Equipment Type

Trimming Concrete Paving Costs

Over the past few years, the roadbuilding industry and the United States as a whole have received harsh economic lessons concerning supply and demand. Growing global demands, from emerging markets like China and India, have put a strain on many natural resource supplies, increasing the costs for the infrastructure's basic building blocks.

June 15, 2007

Over the past few years, the roadbuilding industry and the United States as a whole have received harsh economic lessons concerning supply and demand. Growing global demands, from emerging markets like China and India, have put a strain on many natural resource supplies, increasing the costs for the infrastructure's basic building blocks.

The tightening supplies and an antiquated U.S. refining system have kept the prices for oil and fuel close to record levels for the past two years. This has resulted in skyrocketing liquid asphalt cement prices. What previously cost $180 per ton for AC now consistently tops $400 per ton, doubling the price for asphalt mixes in many regions.

One may think these asphalt price spikes would automatically lead to increased opportunities for concrete paving contractors, but this is not necessarily the case. The concrete industry has recently suffered its own issues with sporadic shortages of portland cement and increases in steel prices. In 2004 and 2005, the Iowa Concrete Paving Association had members reporting ships with imported cement being diverted from the United States to other countries, signifying the struggle for supply to keep pace with demand.

As a result, concrete prices rose. "Concrete previously cost $30 per cubic yard, but it now ranges up to nearly $70 in some regions," says John Eisenhour, district sales manager — concrete equipment for Terex Roadbuilding.

In order for concrete paving contractors to maximize their opportunities to build the nation's roadways and highways, they must work faster, smarter and more efficiently. And manufacturers are responding with equipment designed to minimize expenses.

From the Ground Up

One way for concrete contractors to reduce costs is to control yield loss. During the bid process, companies estimate the amount of material they will need to complete the job. Included in this number is a yield that can account for potential overruns, resulting from deviation to specified grade.

When working the mainline, even small deviations from plan can require significantly more material, resulting in additional expense for the paving contractor. Nowhere is this more evident than when preparing the subbase and base for interstate paving. Deviating as little as 0.5-inch from planned grade in some areas translates into yield loss.

"If you think about it, even a 1-percent higher yield on a 100,000-cubic-yard job means you'll need an additional 1,000 yards of concrete," explains Steve Friess, general superintendent for Valley View, Ohio-based Anthony Allega Cement Contractor, Inc. With concrete prices at $50, $60 or higher, this translates into a material overrun that will cost the contractor tens of thousands of dollars.

Oftentimes interstate jobs will require 200,000 cubic yards or more amounts of concrete, so yield losses can run into the hundreds of thousands of dollars. This is why concrete contractors should consider the fine-grade trimmer/reclaimer. Allega owns multiple Terex® CMI trimmer/reclaimers, employed to reduce yield loss by preparing the base to plan grade.

The bottom-line value of fine-grade trimmers is their ability to deliver a precise cut with only minute deviations to grade, lowering yield loss. Some of these machines on the market "have the power to excavate up to 8 inches and accurately trim the hardest stabilized base material," Eisenhour says.

Fine-grade trimmers are available in two- and three-track designs, both offering their own set of advantages. Two-track models position the cutter in front of the machine, so they can cut close to obstructions. With counter-rotating tracks, these machines can also turn within their own footprint.

However, the resistance of the base material can force the cutter above the cut line with these machines, creating a seesaw effect. The faster the trimmer goes, the more exaggerated this becomes, resulting in a washboard surface where the voids must be filled with expensive material.

Three-track trimmers concentrate the mass of the machine's weight over the cutter drum, delivering a grade with very few deviations. "Focusing the machine's weight directly into the cutting point also allows for much higher breakout forces," says Jim Johnson, manager of key accounts for Terex Roadbuilding.

The key to meeting specified grade and reducing yield loss with trimmers is to have an accurate and reliable grade control system. When running from a string line, it's imperative the system responds quickly to small changes in the line.

This assumes that the stakes are set properly, which can be an area where issues between the dirt contractor and paving contractor (if different) can arise. "The grading contractor is responsible for the grade, but that contractor looks at it as a game of inches. The paving contractor expects to be within millimeters of spec," Johnson explains. And any deviation can be expensive for the paving contractor.

This could be one reason for the growing popularity of 3-D grade control systems. They allow all contractors to work off the same grade map. An emerging stringless technology available from a number of manufacturers, it provides control of the trimmer's elevation in three dimensions (XYZ) to offer accurate grade and elevation control. Allega has installed the Trimble BladePro 3D on two of its Terex® CMI trimmer/reclaimers, and "the trimmers are capable of keeping concrete yield to within 3 percent and stone yield to within 5 percent," Friess mentions.

