Equipment World Digital Magazine
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recently has determined the 6 feet long by 6 feet wide by 6 inches thick joint configuration provides optimum overlay performance under most circumstances. "One of the ideal benefits of having a 6x6x6 panel is that a joint always will fall between the wheels of an automobile," ACPA's Ferrebee said. "Because of that, we always will have one axle per panel at any time. That reduces the stress each panel will experience, keeps stresses at a reasonable level and our pavement in service longer." "Because the slabs don't bend or flex so much, you can have a thin- ner slab stand up to the same truck loadings," Voigt says. Sawing of joints should take place as soon as the pavement has gained enough strength to resist raveling. Crack control joints can be one-third of the slab depth. By closely observing the curing of the slab, traffic can be allowed on the pavement without waiting for full compressive strengths to develop; that eliminates much of the need for accelerating additives in con- crete overlays, Voigt said. Two-lift overlays Another recent concrete overlay technology transfer from the industry/ FHWA scan tour in 2006 that is gain- ing hold in the United States is two-lift paving, dubbed 2LCP, in which wet concrete is placed on wet concrete. The two lifts form a monolithic slab as they cure and set together. Generally, the bottom layer, or bottom lift, consists of lower quality concrete, which can include locally available aggregates not suitable for surface use or recycled aggregates, according to Dr. Peter Taylor of the National Concrete Pavement Tech- nology Center at Iowa State Univer- sity, at a workshop in late 2013. Higher-quality materials are used in the top layer or top lift, he added. "The top lift is generally the thinner of the two layers," Taylor said. "As a result a lower volume of high quality concrete is needed. A high quality top lift provides better durability and skid resistance." 2LCP is constructed as wet-on- wet concrete that not only helps to achieve better bonding between the layers, but also reduces the differ- ential shrinkage problem, he added. This technique is being used now on reconstruction of the Jane Addams Memorial Tollway (I-90) – linking Rockford, Illinois, with O'Hare International Airport – by the Illinois State Toll Highway Au- thority. There, processed and tested fractionated reclaimed asphalt pavement is being used in the base. Dubbed "black rock" by the tollway authority, it enhances the "green" as- pect of two-lift concrete paving. road science | continued EquipmentWorld.com | March 2015 53 2905 Shawnee Industrial Way, Suwanee, GA 30024 T. 866-563-5890 F. 866-472-4950 E. ussales@geith.com Find your bucket at www.geith.com overbuilt to be overworked. Geith and the Geith logo are trademarks of Geith International Limited.