It is common for us to see fresh asphalt being laid on roads from time to time. Most of us also understand not to drive on fresh asphalt but to let it dry first. This may make you wonder when it is the right time to start using the road? How long does asphalt take to dry?
Asphalt takes around 48-72 hours to dry. After it is dry, walking or driving on the asphalt is safe. Many factors, such as humidity, sunlight, temperature, and wind, influence how long asphalt takes to dry. Dried asphalt may take up to a year to fully cure. When cured, the asphalt turns gray and can now handle heavy vehicles well.
This article explores the process of laying asphalt and how long it takes to dry. We also examine what factors affect asphalt’s drying time and discuss the differences between drying and curing asphalt.
What Is Asphalt?
Asphalt is a sticky, black, and thick element usually used to build roads. It binds rocks, sand, and many other materials together to form solid asphalt concrete as the top surface of roads. Asphalt may be mined naturally or refined from petroleum products. Aside from roads, asphalt is also used in waterproofing products.
Asphalt is a type of petroleum-based element. It is sticky, black, and thick, with a semi-solid appearance. Asphalt may be called bitumen in some places, such as the UK. You may also hear people describe asphalt as tar.
Asphalt is commonly refined from petroleum or may be mined from the ground naturally. The world’s largest natural asphalt deposit is in Alberta, Canada. The amount is roughly the size of England.
Asphalt was used as a construction material as early as 5,000 BC. Ancient civilizations such as Mesopotamia and Indus used it as binders for bricks, much as how we use cement to bind bricks today.
Today, the most popular way to use asphalt is as a binder, to be mixed with rocks and other materials to form asphalt concrete. This is then laid on the surface to build roads.
Another popular way to use asphalt is waterproofing since it repels water. Asphalt-based products are regularly used to waterproof building roofs, pipes, cables, floors, etc. These may come in sheets or thick liquid forms to be spread over the surface.
How Is Asphalt Laid?
Before asphalt is laid, there are several steps to prepare the surface. The surface is first cleaned before it is graded and sloped for drainage. Then the sub-base is laid on top before they are rolled and compacted. Then a binder layer is added on top before the hot asphalt is laid on the surface. The edges are then smoothed to join existing roads.
The work process of laying asphalt is not a straightforward job. It takes some serious preparation work to ensure the laid asphalt will last for years. A properly laid asphalt road will also be able to repel moisture better and not build water spots.
Preparing The Surface
The work starts with preparing the surface. If it is raw ground with vegetation and trees, they will be cleared out, leaving only the soil surface.
If the ground already has roads on it. The old asphalt is removed and recycled. Most asphalt roads can be recycled. They are usually reheated to melt the asphalt, mixed with rocks and other materials, and then relaid as fresh asphalt.
Once the surface is completely bare, the soil is graded, and a degree of slope is added. This ensures the water on the road can be drained away naturally. Roads with water spots can be dangerous to drive on, as it may cause your car to skid.
Laying The Sub Base
The main role of the sub-base is to protect the asphalt concrete and provide the concrete with additional strength. A good sub-base will prevent extreme temperatures from cracking and the asphalt from sinking into the ground, forming potholes.
Subbases are usually a mixture of stones, gravel, and recycled materials. They are laid on top of the bare ground evenly, usually using paving machines.
Rolling and Compacting
Once the sub-base is laid in, a roller is used to press these materials into the raw ground to compact it. This process is usually done with a 72,000-ton roller, which will drive around and press in the materials.
For smaller projects, a compacting machine may be used. They are about the size of a floor polishing machine, but it has a flat bottom surface that uses a hammering motion to press the sub-base in.
A compact and solid sub-base will later serve as a good intermediary between the bare ground and the asphalt concrete.
Adding The Binder and Asphalt
After the soil is compacted, the binder is then added. The binder helps the asphalt layer to bind with the sub-base and prevents it from moving. The binder is usually made of asphalt mixed with other oils.
These are usually sprayed onto the road surface, with the hot asphalt road layer laid immediately behind it. Larger projects may see a truck up front, laying in the binder, with the asphalt paving truck laying in the asphalt.
The asphalt is usually hot, as the higher temperature allows the asphalt to be more liquid. This makes it easier to lay and manipulate the asphalt concrete. As the asphalt is being laid, it is compacted again with a roller to create a smooth, dense, flat surface.
Filling Gaps And Smoothening The Edges
As the asphalt concrete is laid, you may notice a crew of men scooping up hot asphalt with shovels and laying in on smaller areas not covered by the paving machine.
They usually ensure that no asphalt covers any culverts, sewage holes, or important markers. Some areas that should have been covered but missed out by the paving machine could be manually covered by laying the hot asphalt with a shovel.
An asphalt laying work usually involves the new road surface joining older roads or other surfaces. The crew may also use their shovels to try and smoothen the transitions to ensure a smooth driving experience. Extreme elevations can be unsafe to drive on.
Once laid, the asphalt surface is given time to dry; when dried, it can be driven on.
How Long Does Asphalt Take To Dry?
Once laid, asphalt needs around 24-72 hours to dry, cool, and harden before walking or driving on is safe. It is advised to wait up to a week. Wet, hot asphalt may stick to the bottom of your car, and it can be hard to remove. Driving on hot, soft asphalt may damage the road, and your tires, since the hot asphalt may melt them.
Generally, when hot asphalt leaves the hot mixer, it starts to cool and dry. As asphalt cools and dries up, it becomes harder and harder to shape. This explains why some asphalt paving machines have heaters to keep the asphalt hot as they are being laid.
Once laid, the asphalt takes 24-72 hours to dry, cool, and harden. Any manipulation work on the asphalt surface should be done as soon as possible. In contrast, the asphalt is still hot and malleable.