Keeping It Smooth

Once the subgrade and subbase are prepped, the name of the game is to lay a smooth pavement, so the roadway lasts longer and requires less maintenance. As some contractors explain it, "we want flat with two T's."

Departments of transportation are building incentives into contracts, giving bonuses to contractors that meet strict ride quality index (RQI) specs. Contractors can earn hundreds of thousands of dollars by simply constructing a high-quality, smooth pavement. "DOTs are discovering that the carrot works better than the stick. Penalties don't work as well as bonuses," Eisenhour observes.

He offers contractors several tips to help achieve spec smoothness. Line pins should be placed at 25-foot centers rather than at 50 feet, and contractors should consider using wire for elevation instead of string. Additionally, line pins should be positioned as close to the paver as possible. "Trucks delivering material to the paver can move the pins," Eisenhour says.

Night headers can be a source of bumps in the pavement that will make the profilograph erratic. The header should be sawed at a 90-degree angle, so the crew can start off fresh the next morning. Contractors should also consider running a profilograph as soon as the concrete sets up, so problems can be corrected immediately rather than when the paver is miles down the road.

Manufacturers are also rising to the smoothness challenge with updated tractor and paving kit designs. Stronger main frame tube sections are being added to the tractor. This rigid frame construction prevents profile deflection, even at extended paving widths, allowing contractors to more easily meet tough Profile Index (PI) and International Roughness Index (IRI) standards.

Longer profile pans offer a smooth pavement without a lot of handwork. "We've increased the pan length on our hydraulic variable width (HVW) pavers to 48 inches and our Series 6 kit lengths to 60 inches," says Tom Devonshire, sales engineer for Terex Roadbuilding concrete mobile equipment.

Increased Mobilization

The buzzword for today's concrete contractor is mobilization. In some states, DOTs estimate a certain cost in bids for paver mobilization, which includes paving width changes of the kit and tractor, installation and removal of the kit, and equipment transport. This has always been somewhat of an Achilles' heel for concrete paving, as it is an unnecessary expense with asphalt pavers.

A few years ago, OEMs responded with HVW-type concrete slipform pavers that offered fast hydraulic width changes, significantly decreasing mobilization expenses and increasing machine versatility. With HVW pavers, contractors are able to pave multiple-width pours in a single day. Complex variable width tasks such as ramps, intersections, widening lanes, and city streets can be accomplished quickly, while still meeting high spec profilograph standards.

When it comes to the mainline, however, paving kits still required many man-hours to change widths. With numerous bolts to remove and adjustments to make, "it takes two to four people two days with impact wrenches and torches to make a width change," Eisenhour explains.

For the northern two-thirds of the country, concrete contractors only pave between 100 and 110 days in a season. A two-day width change is roughly 2 percent of the paving season.

Manufacturers are beginning to borrow some of the technology from the HVW designs for their larger slipform pavers. Today's kits feature more of an enclosed, strong box design with cross bracing to help prevent deflection, thus improving smoothness.

Additionally, the dozens of bolt connections are being replaced by wedge and pin locking systems, which promise fast segment addition/removal. Precision machining of the segment sides and bottoms helps ensure proper alignment of the segments, eliminating the need for shims.

In the past, conventional kits required multiple adjustments that crew members painstakingly made in order to realign a kit after a width change. "At a 24-foot paving width, contractors would make at least 24 adjustments to ensure the profile pan finishing zone was straight," Devonshire comments. "With today's kits, we've eliminated most of the adjustments and reduced the time for paving width changes to about a half-day with two people."

People

Contractors may have the latest technology and the best paving equipment that money can buy, but at the end of the day it comes down to the crews. "This is still a people business, and nothing happens — pavement design, surveys, setting grade stakes and stringline, and operating and maintaining the machine — until people make it happen," Eisenhour comments.

Inexperienced crews will not maximize machine potential nor be able to achieve optimum smoothness. Training the crew on the equipment it operates is essential. So too is having a motivated work crew. "Some concrete paving companies share the smoothness bonus with the crews, and this helps the company to consistently achieve the maximum bonus potential," he adds.

Manufacturers are also making every effort to make their paving equipment as user friendly as possible to give the inexperienced operator a better chance to achieve desired results. But it is the combination of having the right equipment with an experienced and motivated crew that allows concrete paving contractors to efficiently, cost-effectively and profitably get the job done.

 

The Ten Commandments for Smoothness

  1. Sound grade to specification
  2. Monitored supply of concrete
  3. Consistent workability
  4. Controlled density
  5. Sensor common sense
  6. Clean and well-maintained machine
  7. Proper machine attitude
  8. Weight and traction
  9. Method of surface treatment
  10. People

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