Equipment World Digital Magazine
Issue link: http://read.dmtmag.com/i/662812
W hen used with precisely milled as- phalt surfaces and a material transfer vehicle, a high-performance screed – if paired with the right paver tractor – is the fourth element in the search for super-smooth, bonus-winning pavements. Using the right tractor isn't enough. The tractor also must be paired with the right screed, since the screed performs on its own to provide smooth placement of bituminous pavement lifts. An asphalt paver has two inde- pendent units – the tractor and the free-fl oating screed – plus automatic or manual leveling systems that link tractor sys- tems to the screed to place level pavements. The hopper-equipped trac- tor receives the hot, warm or cold asphalt mix from truck or material transfer vehicle (and via slats or rubber conveyors) moves it to the rear of the tractor through fl ow gates to a set of augers in front of the screed. At the front of the screed, the mix builds into a "head" as it's moved outward for distribution by the screed. But it's not so simple. Ideally, the tractor will move a blended, homogenous, segregation-free mix from the hopper into the material head in front of the screed without segregating mix temperature or aggregate particles in the mix. That's important, as thermal or mix segregation vastly undermines pavement smoothness in the short term, and pavement dura- bility in the long term. Free-fl oating screeds The free-fl oating screed – which forms smooth mats mostly inde- pendent of the paver tractor – is the epicenter of the search for super-smooth, bonus-winning EquipmentWorld.com | April 2016 53 road science | by Tom Kuennen SCREED SUCCESS PART WINNING BONUS the 4 WINNING BONUS the Part I: Smooth Pavements through Cold Milling Part 2: Smooth Pavements and Material Transfer Vehicles Part 3: Smooth Pavements and Asphalt Pavers Part 4: Smooth Pavements and Asphalt Screeds Part 5: Compaction for Super Smooth Asphalt Pavements Part 6: Super-Smooth PCC Pavements with Slipform Pavers Part 7: Super-Smooth PCC Pavements with Stringless Controls This month, Equipment World continues its seven-part series on how to optimize pavement construction to win bonuses using screeds. A Vögele VF 600 screed mounted on a 10-foot basic width Vision 5200-2i paver is widened to 28 feet using front-mount extensions, enabling contractor Pioneer Construction to pave two lanes wide without having to use a second paver, eliminating a longitudinal cold joint. Pioneer Construction