Mix Design Stages

The mix design is carried out according to the DOE Method in the following five stages.

Stage (I). Determine Free Water/Cement Ratio Required for Strength

• Either use a specified margin or calculate a margin for a given proportion of defectives and statistical standard deviation.
• Obtain the target mean strength by adding the margin to the required characteristic strength.
• If air entrainment is specified, calculate an artificially raised modified target mean strength.
• Either accept a specified free water/cement ratio or obtain the maximum free water/cement ratio which will provide the target mean strength for concrete made from the given coarse aggregate type and from cement with the given properties.

Stage (II). Determine Free Water Content Required for Workability

• Either use a specified free water content or obtain the minimum free water content, which will provide the desired workability for concrete made with the given fine aggregate type, coarse aggregate type and maximum size of coarse aggregate.
• If the free water content has been determined for workability, adjust the required free water content if air entrainment is specified, and adjust further if a water-reducing admixture is specified.

Stage (III). Determine Required Cement Content

• Obtain the minimum cement content, which is required for strength, by dividing the free water content obtained in Stage (II) by the free water/cement ratio obtained in Stage (I).
• Check the minimum cement content, which is required for strength, against the maximum cement content, which is permitted, and give a warning if the former exceeds the latter.
• Check the minimum cement content, which is required for strength, against the minimum cement content, which is allowable for durability, and adopt whichever is greater to be the cement content in the mix.
• Divide the free water content by the cement content used in the mix to obtain a modified free water/cement ratio.

Stage (IV). Determine Total Aggregate Content

• Obtain a value for the overall aggregate density.
• Obtain the fractional volume of the aggregate by subtracting the proportional volumes of the free water and the cement from a unit volume.
• Calculate the total aggregate content by dividing the volume of the aggregate by the aggregate density.

Stage (V). Determine Fine Aggregate Content

• Either use a specified value of the percentage of fine aggregate, or obtain the percentage of fine aggregate, which will provide the desired workability for concrete made with the given grading of fine aggregate, maximum size of coarse aggregate and the free water/cement ratio obtained in Stage (III).
• Calculate the fine and coarse aggregate contents from the total aggregate content obtained in Stage (IV) and the percentage of fine aggregate.