Before You Fix It, Break It
Multiple-head rubblization, combined with asphalt overlay fixes failing pcc pavement
by Jill Dunlap
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Last fall, the Indiana Department of Transportation (INDOT) found the pcc pavement on State Route 37 (S.R. 37) in dire need of repair. The 7-mile (11.3-km) stretch of four-lane divided highway had transverse cracking every 3 to 4 feet (0.9 to 1.2 m). The centerline joint was open and faulted, and the transverse construction joints were also faulted. In short, the continuously reinforced, 7-inch (175-mm) concrete had simply worn out. INDOT specified the job as a rubblization and overlay job. Rieth-Riley Construction Co. Inc., Goshen Ind., won the contract, and subcontracted Antigo Construction, Antigo, Wis., to perform the rubblization.
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Test holes, like the one above, were dug to check particle size and to determine whether or not the rebar was debonded from the concrete.
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Antigo Construction performs multiple-head rubblization. George Shinners, president of Antigo Construction, explains the process. "The multiple-head breaker (MHB), Badger Breaker, uses a combination of drop hammers, which can be controlled over a wide range of breaking energy depending on impact spacing and drop heights," says Shinners.
Shinners and his company developed the MHB with Badger State Highway Equipment Inc., Antigo, Wis., in 1995, with the goal of creating a machine that could provide full-lane width breaking and eliminate travel on rubblized pavement.
Before the Antigo crew could bring out the Badger Breaker on S.R. 37, traffic had to be rerouted. "We constructed new turn lanes in the northbound lanes, to accommodate the two-way traffic," says Greg Ellis, project engineer for INDOT. "We switched the southbound traffic into the northbound lane. We had one lane in each direction on one side."
Besides traffic, Rieth-Riley had subsurface drainage considerations to tackle before rubblization could begin. "We came in and put all our underdrain in first," says Ellis. "There was existing 6-inch (150-mm) tile, and we put in new 4-inch (100-mm) tile as well."
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Rubblization begins |
The Antigo Construction crew started rubblizing with two MHBs Sept. 26. The MHBs rubblize the pavement from top to bottom, and, at times, leave 3-to 4-inch (75-to 100-mm) particles at the surface. Antigo followed the MHBs with a vibratory steel drum compactor from Ingersoll-Rand, Shippensburg, Pa., equipped with a Z-grid attachment. "The Z-grid breaks the particles down to the 1-to 2-inch (25-to 50-mm) required size," says Shinners. "At the same time, it levels and compacts the loose material, preparing it for paving."
Although the drop hammers provide a powerful impact, Shinners says it is not powerful enough to damage the underdrains. "The MHB stays on the unbroken pavement for the most part, thus avoiding the lower level drainage system," says Shinners.
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Antigo Construction, Antigo, Wis., uses multiple head breakers from Badger State Highway Equipment Inc., Antigo, Wis., on all its projects.
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Antigo completed the southbound lanes, totaling approximately 849,746 square feet (78,944 sq m), in five working days, which was a faster timeline than had been expected. Jeff Peters, one of Rieth-Riley's paving superintendents on the project, was impressed with Antigo's ability to get things done ahead of schedule. "One day they told us how much they could produce per day," says Peters. "They maxed that and did even better.
According to Shinners, his crews average one lane mile (1.6 km), or 7,000 square yards (5,850 sq m), per MHB per 10-hour shift. He adds that when rubblization is going unusually well, they've been known to complete 1.5 lane miles (2.4 km) per shift per MHB. "We do this day after day, week after week due to the reliability of the MHBs and the competency of our operators," he says.
The concrete steel reinforcement was left in place on this project. "We just removed any steel that protruded through, stuck out of the top," says Ellis. "We dug test holes and trenches across the pavement to make sure particle distribution was right."
"Shinners explains the reason for this: "Removing the steel would disturb the interlock between the particles, destroy the smooth pro file of the rubblized pavement and cost more than the salvage value of the steel," he says. "As long as the steel is loose and buried, it is not a factor."
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Timing is everything |
Antigo and Rieth-Riley had to work closely together to coordinate the rubblizing process with the paving. INDOT specs require that rubblized pavement be covered within 48 hours after being broken. For that reason, Ellis says that Antigo was careful not to run too far ahead of the paver. The MHB Badger Breaker performed full-width rubblization, allowing Rieth-Riley crews to pave up to the point where rubblization stopped that same day, if needed.
"The purpose of the 48-hour spec, according to Ellis, is to keep from leaving a rubblized pavement open to the threat of excessive rain. "That would be harmful to the subgrade," he says. "They want it sealed back off as quickly as possible.
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The Z-grid roller from Ingersoll-Rand, Shippensburg, Pa., broke the rubblized pieces down to the smaller, required size, and leveled and compacted the loose material.
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Shinners adds that it is becoming quite common for project owners to require crews to rubblize only what can be paved that same day.
