Investigating the Compactability of Hot Mix Asphalt Utilizing the Concept of the Locking Point

Compaction is an important process for the asphalt mixture service life. An adequately compacted mixture is crucial for long-lasting pavement. Compaction is a procedure utilized to compress and decrease the volume of the material, which provides essential ingredients that influence the pavement's performance. During asphalt mix compaction, the aggregate coated with asphalt binder are compressed together, following an increase of interparticle friction and surface contact and finally interlocking to provide the resistance to deformation. At the same time, the permeability is decreased, and the durability is increased. Compactability is utilized to evaluate how much compaction energy is required to compact asphalt mixture. Locking point is an important concept in selecting a proper aggregate gradation in the asphalt mixture design. The locking point can be defined as the moment during asphalt mixture compaction at which an aggregate structure becomes stable. Beyond this point, further compaction does not contribute much to the increase in mixture density and can even damage aggregate particles. To better understand the compactability and interlocking properties of the hot mix asphalt, the overall objectives of this study are: to develop the method that permits determination of the locking point when impact compaction method is applied, acquire an understanding of the interlocking characteristics of aggregate structure through routine mix design procedure that includes different variables: mixture type, aggregate gradation and angularity, asphalt binder, mixing sequence and compaction method, establish the acceptable over-compaction for common materials utilized in Tennessee, and to quantify the interlocking between aggregates particles by 2D and 3D image processing. The results of this study give a better understanding of the compactability and interlocking of asphalt mixtures.