Cleared for takeoff

Feb. 10, 2005

Not many contractors stay in business for nearly 90 years without taking some calculated risks. From the company’s beginnings with heavy-duty construction equipment to today with its most technologically advanced equipment, Holmes & Murphy Inc., Orchard Park, N.Y., has never backed down from a challenge.

Not many contractors stay in business for nearly 90 years without taking some calculated risks. From the company’s beginnings with heavy-duty construction equipment to today with its most technologically advanced equipment, Holmes & Murphy Inc., Orchard Park, N.Y., has never backed down from a challenge.

Rather, the contracting company faces them head-on, employing the latest technologies available, giving it the best chance for success. “We are not afraid of new technology,” said Richard Holmes, president of Holmes & Murphy. “By having the right machine for the right job, we give ourselves the opportunity to succeed.”

Facing an application normally paved with concrete, the company stayed true to its practice of using the latest technologies available in successfully completing a demanding paving job at the Buffalo Niagara International Airport (BNI). The $12 million project called for 125,000 tons of a tough asphalt mix design to upgrade the crosswinds runway from Class B to Class A, lengthening it by 1,200 ft and installing an ILS system so commercial aircraft can land.

In addition to the runway work, Holmes & Murphy reworked a total of 10 taxiways, performing tasks ranging from rubblization and overlay to reconstruction and widening. Because of the demands exerted on the runways and taxiways of an airport, the work at BNI followed stringent guidelines and included a mix requiring disciplined placement.

A demanding spec

Reconstruction of the runway called for 11 in. of a Federal Aviation Administration (FAA) P-401 mix design for the base and surface courses. The 57,400 tons of base course consisted of a 2-in.-minus coarse aggregate for strength and durability. It was laid in two lifts, the first at 4 in. and the second at 3 in. A surface course of 4 in. with a 1?2-in.-minus aggregate was laid in two lifts at 2 in. each.

“Between designing, mixing and testing, the FAA P-401 is one of the toughest specs to adhere to,” said Curt Resetarits, account representative for Buffalo Crushed Stone Inc., supplier of the asphalt for the BNI project. Buffalo Crushed Stone worked closely with Holmes & Murphy in order to ensure mix and temperature consistency throughout the project, which included at times dedicating the asphalt plant’s entire production or at least one of the 300-ton silos to Holmes & Murphy.

“The window of tolerance for the mix was very tight,” added Richard Holmes. “Buffalo Crushed Stone was very good to work with and supplied a high-quality mix for us.”

Holmes & Murphy went to painstaking lengths to get the job right. The company conducted multiple test strips to determine that it had not only the right paving speed but also the right equipment making up the paving train.

However, this was a necessity, since the tough performance-based spec required elevation tolerances to be within 1?4 in. of plan and minimum density specs of 96% across the mat and 92% at the joints.

“The specifications for the manufacture and application of this material is so stringent that only the most experienced contractor using his best paving crew and equipment should attempt this work,” claimed Paul Kowalski, a resident engineer with DiDonato Associates, consulting engineers for BNI.

Sum of all parts

As Richard Holmes would say, it’s not only having the right equipment on the job. Completing a demanding application like the BNI project is the sum of everything working together. If one element is missing, then the job won’t be as successful as it can be. One has to have the right mix, use the right equipment, have the rollers compact the mat at the right temperatures and get the paving train speed right to ensure maximum densities.

Holmes & Murphy’s paving crew slowed the paving train to a speed that not only ensured a consistent flow of material delivered to the paver but also allowed the Terex/Cedarapids Stretch 20 diesel screed to deliver maximum densities. The uninterrupted flow of trucks to the paver eliminated “stop-and-go” paving and the associated mat irregularities. The paving speed selected by Holmes & Murphy delivered 85% mat density behind the paver before rolling.

