Why no colored concrete?

The monotonous grey color of highway overpasses, high-rise buildings, etc. Why aren’t they in color? Can massive amounts of concrete be dyed to make such structures more eye-appealing? Sure - colored glass and/or paint can beautify buildings - but how about road structures?

I seem to recall seeing some red road surfaces in the UK, but they may have been brick or other material. Such colored roads exist in China.

The caption suggests that road is just painted.

Concrete certainly can be colored, though getting the color to be consistent is a step short of impossible, and if the color’s inconsistent it looks like ass. A road, say, is many, many loads of concrete, allof which are mixed immediately prior to use; achieving a consistent color is awesomely hard, as the tiniest variation in dye, cement, aggregate or water will give it a slightly different shade, and the human eye can pick up on that really well.

In some home improvement project - say you’re pouring a sidewalk or a small pool deck - colored concrete is coming into some vogue, but there you can get away with using one mix because you don’t need as much concrete. However, the concrete will require some maintenance, cleaning, and sealing to retain the color.

Roads are generally made of asphalt today, not concrete, which is black/gray, because oil and tar is black. But one reason not to color such things is maintenance. Today if they have to patch concrete they can use concrete, cement or some similar patch material which they can just use straight as it is already basically cement colored. But having to color match will over time just leave a jumbled patchwork of different shades which is unneeded to begin with for almost all civil projects.

My patio has some dyed sections and some painted sections. The painted sections really should have had a few extra coats of paint (stain?) and sealer. 15 years later and the black stain is pretty light. The dyed sections still look perfect. I powerwash them from time to time and that’s it. The nice thing about the concrete being dyed, as opposed to stained, is that no matter how much wear and tear they get, they stay the same color. For example, if I drag a table across the patio, it might scratch the paint off and leave a mark, but if it scratches the dyed section, it doesn’t.
But, yeah, you wouldn’t want to do this on something that’s going to take multiple (or multiple hundreds) of loads of concrete due to it not matching from one batch to the next.
The only way I could really see it working would be to match each batch as best as possible and then paint over the top of it. Then it would buy you more time before it has to be repainted.

Roads around me are a pretty even split (not that I’ve paid that much attention) between asphalt and concrete. And while patching dyed/painted concrete would leave a big jumbled mess, it’s not like the roads aren’t a big jumbled mess already. Single roads might change from concrete to asphalt for no obvious reason. Sometimes a concrete road has a few feet redone in asphalt (can reopen the road today instead of in two weeks). Concrete is very often patched with asphalt. But we’re used to that. Having a a long stretch of, say, blue or red street with tons of black asphalt or gray concrete pothole repairs would get ugly in a hurry.

Coloured asphalt is quite commonly used on roads in the UK - in particular, for things like cycle lanes (blue), or red routes which are limited to buses/taxis.

I don’t see the mess described above happening here when they patch the roads. Presumably, they just make sure they patch with the right coloured stuff.

Here is one such company that does this. I see one of their other examples is for running tracks in sports stadiums. I imagine they’d use it for tennis courts as well.

Yes concrete [or cement] can be coloured with a myriad of ingredients, but …

Beautiful, carefully designed concrete buildings and structures make use of the consistent tone of concrete and the ability to cast or form it to achieve a more aesthetic outcome. Modern structural cements can be surface finished / textured in different ways that also produce quite starkly different effects depending on how the light hits them, which can be quite beautiful. This is probably a more enduring result than having a green bridge for the sake of having a differently coloured bridge. Architects / engineers will be starting with the premise that these things will be around for an awfully long time, so the design needs to be good enough to age gracefully as well.

Usually colour on structures is achieved by paint or some surface coating, like a tinted render. These are very prone to failure after a while, and once a bit spalls off or gets damaged, the edges will keep being picked back like a scab. A maintenance engineer will try to veto anything like that because it is just a long-term money drain.

Around here, a number of crosswalks on roads are made to resemble brick. I saw one being put in once: They’re made from poured concrete, just like sidewalks, except the concrete is reddish in color, and then they put the “brick” pattern in the top by pressing a die down on the surface.

I’ve also seen decorative concrete used for interior floors. That, too, is often colored, and often with sections in different colors to make pretty patterns.

My stepson does this for a living. He has many variations on the stamps. They are heavy sheets of molded rubber and the finishers stomp around on them to create the pattern. Each sheet interlocks with its neighbors to make a continuous pattern.

One thing not mentioned about colored concrete is the expense. The powered dye is very concentrated so that a fairly small amount is needed. It is quite expensive. He uses the dye and also top colors which soak into the upper layer of the concrete.

Colored concrete as a decorate element is very common out here:

Roads probably are, but highways are generally concrete. The trade-off between asphalt and concrete is that the former is much cheaper, easier to lay, and easier to patch. Concrete lasts much longer and can stand up better to weather and heavy loads. Since concrete is already more expensive, few governments will want to add the extra cost, time, and labor of adding color.

My patio is a stamped brick sort of pattern. The concrete was dyed brick red and the release agent that they sprayed on the forms was a really dark color that gave the ‘bricks’ some depth. It looks really nice, even 15 years later.

ETA: Regarding the release agent, I was given a choice of colors for that.

There’s a neighborhood in San Diego that’s had red sidewalks for 100 years!

So to sum up, it exists, and is one option for making things decorative, but not used when folks don’t care about decoration (which is most of the time).

There’s a neighborhood in St. Louis where the developers constructed all the sidewalks out of red concrete. They’re quite distinctive. Of course, after the developers finished, the city took over maintenance and they refuse to spend the extra money to dye the concrete whenever the sidewalks are replaced.

Adding dye to concrete weakens it, particularly in freeze/thaw climates.

Well, aside from my earlier point that in the UK, it tends to be used as a practical and safety delineation on roads, to mark out lanes for different vehicle or pedestrian use.

Are those actually made with colored concrete or just painted concrete? I’ve seen similar things here in the States, but it’s always painted.

I’ve seen it done both ways (I think it’s asphalt rather than concerete)

Also here in China for pedestrian routes (delineate scenic paths or direct walking / cycling paths where you won’t need to cross any roads). Most likely the OP link was of this kind of colored asphalt, as I haven’t seen any painted paths, so I’m dubious about the description in the link.

Decorative concrete is also sometimes done, not by changing the cement, but by using colored stone for the aggregate. In this case, you usually finish by polishing it a bit, so you see more of the aggregate on the top surface.