Tight on the Taxiway

Florida paving specialist meets tough specs with a millimeter solution.

When it comes to cutting to the chase, it would seem Herb Jacob had few equals. After all, Jacob, the founder of Ajax Paving, selected the name “Ajax” solely because he knew it would appear at the top of phone book listings of paving companies. Long before OSHA, he recognized that safety begets success — a lesson some companies don’t get even today. And he credits the company’s early profitability and acceptance to the high-quality, highly productive tools he made available to his team. Doing so, he believed, would allow them to provide Ajax customers with the highest quality pavement work possible — and ensure repeat business. Today, more than 70 years later, that philosophy is still fully embraced and evident in the work the company just completed at MacDill AFB, Florida. There, the latest millimeter-grade GPS technology drove both the milling and paving operations for a runway apron repaving effort. Seven decades after Jacob brought Ajax to life, the results of using the best solutions available are the same: a dramatic increase in productivity and efficiency, coupled with a safer stakeless, stringless, work environment. Because, when you’re right, you’re right forever.

The Real Big “Mac”

With more than 15,000 military and civilian personnel, MacDill is the largest U. S. Air Force base in Florida — and the third largest in the world. Home to the 6th Air Refueling Wing, MacDill houses a fleet of two dozen Boeing KC-135R Stratotanker aircraft, a long-range aerial tanker capable of refueling a variety of other aircraft in mid-air, anywhere in the world and under any weather conditions.

When a section of one of the major aprons used to stage those aircraft on a daily basis was identified as deficient and slated for repair, the milling and resurfacing project was awarded to Ajax Paving. According to Ben Harlan, Ajax’s field technology manager, it was a perfect fit for the company’s capabilities.

“This company has immersed itself in GPS technology for a long time — easily more than a dozen years now,” he said. “We have GPS machine control on most of our dozers and graders and some of our excavators so it was a natural progression for us to bring it into the paving part of the operation, which we did several years ago. Our management team recognizes the benefits the technology brings in terms of accuracy and productivity and knew those — and more —  would come into play at MacDill.”

In the Milling Cycle

More than 150,000 square feet of apron, deemed to be sorely in need of both restoration and resurfacing, was rehabbed at MacDill. The project was critical to ensuring support for the mammoth tanker aircraft, each of which, when fully loaded, can weigh as much as 322,500 pounds. According to Harlan, while the accuracies demanded in the project were tight at ± .02’ for finished grade, the decision to bypass traditional milling and paving methods was in the works long before they came on site.

“This was a case in which millimeter-grade GPS milling was specifically called out in the specs,” he said. “Again, that played directly to our strengths as one of the leaders in Florida for using that technology. To begin the process, we had a survey team topo the area in 25-foot grids then, from those shots, we created a surface model which was used in both the milling and paving parts of the job.”

For the MacDill project, the Ajax team worked with Tampa-based milling subcontractor BlackRock Milling which supplied a Wirtgen W210-Fi to tackle the milling. Harlan said that, because the 210-Fi is one of the company’s more advanced units, equipping it with the Topcon Millimeter GPS system was a snap.

“That Fi Series mill was awesome to work with, particularly running the Topcon solution,” he said. “Everything on the machine is integrated, so I only needed to attach a couple of cables and we were ready to go. I was also able to use the existing Wirtgen screen to make any necessary adjustments — raising or lowering the mill, for example. It was a great pairing of two excellent technologies.”

Working With the Variables

The Ajax team used a total of four Topcon LZT-5 transmitters — spaced at 250’ intervals — to create an area of data which, when accessed by receivers on the milling unit, ensures an accurate elevation is maintained. When combined with the horizontal accuracies GNSS provides, true millimeter grade milling and paving is made possible. It’s important to note that the laser zone mentioned above is far more efficient than optical control which requires line of sight from instrument to prism and is prone to interruptions when signal blockages occur. By comparison, Millimeter GPS recovers instantly regardless of rover position.

“This project differed from many in that it called for variable-depth milling,” said Harlan. “In a uniform depth milling effort, the machine follows any recesses or dips which are in place. The side gates on the miller want to just follow the existing contour, essentially keeping those low spots in there. Variable depth milling, which is based on the 3D surface model we had created, averages low and high spots and evens it all out. The result is a smoother surface without any of the old flaws. It’s a much better approach and the Millimeter GPS system made it work beautifully.”

Alternatives to the use of the Topcon solution would have included the need to pound stakes for edge lines and shoulders, placing a stringline or manually depicting paint grades.

“This was a much faster, more accurate and far more efficient way of getting the job done,” added Harlan. “There’s a huge saving in survey costs, we eliminated the risk of being out of spec because a stringline sagged or got moved, and it makes the job site so much easier and safer to navigate, both for us and the trucks — we had anywhere from 10 to 20 trucks working at a time — coming into and out of the milling area. Ajax is all about efficiency and this made that happen, big time.”

Limits on the Job

The production gains to which Harlan refers were, indeed substantial. The milling aspect of the project, which, done traditionally, would have been both labor- and time-intensive, was completed in just three days.

“That particular Wirtgen unit has a 7’-wide mill and we made 18 passes at 1,200’ each,” he said. “So, that facet of the the job was done quickly, followed by an additional day and a half of miscellaneous work. Done using traditional means, layout alone would have been a week and a half to two weeks of additional work. There was also another section of the apron — which represented about 25% of the overall job — that needed total restoration to remove a pipe running underneath it. Once that was removed, we put base rock back in and paved it to match the adjoining surface.”

During the course of the milling operation, nearly 4,000 tons of asphalt was removed and hauled to one of Ajax’s area asphalt plants for use as recycled asphalt product (RAP). Although it was assumed that the mill would be making a minimum 4” cut, such was not always the case, said Harlan.

“Once we switched the machine around from Millimeter GPS to the slope sensor, things changed,” he said. “The job limits on the apron were 20 feet away from the crown line, and, even though we were supposed to be cutting 4-inches, between the topo shots we gathered and how bad the asphalt was, there were areas in which we only milled half an inch. So, we calculated the distance from the catch basins to the job limits and cut the appropriate slope to allow the water to drain into the basins. It really worked out well.”

Mid-Night Calling

The MacDill job was not without its challenges, most of which are unavoidable. According to Harlan, issues like stiff winds from the wide-open, water-side location, and trucks being in the way of lasers and temporarily blocking the signal is simply a part of doing business. He said they are fortunate, however, to have the support of Dobbs Equipment, their John Deere and Topcon dealer to keep things running smoothly.

“Dobbs has been an awesome partner throughout this part of the state,” he said. “If needed, I feel that I can call Roger Croft, our salesman, at 3 a.m. and he will work with me — even Facetime with me — for as long as it takes to get an issue resolved. That kind of support means a lot to us.”

The MacDill project is the fourth airport-related project Ajax has tackled thus far in 2022 and they already have work at Sarasota Airport on the books for later this year.

“The Topcon millimeter solution was a great fit at MacDill and checked all the boxes for what we need to continue improving both our milling and paving operations — we definitely see it continuing to play a role in future work for us.”