Paving widths ranged from 12 to 18 ft, with the majority of the widths in the 15-ft range. According to Stuart Culver, project manager for Holmes & Murphy, “By paving with shorter widths, it was easier for us to hit the required elevation. The wider you pave, the harder it is to achieve the tough 1?4-in. elevation spec.”

Varying the paving widths allowed the crew to stagger the joints, giving them the opportunity to achieve the required 92% density. Achieving 85% compaction from the screed made it easier for the rollers to reach the minimum 96% bonus-level density across the mat, but it still did not guarantee that the spec would be met. When the roller hit the mat was equally as vital in reaching final densities as having the right roller.

“There is about a 40° window for each roller to compact the mat to optimum densities,” explained Culver. If one of the rollers does not compact a section of the runway surface at the right temperature, density suffers.

Having such a tight temperature window for the rollers, Holmes & Murphy needed a way to make sure temperatures were uniform across the mat. Knowing that thermally segregated asphalt in the truck would lead to nonuniform mat temperatures behind conventional pavers, Richard Holmes added a new weapon to its equipment arsenal to combat thermal as well as material segregation.

Leap of faith

“We purchased the 552 Remix paver specifically for paving at the Buffalo Niagara (International) Airport,” said Holmes. This move fit perfectly with the company’s philosophy of having the right machine for the job. “The FAA P-401 specification is a demanding and exacting design, and our performance expectations of the Remix antisegregation system were very high,” he continued.

Holmes explained that he was familiar with the Remix paver prior to purchase, seeing it at various trade shows, reviewing the literature and speaking with dealer and manufacturer representatives about the system. He was confident the concept was sound, but until the application at BNI he did not think the company had a need for such a system.

Also prior to purchase, he had not seen a Remix paver in action, so the acquisition was sort of a leap of faith that the paver would perform as described. He had hoped that it would eliminate the occurrence of material and thermal segregation at the airport.

The Terex/Cedarapids Remix Anti-Segregation System paver from Terex Roadbuilding differs from traditional pavers primarily in the receiving hopper design. Two sets of twin counter-rotating augers in the hopper, featuring a constant 10-in.-diam. and variable-pitch design, replace the slat-conveyor delivery system of a conventional paver, combating segregation at the last stage in the paving process. The augers uniformly pull and reblend material from all areas of the hopper to deliver a more consistent mix to the screw-spreading augers. According to documented tests, the paver reblends and spreads segregated material in the hopper over an area five times larger behind the screed than a traditional slat-conveyor paver.

The remixing action was particularly beneficial for Holmes & Murphy’s paving crew on the two lifts of the FAA P-401 base course, which consisted of a 2-in. aggregate.

“This mix design gets its strength from the aggregate and consists of less binder and fewer fines than a typical DOT mix,” said Resetarits. While the coarse-aggregate mix gives the mat its strength, the aggregate has the potential to segregate. Culver said that material segregation was a concern for Holmes & Murphy, but it never materialized. “The paver handled any segregated mix coming out of the truck.”

More significant for Culver, the paver reblended material from the top and sides of the delivery truck because it had a chance to cool during transit. If the material was not reblended, the thermal segregation present in the truck would transfer to the mat, making it much more difficult for the rollers to compact.

However, reblending the aggregate delivered the added benefit of making temperatures more uniform across the entire mat width. “We used three methods to measure both surface and internal mat temperatures,” explained Culver. “Mat temperatures were very uniform behind the paver.”

The payoff

With paving at BNI complete, Holmes & Murphy reported that the runway application with asphalt was a total success. The project was completed on schedule, even though the company had to work through adverse weather conditions.

The company consistently achieved the requirements of the performance-based spec. Every lift elevation fell well within the strict 1?4-in. tolerance, with the paving crew either hitting targeted elevations exactly or, at worst, being 1?8-in. off.

Additionally, Holmes & Murphy bested the minimum compaction standards of 92% at the joints and 96% across the mat.

About The Author: Information for this article provided by Cedarapids Paving, part of the Terex Roadbuilding Group.

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