During the drying process, it is important not to place anything on the surface, as it may leave a mark on it. That means you should not walk or drive on wet, hot asphalt.
Walking on soft asphalt is a no-no, as you will damage your shoe. The hot asphalt may stick to your shoe outsole, and the heat may melt or damage some. You may also leave footprints on your asphalt, meaning you must roll and compact the area again.
You should also not drive on wet and hot asphalt for the same reason; tire marks will be left on the fresh asphalt, meaning the asphalt must roll it again. As you drive on hot wet asphalt, some of it may stick to your tire and get flicked to the underside and wheel well of your car.
This asphalt may damage and melt your tire and can be hard to remove and clean.
What Factors Affect Asphalt Drying Time?
Many factors determine asphalt drying time. These may include humidity, temperature, sunlight, and wind. Dried asphalt road feels hard to the touch and can be walked and driven on by light vehicles. It can also be sealed with road sealer.
There is a reason why road drying times vary so much, between 24 – 72 hours. In fact, some road builders wait until a week before allowing any traffic on it. This is because the time asphalt takes to dry can depend on many factors:
Humidity refers to how much moisture is in the air. If the air is moist, you may sweat a lot more, and breathing may be slightly harder.
When it comes to drying asphalt, the more humidity there is, the more moist the air is. This means there is less oil and humidity space inside the asphalt to escape. As a result, it may mean longer drying times.
Temperature can be seen in two aspects: air and surface temperatures. Surface temperature is about the temperature of the asphalt itself and the air temperature of the surrounding air.
The lower the air temperature, the faster the asphalt dries. This is because the heat from the asphalt can easily escape and warm up the cool air. However, this may challenge the laying crew, as the asphalt may cool too fast, making laying work harder.
Higher air temperature may help the asphalt to cool and dry slower. This may mean an easier job for the road laying crew, but the road may take longer before it is safe to be driven on.
Sunlight may alter drying times by introducing heat sources to the asphalt. Aside from heating the asphalt, sunlight heats up the air, raising the temperature. Generally, sunlight correlates negatively with drying time.
This means the less sunlight there is, the less additional heat source your asphalt gets. The air also is cooler. This means your asphalt will dry faster, and the heat from the asphalt can easily escape into the air.
Wind helps to circulate the air around the asphalt, driving away the hot and humid air and replacing it with cooler and dryer air. This means the asphalt continues to be able to transfer the heat and humidity to the new air. As a result, it dries and cools faster.
When there is no airflow, the humidity, and heat in the air stay close to the asphalt. This means there is little chance for the remaining humidity and heat to escape the asphalt. As a result, drying time becomes longer.
Is Drying and Curing Asphalt Different?
Drying and curing asphalt is different. Drying times are significantly shorter than curing times. Dried asphalt is not as hard as cured asphalt and may not bear heavyweights as well. The dried asphalt surface is usually dark and black, while cured asphalt is usually grayish, as the oils have oxidized.
As you research road construction, you may notice curing and drying asphalt roads. What are the differences?
Generally, it takes around 24-48 hours for asphalt to dry. Some road builders may advise allowing up to a week to dry. However, the process may take up to a full year to cure.
This is because asphalt binds better and becomes harder as time goes on, just like concrete. A fully cured road can bear the maximum weight limit as it was designed to.
A dried asphalt road usually retains its darker color and may look shinier and oilier. A cured asphalt road is usually grayish in color and may look dull.
This is because dried asphalt may retain much of its oil, making it dark and shiny. Cured asphalt roads have lost the oil to the sun, which means the road becomes grayish and dull.
A dried asphalt road may bear much weight, but a cured road can bear the maximum weight it was designed to. This is because cured asphalt is a hardened road with no oils. It can bear much more weight than a dried asphalt road.
Dried asphalt road may look newer, but it may not be able to handle damages as well as a cured asphalt road. This is because it is still not as hard as cured asphalt.
The most common damage you may notice from dried asphalt roads is the ‘power steering tear,’ where the extreme turning of tires actually scraped up some of the asphalt. Heavy vehicles also may leave potholes on the softer side of the dried asphalt. These usually do not happen with cured asphalt.
Can You Protect Asphalt Roads?
If you just laid a fresh layer of asphalt on your driveway, you can protect it by applying asphalt sealer. These are usually a softer layer of resin that you can apply on the asphalt. It fills in any small imperfections on the road and keeps out UV rays, water, and vehicle fluid. Your asphalt may also retain its dark, shiny look.
Suppose you have laid asphalt on your driveway or any of your private property. As you start driving on it, you start to notice some imperfections, such as holes and crack lines. You have also left marks on the road, such as vehicle fluids.
You also start to notice your asphalt has faded, and you prefer a dark, shiny look of fresh asphalt.
Instead of laying a fresh coat of asphalt, you can actually lay in a coat of sealant. Asphalt sealant is essentially a thick liquid-based material. You can apply it on the asphalt to seal it.
The application is simple and can be done with a squeegee. You pour the sealant on the asphalt and then push and pull it over the surface until it is flat and forms a thin film. Once it is dry, the road is good to be driven on again.
It is usually made of asphalt and mixed with other materials to stabilize it. There are also versions made of cold tar, but cold tar is known to be carcinogenic, so they are now less popular.
Asphalt sealer fills the imperfections on the road, such as holes and cracks lines. It also forms a layer of film on top of the asphalt, protecting it against water, UV rays, and vehicle fluid. It also darkens the road, giving your road a dark, shiny look you see with fresh asphalt.
However, if you intend to apply sealant, you want to wait until the road is cured first. This means waiting for at least a year. If you apply sealant too early, the oils inside the asphalt cannot oxidize, meaning the asphalt cannot fully cure.