Asphalt concrete, commonly referred to as just asphalt, blacktop, or pavement, is a composite material that is used extensively in creating and maintaining roadways, highways, driveways, parking lots, and airports. Here is everything you need to know about what it’s composed of, how it’s classified, and how it’s graded for performance and use.
An Overview of Asphalt Concrete Composition
It’s made from a 3-part mixture of aggregates, binder, and fillers, with the general composition break down being: 
1. Aggregates: These are the main component of asphalt concrete, accounting for about 90% to 95% of the total mass. Aggregates are granular materials such as sand, gravel, crushed stone or recycled asphalt pavement. They provide strength, stability, and resistance to wear and deformation for the asphalt concrete.
2. Bitumen – The Binder: Bitumen is a viscous liquid derived from petroleum or natural sources that acts as the binder for the aggregates in asphalt concrete. The role of the binder is two-fold, in that it makes the asphalt cohesive, adhesive, and waterproof, while also giving the asphalt it’s flexibility, viscosity, and durability.
3. Mineral Fillers: These are fine particles of mineral matter such as limestone dust, fly ash or cement that are added to asphalt concrete to improve its properties. As the name implies, these minerals fill-in the voids between the aggregates and bitumen, increasing the density and stiffness of the asphalt concrete, which makes the asphalt more stable and resistant to cracking.
During asphalt concrete mixing, the aggregates are blended with about 5% bitumen to produce the asphalt pavement. This mixture is then heated to an appropriate temperature and mixed to ensure a uniform distribution of the binder and a homogeneous consistency of the final product.
