The heat was on – both literally and figuratively – the Bowes Construction crew as they worked to widen Highway 45 in South Dakota last August. Afternoon high temperatures routinely pushed 100° F, and they had just three weeks to reclaim nearly 32 km (20 miles) of road that had a 229 mm (9″) asphalt layer. Time is so tight, and productivity so crucial, that the firm runs three Cat RM-350B Reclaimers on the job.
“We have a simple philosophy: Put the most productive equipment to work,” says Jason Bowes, co-owner of the firm.
There are two components to Bowes’ work on the 30 km (18.6 mile) stretch of Highway 45. The first component, the widening of the road from 9 to 12 m (30 to 39′), began last spring with the laying of a dirt subgrade for the new shoulders.
The second part of the project is preparing Highway 45 for a new asphalt surface. That work includes pulverizing existing asphalt with three RM-350Bs. South Dakota Department of Transportation (SDDOT) specs call for 95 percent of the pulverized material to pass a sieve size of 25 mm (1″) and 100 per cent of the material to pass a sieve size of 38 mm (1.5″). The pulverized material is used as subbase. It is compacted and a portion is bladed onto the expanded shoulder subgrade. New aggregate base is added, bladed full width and compacted. Specs call for a density of 95 per cent before the placement of the asphalt. Another firm, which hired Bowes for the reclamation work, will handle the paving of the newly widened road.
Bowes Construction specialized in reclamation. “By concentrating in that specific area, we’ve been able to learn some efficiencies,” Bowes says. It was that experience that led Jason Bowes to use three Cat RM-350Bs simultaneously on the Highway 45 project.
“To complete this project on time, we need to finish a mile (1,6 km) of road per day,” Bowes says. “That includes everything: reclaiming, blading, compacting, adding aggregate. Keeping that pace for reclaiming is the most difficult part of the equation. Our productivity really depends on how fast we can pulverize – keeping in mind that we have pulverization specs to meet.”
Maintaining the 1,6 km (1 mile) per day pace requires Bowes to pulverize about 13 712 m2 (16,400 yd2 per day. “We own two RM-350Bs, but realized we needed help to keep that kind of pace,” Bowes says. “We decided to rent another RM-350B because of its productivity and our operators’ familiarity with the machine.”
The operators encountered some challenges during the pulverization process. “We had the drum sunk all the way down to 15″ (381 mm) for miles upon miles, and it did the job,” says operator Brett Westley. “Even at that depth, we move along at 12-15′ (3,7-4,6 m) per minute.”
Often the drum need go only about 305 mm (12″) deep. “The asphalt typically is 9″ (229 mm) deep, and we go a few inches deeper to keep the tips cooler,” says operator Mike Erickson. “At that depth, we’re able to cover about 20′ (6,1 m) per minute.”
But rotor depth isn’t the only factor that affects production. “We routinely encounter quartzite,” says Rodney Anderson, another reclaimer operator. “That stuff is as hard as it comes, but we’re able to get through it. That’s when you’re grateful for the three speeds.”
Rotor speeds on the RM-350B can be set at 115, 160 and 215 rpm. “When we hit the harder material, we grind at 115,” says Westley. “We haven’t come across anything yet that we can’t grind at 115. But if we get in some looser material, we can change the setting and move right along. We usually pulverize at 160. It’s fast enough to be productive, but also ensures we reach our pulveration goals. The third setting (215 rpm) is mostly for mixing.”
The RM-350B also features automatic load control, which adjusts propel speed so that the engine speed is maintained at less than 1,800 rpm. The machine always works at peak efficiency for maximum output.
of Highway 45 in three weeks.
Bowes developed a system to maximize the use of the three RM-350Bs. Most often, two reclaimers work together and pulverize one half of the road. (Traffic continues to use the other half.) The third reclaimer, meanwhile, starts pulverizing 0,8 km (0.5 miles) ahead. The two RM-350Bs pulverize until they reach the starting point of the third. One of the two continues to pulverize, completing the work started by the lone reclaimer. The second RM-350B stops pulverizing and travels down the road to catch up with the lead reclaimer. Those two then become a team.
“It allows us to keep the road open, per SDDOT specs,” Bowes said. “It also enables us to keep the rollers and the blade busy and complete the road in segments, which helps alleviate traffic concerns.”
In addition, the system allows Bowes to customize the rotors used on their reclaimers.
“Two of the three machines have reclamation drums,” Bowes says. “Those drums have 188 carbide teeth and work best on asphalt. The third reclaimer has a combi drum (with 108 teeth). We find that it’s a good strategy to have a blend. The combi still grinds well on the asphalt but works ideally on the shoulder and first part of the existing road, where only portions of the surface require pulverization. Both the reclamation and combi rotors are 96″ (2438 mm), which means we get consistent widths no matter which machines are working together.”
The Bowes crews know that good rotor maintenance is key to high production. Operators check the rotor teeth about every hour. “We usually replace 20-30 tips,” Bowes says. “It takes less than a minute per tip.” When the rotor tools are in good condition, pulverization is faster.
The Cat machines also add productivity in subtle ways, Bowes says. “Our staggering of the machines means that the reclaimer has to be able to move down the road when it’s not pulverizing,” Bowes says of the reclaimer, capable of traveling at speeds of 16,8 kmph (10.5 mph). “The sooner that machine starts grinding at its new location, the more productive it’s going to be.”
Blading And Compaction
Rolling behind the reclaimers is a Cat CP-563C Soil Compactor, which makes two passes. “The padded compactor packs the material right behind the reclaimer so you get some stabilization down deep,” Bowes says. The chevron pattern of the pads concentrates full compactive effort on only two and a half pads at a time for maximum compaction. In addition, the pad height of 127 mm (5″) helps get compaction deep in the lift, which is crucial to Bowes. “We need the roller to bridge the old base with the reprocessed materials,” he says. “We don’t do a compaction reading after the padded roller passes, but our experience and earlier research show that achieving that initial depth of compaction helps us meet our final density target.”
In the next step, Bowes scarfies the surface of the reclaimed subbase, then adds water, blades material out to the edges and creates the required slope. Crushed stone base is transported from a portable crushing plant about 17,7 km (11 miles) from Highway 45 and spread. Pneumatic rollers then make two passes to get density of 95 per cent.
Reclaiming the full asphalt layer in place and converting that layer into subbase adds substantially to the engineering value of the structure. With a strong subbase under the base, less virgin material is required. The savings in material, crushing and transport are significant and make the reclamation process attractive to public works officials. Usually, more miles of road can be improved for the same budget during the reclamation process compared to using total reconstruction for highway widening or improvement.
The day draws to an end. The reclaimers have pulverized and mixed more than a mile of asphalt. The pulverization specs have been met, and the padded roller has laid the foundation for compaction densities.
“It’s an incredible pace, no doubt about it,” says Bowes. “But it can be done. We prove that every day.”
Paving News, The Roadbuiling and Maintenance Magazine from Catepillar© Paving Products, Inc., Volume 10, Issue1