Method of Mix Design from Trial Mix Results

First of all the actual free water/cement ratio is found. The actual free water content of the trial mix is divided by the cement content of the mix recipe. In Stage 1 of the Mix Design Stages, the concrete strength actually attained for this free water/cement ratio is the basis for finding the maximum free water/cement ratio, which will provide the target mean strength for concrete made with the given coarse aggregate type and given cement type. In a mix design where trail mix results are not used, the cement properties of the cement type used are the basis for this calculation. If the specified air content differs from the measured air content of the trial mix, the effect on the concrete strength is calculated.

  • See Strength and Air Entrainment.

    • The actual free water content per unit volume is found by dividing the actual free water content of the trial mix by the actual volume of the trial mix. The free water content is used in Stage 2 of the mix design stages to calculate the nominal maximum aggregate size, which according to the DOE Method would provide the measured workability for the free water content of the trial mix with the given aggregate angularity. This nominal maximum aggregate size is then used to determine the free water content which will provide the required workability for the modified mix design or to predict the workability for a specified free water content. If the air content or the specified action of water-reducing admixtures in the new mix design differ from the trial mix data, the effect on the workability is also calculated.

  • See Workability and Maximum Aggregate Size.
  • Workability and Air Entrainment.

    • In Stage 4 the Aggregate Density is calculated from the Adjusted Fine Aggregate Density and from the Adjusted Coarse Aggregate Density.

    The nominal maximum aggregate size is also used in Stage 5 of the mix design stages to calculate a nominal grading of fine aggregate, which matches the trial mix results according to the assumptions of the DOE method. The nominal grading of fine aggregate together with the nominal maximum aggregate size is then used to obtain the percentage of fine aggregate.

  • See Workability and Fine Aggregate Grading.

    • Finally the quantities of the new mix are factored by the ratio of estimated concrete density to the measured concrete density so that the actual batch volume will match the specified batch volume.