What Makes Up Asphalt?
As the most commonly used material for road systems, every driver has reaped the benefits of ease that asphalt provides. It allows cars, bikes, and other vehicles, to travel great distances without much difficulty. It is also able to withstand massive amounts of weight.
However, the material itself and its composition can lead to difficulties during certain types of weather. An aggregate of crushed stone and sand, petroleum-based bitumen, as well as binders and fillers are the components of the asphalt you drive on every day. These components, though they have their advantages, also have disadvantages during certain extreme types of weather, such as heat.
Composition Of Asphalt And How It Accelerates Heat Damage
First, let’s list the components we’re dealing with and the role some of them play:
- An aggregate of crushed stone or sand
- Petroleum-based bitumen
- Air voids (entrapped air)
Bitumen in asphalt is a sticky black liquid that binds together the aggregate to form a solid mass. The binder then mixes with the bitumen to create an asphalt cement paste that binds together all the various layers. Filler simply fills in the gaps between particles in the mixture in an effort to make it less brittle.
Additionally, asphalt is mixed in a drum at 280 degrees Fahrenheit and installed still warm. This heat keeps the bitumen pliable. The steaming material is then spread out and pressed, and then hardens as it dries.
Due to the chemical and molecular characteristics of some of these components, asphalt can be compromised during certain weather conditions. For instance, bitumen and other present binders are petroleum or oil-based. Consequently, when there’s rain or snow, the binder begins to break away from the aggregate base as oil and water don’t mix. This causes the asphalt to initiate cracking and crumbling.
Furthermore, when combining moisture and extreme heat, one of asphalt’s greatest enemies, humidity, is produced. In other words, humidity greatly weakens the material by allowing for air gaps to form. This humidity causes cracks where water can enter and break down binder cohesion. As a result, potholes and raveling occur.
Oxidation In Asphalt
The oil-based binders and bitumen in asphalt not only accelerate damage during moist weather but assist in accelerating the oxidation process initiated by the sun’s rays. Specifically, these rays fuse with oxygen to break down the chemical bonds that give asphalt its strength. The UV radiation causes the light oils in the asphalt to combine, and as a result, become heavier. Consequently, the weight of these molecules makes the material brittle and continuously more inclined to cracking or raveling.
The Viscosity Of Bitumen And How It Responds To Extreme Heat
As mentioned previously, the purpose of bitumen is to hold the aggregate within asphalt in place. However, bitumen is viscoelastic, meaning it responds to heat through the state of its viscosity. Viscosity is simply the consistency of a certain material, reflected from its internal friction on a molecular level. In other words, it describes a material’s internal resistance to flow or its “fluid friction”. For example, something such as water has an extremely low viscosity, whereas slightly thicker vegetable oil retains a higher viscosity.
When temperatures increase, bitumens viscosity responds by decreasing, making the material soft and almost sticky. This allows for traffic to pick up road surfaces as the bitumen clings to their tires. A spokeswoman from VicRoads described how extreme heat causes “bleeding” of the road surface through the reactivation of bitumen by temperature.
The Effects Of Heat On Asphalt Summary
In general, asphalt is an exponentially useful invention for the traveling purposes of all legal drivers. It’s solid and firm and allows for individuals to get from one place to the next in a condensed amount of time. However, it isn’t the most durable when it comes to certain weather conditions, specifically extreme heat. Its composition can work against it during these temperature trends causing cracking, potholes, and raveling
Accordingly, it’s best to continuously apply sealcoating to any laid asphalt. This protects the material from two of the most damaging ambient conditions: UV rays and rain or moisture. When combining this with scheduled maintenance by paving contractors, asphalt can be enjoyed for years to come.