Why no colored concrete?

There’s a stretch of highway in eastern Wyoming that has weird red-colored pavement, but I’m not sure that it’s decorative. First, it’s out in the absolute middle of nowhere, between Newcastle and Lusk. Second, it may just be some sort of colorful aggregate or sand used in making the concrete.

Usually that’s the color of the aggregate, which is always sourced as locally as possible. It may not show up much when new, but as the asphalt emulsion weathers it reveals the underlying aggregate color. Tennessee has a lot of orange rock which shows in some asphalt roads, and it’s also popular for exposed aggregate concrete where they wash off the cream during construction to bring the aggregate to the surface.

The Dutch pave their bike paths with red asphalt. That looks like a dye in the emulsion. It does fade to more of a pinkish color with time, much like fresh black asphalt fades to gray, but it remains distinct. I don’t know if they also use red aggregate, but something tells me they don’t.

There is one kind of colored concrete that’s becoming rather common: truck aprons in roundabouts and next to slip lanes. They’re colored by adding a brick-red colored powder on top of newly poured concrete. Here’s a video showing them building them:

Personally, I find a newly built and landscaped roundabout, with a green center island, surrounded by a white curb, red truck apron, black asphalt roadway, and then white sidewalk, is a thing of beauty.

There are exceptions, of course. :slight_smile:

Parts of San Francisco have green bike lanes and red transit lanes. We’re getting some red transit lanes here in Northern Virginia as well.

Yes but those are almost certainly just painted rather than integral with the paving.

When I lived on Guam most of the roads were pink, but that’s because they used coral as part of the mix, since the island has no natural sand. It made the roads awful to drive on when they were wet, which was a great part of the time. That’s why the highest speed limit on the island is 35 MPH. (Which in my memory, many people ignored.)

Guam Survival Guide PDF

Many of the roadways are made of coral and promote algae growth. They are subject to surface polishing due to wear. When the pavement is wet, it becomes extremely slippery, much like driving on a sheet of ice. On wet pavement, SLOW DOWN and increase following distance.

As a result of the coral roads, road conditions on Guam are extremely harsh on both car and bicycles causing the tires to wear fast. Pay attention to tire air levels and constantly check for leaks.

Do you have a cite for this? We just had a patio installed (32x20, so decent sized) and we discussed using colored cement with the contractor and no mention was made of it weakening the concrete.

Actually, I think I misunderstood something in that video. After watching it again, it seems that the top layer of concrete has coloring added in the cement truck. Then additional red powder is applied to the top of the concrete after it’s been smoothed but before the “brick” imprint is stamped on it. He said something about that additional powder but I couldn’t understand what he said. But I don’t think it’s just additional coloring.

One thing to keep in mind when talking about dyeing concrete; a concrete dye is typically not something added to the concrete mix itself. As @dtilque mentioned, that is what the video above is talking about. See this page that talks about 4 ways to color concrete:

Notice the second method, called “integrally colored concrete”. As it states, the concrete itself has a different color so it can’t fade, or chip, or get worn away. However, those color changes are pretty subtle. Often it is used in combination with a surface color change to end up with noticeable color difference.

I’m not at all an expert in this but I have done a lot of searching around for colored concrete and I think if there was any accuracy to this claim it would be mentioned. Not only mentioned, but there would be disclaimers all over the place. The fact that I can’t even find this hinted should set your mind at ease that this just isn’t true, Not unless there is some massive colored concrete conspiracy. Rather, the downside to integral color in concrete is that it just doesn’t color it very much; it just gives it a different sort of hue but it’s still going to be some variation of earth tone. You need a surface treatment if you want a dramatically different color and that coloring just doesn’t penetrate down far enough to weaken it structurally even if it could potentially compromise it.

On the other hand, the ‘surface treatment’ used here, a thin cement layer, in this non-freezing city, would rapidly crack and peel if used somewhere with regular free-thaw cycles.

The colored crosswalk I saw being put in around here had uniformly-reddish concrete being poured to a significant depth, at least a foot and a half or two. Though they might have added some additional pigment at the very top. I was surprised by the depth, since I would have expected that a much thinner layer would be both adequate and cheaper. Especially if the pigment really does add significantly to the cost.

I can find no cites for this.
A friend of mine who is a concrete contractor has had this problem when adding powdered dye at levels necessary to satisfy customers color density requests.

I wonder if mixing the additive requires using a wetter concrete mix? Wet concrete cures more porous than a stiffer mix.

