Unless you have already made concrete from the aggregates and cement used in a mix design and is confident that the mix design will produce satisfactory concrete, you should always make a trial mix. It will enable you to check that the strength, workability, density and other properties of concrete made from the mix design are as required and predicted.
A comparison of the expected and actual densities provides a valuable check of the accuracy of the data used in the mix design, in particular of the aggregate density. Unless the concrete density predicted by Firstmix is attained in reality, the actual volume of a mix will differ from the nominal volume.
Firstmix provides the Trial Mix Dialog to make it easy to correct the mix design, so that the required concrete strength and workability will be provided and the predicted concrete density attained.
To modify a mix design on the basis of the test results with the Trial Mix Dialog, you should first open the mix file for the original mix.
The Trial Mix Dialog can be brought up by clicking the button on the toolbar.
You should tick the Use measurements in mix design check box of the Trial Mix Dialog and exit by clicking on its OK button. You will find that the water and cement contents have been modified in the Mix Design Form to match the trial mix results.
It is recommended that you should save the modified mix design immediately in a new mix file with the Save As item of the File menu.
When a mix is designed in Firstmix the usual Mix Design Stages are modified.
If trial mix results are being used in a mix design form, a message “Trial mix results used” will appear at its top. 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.
You can specify a different strength or workability for the concrete, or you can change the air content or specification for Water-Reducing Admixtures to obtain a new mix recipe on the basis of the trial mix results.
The mix design can also be adjusted without using the Trial Mix Dialog.