Question about asphalt

There has been a lot of road construction and repaving this year. Have you noticed how new asphalt is so very black, and as it weathers/wears the entire road surface lightens in color? I do know that asphalt is also called bituminous concrete - the tar compounds are a binder for the aggregate and sand. Ultimately the road's final color is due to the color of the crushed rock (aggregate) after these tarry binders are worn away. There is a section of I-80 in eastern Pennsylvania where the interstate has a reddish hue due to the color of this gravel.

My question is, why doesn't the road wear more quickly in the tire tracks resulting in two lighter paths with a dark center. From what I have seen, the color seems to lighten uniformly across the width of the road.

While newly laid roads are a joy to ride on (after a few weeks to let them weather a bit) I find that they absorb light at night like a sponge. And if it is raining, forget it - I park the bike and get off the road. As I age, my night vision seems to be getting worse and new wet roads equal conditions that are too dangerous for me.

Maybe the colour change is due to fading from sunlight exposure and not tire wear?

hopefully they (the road crew or contractor or DOT) put the plastic stickon line delineation markers on the fresh pavement to help until the stripes are painted. Who cares if you can't see he pavement as long as you stay between the lines and can see anything on the pavement. But I know what yo mean. What gets me more than the invisible wet black pavement is oncoming car or trucks (seems it is usually trucks) with HID headlights with lousy cutoff or high beams in my face.

Andrew pretty much nailed it. The oils in the top layer of asphalt oxidize and turn grey with exposure and time.

--Mark

Another warning--If those new, black paved surfaces are wetted, they're slick. Two reasons for the slickness: 1) the oils from the pavement have not fully evaporated and washed off, 2) the surface is not yet roughened and therefore all the water has to be pushed out from under your tire solely through the tire tread grooves.

But it is nice to ride the smooth black surface in daylight, dry conditions.

There is more recycled asphalt put in the mixes now. For some reason they tend to fade faster than virgin mixes.

DAS said:

hopefully they (the road crew or contractor or DOT) put the plastic stickon line delineation markers on the fresh pavement to help until the stripes are painted. Who cares if you can't see he pavement as long as you stay between the lines and can see anything on the pavement. But I know what yo mean. What gets me more than the invisible wet black pavement is oncoming car or trucks (seems it is usually trucks) with HID headlights with lousy cutoff or high beams in my face.

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+1 on that! tho the HID headlights in general play havoc w my night vision.

Blrfl said:

The oils in the top layer of asphalt oxidize and turn grey with exposure and time.

Click to expand...

+1...
The tar-oils/binders take a while to erode, oxidise, dry up and seep down between granite/pebble (or whatever granules are used) to finally expose them, providing grip.

Also +1 that new black-top/tarmac is very slick, thus especially (but not exclusively) hazardous for motorcyclists; while fully fresh even when dry(!), but especially in the rain where you can often actually see the oil puddles shimmer on the water...
Depending on weather and temperatures can it take up to 6 months till a new roadway cover can be considered "safe" for motorcycles...