ABSTRACT
Dense graded mixtures make up the greatest percentage of all the type of mixtures used for asphalt pavements. They also are the greatest tonnage of all the mixture types produced. Dense graded mixtures are also generally known as hot mix asphalt (HMA). Dense graded mixtures are very versatile and can be used both for the structural component of the pavement and for the wearing course. They can also be used in the maintenance of asphalt pavements as thin overlays, also known as “scratch coats” or thin surface courses. Various specialty types of mixtures have been developed for specific pavement applications and can provide better performance than dense graded mixtures for those specific applications. There are many types of specialty mixtures and not every one is described in this chapter. The more common and relevant mixtures that a designer for a parking lot or city or county road may consider are described. The distribution of aggregate sizes in the asphalt mixture typically defines the type of asphalt mixture. Dense graded mixtures contain a uniform distribution of aggregate particles of different sizes throughout the mixture. Open graded friction courses (OGFCs), popcorn mixtures, or porous mixtures consist mostly of larger aggregate sizes with hardly any of the smaller particles. There are also various types of gap graded mixtures with several different names. Gap graded mixtures are somewhat similar to dense graded mixtures with the exception that several sizes of the aggregate particles are missing, leading to a “gap” in the gradation of the mixture. Various components that have been incorporated into asphalt mixtures for specific purposes are for enhancements in the engineering properties of the asphalt mixture. For example, a dense graded asphalt mixture that incorporates recycled asphalt pavement (RAP) has both economical and environmental advantages over a mixture that does not contain RAP. Or an asphalt binder may be modified with one of the several types of polymers to provide improved performance under high temperatures and loading.
