Which procedure is not recommended during a compressive strength test?

Using a faulty compression machine during a compressive strength test is highly discouraged, as it can lead to inaccurate and unreliable test results. The purpose of the compression test is to determine the concrete's compressive strength accurately. A malfunctioning machine may not apply the load correctly, leading to erroneous readings and potentially causing safety issues in construction applications.

In contrast, visually inspecting the specimen is a standard practice that helps identify any visible defects that might influence the test outcome. Applying pressure evenly on the specimen is crucial for achieving consistent results, as uneven pressure can cause premature failure or misinterpretation of the data. Additionally, calibrating the machine before conducting the test ensures that the equipment is operating within specified tolerances, providing confidence in the accuracy of the test results. Therefore, using a faulty compression machine undermines the integrity of the testing process, which is why it is the procedure that is not recommended.