Although the practice of using a concrete barrier down the center of a roadway to separate opposing traffic dates back to the mid-1940s, the practice seems really to have gained steam when, in 1955, the state of New Jersey began using an 18-inch vertical concrete wall in the median of major highways. The “Jersey” barrier was refined through trial and error until, about 1960, it assumed a profile that loosely resembles an inverted funnel standing usually 32 inches tall. But the Jersey has competition, which means that paving contractors who might install barriers and bridge parapets in several states usually have a substantial investment in molds.
Some states, for instance, have modified the Jersey, maintaining its basic profile but changing heights and widths. Other states have adopted the “F-style” barrier, which has the same basic profile as the Jersey, but shortens by 3 inches the vertical height of the 55-degree slope near the bottom.
Still other states are moving toward use of the single-slope design that tapers upward, to perhaps 42 inches, at an angle (from vertical) of either 10.8 degrees (Texas style) or 9.1 degrees (California style) from a typical 24-inch-wide base. The single-slope design eliminates the 3-inch vertical surface at the base of the Jersey and F-style barriers, which is diminished each time the pavement is resurfaced. Like the Jersey and F-style barriers, the single-slope type might also differ in height and width from state to state.
It’s possible, of course, that a state may choose not to use one of these more standard barrier profiles, but instead to develop its own particular shape. Local jurisdictions, as well, might sometimes choose to deviate from the state standard. This variability in profile and dimensions could mean that contractors might frequently have to buy new molds or modify old molds (if possible) to meet varying specifications.
“A paving contractor’s probably fortunate if a particular mold can do more than one project,” says Mike Rodriguez, district manager for Terex Roadbuilding.
To that point, as we recently walked through the Miller Formless factory in McHenry, Ill., sales manager Kurt Jensen pointed out an immense variable-height mold that a contractor had sent back for modification. A state in which the contractor works had changed barrier specifications by increasing top width from 8 inches to 10 inches, so the shop was cutting the mold in half vertically and adding in a new section.
Jensen explained that a variable-height mold allows one (occasionally both) of the mold’s sides to extend downward hydraulically to compensate for differing requirements in barrier height when opposing roadways are at different elevations, or when the roadway changes to a super elevation (banked curve).
Stephen Bullock, vice president of sales and marketing for Power Curbers, adds that these large molds are complex (with all the added hydraulics), heavy (perhaps in excess of 10,000 pounds), and expensive (perhaps ranging from $50,000 to $70,000). Not all molds are this expensive, of course, but even the most simple might run in excess of $12,000.
“When a customer gets a job and comes to us for a mold,” says Bob Leonard, sales manager at GOMACO, “we need to make sure that we understand his project and his specific requirements. We can then build it anyway the customer wants.”
Concrete paving barrier molds
As complex and expensive as barrier/parapet molds might be, they are, of course, of little value until attached to a paving machine—a machine that can extrude these challenging vertical shapes and make a tall column of fluid concrete stand straight up and leave it with a relatively smooth surface. (To promote good surface finishes, some molds—those from GOMACO, for example—use a stainless-steel insert at the trailing end.)
Machines that are capable of paving barrier and bridge parapet are a bit difficult to categorize, because they don’t, so to speak, fit the same mold. Taking the long view of machines that are “barrier/parapet capable,” three general classes seem to emerge: heftier “curb-and-gutter” machines (maybe “multipurpose pavers” is a more descriptive term); machines that seem designed primarily to perform mainline paving, but are adapted to handle barrier/parapet molds effectively; and machines designed, more or less, specifically with barrier/parapet paving in mind.
But do keep in mind that these are arbitrary categories created to facilitate a more orderly discussion. A quick investigation of a particular machine’s specifications will help you determine for yourself the legitimate range of its capabilities.
“Most of the machines doing barrier paving are multipurpose machines that can take on a variety of applications,” says Terex Roadbuilding’s Rodriguez. “But some manufacturers do make four-track machines aimed specifically at barrier work. These machines are larger, heavier, have more horsepower, and can be used for variable-height applications.”
If representative machines were chosen from these broad categories, then the Wirtgen SP 15 and SP 25, Power Curber 5700-C, and GOMACO GT-3600 and Commander III might be included in the first. The SP 25, for instance, with a maximum weight of 39,600 pounds, can place barrier/parapet to 72 inches, but also can pave to 12 feet wide. The machine’s modular design, says Wirtgen, allows for taking on a diversity of applications with either three or four tracks.
According to Power Curbers, the 5700-C, in addition to curb-and-gutter work, pours such diverse structures as highway safety barrier, bridge parapet, sidewalk, agricultural foundations, irrigation ditches, and stadium risers. When equipped with the company’s C-MAX package, which adds 2,200 pounds to the 5700-C’s operating weight, the machine can pave barrier/parapet to 8 feet (2 feet more than the standard machine) and slabs to 14 feet (4 feet wider than the standard configuration).
