Precision Performance

Precision Performance

3D PAVING HELPS OVERCOME CHALLENGES ON RUNWAY RESURFACING

 

When Kilgore Contracting, headquartered in Salt Lake City, Utah won the bid to replace a runway at the Provo Utah Municipal Airport, the project appeared to be a routine runway resurfacing—but it held a surprise that made the project far more complex.

Specifications for the 45.7 m (150 ft) wide, 2,621 m (8,600 ft) long runway called for full-depth removal of the old runway, placing a 38 mm (1.5 in) leveling course and topping it with two 76 mm (3 in) surface lifts. Unexpectedly, installation of the leveling course resulted in some hidden problems.

Unexpected Challenge

Built in the 1940’s, runway 13/31 at the Provo municipal airport was in pretty bad shape. With severe, widespread cracking and no resurfacing in more than 20 years, the runway surface was badly deteriorated. Furthermore, years of winter frosts had settled the ground below creating many high and low spots in its elevation.

When Kilgore milled 178 mm (7 in) of worn asphalt off the old runway, even larger elevation variations below the surface confirmed that the leveling course was going to be far more challenging than anticipated.

A 3D Solution

To begin, Kilgore had to add varying amounts of 19 mm (0.75 in) aggregate fill to restore the grade along the runway’s entire length. Instead of the anticipated uniform 38 mm (1.5 in) leveling course described in the site plan, the leveling course actually varied from 76 mm (3 in) to 305 mm (12 in) under the entire runway. It resembled a complex, variable-depth paving job, according to Kilgore’s project superintendent Dave Warner.

 

Kilgore chose the right machines to handle the unforeseen variations. Cat® AP1055D and AP1055E pavers, both equipped with the latest 3D paving technology, were linked to onsite Trimble® universal total stations. Tripod-mounted transmitters were strategically placed around the jobsite and spaced about 152 m (500 ft) apart. This technology enabled Kilgore to constantly monitor the erratic elevations and adjust the leveling course to produce the correct elevations.

 

“I LIKE THE RELIABILITY OF THE CAT PAVERS AND SCREEDS, AND THE FACT THAT THEY CAN PAVE ANYWHERE FROM 10 FT TO 20 FT (3 M TO 6 M) WIDTHS. THE SCREEDS ARE AWESOME, EASY TO ADJUST AND LAY A VERY GOOD MAT.”

 

Two Weiler E2850 Remixing Transfer Vehicles (RTVs) were paired with the Cat pavers to ensure smooth, consistent paving. Windrow elevator heads were used to feed the RTV hoppers.

Four Cat CB64 compactors equipped with Intelligent Compaction handled breakdown and intermediate compaction, and one CB44B compactor equipped with a side cutter trimmed cold edges, where necessary. Two Weiler C110 Combination Compactors performed final compaction.

Several Cat Skid Steer Loaders also assisted on the project for removal of excess material, backfilling and other cleanup chores.

Multiphase Process

To accomplish the repaving in the compressed 50-day timeframe allowed, Kilgore chose to tackle the job in phases with crews working 12-hour days, six days per week.

Phase one involved the end of the runway where it intersected with a crossing taxiway. Although only 10 days were allowed to complete phase one, Kilgore completed the work on schedule.

Phase two, an intersection with another runway, intensified pressure on the crews with only eight days allowed to complete that segment. During that time, the entire airport had to be shut down. Weather issues forced some longer workdays, further complicating the plan.

To achieve maximum efficiency, Kilgore chose to operate the paired transfer vehicles and pavers in echelon. Each paver was set to 4.5 m (15 ft) width. They handled the total 45 m (150 ft.) runway width by laying down five 9 m (30 ft) wide mats over 152 m (500 ft) lengths. Echelon paving helped bolster production and reduced the number of hot-to-cold longitudinal joints. Hot mix was hauled some 30 minutes from the plant in sixteen 36 mt (40 t) belly dumps. Mix temperatures batched out at 154º C (310º F) and arrived on site with temperatures still holding at 138º C (280º F) to 143º C (290º F) even without the use of tarps, due to high ambient temperatures. Mix design specified all virgin 19 mm (0.75 in) aggregate and PG72-28 binder for the surface lifts.

