The purpose of this report is to discuss the factors that contribute to the differences that occur in the properties of a Hot Mix Asphalt (HMA) mix designed in the laboratory and the properties of the "same" mix produced in an asphalt batch or drum mix facility. Emphasis is placed on the causes for the differences in the mix volumetric characteristics between the lab and the field with the understanding that laboratory mix design is only a starting point which must be verified through the HMA plant production. Major areas considered are: aggregate, asphalt binder, plant production process, hot mix storage, and hauling of the mix.

This publication provides a ranking system to prioritize the importance of each factor in contributing to the differences which may exist. Therefore, this document is intended to serve as a reference to assist HMA producers in understanding variables affecting volumetric properties.