How to repair and resurface asphalt pavement through milling
By Jeff Winke
When an asphalt surface becomes rough for motorists to drive on or people to walk on that’s the time when it needs to be roughed up further. Milling is the process used before repairs or resurfacing can occur. With pavement milling, a heavy-duty piece of construction equipment known as a milling machine—also known as a cold planer, pavement planer, pavement recycler, or roto-mill—roughs up the surface. Its large, rotating drum with carbide teeth chews up the paved surface. It removes and grinds the bituminous pavement or asphalt concrete from the lot or roadway. Scrolls of tool holders cover the exterior of the drum and hold the carbide cutters that actually cut up the pavement.
The surface material that is removed is normally fed by conveyor into a dump truck or semi-trailer, but can be left in place or windrowed to be removed or recycled later. A water spray system generally provides cooling for the mandrel, as well as dust management.
The somewhat rough, but even surface, can immediately be opened to traffic until repaving occurs.
In addition to large dedicated milling machines, there are milling attachments that can be affixed to heavy equipment such as skid-steer loaders, wheel loaders, and backhoes. For example, “RoadHog offers a line of engine driven units from 67hp for skid-steers, 74hp units for loader backhoes, to 275hp units for wheel loaders, so the customer has a wide range of host carrier options to choose from their fleet,” stated Bill Bethards, OEM manager, RoadHog, Inc., Brownsburg, Ind. “This lineup of machines allows greater fleet utilization, while filling the price and performance gap between large dedicated milling machines and skid-steer planers. Additionally, there are no electrical or hydraulic connections required, making them compatible with any carrier capable of propelling them during operation.”
Early milling machines were simply a mining mandrel attached to a mobile undercarriage. They were designed to remove a layer of old concrete or asphalt so that a new layer could be applied to a better-quality base than resurfacing over the old road surface.
From the start, the emphasis for milling machines was to place more power to the cutting drum, which is needed to remove more material. Thus, the cutter head itself and the cutting teeth designs became critical. The cutting teeth would dull fairly quickly and needed frequent replacement. The replacement process could cause enough downtime to greatly detract from the initial efficiency of the milling process itself. So, manufacturers worked on designs for quicker replacement, as well as increased durability of the cutting teeth. Different sized cutting drums were offered so that machines could mill at different widths.
Today’s machines and attachments are more technologically advanced. They are designed to handle any asphalt aggregates in use today. Depending on the depth of the cut, some of the larger machines can cut close to 15,000 square yards (13,000 m²) a day, at 75 feet per minute.
In addition to faster speed, added precision to the milling process has become important. The innovation of controls and automation has brought greater precision for controlling slope, depth, and speed.
There is no question that the technological advancements made in microelectronics have benefited milling machines and attachments. Electronics designed to improve performance, include electronic sensors and a built-in cross slope. A pair of sensors can read a variety of references from 12 to 55 inches directly below the bottom of the sensor. Each sensor can be calibrated and adjusted from the ground level or at the operator’s console.
The position of the rotor in relation to the grade reference can be constantly displayed on the central controller. Changes to the elevation controls include the addition of a raise/lower switch that is used when milling around obstacles. In many cases, the electronic control module monitors and regulates the performance of major machine systems, including speed, steering, rotor drive, and other functions. If a problem occurs, a warning is issued.
“The way in which milling is performed is constantly changing and evolving, thanks to new technologies,” stated Matt White, North American sales manager-milling & RS for BOMAG Americas, Inc., Ridgeway, S. C. “More productive, powerful machines with improved cutting technology, electronics and grade control systems require much more skill in the area of electronics than ever before. This can create new challenges for operators, service technicians and manufacturers alike.”
Along with the electronic features that keep milling machines on track are the advances being made in the cutting end of the machines. The ability to change cutting drums quickly to achieve multiple cutting widths with the same machine is a benefit to contractors who may only need one machine to accomplish multiple job requirements.
Today’s milling machines also reduce the time required to change the all-important cutting teeth. Early machines had the teeth welded on, so tooth replacement required a fair amount of downtime as each had to be re-welded to the drum. Now, teeth are held in variously designed bolt-on housings that permit faster changing.
