Launch Slideshow

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Small pavers, big differences

Small pavers, big differences

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    As the name suggests, gravity-fed pavers rely solely on gravity to feed asphalt from the hopper to the screed assembly. When asphalt is dumped into the hopper by feeder trucks, the paver's bed is hydraulically raised until gravity takes effect. Photos: BOMAG Americas Inc.

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    When paving at full width, consistent material flow to the entire screed can be a problem. Some manufacturers are countering this through the implementation of material-feeder augers mounted directly to the screed.

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    Relying on conveyors, not gravity, to deliver asphalt to the screed, conveyor-fed pavers can continuously receive new asphalt while pushing the feeder truck. Also, there is enough hopper capacity to continue paving while swapping a new, full truck into the operation.

Bigger is better—or so the cliché goes. In the asphalt market, it seems the big mainline pavers get all the attention in trade magazines, while the smaller, commercial class of pavers (basically anything 16,000 pounds or less) are relegated to a sidebar. But regardless of this lack of exposure, the fact is that these smaller pavers fill quite a large niche.

One common misconception is that compact, commercial-class pavers are simply smaller versions of larger, mainline-class pavers. But aside from both being used to lay down hot, black asphalt, the two machine classes are completely different in design, capabilities, and quality expectations.

Commercial pavers can be separated into two categories: gravity fed or conveyor fed. This is differentiated by how the pavers deliver asphalt from the hopper to the screed. Given a contractor's preferences and workload, each machine type has its advantages and disadvantages.

Usually weighing less than 10,000 pounds, gravity-fed pavers rely solely on gravity to feed asphalt from the hopper to the screed assembly. As asphalt is delivered into the hopper by feeder trucks, the paver's bed is hydraulically raised until gravity takes effect and draws the asphalt toward the screed.

Gravity-fed pavers can't be considered high-capacity machines. Though some contractors will pull 500 to 600 tons of material though them in a day, they're more commonly used as 200-tons-per-day machines. Therefore, it's very common to see gravity-fed pavers being used for driveways, small parking lots, and general road maintenance, but not for more demanding paving jobs.

Conversely, because conveyor-fed commercial pavers rely on a system of conveyor belts that move the asphalt from the paver to the screed, they offer more consistent and controlled delivery. Also, these units allow for much greater asphalt capacities. It's quite common that a smaller conveyor-fed paver would average 500 tons per day, while the largest units often handle up to 1000 tons per day. In fact, it's not unheard of for a contractor to push up to 2000 tons per day of asphalt through a large, conveyor-fed paver. Therefore, conveyor units are typically considered production machines.

Conveyor-fed commercial pavers can push more asphalt, but this is not where their advantages end. The increased capacities of these units also allow for a much higher-quality finish. With any paving job, every time the paver stops, a bump is formed in the mat. This diminishes the overall quality of the application. Unfortunately, the very nature of a gravity-fed machine lends to frequent stopping because once the hopper is emptied, the paving train must stop so the bed can be lowered and the hopper refilled.

Conversely, conveyor-fed pavers can continuously receive new asphalt while pushing the feeder truck. Additionally, hopper capacities are typically larger on conveyor-fed machines. Even when the feeder truck empties, there is enough hopper capacity to continue paving while swapping a new, full truck into the operation.

Another conveyor-fed feature that promotes higher-quality results is the machine's weight. Since they're heavier than gravity-fed pavers, conveyor units can accommodate larger, heavier screed assemblies. Generally speaking, the heavier the screed, the more structurally sound it is, and the better finish it produces.

SELECTING PAVER OPTIONS

Though the two basic categories of commercial pavers are relatively simple to understand in terms of capabilities and merit, a wide range of available equipment designs and options can complicate the selection process.

One variable relates to how the equipment is propelled. Units are available that are either track- or wheel-driven. Today this is almost a moot point since roughly 95% of all commercial pavers being used in the United States are track-driven. Even so, there are some specific advantages of wheel-driven units that have kept this option in the market.

First of all, wheel-driven pavers offer higher travel speeds than track-driven units. When working on road-maintenance applications, this can be a major benefit, allowing operators to quickly travel from one pass to another and reducing the amount of time that traffic is impeded. Secondly, wheel-driven units travel on pneumatic tires that can safely roll over surrounding structures, such as curbs and sidewalks, without fracturing the concrete. This is a hazard presented by pavers with steel tracks.

Why, then, do wheel-driven pavers make up such a small portion of the market? Traction, or lack thereof, is the culprit. When working on unstable bases or subgrades, wheel-driven units have a tendency to spin their tires and get stuck. And getting stuck is one of the worst things that can happen with a paver—next to breaking down. Therefore, wheel-driven pavers are feasible only for those who almost exclusively do maintenance work where they are working on a stable base.

