Cold case: 360 miles of recycling

Brown Brown, a road building contractor, located in Paulinia, in southeast Brazil, took on a two-year project to rehab portions of highway BR-381 from São Paulo to Belo Horizonte. Highway BR-381 or Rodovia Fernão Dias, as it is called, stretches some 360 miles through the Brazilian states of São Paulo and southern and eastern regions of Minas Gerais.

Because hot-mix asphalt (HMA) costs are expensive in Brazil, Brown Brown owners Edgardo and Max Lucas, in conjunction with technical staff from Roadtec, Chattanooga, Tennessee, developed cold in-place recycling (CIR) processes and techniques that are tailored for the tropical climates and for roadways with heavy traffic. Over many years of research and application experience they have improved emulsion chemistry, milled cut surface preparation, CIR plant configuration, paving techniques and pavement compaction to produce a high-quality CIR roadway with an excellent surface finish.

The cold recycler train startup for the BR-381 project was located near the city of Pouso Alegre, Brazil. The two-lane highway has heavy truck traffic. Federal and state highway inspectors closely monitored the work and the process and took test samples of the product to measure emulsion percentage, water content, aggregate size and other variables. Brown Brown has its own mobile test lab to test its own samples and monitor quality control.
 

The process

The company used an experienced crew to work the CIR train. Safety was an ongoing concern as traffic was diverted to one lane and the speed was posted at 35 mph while the crew worked on both sides of the equipment train.

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 rubber tire compactor all from Peoria, Illinois-based Caterpillar.

The pairing of the two Roadtec pieces created the CIR process, which was essential to the highway BR-381 project. According to Max Lucas, the Roadtec RT-500 functioned like a material transfer vehicle by providing a steady flow of recycled asphalt pavement (RAP) material to the paver, allowing for continuous, steady production runs, which resulted in smooth pavement.

The emulsion system in the Brown Brown CIR system worked as follows: Ground asphalt road base or RAP material from the 950-horsepower RX-900e milling machine is conveyed to the RT-500 overhead feed conveyor. The RAP material is screened and crushed to 1¼-inch or smaller material. All sized RAP material product is discharged from a JCI 5142 LP screen onto an under-screen conveyor. A precision belt scale built into the under-screen conveyor measures 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 maintains 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 is 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 number of spray nozzles that were active in the emulsion spray bar located in the pugmill.

Cement was laid 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-pound (50-kilogram) sacks per 22 yards (20 meters) of roadway. Max Lucas says lime is better overall for the roadway, but cement was used instead because it reacts more quickly. Due to the tropical climate and heavy rains, both the composition of the emulsion and use of cement are 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 had a density of 2.2 pounds per liter, so it was almost the same as water. When the emulsion set and dried it became very sticky and stringy when pulled. The long strings were caused by the polymer additives.

BR-381 is constructed with fine grain hard granite aggregate, which is a challenge to mills. The contractor used Kennametal teeth, which were replaced every two to three days of operation. The mill typically cut 4.33-inches (11-centimeters) deep and averaged 30 feet per minute (9 meters per minute).
 

Milling challenges

The condition of the roadway was so cracked that in some spots it proved to be a challenge to the mill. 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 is poured on the sides and top of the milled road edges to bond and seal the cold asphalt.

One crew member was responsible for operation of the Roadtec RT-500. This worker adjusted 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 was 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 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 says during hot days, the water requirements can go as high as 4.5 percent.

Workers stationed between the RT-500 and the paver scrape 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 also are removed at this point.

Brown Brown had modified the paver hopper to add capacity and installed sloped diverters in the hopper corners to help prevent material build-up. 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 center-line separation.

The steel roller compactor followed closely behind the paver due to the fast-breaking emulsion. A rubber wheel compactor served as the final compaction. Each compactor made six passes without using vibration.

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,” concludes Mike Fischer, a Roadtec?field service technician.

Jeff Winke is a business and construction writer based in Milwaukee.