Use cold-in-place recycling to help repave a busy highway in Brazil
The costs associated with hot mix asphalt are very expensive in Brazil, so Sao Paulo road building contractor Brown Brown used cold in-place recycling (CIR) processes and techniques tailored for tropical climates during the two-year rehab of portions of Highway BR-381 from Sao Paulo to Belo Horizonte in Brazil.
In conjunction with technical staff from Roadtec, Brown Brown owners Edgardo and Max Lucas 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 in tropcial climates and for roadways with heavy traffic.
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 was monitored by both federal and state highway inspectors who closely monitored the process and took test samples of the product to measure emulsion percentage, water content, aggregate size and other variables. Brown Brown had 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 crew worked on both sides of the equipment train so there was always the safety concern.
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 Caterpillar steel roller compactor and a Caterpillar rubber tire compactor.
The Roadtec RT-500 functioned like a material transfer vehicle by providing a steady flow of RAP material to the paver allowing for continuous, steady production runs, which resulted in smooth pavement, Max Lucas pointed out. “There were no ripples, rough spots or dips in the finished road,” he said.
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 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 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) 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 Kg sacks per 20 meters of roadway. Cement was used instead of lime because it reacts quicker, Lucas said. Due to the tropical climate and heavy rains both the composition of the emulsion and use of cement are designed to accelerate the aspalt break and hardness.
The emulsion used was an engineered emulsion that was polymer modified and designed to break just after the paver. The emulsion has a density of 0.998 Kg/L, 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 was 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 would adjust the emulsion and water additive percentages for the proper mixture based on the current roadway moisture content, evaporation rate and weather conditions. The worker 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 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. During hot days the water requirements could go as high as 4.5 percent, Edgardo Lucas said.
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 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.
“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,” said Mike Fischer, Roadtec field service technician.