“Milling fits into a contractor’s paving portfolio as it gives both strategic and scaled options for re-paving of existing roads,” stated Marlene Soligo Bruce, business development manager, Maddock Construction Equipment, LLC, Bloomington, Ind. “This cuts cost. It also increases the use of underutilized equipment such as backhoes.”
Bethards said, “Many contractors are now offering asphalt milling as part of their overall paving services in order to reduce delays associated with sub-contracting this service. By offering it ‘in house,’ it also reduces costs and usually improves overall job quality.”
Asphalt milling is a niche service, so can really fit into a contractor’s portfolio of services under several different classifications.
“Contractors range from milling only companies, to milling and paving, to general contractors who only mill for their own jobs,” White said. “Depending on the desire of the contractor, as far as growth and diversification or the desire to be in control of their own destiny, the range of services can vary quite differently.”
The market for asphalt milling services appears strong and in some areas it is growing.
“The milling marker is growing rapidly in urban areas,” Bruce said. “The need for speed and surgical precision of cut is necessitated by traffic patterns and urban renewal in previously depressed areas.”
RoadHog is seeing an uptick in municipal customers purchasing equipment and setting up milling crews to complement their asphalt paving, thus reducing annual road maintenance budgets.
Some contractors see the costs of investing in a milling operation to be too costly, but prefer to still offer the service to their customers by renting the equipment when necessary.
“If the equipment is used less than 30% of the time, it’s probably best to rent,” stated Bethards. “Another question to ask is whether you have the ability to repair the milling machine. A rental source is often equipped to handle both rental and repair of their fleet. There are other financial considerations to consider. For instance, rental bills can be tax deducted, while a purchase is a capital expense that will be amortized.”
Bruce added, “It is better to rent equipment when you have specific needs which may not repeat. It is also better to rent until you become comfortable with the application and equipment you have chosen.”
Renting for many contractors can be a better solution to owning on many fronts.
“The rental, in many cases, can be a 100% tax write-off giving an advantage over certain depreciation limits when purchasing,” White said. “Owning a machine can affect the contractors bonding capabilities, which can be critical for certain large-scale projects. Costs for rentals are many times put towards the job cost and not towards the contractor’s cap-ex budget. During the rental period, most dealers cover any repairs needed, not caused by normal wear and tear or maintenance, as well as supporting the contractor with a replacement machine if the unit goes down and needs major repair. Milling machines, especially ½ lane and above, are extremely high production units and require a steady diet of asphalt. If the contractor does not specialize in this type of repair or only has a small job, renting is likely a better solution. If a contractor is looking to get into the business, renting may be the first step to purchasing. Most dealers offer a ‘rental purchase option’ (RPO), in which the customer can ‘try it before you buy it.’ This provides minimal financial exposure to the contractor and the chance to experience the machine, dealer and/or manufacturer. If the contractor rents for a few months and determines it’s a proper fit, he can usually apply a portion of the rental to the purchase price of the unit.”
Considering adding asphalt milling to the service mix, here are points to consider from the experts:
• Make sure you understand acquisition and operating costs, and budget accordingly.
• Have a properly trained operating and maintenance crew.
• Buy the machine or milling attachment best suited for your host carrier and typical milling workload.
• Milling can be an efficient and cost effective option.
• Find and go with equipment that is easy to operate.
• The manpower needed to run the equipment is often low, at most one or two workers.
“Last but not least,” White added, “aftersales support is critical. Whether it’s parts, service/maintenance, or knowing what to do when there’s a breakdown, aftersales support is likely the most important piece of the puzzle. All machines will fail at some point, and they usually don’t break while sitting in the yard. When this happens on a milling and paving job site, it’s a domino effect that can cost tens of thousands of dollars per hour. Having skilled operators, properly trained mechanics (either with the contractor, dealer or manufacturer) and parts availability is all part of a solid plan that can keep the operation running as smoothly as possible.”
All the experts will likely agree that jumping into the asphalt milling arena doesn’t need to be a rough road if it is planned and carefully thought out.
Jeff Winke is a business and construction writer based in Milwaukee, Wisconsin. He can be reached through firstname.lastname@example.org