Better Roads

April 2013

Better Roads Digital Magazine

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Page 11 of 90

HighwayContractor A Base Stacked for Strength By Daniel C. Brown, Contributing Editor I f it���s a super-stout pavement base model you���re The engineering fabric looking for, look no further than the Des shown here forms a bond breaker between the Moines (Ia.) International Airport. Last sumcement-treated base and mer, Manatts Inc. built a subgrade, base and the concrete pavement. taxiway there that would prevail against the fury of the Devil himself. The taxiway is more than a mile long. It is 75 feet wide with 25-foot shoulders on each side. Aided by several subcontractors, Manatts put together a $16.5 million project ��� using speci���cations from the Federal Aviation Administration ��� that has the following elements, taken from the bottom up: ��� a 9-inch-thick layer of FAA-speci���ed P152 subgrade ��� very densely compacted soil; ��� one layer of geogrid for stability and strength; ��� a 9-inch-thick layer of FAA-speci���ed P-219 crushed, recycled vibrating and compacting the dirt before it���s actually accepted and ready for rock.��� concrete base course; For subgrade compaction, Reilly used Caterpillar 563 ��� a 6-inch layer of FAA-speci���ed P-307 drainable cementsheepsfoot rollers, as well as a pull-type roller towed behind treated base; a John Deere wheeled tractor. ���On the areas where there were ��� an engineering fabric bond breaker; cuts, they had to disk down 9 inches,��� says Sawin. ���The engi��� all topped by 16 inches of P-501 concrete. neering ���rm would test density down to 9 inches.��� The oneThe existing taxiway was concrete pavement with an asphalt overlay. Manatts, which is based in Brooklyn, Ia., began by mill- ply geogrid came next. Next came Caterpillar 740 trucks hauling 1.5-inch top size ing off the asphalt. Next Antigo Construction, a subcontractor, broke the concrete with a guillotine breaker. Another sub, Reilly crushed concrete back onto the grade. Cat D6 dozers spread and shaped the concrete in two 4.5-inch lifts. ���It was comConstruction, used Caterpillar Model 330 and 345 excavators pacted with steel drum rollers and a lot of water,��� Sawin says. to load the broken concrete into Cat 740 articulated trucks, ���Again, that base stone had to meet a density speci���cation. which hauled it to the on-site crushing plant. They packed it in there tight with Caterpillar steel drum rollers. ���At that point, once the pavement removal began, Reilly folThey had to roll in static mode because they could not break lowed up with dirt excavation,��� says Chris Sawin, project manager/estimator for Manatts. ���Much of the dirt was hauled away down the aggregate. In-place gradation tests veri���ed that the crushed rock would maintain drainability.��� to a waste area. And some of the dirt was carried to a ���ll area, Then Manatts ���ne-graded the rock that Reilly had placed. because we adjusted the alignment of the taxiway. They shaped ���We trimmed it with a GOMACO 9500 trimmer,��� says Sawin. the new taxiway with Caterpillar D6 dozers and a variety of To control line and grade on the trimmer, Manatts used a Leica motor graders. PaveSmart 3D system with robotic total stations. The system ���We had to meet compaction, moisture and density specirequires no stringline, and it cuts the grade to an accuracy of 3 ���cations on all the subgrades,��� says Sawin.���That is what the millimeters. FAA���s P152 spec calls for. You have to get the dirt to optimum The 6-inch cement-treated base, laid by a Caterpillar 1055 moisture content and compact it to 95 percent of modiasphalt paver, came next. ���The cement-treated base is kind of ���ed Proctor density. You really have to put a lot of effort into 10 April 2013 Better Roads HighwayCon_BR0413.indd 10 4/1/13 3:42 PM

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