There’s nothing like colored concrete to make a crosswalk, sidewalk or breezeway look snazzy.

But the extra touch that many cities are putting into their downtown streetscapes may not be so pretty in just a few short years.

Early cracking has prompted the city of Vadnais Heights to tear up its colored concrete, and the city of Centerville — which installed colored concrete only six years ago — plans to follow suit, said MnDOT’s Senior Road Research Engineer Tom Burnham.

Both cities participated in a recent study, sponsored by the Local Road Research Board and conducted by MnDOT, to determine what is causing the early deterioration.

Across Minnesota, many of the estimated 45 colored concrete projects have experienced early deterioration, particularly microcracking near contraction joints. While this type of distress also occurs with regular concrete, it appears to be accelerated in the colored concrete projects, within five years in some instances.

Although the newly released study identifies likely causes for the failing colored concrete, further research is needed to evaluate proposed solutions.

Researchers determined that the colored concrete mixtures have likely been too porous for Minnesota winters, allowing deicing chemicals to leach in and wreak havoc. Although not quite as problematic for sidewalks and medians — which aren’t salted as heavily — it is especially bad for colored crosswalks.

A denser concrete mixture (one formed with less water) is recommended; however, constructing the concrete panels this way will require extra steps.

“There are chemicals that can be added to the mixture to artificially lower that water-to-concrete ratio,” Burnham said. “This will allow a  denser mixture to be more easily placed.”

Although there was a spate of colored concrete construction in Ramsey County in the late 1990s, it has only come into fashion in the rest of the state within the last five to six years, according to Burnham.

“You go to almost any community and they’re installing it — on their sidewalk and medians and also crosswalks,” said Burnham, who coordinated the research study.

Because of the added expense, cities may be very disappointed in the results.

The city of Stillwater, which installed a colored concrete panel crosswalk on its main street just two years ago (see top photo), is already experiencing cracking and deterioration in several panels.

Although reducing the porosity of the colored concrete mixture should help,  it won’t solve everything.

Another issue is the curing. The typical white curing product can’t be applied like it is with standard concrete, so curing the colored panels is more challenging, Burnham explained.

There are possible remedies, however, to assist with the curing, such as wet burlap or curing blankets.

Adding complexity to the issue are the new deicing chemicals on the market, which are also impacting regular road materials.

Several test samples showed evidence of chemical attack of the cement paste and fine aggregates, as well as an alkali-silica reaction, which can cause cracking or spalling and isn’t normally seen in regular concrete.

“Is there anything unique with the coloring that would accelerate the observed chemical reactions? We didn’t feel we had enough samples and knowledge at this point to conclusively say,” Burnham said.

Different construction techniques could go a long way toward increasing the livelihood of colored concrete; however, it could take several years of observation to determine if other methods work.

MnROAD is considering adding colored concrete panels to its facility for testing.

Until more questions are answered, MnDOT researchers are recommending repair techniques and alternative streetscaping ideas to cities, such concrete stains, pavers or colored high friction surface treatments.

In addition to sharing the findings with cities and counties, Burnham wants to educate contractors.

“We hope this research is a wake-up call for the colored concrete industry too because we don’t want the industry to die in Minnesota,” he said. “If it can work, we want cities and counties to be able to use it.”

*Editor’s Note: This story was updated 09/04/2014 to specify that this research project was funded entirely by the Local Road Research Board, and that MnDOT conducted the research.

There are several inaccuracies in this article and I feel strongly that there needs to be more investigation before the colored concrete is blamed. There is no reason integrally colored concrete would deteriorate any sooner than plain gray concrete. If there is premature deterioration it’s due to other causes than the color and those need to be pinpointed and corrected.

There is no reason, except for the reasons cited in the article. Most pigmented concrete carries with it the caveat that a white pigmented curing compound is not used, for obvious reasons. The lack of proper curing is as valid a reason for pigmented concrete to show early signs of deterioration, just as for plain concrete that is improperly cured.

The problems noted with the concrete, and the photo showing joint deterioration, have little to do with the lack of surface curing. I’m concerned that there are problems with the concrete but even more concerned that the problems are being blamed on the use of colored concrete. We know how to control cracking, joint deterioration, and other problems–I would simply like to see some unbiased research done before jumping to conclusions about the cause.

I agree with Bill. Colored concrete is no different than plain gray, other than that a pigment is added (except in the case of some black pigments, which can knock down the content of air entrainment.) Where colored concrete differs most is in the customers’ expectations. No one notices or seems to care about color differentiation or defects with gray concrete, but add some color and customers go nuts when they notice a defect. In the Minnesota cases, my suggestion would be to try a different curing method such as the immediate application of a penetrating cure and seal product which creates a polymer chain within the pores to block moisture and chloride intrusion. These types of sealers are far better at resisting chloride attack than film forming sealers, and do not create a slippery surface. In addition, all saw cut joints should be caulked with urethane to prevent moisture and harsh deicing chemicals from entering through joints. It would also be wise to try a concrete admixture that makes the concrete cure more fully (by allowing more of the free lime to hydrate).

The coloring and texturing do not help. Nor does the paint. Drivers still stop right in the middle of the cross walks. A simple painted line is going to work for those who care and pay attention. For the others nothing short of a pop up barrier is going to get them to stop outside the cross walk.

Steve and Bill are right on… being involved with past and current studies on concrete joint deterioration, none of them were concerning colored concrete but rather issues with gray concrete, with specific attention at the crosswalk areas. The use of liquid brine materials on our roads as ice deterrents for the past several years is a prime suspect with concrete deterioration, regardless of color use. Obviously human nature is to notice issues on the color portions first. Proper curing, joint filling, sealing or even the use of a silane /siloxane material will ease the detrimental effects of the liquid brines on gray as well as colored concrete. Most color now used is in a liquid form, which does not have the negative air effect. Simply to say color is the problem is somewhat irresponsible when just about all the Midwest States are working on solutions to early concrete deterioration. Actually the colored portions usually stand up better because more attention was payed to proper cure and sealing.

I just wanted to comment that the suggestion of using wet burlap or curing blankets is not a great idea for colored concrete. Our past experience with any type of covering over colored concrete has led to shading in the colors, almost a “tie dyed” effect – not something that would be acceptable.

If the deterioration is a function of porosity try using micropoz concrete, totally different in so far as water will not penetrate and there are special curing requirements that are easily met and excellent for roads and pavements.

This is simply freezethaw damage. The use of modified densifiers solves this problem. If there are less and smaller capallaries the water turned to ice cannot expand and deteriorate. Also if the edges are denser then the edges will not break away.

I agree don’t give colored concrete a bad rap . Just look at all those joints( were they caulked?)I’ll bet they’ve got a really hot mix. Looks like concrete joints are probably curled ( because of the mix) my opinion is joint movement that leads to break down in the joint, really no different than a floor. Get a good flex mix and eliminate some of those joints. I’d love to see the mix design. Thanks Steve Lloyd

Has the use of color resulted with a higher water/cement ratio? Increased water content can be the cause of many issues.

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Crossroads is a collaborative effort among MnDOT’s Office of Research & Innovation, the University of Minnesota’s Center for Transportation Studies and the Minnesota Local Road Research Board. This jointly produced blog is devoted to highlighting the latest news and events in transportation research and innovation in Minnesota.