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"PWL makes for a much smaller margin of error in paving," says Ganske. Because of this, Northstar Materials checked the base and the asphalt on a test strip to ensure everything worked according to plan.

During testing, Northstar Materials decided the best way to compact the mat. "With compaction, each project is unique, so we go through a process to establish what we have to do to get compaction," says Ganske. "Each mix compacts a little differently. We'll determine a pattern that works and then try to consistently stay with that pattern while continuously monitoring the results."

Northstar Materials used part of the taxiway that was being reconstructed as the project test strip, laying 300 tons of asphalt. When the compactors started working on the test mat with vibration, the contractor discovered that the Portland cement powder rose to the top of the base. "The powder was making a barrier that was causing the asphalt to slip during compaction," says Ganske. "We decided to spray prime coat down to make the asphalt adhere to the base, and that solved the problem."

Due to the project's PWL requirements, Northstar Materials decided to purchase an Ingersoll Rand DD-158HFA compactor to use as the breakdown compactor. "We hadn't used the DD-158HFA before. We had demoed an Ingersoll Rand DD-138HFA earlier this season and liked how that machine performed. We knew that the DD-158HFA was one step up because of size, so that gave us confidence. We have a lot of Ingersoll Rand compactors so we knew what we were getting."

Efficient compaction
Achieving the necessary compaction and consistency in compaction aren't the only benefits of the DD-158HFA. Northstar Materials discovered that the DD-158HFA allowed the company to eliminate a compactor in the paving train. "We used five compactors on the test strip - two pneumatic tire compactors and three steel compactors," says Ganske. "Then we got the DD-158HFA and we used it with vibration and achieved better densities. The densities were so much better that we were able to eliminate one of the steel compactors. During paving of the runway, we used the DD-158HFA, two pneumatic tire compactors and a DD-130 steel-drum compactor as a finish compactor."