"After the rubblization, but prior to the paving, Rieth-Riley primed the rubblized sections with AEP Prime, from Ashland Materials, Dublin, Ohio. "It's a state specification," says Peters. "that prime must be applied prior to paving, and then the rubblization has to be severed within 48 hours after that. It wasn't too difficult. It lust took a little bit of special planning.
Rieth-Riley paved the southbound lanes, using a paver from Blaw-Knox, Mattoon, ILL., a transfer machine from Roadtec Inc., Chattanooga, Tenn., and Ingersoll-Rand DD130 and DD90 rollers to lay a 4-inch (100-mm) initial lift, and a second 4-inch(100-mm)lift. Then they laid a 2.75-inch (75 mm) intermediate lift, and finally a 1.25-inch (32-mm) surface course. Quality control / quality assurance (QC/QA) methods were used to prepare all the mixes. Rieth-Riley set up a twin silo, portable batch plant from CMI Corp., Oklahoma City, on the site.
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Second stage similar to the first |
Crews switched traffic flow from the northbound to the southbound lanes, and Antigo returned Nov. 4 to rubblize the remaining two lanes. In a little more than four working days, Antigo rubblized 851,974 square feet (79,151 sq m). The two-man crew added a third man and MHB for two days during the second stretch.
Both Rieth-Riley and Antigo crews gave this project their all. Rieth-Riley used a nighttime mainline crew, a daytime mainline crew and a miscellaneous paving crew for doing turn lanes and shoulders. They laid approximately 240,000 tons (217,680 Mg) of asphalt between September and the middle of December. "That's the phenomenal part of it," says Peters. "We ran seven days a week, 24 hours a day."
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Rieth-Riley crews paved seven days a week, 24 hours a day, on the State Route 37 project.
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Antigo met all the INDOT specs for rubblized concrete particle size, according to Ellis. He says INDOT requires a maximum particle size of 6 inches (150 mm). Shinners says that the end product of rubblization depends on several factors:
· strength of the subgrade material
· the presence or absence of granular or crushed aggregate base material
· the condition of the pcc pavement
· effectiveness of the pavement drainage system, both before and after rubblization
· traffic loading during construction
· type and amount of hot mix asphalt (HMA) applied after rubblization
· the presence or absence of reinforcing steel
· type of rubblization equipment used
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Crews adjust for road surface oddities |
Shinners explains that Antigo often has to adjust for less than optimal road conditions "Rubblization is an extreme rehabilitation process used on seriously deteriorated pavements," says Shinners "The more optimum the above factors are, the smaller we can make the rubblization particles. As we begin to lose structural strength or increase loading, we have found that the maximum particle size must be increased accordingly. Shinners also says that the MHB is designed to vary particle size easily by adjusting the spacing between hammer blows, as well as the drop height of the individually controlled drop hammers.
There were a couple of instances during the rubblization process where crews needed to vary particle size, according to Ellis. "We encountered, I'm going to say, two or three areas where there seemed to be a softer subgrade," says Ellis. "We increased the spacing between hammer blows and reduced the height of the drop on the hammers to increase the particle size and kind of bridge the soft areas to try and get a more stable base."
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Between September and the middle of December, crews from Rieth-Riley Construction Co. Inc., Goshen, Ind., laid approximately 240,000 tons (217,680 Mg) of asphalt, according to Jeff Peters, one of the company's paving superintendents on the job.
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Since the process is fairly new, the long-term results of multiple-head rubblization are unknown, but Ellis is optimistic and sees the logic behind the process. He believes multiple-head Rubblization reduces the risk of reflective cracking that can occur when large slabs of pcc are overlaid with asphalt.
"When you've got larger segments of the concrete, they tend to wobble on grade," says Ellis. "After you rubblize the concrete, it's open-graded. That helps out with any moisture problems you might have with carrying the moisture out to the subdrains and getting rid of it." Ellis adds that the HMA bonds more easily to the rubblized surface than the slick finish on concrete that is left in place.
Shinners explains that although simple overlay projects improve the ride quality of a road, the underlying cracks and joints will eventually, depending on overlay thickness, reflect through the HMA. "This is most often caused by vertical and/or horizontal slab action," says Shinners. "Rubblization breaks the slab into small pieces, less than 12-inches (300 mm), which eliminates concentrated slab movement. It also pulverizes the surface, which eliminates the sharp edges of joints and cracks."
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Teamwork produces results |
The Rubblization was completed ahead of schedule, and all parties involved with the S.R. 37 project seem pleased with the results. Ellis believes that Antigo's experience helped everyone face the challenges that the job presented. "They were real helpful as far as the experience they've got, problems they'd had on other jobs, and sharing things they've done in the past that seemed to work."
Placement of the surface course on the northbound lanes is the last thing to do in order for the project to be complete. Rieth-Riley crews are scheduled to finish the asphalt work May 2001.
Source: The asphalt contractor, PAVING AMERICA April, 2001
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