Why do we use Asphalt for roads?

When you hear the word “Asphalt”, most probably you think of the black tar stuff on roads and highways, right? But that’s not exactly correct. Asphalt is the liquid that is in the road, it’s the binding agent that kind of holds the rocks together. The difference is that the Asphalt comes from crude oil, while tar comes from coal. Therefore that Black Stuff you see on the Road, technically it´s not Asphalt.

Asphalt also is found naturally in the earth, and there are lakes of it where oil from underground has risen to the surface, like the La Brea Tar Pits in Los Angeles and Pitch Lake in Trinidad, which is the largest natural deposit of asphalt in the world. But the most common way the binder is made today is through the crude oil refining process. Asphalt is the heaviest of materials in a barrel of oil; it’s basically the waste product. Asphalt is the heavy sticky residue that settles to the bottom. It cannot be used for energy, so it takes on new life as the sticky stuff that holds materials together. Combined with various amounts and types of rocks and other substances, it eventually becomes the mixture we drive on. The road is really an asphalt mixture or better termed “asphalt pavement.”

It has been used in paving for more than a hundred years.  When English explorer Sir Walter Raleigh turned up at Pitch Lake in Trinidad in 1595, he used the asphalt for caulking his ships.This stuff It’s been used in other non-road functions throughout history. Using it as a binder in roads became more common in the 1800s. John Loudon McAdam, who built the Scottish turnpike, added hot tar to reduce dust and maintenance on roads. This method also improved driving conditions. In the United States, bituminous mixtures (asphalt concrete) first appeared in the 1860s, and the 1st “true asphalt pavement” was laid in Newark in 1870 by Edmund J. DeSmedt, a Belgian inventor. This asphalt was modeled after a natural pavement highway in France. DeSmedt then paved Washington, D.C.’s Pennsylvania Avenue with asphalt from Trinidad, further proving its durability.

How Asphalt Is Used Today

When asphalt first came into use, oil refiners would give it away. Today, however, it is a highly traded commodity that demands premium prices. The Asphalt our roads are made of is actually is a composite material with two primary ingredients: aggregates and bitumen. Aggregates – usually crushed stone, sand and gravel – are bound together with bitumen (a viscous and waterproof substance) at high temperature to  become asphalt. Typically, the aggregate size decreases as you move up through the construction from the base to the surface course, whilst the bitumen content increases. 

Although it’s most often associated with roads, asphalt is used for many purposes, though roads account for its most extensive use. Of the more than 4.3 million kilometers of paved roads in the U.S., 94% are surfaced with asphalt, according to National Asphalt Pavement Association (NAPA). Asphalt is cost-effective, low maintenance and extremely durable, making it an ideal road surfacing material. It is a popular choice because:

• It is fast to construct
• It can withstand significant weight and temperature fluctuations
• It is easy to maintain and repair
• It produces a smooth surface for maximum tire grip
• It reduces noise pollution
• It rapidly disperses surface water, reducing spray, the risk of aquaplaning and improving visibility for drivers 
• It increases the visibility of road markings

Interestingly, though, all of that includes a mixture of about 95% stone, sand and gravel, and just 5% asphalt cement. Asphalt also is used for parking lots, airport runways and racetracks. . Asphalt is a really flexible and versatile product, it can be used to line fishponds and water reservoirs or for sporting purposes like tennis courts. A couple of years ago, it was chosen as the base surface for the field at the Minnesota Vikings stadium in Minneapolis. Since the early days of asphalt production, the industry has continued to innovate new products, becoming more scientific and rigorous.

5 Different Types of Asphalt

Asphalt can take on many types of jobs, depending on the process that mixes the aggregates with bitumen. Choosing the right type of asphalt can mean the difference between success and failure.

Hot-Mix Asphalt – This is probably the most common type of asphalt. It is produced at very high temperatures between 300 and 350 degrees Fahrenheit. Hot-mix asphalt is highly weather resistant and used on highways and runways. When the asphalt is hot, it is easy to work with. It cools quickly, so some expertise is required to use it. HMA is our choice for creating a durable pavement that meets your requirements.

