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CLEAN SWEEP

F2 Prairie
Prairie Material, paving crew demonstrate power-troweled, broomed RCC

A new finishing method for roller compacted concrete pavement nets surface durability and uniformity to give contractors or owners pause on incurring the expense of asphalt wear courses commonly specified over RCC bases. The first commercial application took place at a suburban Chicago jobsite with Bridgeview, Ill., ready mixed producer VCNA Prairie Material leading the charge.

The method calls for standard placement of RCC mixes in 6-in. or less lifts or layers, followed by vibratory and static drum roller compaction. Crews then spray slabs with RCC Surface Pro, a silica-rich troweling aid specifically engineered for low slump concrete. Troweling creates a float-ready paste, while the agent’s chemistry promotes additional cement hydration, ultimately hardening and densifying the upper slab layer.

“RCC Surface Pro could be a game changer. We can now offer a monolithic roller compacted concrete slab with a finish much more typical of traffic-ready asphalt or conventional, broom-finished concrete,” says Prairie Material Marketing/Product Specialist Theron Tobolski, who oversaw placement of 1,000 yd. of RCC mixes at 246-acre Maryhill Cemetery in Niles, Ill. Troweled, monolithic RCC economizes pavements when factoring material, crew and equipment mobilization costs associated with adding a 2-in. asphalt wear course, he adds.

During an early-summer window, Prairie Material and Hickory Hills, Ill., contractor J&R 1st in Asphalt Inc. offered RCC pavement options to replace old driveway, parking lot and service area asphalt at Maryhill—one of the Archdiocese of Chicago’s 46 Catholic Cemeteries properties. An initial placement involved 4,000 sq. ft. of inconspicuous pavement at the rear of the facility’s maintenance shop. It consisted of conventional, two-layer RCC with rougher surface prone to superficial crazing, but density characteristics assuring long service life in the face of vehicle loads and Upper Midwest freeze-thaw cycles.

Catholic Cemeteries and Arlington Heights, Ill., civil engineer Ament Design approved a Prairie and J&R-proposed demonstration for the second placement: A more prominent shop area with power-troweled, broom-finished pavement, its top 1/4 in. hardened and densified with RCC Surface Pro. Finish quality compelled the decision to maintain the new specification for two subsequent pavement sections under the Prairie and J&R contract, totaling 54,000 sq. ft.

Conventional RCC pavement (vibratory and static roller drum pass only) was placed at the back of the maintenance facility. Results from the first troweled/RCC Surface Pro placement (foreground) drove subsequent specifications for more prominent, higher traffic areas.
Conventional RCC pavement (vibratory and static roller drum pass only) was placed at the back of the maintenance facility. Results from the first troweled/RCC Surface Pro placement (foreground) drove subsequent specifications for more prominent, higher traffic areas.

COTTON CURE
Catholic Cemeteries staff will monitor Maryhill maintenance shop slab performance with an eye toward broader use of troweled RCC throughout northern Illinois properties, which encompass 100-plus miles of lighter duty, primarily asphalt roads. The organization has enlisted Prairie Material and J&R to deliver broom-finished RCC for a section of road at Resurrection Cemetery in Justice, Ill.

The Catholic Cemeteries’ contracts join an RCC pavement roster Prairie has built since 2009, with this year’s volume reaching 40,000-plus yd. The producer has promoted RCC for a) heavy industrial pavements, where surface aesthetics or smoothness are secondary to load-bearing; and, b) municipal projects, where agencies typically call for an asphalt wear course over a 5 or 6 in. RCC base.

J&R 1st in Asphalt teamed with Prairie Material from the outset to convert the Maryhill maintenance shop pavement. “The contractor has embraced the RCC concept and aggressively worked with us to move several of clients from asphalt to RCC,” notes Theron Tobolski.

In advance of Maryhill slab troweling and floating, he pointed J&R crews to a recently established RCC pavement practice: Placement of water-soaked cotton blankets along lift or layer edges considered fresh joints. Standard in Illinois Department of Transportation concrete bridge deck curing specifications, the blankets maintain moisture levels critical to proper RCC base and top lift conditions. By eliminating edge drying, contractors gain efficiency in longer paving trains and drum roller passes.

“One of the hardest things in RCC mix and asphalt paving is to blend fresh joints in a timely manner so they don’t ravel. I recommended a contractor on a previous RCC project use wet burlap on the fresh joints to keep them from drying out,” Tobolski recalls. “The contractor agreed with the concept but used cotton blankets. The process gave crews the ability to pave longer lanes and noticeably raised fresh joint density.”

As demonstrated during the Maryhill Cemetery maintenance shop placement, RCC Surface Pro
As demonstrated during the Maryhill Cemetery maintenance shop placement, RCC Surface Pro is generously applied to a top RCC layer or lift shortly after a final drum roller pass. Upon troweling, the agent imparts an optimally thin paste, ready for smooth float or broom brush. RCC properties necessitate the use of trowel pans versus blades. The four-day Maryhill project demonstrates for owner Catholic Cemeteries—plus a growing pool of public and private accounts to whom Prairie Material is presenting the RCC pavement option—how engineers and contractors can sidestep an asphalt wear course thanks to the performance and surface characteristics of slabs finished with RCC Surface Pro.

SILICA RULES
Power-troweled, roller compacted concrete with surface characteristics and performance potential approaching conventional flatwork has turned on Maryhill and a handful of other RCC Surface Pro troweling aid demonstrations.

Springfield, Ill.-based Solomon Colors Inc. is launching the new agent in the U.S. and Canada as part of distribution partnership with Lythic Solutions. The 10-year-old Vancouver, Wash., company has parlayed surface finishing products in applications beyond its core concrete floor polishing market, formulating RCC Surface Pro from nearly pure (> 99.5 percent) silicon dioxide or silica.

Measuring as little as 1/1,000 the size of typical concrete binder particles, the silica particles are suspended in ultra-low surface tension liquid. RCC Surface Pro is spray applied in tandem with troweling, which generates a paste ready for floating or brooming. The agent’s chemistry and particle sizing are well suited to fostering additional calcium silicate hydrates, the principal binders in portland cement concrete.

Solomon piloted RCC Surface Pro earlier this year in Texas and Arizona, Cemex USA supplying the RCC mixes on each. The Prairie/J&R project marked the agent’s commercial debut. Spearheading the official RCC Surface Pro rollout this fall are Solomon’s Director of Business Development–Decorative Business Unit John Anderson, 217/527-1146 or janderson@solomoncolors.com, and Area Manager Keith Nault, 262-227-9194 or knault@solomoncolors.com