Asphalt is a typical material used in the construction of roads, driveways, and parking lots in the United States. But have you ever wondered how hot asphalt is when it is being laid down? Knowing asphalt temperature during paving is not only important to the contractors, but also to the homeowners and motorists who wish to be safe.
In this article, we will deconstruct the process of asphalt getting hot when it is paved, why it is important, and what you need to know either as a contractor or as somebody passing by newly-paved roads.
What Is Asphalt?
Asphalt (or blacktop, or hot mix asphalt) is a combination of aggregates (crushed stone, sand, and gravel), and bitumen, a sticky petroleum-based binder that is black in color. It is heated up to high temperatures to be mixed, poured, and compacted into a smooth and durable surface.
Why Is Asphalt Heated?
Asphalt must be heated to be workable and malleable. The bitumen is more fluid when heated, which means that the mix can be easily spread and formed. Without ensuring that the asphalt is hot enough, it gets hard and difficult to compact, hence creating weak spots and premature deterioration of the pavement.
What is the Temperature of Asphalt When it Leaves the Plant?
Asphalt temperature at the time of its manufacture at the mixing plant is dependent on the mix in which it is made, although on an average it maintains a temperature between:
- 275°F – 325°F (135°C to 163°C)
This is the temperature at which hot mix asphalt (HMA) is loaded to trucks and taken to the worksite. Storing the material in this temperature range is very important in quality paving.
Asphalt Mixes and Temperatures
| Asphalt Type | Typical Temperature Range |
| Hot Mix Asphalt (HMA) | 275°F – 325°F |
| Warm Mix Asphalt (WMA) | 200°F – 275°F |
| Cold Mix Asphalt | No heating needed |
Note: Cold mix asphalt is utilized in patching and temporary repair and does not have to be heated as opposed to HMA or WMA.
Temperature When Asphalt Is Laid
At the time asphalt is delivered to the laying location, it normally must be:
- Poured between 275°F – 325°F, and
- The mix should be compacted prior to taking the temperature to less than 175°F.
In cold weather (cold winds, etc), asphalt may tend to cool too fast, thus failing to compact correctly resulting in poor quality pavement.
What is the Temperature of Asphalt?
Newly laid asphalt is very hot, and it can burn human skin in a few seconds. It is not only uncomfortable, but it can also be dangerous.
- Asphalt can give a third-degree burn within seconds at 300° F
- It can still be hot enough to burn human skin and even destroy pet paws and bike tires even after 30 minutes or an hour
- Therefore, when there is a newly paved blacktop road, avoid it until it is completed cooled down and cured
How Long Does Asphalt Stay Hot?
The cooling time is subject to a number of factors:
- Thickness of the Layer: Layers that are thicker have longer heat retention
- Weather Conditions: Hot and sunny weather make asphalt hotter in the long term
- Speed of Wind: Fast rate of wind cools the surface
- Surface Underneath: Asphalt laid on hot subgrades (as is the case with another pavement) will cool more slowly.
General Cooling Guidelines
| Asphalt Thickness | Approximate Cooling Time |
| 1 inch | 30–45 minutes |
| 2–3 inches | 2–3 hours |
| 4+ inches | 4+ hours |
What Is So Important About Asphalt Temperature?
Temperature that is proper in paving influences:
Pavement Durability
Asphalt that is too cool will not compact correctly resulting in cracks, potholes, or raveling (loose stones).
Surface Smoothness
Asphalt becomes hotter and flows more easily, thus creating a smoother and more even surface.
Construction Schedule
When the asphalt solidifies too early, crews can be forced to stop or scrap off the cooled material resulting in delays and increased expenses.
Asphalt Safety Tips: Stay Safe Around Hot Asphalt
As either a passerby, driver, or property owner, you can observe a few simple tips to be safe:
- Do not walk on fresh asphalt until it is completely cooled and cured (they can take 24 to 48 hours).
- Pets should not be on new pavement; their paws are very sensitive to heat.
- Never disobey road signs and cones; they are there to protect your safety.
- Instruct children not to play around paving sites because the machines and materials are hazardous.
For Workers and Contractors:
- Wear protective equipment: gloves, boots, and long sleeves.
- Be aware of heat diseases like heat stroke.
- Keep hydrated and keep off hot mix.
Asphalt vs. Air Temperature: Why Summer Paving Is Challenging
In the hottest summer seasons, the ambient temperature may reach 90° to 100°F (or higher) and this means that asphalt is even hotter.
Black surfaces absorb sunlight and:
- Can reach 140°-160° F, even without fresh paving on a hot summer day.
- If you pour fresh hot mix over the top, the surface temperature can rise to more than 300°F posing a hazardous condition both to workers and pedestrians.
Can Asphalt Be Too Hot?
Yes, when it is overheated during manufacturing (over 325°F -350°F).
Asphalt May:
- Reduce durability by cutting the binder
- Increase risk of smoke and fumes
- Cultivate a fire hazard in extreme cases
That is why the temperature in the production and transportation is closely controlled by manufacturers.
Key Takeaways
Highlights and Main Points:
- New asphalt is normally in the range of 275°F to 325°F when placed
- When it reaches temperatures below 175°F, compaction should be done
- The asphalt can burn even if it’s not fresh
- Time of cooling can take between 30 min and 4 or more hours under different circumstances
- Temperature is quite important for asphalt strength, performance, and safety.