In addition to the required mix design strength, the job control strength shall be established. The job control strength is used to verify that the concrete being used on the project will perform similarly to the concrete used to develop the mix design. The default is to use the 7-day mix strength as the job control strength. This 7-day strength testing may be altered with the approval of the engineer. The contractor may want to develop job control strengths at an earlier age, such as four days, to permit the job control specimen to also be used to open the pavement to traffic at an earlier age. Reduction of curing time for the job control specimens may reduce the reliability of the test in ensuring that the specified strengths will be reached. Testing at four days should still provide a reliable estimate of the long term strength.

The standard job control testing at seven days was established many years ago and ensured that the strength test of the job control specimens occurred on the same day of the week as the concrete paving. The result is that there would be no testing on Saturday or Sunday, unless the paving work was performed on those days. This was also a management tool to eliminate the need for laboratory technicians to report to work on Sunday to perform a single strength test.