How long does the vacuum and oscillating test for GMM continue once it reaches target pressure?

The vacuum and oscillating test for the specific gravity of compacted asphalt mixtures, often referred to as the GMM (gmm - specific gravity of the mixture), is designed to ensure that the sample is subjected to a specific duration under controlled conditions to achieve accurate measurements of air voids.

Once the target pressure is reached during this test, it is crucial to maintain that pressure for a specific amount of time to allow for the proper evaluation of the sample's response to the vacuum condition. The standard duration for this period is 15 minutes, plus or minus 2 minutes. This timing ensures that any air that may still be trapped within the sample has sufficient time to be removed, providing accurate results regarding the specific gravity.

Maintaining consistency in testing conditions, such as time under vacuum at a specified pressure, is vital for the reliability and repeatability of results in asphalt testing. In this case, 15 minutes is a well-established protocol that aligns with industry standards and practices. Thus, the correct answer reflects the established testing methodology for GMM within the context of the FDOT Asphalt Plant Level 1 examination.