-omitted"
source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/mix-design-principles-doe-omitted
site: BCT Engineering
---

# Principles of mix design; factors not in DOE

Concrete Technology and Masonry Structure · Chapter 3: Mix design of concrete and property of green concrete

- Asked in: 2066 Chaitra (old course), 2+3 marks
- Video: [Concrete Mix Design | Part-01 | Technical Civil](https://www.youtube.com/watch?v=eJ1kIO4JfSo) — Technical Civil
- 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/mix-design-principles-doe-omitted
- Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-3

## Question

What are the basic principles of mix design of concrete? Which factors are not considered in the DOE mix design method? Explain in brief.

## Answer

#### Basic principles of mix design
1. **Strength-w/c relation (Abrams' law)**: the w/c ratio governs strength and durability.
2. **Workability** is governed by the water content, which depends on the aggregate size, shape and grading and on the slump required.
3. **Target mean strength** = specified strength + a margin for variability ($k s$), based on the degree of quality control.
4. **Durability limits** (maximum w/c, minimum cement content) for the exposure.
5. **Aggregate grading** and the proportion of fine to coarse aggregate, to get a dense, cohesive mix.
6. **Absolute volume** concept: the sum of the volumes of all ingredients = 1 m$^3$ (or the wet density method in DoE).
7. **Economy**, with trial mixes and field adjustments.

#### Factors not considered in the DoE method
- **Chemical admixtures** (plasticisers, superplasticisers) are not covered; the basic procedure is for non-air-entrained OPC concrete, and air entrainment and mineral additions (fly ash/pfa, slag) are handled only as separate modifications.
- The **fineness modulus of sand** is not used (grading is described by the % passing the 600 µm sieve), and neither is the **dry-rodded bulk density** of the coarse aggregate.
- The **specific gravity of cement** is not used, since the aggregate content is found from the wet density of concrete.
- Aggregate **shape and texture** enter only as "crushed" or "uncrushed"; flakiness and elongation are not considered; the maximum size is limited to 10, 20 and 40 mm.
- **Durability** is considered only through checks on the maximum w/c and minimum cement content.
- The **bulking of sand, absorption and moisture content** are applied only afterwards, as site corrections.
- The **placing conditions** (congestion of reinforcement, method of placing, temperature) are not considered directly, and special concretes (lightweight, pumped, high-strength with superplasticisers) are outside its scope.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What mainly governs the workability of a mix according to the principles?
   A. Cement grade only
   B. Curing method
   C. Mixer speed
   D. Water content, depending on aggregate size, shape, grading and slump
   Answer: D. Workability is governed by water content which depends on aggregate and required slump. (Key point: Water and workability)

2. The DoE method finds total aggregate content by
   A. wet density of concrete from a chart minus cement and water
   B. absolute volume with SG of cement
   C. fineness modulus tables
   D. bulk density of CA
   Answer: A. DoE uses wet density from Fig 3; total aggregate = wet density - cement - water. (Key point: DoE density method)

3. Which is NOT directly considered in the DoE method?
   A. Slump
   B. Air entrainment and admixtures
   C. w/c ratio
   D. Aggregate size
   Answer: B. DoE is for non-air-entrained concrete and ignores admixtures and mineral additives without modification. (Key point: DoE omissions)

4. Which concrete lies outside the DoE method's range?
   A. Ordinary 30 MPa concrete
   B. Concrete with 20 mm aggregate
   C. High-strength above 50-60 MPa, pumped and lightweight concretes
   D. Concrete of medium slump
   Answer: C. High-strength, pumped and lightweight concretes are outside its range. (Key point: DoE range)

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