While PCC pavement is a more rigid material and appropriate for some applications, other pavement settings require a bit more flexibility due to the wear and tear of traffic – all without sacrificing durability. Knowing this, materials designers and engineers take a formulaic approach to how they specify asphalt pavements (HMA, RHMA, ARHM, etc…).
We’ve already discussed what hot mix asphalt is, but what is it composed of, and what factors play into performance?
According to Zachary Wheeler, G3 Quality’s Director of Operations, it is the control of core elements within the mix that allow for its flexibility, durability, and longevity for road surfaces.
Find out what these components are and why a precise mixture is integral to performance. If you require support for your hot mix asphalt materials, reach out to the geotechnical consultants at G3 Quality for guidance you can trust.
The 3 Elements of Hot Mix Asphalt (HMA)
Asphalt Binder
Asphalt binder is the heart of any mix, a crucial component responsible for holding the entire mixture together.
Unlike rigid materials like concrete, HMA relies on the flexibility of the asphalt binder to provide strength and durability to the pavement. This binder is a derivative of crude oil produced during the refining process that is then carefully formulated to ensure optimal cohesion and adhesion with the other materials in the mix.
One of the core purposes of asphalt binder is to bind various aggregate materials together, making for a single, sturdy mixture. Engineers can introduce additives to mixtures as well, whether to make it stiffer for heavy traffic loads or to enhance flexibility for climates that see drastic temperature fluctuations.
“The key to a successful HMA mixture lies in specifying the binder to match the individual aggregates, intended use, and environmental conditions. It’s a precise balance that leads to long-lasting and high-performing roads.”
- Zachary Wheeler, G3 Quality Director of Operations
In other words, to determine the most suitable binder grade, it’s important to consider the expected usage of the pavement. Different road applications demand varying levels of durability and resistance to factors such as heavy traffic, temperature variations or other environmental conditions. By choosing the right binder grade, engineers can ensure that the final asphalt mixture meets the specific demands of the project at hand.
Aggregates
Another critical element of HMA is aggregates, which form the fundamental structure of the pavement mix. Designing an aggregate structure that will optimize mix design parameters is critical for long-term performance.
Aggregates encompass a combination of rock, sand, and dust, which provide the necessary stability and load-bearing capacity for a road’s surface. Aggregate properties play a supporting role in overcoming pavement deformation and the quality of the aggregate is a critical component to the overall mix.
Plenty of engineers take an environmentally-conscious approach to their aggregates, often using recycled materials like old pavement or rubber tires. Adding crumb rubber as a modifier can help cut back on waste and enhance a road’s durability, making for a longer-lasting and sustainable roadway.
Air Void
Rock, sand, and dust also play a role in creating and optimizing air voids within the hot mix asphalt. These voids are more important than you’d think; by acting as spaces for water to enter and exit, the potential damage caused by freezing and thawing cycles can be avoided. The contact between aggregates in the mix also prevents asphalt from disintegrating under the stresses of extreme traffic and weather conditions, as long as it’s mixed correctly. These tiny pockets of air, dispersed throughout the mixture, play a big role in a pavement’s flexibility. The presence of air voids allows asphalt to expand and contract as temperatures change, reducing the risk of cracks and pavement failure.
However, the air void content within hot mix asphalt can’t be too off-base. Too many or too few air voids can lead to premature deterioration. Skilled mix designers can carefully control air void content to optimize both the performance and longevity of HMA.
Hot Mix Asphalt Case Study: CALTRANS I-5 North/Valley View
The Interstate 5 Valley View Interchange Project sought to add a High Occupancy Vehicle (HOV) and mixed-flow lane in each direction along an estimated one-and-a-half miles of I-5 at Valley View Avenue. The project spanned through Buena Park, Cerritos, La Mirada, and Santa Fe Springs, and required hot mix asphalt services which G3 Quality promptly provided. On a broader scale, G3 delivered quality control inspection, sampling, and testing services from the beginning of the project to its completion.
Hot Mix Asphalt Design & Testing with G3 Quality
With over a decade of delivering pavement engineering and materials design services for some of California’s most notable highway and roadway projects, G3 Quality is the preferred QA/QC firm in the golden state. For any upcoming pavement work, partner with us and leverage our local and mobile testing laboratories to ensure your hot mix asphalt materials are durable, compliant, and designed for long-term performance.
Fill out a form on our Contact page to keep your materials in line with project and safety requirements.
