Project Profile: Brazilian Contractor Uses Cold In-Place Recycling in Major Highway Rehab
Brown Brown, a road building contractor, is located in Paulinia in the state of São Paulo in the southeast of Brazil.
A recent two-year project for the company was the rehab of 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 very expensive in Brazil, Brown Brown owners Edgardo and Max Lucas, in conjunction with technical staff from Roadtec, have 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 good surface finish.
The cold recycler train start-up for the BR-381 project was located near the city of Pouso Alegre. The two-lane highway has heavy truck traffic. The work is monitored by both federal and state highway inspectors who closely monitor the process and take 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 company had an experienced crew to work the CIR train. Traffic was diverted to one lane and the speed was posted at 35 miles per hour. 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 Caterpillar paver, a Cat steel roller compactor, and a Cat rubber tire compactor.
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 by 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 adds.
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 1.25-inch or smaller material. All sized RAP material product is discharged from the JCI 5142LP screen onto a underscreen conveyor. A precision belt scale built into the underscreen conveyor measures the mass rate of wet RAP material being conveyed into the pugmill. The computerized rate control system (CRC) receives the instantaneous scale RAP weight data and automatically maintains the proper percentage amounts of emulsion and water added to the RAP material. A pugmill mixes 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 controls flow of emulsion into the pugmill by regulating the emulsion pump speed and the number of spray nozzles that are active in the emulsion spray bar located in the pugmill.
Cement is 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 50-kilogram sacks per 20 meters of roadway. Max Lucas commented that lime is better overall for the roadway, but cement was used instead because it reacts quicker. 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 engineered, polymer-modified, and designed to break just after the paver. The emulsion has a density of 0.998 kilograms per liter, so it is almost the same as water. When the emulsion sets and dries, it becomes very sticky and stringy when pulled. The long strings are caused by the polymer additives.
BR-381 is constructed with fine grain hard granite aggregate, which is 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 inches deep and averaged 30 feet per minute.
The condition of the roadway was so cracked that it was in some spots a challenge to mill. 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 is poured on the sides and top of the milled road edges to bond and seal the cold asphalt. One crew member is responsible for operation of 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 adjust the end delivery conveyor position. Typically, more cold asphalt is generated then required for the roadway, so at times the end delivery conveyor is pivoted to discharge on the side of the road or into the loader bucket.
The emulsion percentage was adjusted from 2.8% to 3.5% and the water was adjusted from 1.8% to 3.5% during operation. Edgardo Lucas commented that during hot days the water requirements can go as high as 4.5%.
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 are also 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 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.
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, Roadtec field service technician.
