I was going to call this thread "Why is asphalt black", but then this morning I was on a very light gray road...
...still, most roads, this includes most F1 tracks, are black-ish, as in a rather dark shade of gray.
The reasons are possibly obvious: tar and bitumen are black, rock aggregate mostly dark gray, so any combination of those ends up in a very dark tone.
Then again, nowadays technology is such that, really, a tiny amount of additives could turn the surface into basically any desired color with minimum effect on grip properties. Paint is out of the question as it gets slippery, but light gray or even, say, light green asphalt should be easy pickings... so they are not desired? Why?
Visibility is an obvious point, lighter colors reflect more light thus can be problematic in sunny days. White road markings would bneed to become black, maybe. But then of course that same asphalt would be more visible in the dark. Does any pavement engineer here know if this, visibility, is a factor? I guess most cars drive in daylight...
What really got me intrigued, though, is the thermal aspect of that color. We are all tired of cars getting super hot in sunny days in a parking lot, and the "air temp 30C, track temp 50C" sign is there all summer in F1. Black-ish asphalt colors are a great part of this, they suck soak up the photons from the sun, heating the asphalt and then the air and any object on it. (I know, I know, the car itself is a green house, I know, but it all adds up).
Still, light colored asphalt ought to be much less effective at heating up in the sun, no? Wouldn't this increase the durability of the asphalt and even increase tire life for the cars rolling on it?
Even more subtly and not as black and white, the same properties that make black objects absorb visible light often make them absorb IR as well, and if they absorb IR, they will be about equally good at emitting IR radiation. Thus, in cold nights, black asphalt should, in general cool down faster and further than light colored asphalt, as it is quite good at radiatively cooling itself.
This means that in a winter day when temperature briefly drops to -2C, dark asphalt might lead to ice formation where light gray asphalt likely would have enough thermal inertia to not do that. No ice --> good for the asphalt and good for the cars rolling on it.
On a very cold night, light asphalt ought to be better at retaining heat from the day, so again, cool down later and less than black asphalt, or so I would think. Less ice should lead to less cracks in the pavement, less growth of those cracks once formed, etc, leading to longer road life, no?
I might be completely off here, I just though I'd share the assumptions and the questions and pick everyone's brains, any takers?
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