The dry back procedure is primarily used to determine what factor in GMM?

The dry back procedure is used primarily to determine the GMM correction factor, which is essential for accurately assessing the maximum specific gravity of the asphalt mixture. This procedure involves calculating the density of the mixture after it has been dried to a specific temperature and moisture level, allowing for a more precise evaluation of the mixture's properties.

Getting the GMM correction factor right is crucial because it helps in compensating for any air pockets or moisture that may affect the density measurements of the asphalt mix. This ensures that the mix design and quality control processes yield reliable results, as accurate density calculations are fundamental in determining air voids and volumetric properties of the asphalt.

Other factors, while important to asphalt mix design and performance—like moisture content, air voids, and maximum density—are not the primary focus of the dry back procedure. This procedure specifically hones in on obtaining an accurate GMM correction factor to ensure the overall assessment of the mixture is based on true material density without the interference of moisture-related inaccuracies.