Paved surfaces are a dominant feature of the modern landscape, and these materials can become intensely hot. The heat is not uniform across all surfaces, however, and the difference between common paving materials can be significant. The comparison between asphalt and concrete reveals a clear disparity in how much solar energy each material absorbs and retains. Understanding this difference is important for urban planning, environmental health, and personal safety during warm weather.
The Direct Comparison: Surface Temperature Readings
The answer to which paving material gets hotter is definitive: asphalt consistently reaches higher surface temperatures than concrete under the same conditions. During a typical summer day with an air temperature around 90°F, asphalt surfaces frequently soar past 140°F. In contrast, concrete surfaces exposed to the same sun might only reach 120°F to 125°F. This difference means that asphalt can be 20 to 30 degrees Fahrenheit warmer than an adjacent concrete surface. This empirical observation establishes that black asphalt is a much more effective collector of solar energy than lighter-colored concrete.
Material Science: Why Asphalt Absorbs More Heat
The primary reason for this temperature difference lies in albedo, which measures how much solar radiation a surface reflects. Asphalt, due to its dark color from bitumen, has a low albedo (0.05 to 0.10 when new), meaning it absorbs 90% or more of the sunlight that hits it, converting that energy into heat. Concrete, made from cement and aggregate, is much lighter in color, giving it a higher albedo (0.35 to 0.40). This lighter color allows concrete to reflect a larger portion of the sun’s energy, limiting the amount absorbed and converted into heat. Pavement materials also possess a thermal mass, relating to the energy required to raise their temperature, and the low albedo of asphalt means it absorbs a high amount of solar energy that it then holds and re-radiates.
Practical Implications of Pavement Heat
The high surface temperatures of dark pavements contribute significantly to the Urban Heat Island (UHI) effect, making metropolitan areas noticeably warmer than surrounding rural regions. Large expanses of heat-absorbing asphalt raise the ambient air temperature, increasing the severity of heat waves and energy demand for cooling buildings. These hot surfaces also pose immediate safety concerns for humans and pets. Pavement temperatures exceeding 120°F are hot enough to cause burns to a dog’s paw pads, and at 125°F, burns can occur in as little as 60 seconds. For human skin, temperatures above 140°F can cause rapid tissue damage, creating a serious risk of second-degree burns upon contact, making simple precautions necessary.