According to GOMACO, the three-track GT-3600, with an operating weight approaching 26,000 pounds, is a “multi-application” unit capable of pouring curb-and-gutter, sidewalk, recreational trail, barrier wall, bridge safety parapet, and surfaces up to 10 feet wide. The GT-3600 hydraulically elevates to slipform barrier or parapet without modifications, and the machine features GOMACO’s Hook-and-Go mold mount system.
In the middle group we’d place machines such as the new Guntert & Zimmerman S600, the Terex SF2204C HVW, and the GOMACO Commander III, although the versatility of the Commander III seems to make it fit in the first category as well. Guntert & Zimmerman’s David Lipari says that the S600 is designed around a multipurpose tractor frame that makes it suitable for paving city streets, secondary roads, highways and airports, as well as a range of other applications, including offset paving and placing barrier walls.
The Terex SF2204C HVW, says Rodriguez, is a four-track machine capable of curb-and-gutter work, pouring sidewalks, mainline paving from 8 to 20 feet, and barrier installation.
The GOMACO Commander III is another multi-application model in the company’s broad product range, available in three- or four-track configuration. In the latter configuration, the Commander III can pave to 20 feet wide, and its three-track configuration, says GOMACO, promotes stability over grade variations when placing barrier and parapet. Minimum clearance requirements are achieved with the side-mounted mold, says GOMACO, and the mold can be center-mounted to allow working in a 10-foot-wide area. The machine features GOMACO’s proprietary G21 software and control system.
Representatives of “barrier specific” machines might include the GOMACO 4400 and the Miller Formless M8800.
“Some contractors specialize in barrier paving and have no interest in curb-and-gutter attachments,” says GOMACO’s Leonard. “The 4400 is designed so that the mold can be used on both sides of the machine with really no modification—it’s simply moved from side-to-side. And the machine’s four-track design provides stability. The 4400 could do curb-and-gutter, but that’s not its primary purpose.”
Likewise, the four-track Miller Formless M-8800 can do offset pouring other than barrier and parapet, but the machine’s overall design suits it especially well to barrier and parapet work. According to Jensen, the M-8800 can place barrier up to 102 inches high and can be converted from left-side to right-side pouring in three or four hours.
Concrete barrier paving machine features
Barrier molds can be positioned either under the machine or mounted at the side, and some machines accommodate both mounting positions. Under-machine molds, of course, are limited in the height of structure they can accommodate, but an advantage, says GOMACO’s Leonard, is a smaller overall footprint for the machine and the ability to transport the machine with the mold in place. Terex’s Rodriguez adds that if the machine is a multipurpose type, then under-machine mounting places more weight on the mold to keep it stable.
It’s probably safe to say that most barrier-capable machines are set up to pave from the left side, but factory options may allow a standard right-side configuration. When a contractor’s work necessitates that barrier/parapet—whether on the inside or outside of the roadway—be installed in the direction of traffic flow, then the ability to mount the mold on either side of the machine is an advantage.
Because most molds are directional, that is, can only pave effectively in one direction, simply turning the machine around and operating in reverse doesn’t work. This strategy would work with another properly oriented mold, or with a bi-directional mold (which aren’t frequently seen), along with a reoriented conveyor system.
The GOMACO 4400, capable of accommodating both under-machine and side-mounted barrier molds, allows molds to be moved side-to-side, using hydraulically powered mold-mounting beams that can extend 36 inches to the right or left side of the machine. The Power Curber 5700-C can be equipped with the a dual-side pouring option, which converts the machine from left-side to right-side operation in three to four hours. For both machines, the auger-type conveyor can be reoriented.
On the other hand, some machines that accommodate the mold on only one side, such as the Miller Formless M-8800, can still be reconfigured from left-side to right-side operation. According to Jensen, since the M-8800 is a symmetrical machine, the conveyor can be moved end-for-end and the machine turned around and operated in reverse with a properly oriented mold. The conversion, he says, requires three or four hours.
Although most multipurpose machines used in barrier/parapet placement are equipped with a trimmer, this feature typically is not used, because most barrier/parapet is placed over an existing footing. According to Power Curbers’ Bullock, not using the trimmer frees horsepower for more efficiently handling the large barrier molds.
Most machines also use an auger-type conveyor as standard equipment with a belt conveyor as an option. The auger, says Terex Roadbuilding’s Rodriguez, remixes the concrete, which is an advantage. The belt is probably faster, he says, but has the potential to cause segregation.
“Auger advantages include taking up less room, running at steeper angles, less segregation, and allowing for remixing,” says Guntert & Zimmerman’s Lipari. “Disadvantages are higher wear, the need for careful guarding, and more cost to manufacture and maintain.”
“Some contractors prefer the belt, because low-slump concrete in hot areas can dry out too much in the auger,” says Power Curbers’ Bullock. “For some larger molds, you also might get higher volume with a belt, and the belt might give a bit more reach. But for the majority of barrier pours, the auger is fine.”
One final point might be the potential that “string-less” paving systems have for barrier/parapet placement.
“We’ve not seen many contractors convert to string-less operation just yet—just a handful—because it’s an expensive option, so most are still using string lines,” says GOMACO’s Leonard. “But stringless technology is available for barrier paving, and it works well.”