Understanding the Process Behind the Most Common Road Material
Asphalt is everywhere. It is one of the most utilized paving materials, used in highways and driveways, airports and parking lots. But have you ever thought of how asphalt is produced? This article simplifies the process of manufacturing asphalt into an easy-to-understand process. As a homeowner, contractor, or simply a person who is curious, you will derive from this blog the information of how asphalt is manufactured and why it is important.
What Is Asphalt?
Before diving into how asphalt is made, let’s quickly define what it is. Bitumen, also referred to as asphalt, is a liquid or semi-solid and sticky, black, and very viscous petroleum product. Asphalt is a mixture of bitumen, sand, and gravel, and this varies slightly in the U.S. as the term simply means a blend of bitumen and aggregates. It is this composite that we pour on the roads to pave them.
Why Asphalt Is So Popular
Pavement is made of asphalt due to several reasons:
Durability: It is able to withstand heavy traffic and weather.
Cost-Effective: Asphalt is comparatively low in cost to make and install.
Quick Installation: It can be used to construct roads and driveways within a short period of time.
Recyclable: Old asphalt could be used in other new projects; hence, it is environmentally friendly.
Types of Asphalt
Before we get into the making of asphalt, it’s helpful to know the main types used in construction:
Hot Mix Asphalt (HMA)
This is the most widespread of the roads, highways, and runways in airports. It is made in high heat (approximately 300°F to 350°F) and plied when warm.
Warm Mix Asphalt (WMA)
This version is made at lower temperatures (usually 200°F to 275°F) and has additives to be handled more easily and is more environmentally friendly.
Cold Mix Asphalt
Cold mix, which is most commonly used to patch potholes or in minor repairs, is a mixture of materials that is not heated, and is used in temporary repairs.
Raw Materials Used in Asphalt Production
There are two main components of asphalt production:
Bitumen (Asphalt Cement)
Bitumen is the result of crude oil refining. It is the gluing element that holds the mixture together and is warmed to allow it to flow and to mix easily.
Aggregates
This is a mixture of crushed materials which constitute the majority of the asphalt.
Common aggregates include:
- Sand
- Gravel
- Crushed stone
- Slag (byproduct of steel-making)
The performance and durability of the asphalt have been influenced by the quality and type of aggregate.
The Asphalt Manufacturing Process
Asphalt making typically takes place at an asphalt plant, and the steps are as follows:
Step 1: Drying and Heating Aggregates
This is done by passing the raw aggregates through a dryer drum that heats and dries the aggregates. In order to mix well with bitumen, moisture must be eliminated. The temperature is determined by the type of asphalt that is being manufactured, but can reach temps of 300°F or higher.
Step 2: Mixing with Bitumen
After the aggregates have been dried and heated, they are transferred into a mixing drum. The asphalt mix is then prepared by pouring hot bitumen into the aggregates and properly blending them together.
This is an ongoing process in modern-day plants closely watched in terms of consistency, temperature, and quality.
Step 3: Loading and Transporting
Once the mix has been finished, it is loaded into trucks and ferried to the construction site while it is still hot. Time is of the essence; when the mix starts to thicken and harden and is not liquefied enough, the mix will be wasted.
How Recycled Asphalt Is Made
Recyclability is also one of the greatest benefits of asphalt (it can be recycled 100 percent).
Reclaimed Asphalt Pavement (RAP) is old asphalt that has been taken off the roads and crushed into smaller fragments. The recycled material is introduced into new asphalt mixes in the plant, thereby saving the use of new raw materials and expenses.
Recycled Asphalt Shingles (RAS) that is used on old roofing materials is also used in some plants.
The advantages of recycling asphalt are it:
- Reduces landfill waste
- Saves on natural resources
- Reduces the cost of production
- Reduces environmental effects
Quality Control in Asphalt Production
The process of producing high-quality asphalt involves a lot of control over all aspects of the process.
The plants that are made of asphalt have sophisticated sensors and systems of control that aid in monitoring:
- Temperature
- Aggregate gradation and size
- Bitumen content
- Mixing time
In order to confirm the asphalt conforms to the DOT (Department of Transportation) standards and project specifications, samples are regularly taken and tested in a lab.
Environmental Considerations
Although the process of asphalt production does presuppose the usage of fossil fuels, the contemporary approaches are becoming greener.
Here’s how:
Use of Recycled Materials
As stated, RAP and RAS decrease the necessity to create new materials.
Emission Control Systems
The majority of asphalt plants today are provided with a pollution control system which minimizes dust, fumes, and greenhouse gases.
Warm Mix Technology
Warm mix asphalt uses less fuel to manufacture, and this lowers emissions and enhances the working conditions of the paving crews.