The title is the question.
Maybe it’s the cheapest thing with the right properties, but can’t it be painted with something a little more reflective, that won’t absorbe so much heat from the sun?
In: Technology
Bitumen is a byproduct from the oil refinery process. It’s produced in huge amounts and the easiest way to get rid of it was to mix it with gravel, name it “asphalt” pour it over all the bumpy roads. It has to be cheap, because of the incredible amount of roads. White pigments would cost a lot and blind the drivers.
The cost of painting an entire road surface would be disproportionate both in terms of the chemicals and materials used as well as the maintenance to keep them white.
You don’t flant reflective streets. I don’t know if you been to the Nordics but the mix of a very low sun, and either wet or snowy streets with cobblestones have sometimes felt like I was walking through a mirror. Couldn’t not look up without sunglasses sometimes
The simple answer is cost.
Straight-up black asphalt is not even cheaper over the long run, just up-front, and most cities (especially in the US) don’t have the budget and luxury to think over the long run. (and *especially* about experimental stuff like reflective additives)
In newer cities in the US the streets are concrete and can be patched with more cement, but even in some of the upper-middle-class suburbs i return to or visit I’ve noticed that I’m seeing increasingly more black asphalt, not just for patch jobs but also for full re-builds. High construction costs come for us all.
It’s not the only one used. In addition to asphalt concrete, we also use dirt, gravel, chip seal (little bit of asphalt thrown on gravel), cement concrete, cobble stones, and paving stones.
Dirt obviously quickly deforms and get ruined in rain. Gravel is better, but still get deformed over time and loose rocks get thrown. Chip seal is a little better for the loose rocks, but still not that durable.
Cobble stones are expensive to install. Also very loud for vehicle traffic. Formed paving stones even more expensive.
So this leaves concretes as the best options. Strong, durable, flat and relatively quiet. Somewhat cheap to install. No loose stones to throw.
Of this we have cement concrete and asphalt concrete. Cement concrete (aka concrete) is aggregate (stones) glued together with Portland cement. Asphalt concrete is aggregate glued together with bitumen/ tar.
Cement concrete is strictly speaking better. It’s more durable, deforms less, longer lasting. It is however more expensive and louder (thanks to expansion cracks). It’s also not as dark, though still gets hot in the sun. You wouldn’t want a pure white surface, that would be horribly blinding. Try driving in snow on a sunny day. Not fun. You need to make cement obviously, which isnt cheap, and takes energy. A very large source of CO2 emmisions actually.
Asphalt concrete is cheaper to install. Arguably more expensive in long run. You just get bitumen from the ground, as a byproduct of oil extraction. The bitumen is also very recyclable, you just heat it and do it again. It’s also much easier to install that pouring cement concrete. The downside it is weaker. Heavy vehicles will eventually leave ruts in it. It doesn’t last as long. Contrary to the premise of your question, its actually great in hot climates. It’s cold climates that asphalt gets torn apart in. The hot surface in the sun is a minor issue, really only if people are walking bare foot or with dogs on it.
There are other concretes. Say polymer concrete. You could theoretically make a road out of this. But not going to beat the other two if you’re making a highway. Will we eventually find a better one? Maybe.
So asphalt is just the sweet spot of durability versus cost. Want more durability, cement concrete. Want less, chip seal or gravel. Want to look fancy but cost a lot and be less useful? Stonework.
Have you ever been to the beach during the summer and realize how hard it is to look down without sunglasses?
Imagine that on the road.
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Recent trip to Texas where all the roads are concrete. In an area as sunny as Dallas–and concrete 12 lanes wide, I couldn’t see–was like driving on a sunny day with snow. But then obviously as well, they can’t use asphalt for the heat/sun as well.
I’m by no means an expert here, but as many other have said there are certainly quite a highways and city streets that are concrete instead of asphalt.
From my father that works in construction, it certainly is more expensive, but as others have said it also tends to last longer.
The main issue he’s told me about is that it is also much more technically difficult to lay it correctly. Near me there are several concrete highways, some ride perfectly smooth and comfortable, however the others that I guess weren’t done as well are incredibly uneven and bumpy and have been since they were brand new.
So higher costs as well as the potential to make errors that persist for long periods of time are definitely considerations.
Cheap, good for tires. Light gray concrete is more expensive, louder, but more durable. Depends on what the client wants
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