Asphalt is a scientifically-designed mixture of aggregate (rock and sand) and asphalt cement binder (glue) that can be customized to specific paving applications. Interstate highways place different demands on the mixture than a driveway or bike path, and Asphalt can be designed for either application or everyone in between. There are several procedures currently available for designing Asphalt mixtures. The most common method currently used is the Superpave Mix Design System, which replaced the Marshall Mix Design System in the 1990’s.
These mix design systems optimize the best combination of aggregates and asphalt cement to meet a specific need. The result of this process is a mix design (or recipe) that the Asphalt producer uses to blend the different materials together at an asphalt plant.
Aggregate is obtained mostly from naturally occurring mineral deposits (quarries or pits). The most common type of aggregate in Florida is called “Limestone” or “Limerock”, a sedimentary rock, and the main quarries are in South Florida. Sands are very common in Florida, but only a small amount (typically less than 20%) is used in Asphalt mixes. Florida also imports aggregate from as far away as Nova Scotia and Mexico, as well as from our neighbors of Georgia and Alabama. Much of this imported rock is “Granite.”
In addition, Florida has been a leader in recycling old pavements into new ones since the 1970’s when recycling really started in the U.S. “Reclaimed Asphalt Pavement” or RAP is the term that’s used commonly to refer to the end product of removing old asphalt roads during re-construction or rehabilitation. This material is typically re-processed (crushed and screened) to ensure quality. It very consistent and uniform and most all the Asphalt made in Florida contain RAP, averaging 20-30% of the mix. Asphalt is considered a 100% recyclable product and is used as the best and highest form of recycling.
Recycling reuses the valuable aggregate and the asphalt cement contained in the RAP, saves valuable landfill space, and provides a high quality product at a lower cost to the taxpayer (a win-win for all). There is a big push for being “green” in the last few years, Asphalt has been green for over 30 years and gets greener every year. You could say we were green before green was the thing to be.
Asphalt FACT #11 The U.S. recycles about 2 million ton of plastic a year while recycling and reusing over 60 million tons of asphalt. Plus, plastic recycling alters the chemical structure, so many plastics become different types of products once recycled. Roads, on the other hand, are reusable and renewable infinitely.
Asphalt binder is the glue that holds all aggregate together and is a product of the refining of crude oil. A barrel of refined crude oil will typically yield gasoline, kerosene, diesel fuel and asphalt cement as well as variety of products used for other applications. Crude oil has different properties depending on the source, and oil companies either use single crude or a blend of different crude to make asphalt binders.
Asphalt Binder is graded by its physical properties and must meet certain safety, purity, and consistency standards. Depending on the pavement design, the asphalt binder may be required to be modified to improve its inherent properties, such as strength and flexibility at different temperatures. Other additives such as ground tire rubber (from automotive and truck tires) as well as specialized polymers add strength and flexibility to the binder and are commonly used today. Asphalt cement modified with various additives become the asphalt binders used today.
Due to recycling old pavements into new high performance pavements, Florida has truly become a leader in managing our natural resources while providing a smooth, durable ride to its citizens and visitors, making Asphalt the paving material of choice.