Anyone who has walked barefoot across a driveway in a Queensland summer knows asphalt gets hot. That heat is both a strength and a challenge, and understanding why it happens helps explain how surfaces are designed to cope with it. Here is the simple science.
Why asphalt heats up
Asphalt is dark, and dark surfaces absorb more sunlight than light ones. They take in more of the visible light spectrum and convert it into heat, so an asphalt surface warms up quickly in the sun. This is called solar absorption, and it is why a black driveway can feel a good deal hotter than the air around it.
Why it stays hot
Asphalt does not just absorb heat, it holds onto it. Once warmed, the surface stays hot for hours, releasing the heat slowly, often well into the evening. Across a whole city of dark roads and roofs this adds up to what is known as the urban heat island effect, where built-up areas run warmer than the surrounding countryside.
Its low thermal conductivity is part of the reason. Asphalt takes in heat faster than it can shed it, so heat builds up during the day and radiates back out slowly at night. The thickness plays a role too: a thicker layer has more mass, so it takes longer to cool than a thin one.
Keeping surfaces cooler
The good news is that heat absorption can be managed, and there are a few approaches that help:
- Reflective surfaces. Traditional asphalt reflects very little sunlight, but lighter-coloured coatings and cool-pavement treatments raise its reflectivity, so it takes in less heat and runs cooler.
- Heat-managing mixes. Some mixes include materials that store heat and release it more slowly, evening out the temperature spikes through the day.
- Cool pavements. These treated surfaces lower both the surface temperature and, across a wider area, the air temperature around them.
Why it matters for your driveway
Heat is not just about comfort. It affects how a surface is laid and how it wears. Fresh asphalt should not be laid in the peak of the day's heat, because it affects how the surface sets and finishes. And over its life, a driveway that runs very hot benefits from a good seal and, where it suits, a lighter or reflective finish to reduce the strain the sun puts on it.
Understanding the way asphalt handles heat is part of building a surface that lasts in our climate, which is exactly what we plan for on every job.
We surface driveways, roads and car parks across Brisbane, the Gold Coast, Ipswich, the Sunshine Coast and Toowoomba. If you want a surface built to cope with the heat here, whether standard asphalt or a cooler finish, look at our asphalt driveways page, then get in touch for a written quote at no cost.