Equipment World Digital Magazine
Issue link: https://read.dmtmag.com/i/473140
EquipmentWorld.com | March 2015 51 ing pavement is in worse structural condition, you can add an interlayer that will result in a thicker pavement, but bridge over the problems below," Voigt said. "Whereas if you are bond- ing to the pavement below, you will not require an interlayer." On unbounded overlays, the concrete serves as a base layer, as opposed to actually carrying the load, says ACPA's new technical services engineer, Eric Ferrebee. "The interlayer or bond-breaker distributes stress to the lower layer, but the base does not carry the load directly," he says. "If it's bonded, then the design requires the existing or bottom layer to carry more of the stresses, so you don't have higher stresses in the overlay." Engineering the overlays Today's concrete overlays are engi- neered projects that involve evalua- tion field work to obtain cores, and to judge existing conditions and materials. These data determine, for example, whether to bond or not bond a concrete overlay. This primarily depends on the con- dition of the exsiting pavement and whether it will carry part of the load of the overlaid structure, Voigt says. If it's in good shape, you can use a bonded overlay. If not, an unbound- ed overlay is best. Bonded overlays typically have been placed with a cement-in-water "grout" spread between lifts, but cur- rent practice has the grout eliminated and the concrete placed directly on the existing pavement. "It still will bond to concrete and older, oxidized asphalt," Voigt said. "With newer asphalt, the surface may be milled, swept and blown to keep it clean. With concrete as well as asphalt bas- es, keeping them clean is the key." In unbonded overlays, the "bond breaker" or interlayer prevents the base layer from interfering with the performance of the overlay. The in- dustry now is turning more to fabric interlayers instead of thin asphalt layers Voigt says. Typically this fabric will be around a quarter to a half- inch thick and helps cracks or joints in the underlying layer from reflecting to the surface layer. It also can help drainage, reduce bearing stresses and the effects of traffic loads, according to The Transtec Group. Transtec says benefits include lower cost for material and installa- tion, installation rates exceeding that of paving, and ease of construction, with placement requiring a mini- mum of training and equipment. 6x6x6 = success Concrete always will crack as it cures, and the point of providing sawn joints is to control where it cracks. The industry has used a variety of joint configurations and in Follow us on social media for regular updates from Montabert! Montabert breakers sense the hardness of material, adapting their power and strike frequency to deliver just the right amount of energy. You get the best possible performance every time, without all the wear and tear. More breakups… Fewer breakdowns. That's Montabert. Tougher Than Everything. 2905 Shawnee Industrial Way Suwanee, GA 30024 ussales@montabert.com 866-588-8690 fax: 866-472-4950 Engineering Innovation since 1921 See our attachments in action! montabert.com Montabert and the Montabert logo are registered trademarks of Montabert S.A.S. in the United States and various countries around the world.