In the reading I did looking for cites, it was stated that when using powdered additive dyes, the least slump possible was desired.

Yes, they can throw some of the dye around the already dyed concrete to give it a stone look.

It’s a very versatile concept. I saw a do-it-yourselfer pour a solid floor in a walkout basement and then sawed lines in it to form large squares. He then mortared it in to look like a slate floor.

Well - another use. When we blow up buildings (test purposes), the poured AND block walls are dyed concrete. The walls/roof are all different colors. After the boom we go out and measure the fragment fall; dispersion and weights. 15 seconds for the flash, bang, and fragment fall followed by a painstaking week of plotting, gathering and weighing the remains. A lovely vacation in that luxury resort area known as China Lake.

A patio has no live load- no need for structural strength beyond foot traffic. I assure you that your patio is fine unless you are going to run 80,000 pound trucks across it daily.

Roads are very different as they carry a lot of weight and are long, continuous stretches of material that expands and contracts quite a bit and does not flex at all. Putting expansion joints in a patio or house slab is cheap and easy. In a (now standard five foot wide residential) sidewalk you need an expansion joint about every ten feet. To hide cracks in any patio or house slab it is also common to either make scoring in ten foot by ten foot maximum sizes with tools when pouring it, or if it will be covered with flooring or such, by just making very shallow saw cuts in it once it is solid enough to drive on which is usually the next day. (That way if it does crack it will crack where it was scored or saw cut and there will be no ugly diagonal cracks making it look like a third grader poured it.) Putting expansion joints in roads is hard and expensive. Often where a bridge meets a roadway there is a several inch wide open space covered by a steel plate that is attached to one side but not the other. As the seasons change and the expansion joint opens up or narrows- the steel plate slides inside a steel track the entire width of the roadway/bridge. Since the bridge is exposed on all sides and the roadway is only exposed on one side they often expand or contract at different rates. There may be a two inch gap below that steel plate, or a five inch gap below it.

But putting an expansion joint the entire width of an interstate highway is difficult and must occur pretty often. The roadbed below the highway is a pretty deep bed of gravel over highly compacted soil (they like to dig out all the tree roots and other biological material because it rots rather quickly and forms pockets where water may collect and freeze – or in dryer climates might create a void that might cause the roadway to crack since it is unsupported. Concrete roads are 12 inches or more thick for the most part, and they will poor a twenty foot length at a time (give or take). At the end which will continue to be built they often place large steel rods about every 12, 16, or 24 inches that extend into each pour about two feet. One side of these rods will have gripping patterns on them so they are locked into place on that side of the joint. The other side is coated with a plastic coating (sometimes inside a sleeve that has free room in the end for future expansion- and that sleeve also has gripping patterns on the outside like rebar does. That way when the inch or less of expansion joint that separated the two pours rots away the two separate sections can expand and contract toward or away from each other, but one side will not sink or heave up causing an uneven driving surface.

Concrete is very strong in compression but very weak in tension, you can pile a lot of weight upon concrete, but you cannot hang very much weight from it (in fact poured concrete that hangs down at all must have reinforcing members within it). Concrete must reach a certain level of hardness within twenty-eight days, but it continues to harden almost forever (until it starts to crumble apart I guess). Concrete is made of small aggregate, large aggregate, and cement. The cement holds it together - but the aggregates provide the bearing strength. Dyes would provide neither so yes they would make concrete less strong but by a small fraction.

Too small to matter?

Much too small.
Say a ton of concrete would be a cubic yard (which isn’t a bad guess if my memory serves me); three feet, by three feet, by three feet. A ton of concrete with dye saturated throughout it would be a cubic yard plus a large coffee cup.

For a patio a much bigger concern would be if it was built upon expansive soil, if it has a good base of gravel under the concrete, if it slopes at a quarter of an inch to a half an inch per foot so water runs off it (but wheelchairs do not).

It might be possible that it would matter for a roadway however. That would be beyond anything where I have experience or training. I am not even sure a civil engineer would know off the top of his or her head unless they have done calcs at some time in their past. My gut feeling would be however that adding dye would be less significant than most other factors. Also, I live in a very dry climate and was shocked to see the photos of the building that collapsed in Florida. Water is a destructive force for all building projects but for us here it is always a liquid enemy. Perhaps back east where moisture is everywhere, even in the air and salt is a factor – what is negligible here could be significant there.