Hot Mix Asphalt is a scientifically-designed mixture of aggregate (rock) and asphalt cement (glue) that can be customized to specific paving applications. Interstate highways place different demands on the mixture than a driveway or bike path, and HMA can be designed for either application or every one in between. There are several procedures currently available for designing HMA mixtures. The most common method is the Marshall mix design method, the newest is the Superpave Mix Design System.

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 HMA 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. Sands are very common in Florida, but only a small amount (typically less than 30%) is used in HMA mixes. Florida also imports aggregate from as far away as Nova Scotia and Mexico, as well as from our neighbors of Georgia and Alabama.

In addition, Florida has been a leader in recycling old pavements into new ones since the 1970's when recycling really stated 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 may be re-crushed or used as is depending on how it is removed from the existing pavement. It very consistent and uniform and most all HMA in Florida contain RAP, averaging 20-30% of the mix.

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).

Asphalt cement (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 a single crude or a blend of different crude to make asphalt.   

Asphalt Cement is the material used in paving applications.  It 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.  Florida DOT does specify the use of a blend of Asphalt Cement and Ground Tire Rubber for certain applications.  Since 1994, Florida has recycled the equivalent of over 8 million passenger tires into asphalt pavements, saving valuable landfill space while improving the performance of our highways.

Due to recycling old pavements and tires 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 it the paving material of choice.