Warm-Mix Asphalt – This type of asphalt is a newer technology in which the mixture is only heated up to 120 degrees Fahrenheit. It is safer for workers because of the lower temperatures, and it uses less fuel than hot-mix asphalt, making it better for the environment. Because the asphalt mix cools down slowly, it can be applied even when the weather is cooler. Warm-mix asphalt is easier to transport long distances without losing quality.

Cold-Mix Asphalt – This type of asphalt is used when it’s cold outside, usually to make temporary repairs that can’t be done when the weather doesn’t cooperate with hot-mix asphalt. Cold-mix isn’t as strong as hot-mix asphalt, but it will patch areas that don’t get heavy traffic. When permanent repairs can be made, the cold-mix asphalt can be removed.

Dense-graded asphalt – This type of asphalt is a type of hot-mix asphalt that is impermeable and more durable than a general hot-mix asphalt. However, it does need to be used properly to achieve a stronger surface.

Porous asphalt – This type of asphalt allows water to drain through it to the soil underneath. It’s popular for playgrounds and parking lots because it improves safety by eliminating puddles. Porous asphalt is also good for the environment and places less stress on sewer systems.

Recycling Asphalt

What a lot of people don’t know is all of the environmentally friendly things the asphalt industry is actually doing. For starters, asphalt is 100% recyclable, and more importantly, it actually does get recycled. In 2018, 74.5 million metric tons of Reclaimed Asphalt Pavement (RAP) was put back into new mixes. That means every asphalt mix put down in the U.S. included about 21 % RAP. In fact, the combined weight of all items people recycle annually in the U.S. — paper, plastic and aluminum — totaled a fraction of (about 68 %) of the weight of RAP the asphalt industry recycles annually. That’s just one material we recycle, the asphalt industry is the most active recycling industry in the country. Asphalt pavements take less energy to produce, resulting in fewer greenhouse gases than concrete pavement. Warm-mix asphalt further reduces greenhouse gas emissions. Additionally, smoother roads are better for the environment because fuel economy is increased on smoother pavements.

It is also one of the biggest recyclers of tire rubber, which is used as a modifier for mixtures in some states. Roof shingles also are recycled into new asphalt mixtures, and the industry is looking into how plastic might become part of the discussion. A lot of engineering and material science goes into constructing a road. Today, asphalt roads are designed around the concept of “perpetual pavement,” or at least to last 40 years or more. Routine maintenance consists of “milling” the surface — taking off the top inch or so — every 12 to 20 years and replacing it with a new overlay. That top inch can be recycled, and the periodic overlays significantly improve the ride quality and fuel consumption of vehicles traveling on these roads.

Criticism of Asphalt

Asphalt probably isn’t something you think of as eco-friendly; it could be partly guilt by association because asphalt is naturally aligned with major polluters — driving automobiles and oil production. And some of the negativity is warranted: Because asphalt has low reflectivity, it has been determined to be a significant contributor to the Urban Heat Island (UHI) effect. Anyone who has sat in a highway traffic jam on a hot summer day can attest to that. As far as asphalt’s contributions to the UHI, the Environmental Protection Agency states that conventional asphalt pavements can be modified with materials or treated after installation to raise reflectance. For decades, this has been sometimes implemented on surfaces like parking lots and highways. The EPA includes porous asphalt and rubberized asphalt as examples of permeable pavements.

Asphalt has also earned bad marks for being impermeable, for the gases it produces when melted and the fumes it exposes workers to during paving and roofing. Occupational Safety and Health Administration (OSHA) says those fumes can lead to headache, skin rash, fatigue and even skin cancer. While OSHA’s standards do not specifically address asphalt fumes, the administration recommends that controlling exposure can be done through “engineering controls, administrative actions and personal protective equipment.” And of course, there’s still the fact that asphalt is made from petroleum. But asphalt does have positive eco-qualities too.