One of the critical elements in a successful paving project is the asphalt mix design. Another term for mix design is the “job mix formula” or “JMF”. The two main components in hot mix asphalt are mineral aggregate and the liquid asphalt binder. To develop a successful JMF, an aggregate type, typically determined by the area geology, along with an asphalt binder type are required. This is accomplished by reviewing the available aggregates and their gradations (the size, structure and distribution of the stone), selecting the applicable aggregate profile and combining the selected aggregate with the calculated ratio of asphalt binder.
It is well known in the asphalt-paving industry that the correct temperature of a finished asphalt mixture is vital to achieving a high-quality, long-lasting pavement. However, there are other environmental factors that must be taken into consideration, such as
Tack Coat: The Bond That Promotes Optimal Performance
A vital but often overlooked part of an asphalt pavement is the bond strength between the layers that make up the finished structure. Tack coat is the main component responsible for ensuring a sufficiently strong bond.
What is a tack coat?
- It is an asphalt binder that is spray applied onto a substrate material -- typically cement, asphalt or steel (in the case of orthotropic bridges) -- prior to placing a new asphalt overlay.
- This thin application of bitumen is the glue that binds the two layers of pavement resulting in a uniform structure.
- This bonding of the layers creates a structure that behaves as a single unit as opposed to unbound, independent layers.
Asphalt has been used on bridge decks for over 100 years with the intent of providing an effective road surface area for traffic and limited water-proofing properties. Historically, standard materials have functioned well without the need for modification but as traffic volumes and loads have increased, demand has necessitated a shift to high- performance surfacing materials.