What Is Asphalt Concrete: Composition, Classification, and Performance

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.

Asphalt Temperature Classification & Production

Asphalt mixtures are designed and classified based on the temperature at which they are applied and the desired function and performance in the pavement structure. A large variety of asphalt mixes are available to cater to different sectors’ requirements and achieve different performance characteristics in terms of surface durability, tire wear, braking efficiency, and roadway noise. These include Hot Mix Asphalt (HMA), Warm Mix Asphalt (WMA) and Cold Mix Asphalt (CMA).

1. HMA has a laying temperature above 150˚C (302˚F) and is produced by heating the asphalt binder to decrease its viscosity and drying the aggregate to remove moisture from it prior to mixing.

2. WMA has a lower temperature compared to HMA, between 110˚C to 140˚C (230-284˚F), and is produced by adding either zeolites, waxes, asphalt emulsions, or sometimes water to the asphalt binder prior to mixing.

3. CMA has a paving temperature below 60˚C (140˚F), and is produced without heating the aggregate. CMA is the most environment-friendly among all, but it is not commonly used as a paving method due to its lack of performance.

One important point to mention is that hot mix asphalt (HMA), which used to be the most popular choice for paving asphalt temperature, is now facing strong competition from warm mix asphalt (WMA). WMA has shown similar or even better performance than HMA in some cases, and it also offers benefits such as reduced energy use, improved workability, lower emissions and less fuel consumption.

Asphalt Concrete Technology: Performance & Intended Use

Asphalt concrete technology is the science and engineering of designing, producing, and grading asphalt mixtures in different ways so that they achieve unique properties and functions for various applications.

1. Dense graded asphalt technology uses a wide range of aggregate particle sizing, from coarse to fine, with few or no gaps. This creates a dense and strong mixture that can resist deformation and cracking. This is suitable for general use, such as highways and parking lots.

2. Open graded asphalt technology uses aggregate with a uniform particle size, with large gaps between them. This creates a porous and permeable mixture that can drain water and reduce noise. This is suitable for specific use, such as overlays and surface courses.

3. Gap graded asphalt technology relies on aggregate with a discontinuous particle size distribution, where some middle sizes are absent or scarce. This creates a mixture that can combine the benefits of both dense and open graded asphalt, such as stability and drainage. This is suitable for special use, such as stone matrix asphalt and porous friction courses.

Asphalt concrete is a versatile and durable material that can be used for various construction projects. It is composed of aggregates, bitumen, and mineral fillers that give it different properties and characteristics. If you are looking for a reliable and experienced asphalt paving contractor in Orlando, FL, contact DCPLM today and get a free estimate for your project.