What is Asphalt Pavement?
by Brett Neal
Asphalt pavement is known for its durability and resilience. It is this strength which makes asphalt pavement the best option for most all paved surfaces. Most state and federal governments highly prefer asphalt pavement because of its reliability and lasting life. If it is properly laid, it need not be replaced for twenty to twenty five years. Asphalt pavement is also the most popular choice for applications such as driveways, parking lots, roadways, airstrips and more. Asphalt is everywhere. Asphalt is also the most commonly recycled material in the United States—before paper or plastic! Approximately 80% of all asphalt pavement is recycled when it is removed. Without question, if you are looking for lasting pavement for these applications, and one that can be used over and over again, asphalt pavement is the best choice.
What makes up asphalt pavement?
Asphalt pavement is made up of stone (aggregate), sand, additives and liquid (petroleum) asphalt. Liquid asphalt – a sticky black substance – is used as the binding material in asphalt pavements. It is viscous in nature and can also be found in semi solid forms. Another common term for asphalt is bitumen.
The pavement – once mixed – consists of 90 to 95% aggregate and sand, and 5 to 10% asphalt or bitumen. Asphalt pavements high viscosity binds the materials that make up asphalt, while allowing it to simultaneously retain flexibility. The cooler the asphalt surface the less flexible the overall pavement. This flexibility found in asphalt pavement is one of its greatest strengths, allowing the surface to adapt to changing conditions produced by weather and the constantly changing surface beneath it. Another chief characteristic of asphalt is its ability to repel water. This is important because water, as we will see, is the greatest enemy of the asphalt surface. It is also the reason why asphalt contractors such as yourself are in business.
How is asphalt created?
The first step in creating asphalt pavement is called Predose. Here, depending on the asphalt recipe, the aggregate components of asphalt pavement are weighed using a belt weighing instrument. A belt weigher is used so that the materials can simultaneously be weighed and taken to the next step in the process.
Step two involves drying of the aggregate components. A rotary drying drum is used to dry the components at roughly 300 degrees. After drying the aggregate it is reweighed as drying can alter its weight. The preheated or dried components are now sifted and store in silos.
Next, the aggregates are transferred to the mixer. The binding element, or liquid asphalt, is kept in separate heated tanks so that it remains liquid suitable for mixing. Once the aggregate is in the mixer, the asphalt is added to the mixer according to a measured rate of flow. Both aggregate and binder are mixed thoroughly to form the paving material.
After the hot asphalt mix is created it is stored in a heated silo. Most asphalt plants have several chambers to store different recipes. The asphalt is stored and kept hot until it is transported by dump trucks to the job site. From the time the asphalt leaves the plant and throughout the paving process a high temperature has to be maintained. If the asphalt mix cools it cannot be compacted.Additional Stories: Parking Lots - The Basics