Trial Mix Dialog

The results of tests of the actual properties of the concrete made to a particular mix design can be entered on the Trial Mix Dialog, which is brought up either by ticking the Use Trial Mix Results check box at the top of the Mix Design Form or with the Trial Mix item of the Laboratory menu.

Shortcut:

Mouse: Click the button on the toolbar.

Before you bring up the Trial Mix Dialog, you should open the mix file from the mix for which test results are available, and this mix file should be loaded into the active mix design form, so that the test results can be used to modify the original mix design. If you attempt to bring up the Trial Mix Dialog for a new mix file, you will be given a message asking you to load an old mix file.

For the trial mix results to be valid, it is essential that the aggregate and cement properties should not have been changed from the original mix. Firstmix therefore checks whether the user has opened either the Laboratory Measurements Dialog or the Cement Properties Dialog without cancelling and whether the aggregate characteristics or density have been changed since the mix file was opened. In any of these cases the user will be asked to open the mix file again.

The following trial mix results should be entered:

• The actual free water content (per nominal m³ or yd³) used in the trial mix. Since it is easier to adjust a mix design for strength than for workability, the water content of the mix recipe is often adjusted to provide the required workability on the spot as the trial batch is mixed. This procedure is recommended in the DOE Method, used by Firstmix. The Trial Mix Dialog therefore does not assume that the free water content of the original mix design was not modified in the actual the trial mix. The free water content should represent the water content of the concrete at the time of setting and therefore allow for water absorbed by the aggregate or surface water on the aggregate as appropriate.

• Concrete strength (Cube Test or Cylinder Test depending on your settings).
• The Age at Testing of the concrete strength, in case this is different from that specified in the original concrete mix design.
• Density of the freshly mixed concrete.
• Air content percentage, in case this is different from that assumed in the original concrete mix design.
• Measured workability (Slump Test or Vebe Time Test depending on your settings).
• The assumed action of the Water-Reducing Admixtures used, specified as either the anticipated amount or the anticipated percentage by which the free water content needed to provide a given workability has been reduced.

FirstMix calculates an Adjusted Fine Aggregate Density and an Adjusted Coarse Aggregate Density from the Trial Mix results, which are displayed at the bottom of the Trial Mix Dialog. If the Trial Mix results are used in a mix design the Relative Aggregate Density is calculated on the basis of these adjusted aggregate densities.

The Calc and Check Button may be used to update the values of the adjusted aggregate densities to match the data entered on the dialog. The data entered will also be checked for errors.

The trial results will only be incorporated into the active mix design form, if the Use measurements in mix design check box is ticked and the ‘OK’ button is clicked to return to the mix design form.

If the Use trial mix results in mix design check box has been ticked, a message “Trial mix results Used” will appear at the top of the active mix design form. All the items in the mix design form which relate to the aggregate or cement properties will become read only, since a mix design based on the trial mix results is only valid for the aggregate and cement properties to which the trial mix results relate.

If you wish to cease using trial mix results in a mix design, you should bring up the Trial Mix Dialog, uncheck the Use trial mix results in mix design check box, and return to the mix design form by clicking the OK button.