ACI Certification Practice Exam

In the context of the slump test used for determining the consistency of concrete, the slump cone must be raised straight upwards in a specified time frame to ensure accurate and reliable results. The requirement to raise the cone at least 12 inches above the ground within a certain duration allows for the proper measurement of the slump without disturbing the concrete sample. The time frame of "plus or minus 5 seconds" indicates that some flexibility in timing is acceptable while maintaining the overall integrity of the measurement. This accounts for slight variations in the execution of the test while still adhering to the standard practices established for the slump test. By following this guideline, the results will reflect the true workability of the concrete mix under test.

The other responses represent fixed timings that do not allow for the minor variations that can occur during testing, which is why they do not align with the accepted practices for this procedure.