Concrete Links the Loop

Prairie Material teamed up with Butterfield Color, project designer Alfred Benesch, the Chicago DOT, and concrete contractor Capitol Cement to develop a unique red mix that would delineate the bus-only concrete lanes on 14 blocks.

Prairie Yard 33 on Chicago’s near Southwest Side produced the integrally colored mix for the new bus 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 jobsite, says QC Field Rep Mike Urlacher.

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

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

A high-early-strength requirement of 3,500 psi at three 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.

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.

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