Equipment World

March 2015

Equipment World Digital Magazine

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N ew methods, con- cepts, materials and even new terminolo- gy are changing how concrete overlays are being promoted, designed and built. The industry has developed an op- timal joint configuration for concrete overlays, 6x6x6 for short, describ- ing panels that are 6 feet long by 6 feet wide by 6 inches thick. This standard configuration minimizes moment axle loadings, which in turn, reduces slab curling. While not completely universal this configura- tion is applicable for a wide array of projects from the national highway system to county roads. And so the term "ultra thin whitetopping" is out. BCOA, for bonded concrete overlay of asphalt, is in. BCOAs are one of five freshly designated variations of concrete overlay designs. New materials support an em- phasis on optimum durability rather than compressive strengths. A new emphasis on closely gauging matu- rity of fresh placements – opposed to accelerated curing – is changing how quickly concrete overlays are opened to traffic. For example, in a 2014 Transpor- tation Research Board paper, au- thors Kivi, Tighe, Fung and Grajek cite the example of Toronto. 1 The city attacked rutting and shoving problems that refused to respond to regular maintenance. Their research showed concrete overlays and inlays are excellent rehabilita- tion options for urban pavements subjected to volumes of traffic. "The pavements are in very good condi- tion visually, ride quality remains excellent and the recurrence of the regular rutting and shoving prob- lems that were being observed prior to rehabilitation has been mitigat- ed," the authors say. Photo: ACPA 6x6x6 = SUCCESS FOR CONCRETE OVERLAYS Unbonded concrete overlay on concrete (UCOC) is placed on milled asphalt pavement. road science | by Tom Kuennen EquipmentWorld.com | March 2015 49 1 Rehabilitating Urban Pavements with Con- crete: A Municipal Case Study by Aleks Kivi and Susan L. Tighe, PhD, P.Eng, Department of Civil and Environmental Engineering, Univer- sity of Waterloo, Rico Fung, P.Eng, Cement As- sociation of Canada, and Jozef Grajek, M.Sc., P.Eng, City of Toronto, Ontario (TRB, 2014).

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