Concrete Products covers the issues that attract producers of ready mixed and manufactured concrete focusing on equipment and material technology, market development and management topics.
Issue link: http://concrete.epubxp.com/i/97019
FEATURE COVER STORY job in Wilmington, one hour southwest of Chicago, called for 2,000 cu. yd. of RCC pavement mix on a portion of the main entry plus dispatch and staging area accommodating up to 500 trucks per day. The project comprises 6 inches of RCC pavement on an asphalt grindings base of the same thickness. It is the first RCC job for Coal City, Ill., concrete and asphalt contractor "D" Construction Co. "With roller compacted concrete," notes "D" Asphalt Superintendent Dave Manfred, "we can be competitive on more jobs and go after new markets." "I believe roller compacted concrete is as cost effective as asphalt and more durable under high truck traffic," adds Ray Norkiewicz, senior project superintendent for Illlinois Transport lead contractor, FCL Builders of Itasca, Ill. On Illinois Transport and other projects, conventional asphalt crews have seamlessly transitioned to RCC mix placement and pavement finishing, he observes, noting, "The biggest issue with RCC pavement compared to asphalt is sensitivity to wind. Heavy wind can dry out the RCC mix too quickly for crews to effectively finish a pavement." Days after the Illinois Transport pavement was finished, Prairie Material prepared for a second, larger project where value engineering carried the day for an RCC proposal. "Once you start looking at the price differential between roller-compacted concrete, conventional concrete and heavy-duty asphalt, and the pros and cons of each, RCC is a more attractive option for certain projects," explains Christian Evangelista, who as project manager for Arco Murray National Construction Co. has overseen placement of 7,000 yd. of RCC mix for the Central States Trucking Co. terminal in Joliet. "RCC can bear comparable loads to conventional concrete, but is more cost competitive against it and heavy-duty asphalt pavement." Central States is the tenant at a build-tosuit trailer facility within Centerpoint Properties' CIC-Joliet Development. An inaugural RCC job for Arco Murray subcontractor K-Five Construction, the Central States plan included a specification simplifying the facil- ity's pavement design. A monolithic, conventional concrete slab was ruled out for cost considerations, while an asphalt alternate would have required placement of 7- to 8-in.-thick, 12-ft.-wide concrete dolly strips to support trailers and their pavement-puncture prone legs. In addition to upfront costs, the strips limit the owner's flexibility in yard space allocation and utilization as new trucking clients join the terminal. "The RCC bears truck traffic and trailer leg loads like regular concrete, but a yard owner or operator needs to understand the material's differences from alternate pavements," Evangelista affirms. "RCC presents a different appearance that might turn off some owners—a rough finish that tends to dust somewhat and possibly exhibit some roller marks. In a trailer facility adjacent to an intermodal yard, appearance doesn't matter. Dusting and minor gravel spalling are confined to the top 1/16-in. of a 7-in. or thicker RCC pavement, but the structure is set to deliver a long service life, just as it is engineered." QUALIT Y C ON TR O L During an Illinois Transport project (opposite page) placement, Joliet yard staff retrieves RCC mix sample. Prairie Material finds the AASHTO T318 method best suited to gauging moisture content, RCC mixes weighed before and after microwave oven drying. Throughout RCC placement, technicians use a nuclear gauge to determine pavement density and direct vibratory and static roller equipment patterns to achieve a 98 percent density of the modified proctor test. The producer has also turned to the 6-in. Humboldt Marshall heavy-duty compacter hammer—a 22-lb. drop weight used for asphalt specimens—for testing RCC in 6 x 12 plastic molds. A first cylinder lift is compacted with 25 hammer drops, a second lift with five drops. The mold is then topped off with RCC mix and 15 hammer drops; following excess-mix strike off, the specimen is capped and subjected to five final hammer drops. The method was proposed by S.T.A.T.E. Testing and adopted by Chicago DOT during the city's RCC residential street project in 2011. A more established method, ASTM C 1435 Standard Practice for Molding Roller-Compacted Concrete in Cylinder Molds Using a Vibrating Hammer, requires the dry mixes to be placed in heavier and much costlier stainless steel molds, then compacted by a power hammer. PHOTOS: Concrete Products (yard, nuclear gauge testing); National Ready Mixed Concrete Association (microwave/scale specimen); Humboldt Mfg. (hammer). WWW.CONCRETEPRODUCTS.COM DECEMBER 2012 | 31