On the other hand, the only limiting factor of track-driven pavers is travel speed. Tractive effort, gradeability, and maneuverability are all greatly enhanced with tracks.

The next variable to consider is the screed. This is the last part of the paver to come in contact with the fresh asphalt—forming and smoothing the material as it leaves the machine. To do this more effectively, one common option is the bolt-on screed extension. With most mainline pavers, the ability to produce a raised or tapered edge in the asphalt is integrated into the screed itself, but commercial pavers must offer bolt-on alternatives to achieve the same results. Bolt-on screed extensions give the operator more control over the material while offering variable finishing configurations. Additionally, special plates are available from several manufacturers that attach to the screed and narrow the paving width. This is ideal when paving bike or cart paths.

Another option found on many commercial-class pavers is screed automation. This provides the paver with the ability to adjust screed depth or material thickness automatically through the use of onboard computers. Eliminating some of the human element during operation provides more consistent paving results.

When paving at full width, consistent material flow to the entire screed often can be a problem. Some manufacturers are countering this through the implementation of screed-mounted, material-feed augers.

On most pavers—mainline or commercial class—the material augers that displace asphalt to both sides of the screed are mounted in the hopper. As paving widths increase, these augers typically have difficulty shoving material efficiently to the widest expanses of the screed. This is why it is not uncommon to see laborers with shovels on either side of a paver helping direct asphalt to the entire length of the screed—often slowing production.

Some machines now use material flow augers mounted directly to the screed. As the screed extends to handle wider paving widths, so too do the augers. This eliminates the need for laborers to redirect asphalt by completely automating the material flow process.

Productivity features are important, but is the paver built to handle the ceaseless demands of asphalt paving? Bear in mind that from the moment a paver hits the jobsite, it's receiving several tons of hot, abrasive aggregate from sunrise to sunset with few breaks in between. No matter how durable the paver, regular maintenance is unavoidable. But will it be something that needs to be maintained once a week or once a day? Maintenance intervals can make a big difference to the bottom line of any operation—and the materials that make up a paver's wear components can be key.

All manufacturers will list the materials that make up their respective augers and screed surfaces. Durability usually is indicated through a hardness rating. For instance, depending on the manufacturer, one might find the option of having wear components constructed of heavy-duty steel with hardness levels of 400 or more. Compared with standard-grade steel components, a level 400 hardened steel will offer four to five times longer life. This added life comes with a price, but contractors typically will find that the extra price will be offset by the reduced maintenance costs.

TECHNOLOGY INCREASES CONTROL OPTIONS

No matter the type of compact paver, one of the biggest technology changes taking place today is the implementation of electronics. This is apparent not only with the available full-screed automation packages, but also with operator controls.

Instead of presenting a series of levers that manually control paver operations, digital controls use a series of toggle and jog switches that offer numerous benefits. Electronic controls are more precise and efficient, and they're easier to use for operators of any experience level. But there is a catch. Electronics don't mix well with a few elements—heat, liquid, and dirt—all of which are omnipresent on a paving job-site. Therefore, the choice of electronic controls poses a reliability concern.

For some operators, electronic controls are too foreign to merit consideration. With manual controls, if something fails, operators usually can repair it on the spot and continue paving. But if something electronic fails, it probably requires a certified technician to remedy the problem, meaning dreaded downtime. This is the main reason why most manufacturers offer two configurations for each paver model—one with electronic controls and one with manual.

But with greater risks come greater rewards. Electronics help ensure better, more easily repeatable results. Also, as the technology progresses, manufacturers are finding ways to better protect the electronic components, reducing reliability concerns.

— John Hood is manager of product development with BOMAG Paving Products, Warrensburg, Mo.


Looking for a commercial paver?

Here are a few simple questions and answers that will help narrow your focus:

1. What will it be used for?

If small parking lots and general road-maintenance applications are the toughest jobs this paver will see, consider a gravity-fed unit. Otherwise, anything more demanding would be better served by a conveyor-fed paver.

2. How much asphalt do you intend to pull each day?

If it's more than 600 tons per day, look to a conveyor-fed paver. The most you can expect from a gravity-fed unit is 500 to 600 tons, but a conveyor-fed paver, in extreme cases, can handle up to 2000 tons per day.

3. What's your budget?

Gravity-fed pavers will cost $25,000 to $50,000, whereas a conveyor-fed unit will run anywhere from $50,000 to $110,000.

4. What type of bases will you be working on?

If all of your work will be done on stable bases, as when doing road maintenance, consider a wheel-propelled unit. Otherwise, if you ever intend to work on unstable bases or subgrades, it's best to choose a track-propelled unit for better traction and more reliable results.

5. How important is equipment portability?

Gravity-fed pavers are smaller and can typically fit on a standard flatbed trailer along with a roller, skidsteer, and other necessary tools. On the other hand, a conveyor-fed paver will typically require a dedicated trailer.