That colorful concrete that's been used to dress up many streets in Minnesota won't be so pretty in the next few years.
It turns out colored concrete crosswalks, sidewalks and medians – which cities are paying more money for – are deteriorating faster than plain gray concrete, a study by the Minnesota Department of Transportation found.
"You go to almost any community and they're installing [colored concrete] on their sidewalk and medians and also crosswalks," MnDOT’s Senior Road Research Engineer Tom Burnham told Crossroads, a joint transportation blog between MnDOT Research Services & Library and the University of Minnesota's Center for Transportation Studies.
Cities typically add color to concrete for aesthetic reasons, which is referred to as "streetscaping," but also to differentiate paths for both traffic and pedestrians.
Many of the estimated 45 colored concrete projects across the state have experienced early deterioration, and because of the added expense, cities will likely be disappointed in the results, Crossroads notes.
This added feature comes at a cost, though. Coloring concrete costs on average $5 to $10 per square foot, compared to the $2 to $5 per square foot plain concrete costs, according the Landscaping Network.
MnDOT's report, which was released at the end of August, shows many colored concrete projects are deteriorating faster, with the most common issue being "microcracking" near contraction or control joints – this distress occurs with regular concrete, but the cracking is accelerated in the colored concrete projects.
Researchers found at least one possible reason, noting colored concrete mixtures are likely too porous for Minnesota's winters – that's allowing deicing chemicals to seep in and eat away at the concrete. The study notes this is especially bad for crosswalks, which tend to be salted more than sidewalks and medians.
Pictured above is just one example of the deterioration near the control joints of a colored crosswalk in Centerville, Minnesota. Centerville officials plan to rip up the colored concrete, which was installed about six years ago, the report says. The city of Stillwater, which installed colored concrete crosswalks about two years ago, is already seeing signs of deterioration, the report notes.
Researchers say they need to further evaluate possible solutions to improve the life of colored concrete, but one possibility is to make a concrete mixture with less water. Burnham notes that won't solve everything, adding different construction techniques will also improve the longevity of the concrete, but it could take years of study to determine what methods work best.
MnROAD, MnDOT's pavement test track, is considering adding colored concrete panels for testing, Crossroads says. Until the research is complete, MnDOT has several repair techniques and alternative ideas to beautify concrete, like stains, pavers or colored high friction surface treatments.
MnDOT is sharing its findings with cities and counties, as well as education contractors who use colored concrete.