Traffic congestion causes real misery for commuters who rely on Chicago Transit Authority (CTA) buses that travel between train stations in the city’s West Loop and the Michigan Avenue business district. The buses make more than 1,000 trips across the Loop daily – and with rush-hour speeds as slow as 3 miles per hour, an 8-block trip can take a whopping 45 minutes.

Planners from Chicago’s Department of Transportation, the CTA and the City of Chicago have come up with a plan to speed bus traffic while supporting pedestrians, bicyclists and car traffic. Known as the LoopLink , the $31.8-million project creates dedicated bus lanes on 4 arterial streets, where buses will make limited stops at train-like stations along the way. New, separated bike lanes on 3 of the routes will move cyclists safely through the Loop.​

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Designing for visibility and strength

CNA Prairie teamed up with Butterfield Color , project designer Alfred Benesch , CDOT , and concrete contractor Capitol Cement to develop a unique red mix that would delineate bus-only concrete lanes on 14 blocks of Madison and Washington streets.

“Prairie performed 3 trial batches to get the look CDOT was after,” says Capitol Cement Project Manager Dan Melnyk , who is overseeing the 1,400-yard job.

Original mix specifications came from an exposed-aggregate mix developed for another project, which included specialty red-granite coarse aggregate, explains Prairie’s Senior Technical Support Rep Gary Hall . “The proportions were not appropriate for a traditional finish,” he says, “so we had to significantly cut back the aggregate mass to make this mix more workable, finishable and cost-effective.“

A high-early-strength requirement of 3,500 psi at 3 days was also factored in, says Hall, with red granite remaining in the mix to help maintain color integrity throughout the life of the concrete.

Teamwork for precise color consistency, slump

Prairie Yard 33 on Chicago’s near Southwest Side produced the integrally colored mix for the new lanes. Since the pigment comes in powder form, dialing in the correct amount of water was critical to maintaining required slump and air entrainment at the job site, says QC Field Rep Mike Urlacher .

No water could be added on site, since it would dilute the color, Urlacher notes. Prairie assigned 4 to 6 dedicated drivers and trucks to each of the 220-to-260-yard pours to assure careful attention to all QC requirements.

“At the start of every pour, we checked the first loads of the day with our drivers, confirming how the mix should look,” says Urlacher. “We showed them how to slowly bring all the powder down and roll the load from the back of the drum to the front, which uses the concrete itself to incorporate all the color without adding water.”

The right finish for lasting strength

Finishing the colored mix correctly is critical to its long-term durability, says Melnyk.

“We used a color hardener on the lane surfaces, broadcast at half a pound per square foot. To achieve the correct density, we used two passes of shake with bull floating in between,” he says. The final finish was broomed to further close the surface.

Most placements were set for Saturdays and evenings to avoid traffic and inconvenience to commuters. The new east-west lanes will open this September, with dedicated lanes on north-south routes set for completion in 2016.

More color across the​​ region

Prairie is providing colored mixes for a host of projects this year, says Sales Coordinator Ashlee Sawicki . “We’re getting a steady stream of color requests for all sorts of applications. Designers are looking for durability as well as the aesthetic quality of colored concrete.”

In South Suburban Oak Lawn, Abbey Paving is placing 200 yards of integrally colored mixes to create a dramatic entry plaza for the new in-patient tower addition at Advocate Christ Medical Center. Solomon’s Soapstone and Smoke colors will be used to construct a new fountain, retaining walls, driveways and walkways that will help to unify the site. The project will finish up by late 2015.

In Peoria, Wm. Aupperle & Sons placed 300+ yards of Solomon 920 Black mix to create a new parking lot for the Bushwhacker store near Junction City Shopping Center . Original specs called for bituminous pavement to match other Junction City lots and drives, but general contractor Craft Building Services converted the job after showing how integrally colored mix would deliver strength and savings while matching the center’s existing color palette.

On Chicago’s North Side, Martin Cement placed 75 yards of Scofield’s Quicksilver integrally colored concrete for the new outfield concourse at Wrigley Field. A special solar-reflective additive that keeps the finished concrete cooler helped the project meet LEED standards for Solar Reflectance Index (SRI) of 29+ for hardscapes, gaining credits via SS 7.1 Sustainable Sites: Heat Island Effect ​.