Avoids high cost of HMA, achieves quality needed
Brown Brown owners Edgardo and Max Lucas, in conjunction with technical staff from Roadtec, developed cold in-place recycling processes and techniques tailored for tropical climates and roadways with heavy traffic.
Ground asphalt road base or RAP material from the 950 hp Roadtec RX-900e milling machine was conveyed to the Roadtec RT-500 overhead feed conveyor as part of Brown Brown’s cold in-place recycling system.
Brown Brown is a road building contractor located in Paulinia in the state of Sao Paulo in the southeast of Brazil.
A recent two-year project for the company was the rehab of portions of Highway BR-381 from Sao Paulo to Belo Horizonte. Highway BR-381, or Rodovia Fernão Dias, stretches some 360 mi (579 km) through the Brazilian states of São Paulo and southern and eastern regions of Minas Gerais.
The advantage of this style of CIR plant is that material from the pugmill is directly deposited into the paver, improving the pavement surface.
Cold In-Place Recycling
Because hot-mix asphalt (HMA) costs are very expensive in Brazil, Brown Brown owners Edgardo and Max Lucas, in conjunction with technical staff from Roadtec, developed cold in-place recycling (CIR) processes and techniques tailored for tropical climates and roadways with heavy traffic. Over many years of research and application experience, they improved emulsion chemistry, milled cut surface preparation, CIR plant configuration, paving techniques, and pavement compaction to produce a high-quality CIR roadway with good surface finish.
The cold recycler train startup for the BR-381 project was located near the city of Pouso Alegre. The two-lane highway has heavy-truck traffic. Monitored closely by both federal and state highway inspectors, test samples of the product were taken to measure emulsion percentage, water content, aggregate size, and other variables. Brown Brown also has its own mobile test lab to monitor quality control.
The company had an experienced crew to work the CIR train. Traffic was diverted to one lane and the speed was posted at 35 mph (56.33 km/h). The crew worked on both sides of the equipment train, so there was always the safety concern with traffic.
The roadwork train consisted of a water truck in front, emulsion tanker truck, Roadtec RX-900e cold planer, Roadtec RT-500 mobile recycle trailer, a paver, a steel roller compactor, and a rubber tire compactor.
Steady Flow of Rap
The pairing of the two Roadtec pieces created the CIR process, which was essential to the Highway BR-381 project. Max Lucas pointed out that the Roadtec RT-500 functioned like a material transfer vehicle, providing a steady flow of reclaimed asphalt pavement (RAP) material to the paver allowing for continuous, steady production runs, which resulted in smooth pavement. "There were no ripples, rough spots, or dips in the finished road," Max added.
The pairing of the two Roadtec pieces created the cold in-place recycling process, which was essential to the Highway BR-381 project.
The emulsion system in the Brown Brown CIR system worked as follows: Ground asphalt road base or RAP material from the 950 hp RX-900e milling machine was conveyed to the RT-500 overhead feed conveyor. The RAP material was screened and crushed to 1.25 in (3.17 cm) or smaller material. All sized RAP material product was discharged from the JCI 5142LP screen onto an under screen conveyor. A precision belt scale built into the under screen conveyor measured the mass rate of wet RAP material being conveyed into the pugmill. The computerized rate control system (CRC) received the instantaneous scale RAP weight data and automatically maintained the proper percentage amounts of emulsion and water added to the RAP material. A pugmill mixed the RAP material and emulsion to generate cold asphalt, which was loaded into a paver from the pugmill by an end delivery conveyor. The CRC controlled flow of emulsion into the pugmill by regulating the emulsion pump speed and the number of spray nozzles active in the emulsion spray bar located in the pugmill.
Cement was layed in front of the cold planer using a skid-mounted hopper with adjustable weir to control the amount of cement. The contractor used four 110 lb (50 kg) sacks per 21.87 yd (20 m) of roadway. Max Lucas commented that lime is better overall for the roadway, but cement was used instead because it would react quicker. Due to the tropical climate and heavy rains, both the composition of the emulsion and use of cement were designed to accelerate the asphalt break and hardness.
The emulsion used was an engineered emulsion that was polymer-modified and is designed to break just after the paver. The emulsion has a density of 8.33 lb/gal (0.998 kg/l), so it is almost the same as water. When the emulsion sets and dries, it becomes sticky and stringy when pulled. The long strings are caused by the polymer additives.
Meeting the Milling Challenge
BR-381 was constructed with fine grain hard granite aggregate, which was a challenge to mill. The contractor used Kennametal teeth, which were replaced every two to three days of operation. The mill typically cut 4.33 in (11 cm) deep and averaged 30 fpm (9.14 m\min).
The condition of the roadway was so cracked that several crew members cleaned the sides of the cut with shovels and brooms. If the side of the cut cracked from the mill side guides, then the crew would break and remove the cracked material. As the crew working on the passenger side of the road cleaned the area, the loose material was deposited on the side of the road. The crew on the driver’s side deposited the loose material in piles located in the center of the cut.
A mixture of emulsion and water was poured on the sides and top of the milled road edges to bond and seal the cold asphalt.
One crew member operated the Roadtec RT-500. This worker would adjust the emulsion and water additive percentages for the proper mixture based on the current roadway moisture content, evaporation rate, and weather conditions. They also adjusted the end delivery conveyor position. Typically more cold asphalt is generated than required for the roadway, so at times the end delivery conveyor was pivoted to discharge on the side of the road or into the loader bucket.
The center augers on the paver were switched to convey inward to prevent centerline separation leaving no visible signs of centerline separation.
The emulsion percentage was adjusted from 2.8 percent to 3.5 percent and the water was adjusted from 1.8 percent to 3.5 percent during operation. Edgardo Lucas commented that during hot days the water requirements could go as high as 4.5 percent.
Workers stationed between the RT-500 and the paver scraped the cut surface using large flat-plate hoes and shovels to remove the loose material. The piles from the driver’s side crew near the RX-900 milling machine were also removed at this point.
Brown Brown modified the paver hopper to add capacity and installed sloped diverters in the hopper corners to help prevent material buildup. The paver hopper was kept full of material to add weight to the paver to improve the stability of the screed. The screed was set with a slight incline on the leading edge to push down on the cold asphalt generating a smooth surface. The center augers on the paver were switched to convey inward to prevent centerline separation. This finessing worked well with no visible signs of centerline separation.
The steel roller compactor followed closely behind the paver due to the fast breaking emulsion. A rubber wheel compactor was the final compaction. Each compactor made six passes without using vibration.
Roadway Quality Achieved
As the Lucases look back on the finished roadway, they credit the CIR system as being instrumental in the quality achieved. "The advantage of this style of CIR plant is that material from the pugmill is directly deposited into the paver—much like a shuttle buggy—which appears to help generate an improved surface finish on the new pavement," concluded Mike Fischer, Roadtec field service technician.BACK TO ISSUE