 

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Powered by 224 kW (300 hp) Cat C9 engines, the 23 mt (25 t) capacity E2850 Remixing Transfer Vehicles (RTVs) helped keep the mix at a uniform temperature. And although the material was sticky, the efficiency and smooth performance of the E2850s ensured there were no handling problems, and according to Warner, they never experienced any segregation issues. Dump men assigned to each paver and RTV team coordinated timing.

To match material delivery, the pavers ran at a relatively slow speed of just 3 m (10 ft) per minute. The crews were able to achieve 80 percent continuous operation and laid down 254 mt (280 t) per hour and 2,721 mt (3,000 t) on most days, and actually achieved 3,175 mt (3,500 t) on some days more conducive to continuous paving.

“The smooth performance of the pavers’ augers enabled us to feed continuous heads of material to the screeds. The pavers are super efficient in that mode. It’s very important to have that consistency in all things to ensure mat smoothness,” says Warner.

The pavers used Cat AS3301C Extend-A-Mat rear-mount screeds equipped with hydraulic extensions and optional power-extending main frames. “I like the reliability of the Cat pavers and screeds,” says Warner, “and the fact that they can pave anywhere from 10 ft to 20 ft (3 m to 6 m) widths. The screeds are awesome, easy to adjust and lay a very good mat.” Virtually no handwork was required prior to rolling.

The pavers’ Mobil-Trac undercarriage combines the traction and flotation benefits of a track machine with the mobility, speed, and ride characteristics of a wheel paver. “I like the Mobil-Trac system,” says Warner, “because it delivers good traction, good speed and good maneuverability—although maneuverability might not be too applicable on a runway project—but we’re not always paving runways.”

 

“I LIKE THE MOBIL-TRAC™ SYSTEM ON THE PAVERS BECAUSE IT DELIVERS GOOD TRACTION, GOOD SPEED AND GOOD MANEUVERABILITY.”

 

The Cat CB64 compactors utilize Intelligent Compaction that incorporates GPS to track the pass count and map the compaction pattern. Two compactors operated in tandem behind each paver making a total of 12 passes, six breakdown and six intermediate, with a pattern length of 61 m (200 ft) in order to achieve the density targets and match the pavers’ production.

The CB44B’s side cutter produced perfect transverse joints, and the skid steer loaders carried away the excess material.

Two 97 kW (132 hp) Weiler C110 Combination Compactors performed final compaction operating in static mode. Asphalt temperatures were approximately 76º C (169º F) during the finish phase.

People Make the Difference

Warner was quick to emphasize that Kilgore’s crews are his most valuable assets. “You can have the best machines in the world, but if you don’t have the right people, the process doesn’t work.”

Led by veteran foreman Hugo Zagal, 18 Kilgore crewmembers were assigned to the project on most days including paver operators, screed men, RTV operators, dump men, roller operators and laborers. Kilgore’s crews were complemented by two quality control supervisors and four surveyors added specifically to verify elevations on the runway project.

Warner says that Kilgore’s crews are skilled and experienced, demonstrate leadership and have a willingness to learn. “Our young guys are eager to learn, and we encourage them to ask a lot of questions,” says Warner.

Solid Success

The specified runway crown was a slight, but important 1.5 percent pitch to both sides to enable adequate drainage. Compared to a 15 percent out-of-tolerance grade and slope allowance, Kilgore held to 2.43 percent over the entire length of the runway. Density averaged 97 percent, and exceeded the 93 percent specified for joints as verified by inspections.

The Kilgore crews hit the 6 mm (0.25 in) smoothness tolerance for both length and width. They also met the target for bump detection, having no longitudinal or transverse deviation in excess of 6 mm (0.25 in).

Paving Simulation

“The total customer support was great,” says Warner. “I can’t put a price on the value of Wheeler Cat’s contributions.”

In cooperation with SITECH™, an extraordinary level of support was provided well before the project began. The Kilgore crews were trained on the operation of the 3D pavers and the SITECH system during a four-day seminar at the dealership. The seminar included both classroom sessions and simulated hands-on sand paving using a unique 3D model.

Wheeler and SITECH representatives were also onsite for half of the first week, says Warner. “We could not have done this job without their help, no way! If we did another job like this, I’d follow the same pre-project procedure and seek their help to better prepare us.”

 


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