Cold-in-Place Asphalt Recycling: Engineering Tropical Highway Rehabilitation on Brazil’s BR-381

When highway agencies face tight maintenance budgets and aging pavement, Highway Superelevation strategies matter, but the rehabilitation method itself determines long-term performance. Cold-in-place recycling (CIR) has emerged as a powerful technique for major rehabilitation, and few projects demonstrate it better than the rehabilitation of Brazil’s BR-381 highway. Running from Sao Paulo to Belo Horizonte, this critical two-lane corridor carries heavy truck traffic through tropical climate conditions. Brazilian contractor Brown Brown tackled this challenge using a full CIR train approach, proving that engineered emulsion chemistry, precision milling, and meticulous compaction can produce high-quality recycled pavement capable of withstanding heavy loads and tropical weather.

Understanding Cold-in-Place Recycling Technology

Cold-in-place recycling is a pavement rehabilitation process that reuses the existing asphalt pavement material without applying heat. Unlike traditional hot mix asphalt rehabilitation, which requires transporting old material to a plant, heating it, and returning it to the site, CIR processes the material directly on the roadway. This eliminates multiple hauling trips and significantly reduces energy consumption and emissions.

The CIR Equipment Train

The BR-381 project deployed a coordinated equipment train that demonstrates the full CIR workflow. Understanding how these machines interact is essential for construction professionals evaluating this method for their own projects.

1. Water truck positioned at the front for dust control and moisture management
2. Emulsion tanker truck supplying the binding agent that replaces virgin asphalt binder
3. Roadtec RX-900e cold planer milling the existing pavement to a controlled depth
4. Roadtec RT-500 mobile recycle trailer functioning as a material transfer and processing unit
5. Caterpillar paver with modified hopper for increased capacity and improved material flow
6. Steel roller compactor for initial breakdown compaction
7. Rubber tire compactor for final densification and surface sealing

This train configuration allowed continuous production runs, which Highway Alignment projects benefit from through consistent pavement quality. The RT-500 unit functioned similarly to a material transfer vehicle by providing a steady flow of reclaimed asphalt pavement (RAP) material to the paver. This continuous feed eliminated the start-stop cycles that cause ripples, rough spots, and dips in finished pavement surfaces.

Material Processing Inside the CIR Train

The core of the CIR process occurs within the mobile recycle trailer. Material flow follows a precise sequence that ensures consistent output quality:

• Ground asphalt base material from the cold planer is conveyed via an overhead feed conveyor to the RT-500
• RAP material passes through a screening and crushing stage, reducing particles to 1.25 inches or smaller
• Sized material discharges from the JCI 5142LP screen onto an under-screen conveyor
• A precision belt scale measures the mass flow rate of wet RAP entering the pugmill
• A computerized rate control system uses scale data to automatically adjust emulsion and water addition percentages
• The pugmill blends RAP, emulsion, and water to produce uniform cold asphalt, discharged via an end delivery conveyor into the paver

The computerized rate control system receives instantaneous weight data from the belt scale and automatically maintains the correct proportion of emulsion and water. This closed-loop control eliminates guesswork and ensures consistent material properties throughout the production run.

Tropical Climate Emulsion Engineering

One of the most instructive aspects of the BR-381 project was its adaptation of CIR technology for tropical conditions. Standard CIR emulsion formulations developed in temperate climates do not perform adequately under the intense sun, high ambient temperatures, and heavy rainfall patterns found in Brazil. The Brown Brown team, working with Roadtec technical staff, engineered an emulsion system specifically for these conditions.

Emulsion Composition and Behavior

The emulsion used on BR-381 was polymer modified and formulated to break immediately after the paver passed. Breaking refers to the point at which the emulsion separates into asphalt binder and water, allowing the binder to coat the aggregate and develop strength. The emulsion density was 0.998 Kg per liter, nearly identical to water, simplifying calibration.

When properly set and dried, this emulsion became highly sticky and stringy when pulled. The elongated strings are a visible indicator of polymer modification, which improves the elasticity and temperature susceptibility of the final pavement. For Highway Sound Barrier Masonry Walls and other roadside infrastructure that share the corridor with recycled pavement, the improved binder properties translate to longer service life and reduced maintenance demands.

Cement as an Accelerating Additive

Rather than using lime, which is more common in North American CIR applications, the contractor specified cement as the accelerating additive. Cement reacts more quickly than lime, which is beneficial in tropical climates where rapid strength gain helps the pavement resist early damage from rain or traffic. The application method was straightforward:

• Cement was spread in front of the cold planer using a skid-mounted hopper with an adjustable weir
• The contractor used four 50 kg sacks per 20 meters of roadway
• The cold planer incorporated the dry cement into the milled material, where it mixed with emulsion and water in the pugmill
• This approach accelerated asphalt break and hardness development to match the tropical curing schedule

Dynamic Emulsion Adjustment During Production

CIR emulsion and water percentages cannot remain static throughout a production shift. Environmental conditions change constantly, and the operator must adjust accordingly. The project demonstrated these real-time adjustment ranges:

The operator stationed at the RT-500 was responsible for monitoring roadway moisture content, evaporation rate, and weather conditions to fine-tune these percentages. On hot days, water requirements could rise to 4.5 percent to compensate for rapid evaporation before compaction could be completed.

Milling, Surface Preparation, and Quality Control

The BR-381 pavement was constructed with fine-grain hard granite aggregate, which presents significant challenges for milling operations. The contractor used Kennametal milling teeth, replacing them every two to three days of continuous operation. The RX-900e cold planer typically cut to a depth of 4.33 inches and averaged 30 feet per minute, though the heavily cracked condition of the existing pavement occasionally made consistent milling difficult.

Surface Cleaning and Edge Preparation

Surface preparation between the milling and paving stages was more labor-intensive than typical CIR projects because of the deteriorated condition of the original pavement. Several crew members were assigned to cleaning the sides of the milled cut using shovels and brooms. When the mill’s side guides caused cracking along the cut edges, the crew broke away and removed the loose material.

Workers on the passenger side of the road deposited loose material on the shoulder. Workers on the driver’s side piled material in the center of the milled cut. A mixture of emulsion and water was poured along the sides and top of the milled road edges to bond and seal the cold asphalt at the interface. This edge sealing step is critical for preventing water infiltration and edge deterioration in the finished pavement.

Additional workers stationed between the RT-500 and the paver scraped the cut surface using large flat-plate hoes and shovels to remove remaining loose material. The piles from the driver’s side crew near the milling machine were also removed at this intermediate stage. For Curves Highway Alignment sections, this meticulous cleaning becomes even more important, as improper preparation on curves can lead to differential compaction and premature failure.

Quality Assurance and Testing

The BR-381 project was subject to rigorous oversight from both federal and state highway inspectors who took test samples to measure emulsion percentage, water content, aggregate size, and other variables. Brown Brown supplemented this with its own mobile test laboratory, allowing the crew to monitor quality control in real time and make adjustments before problems compounded.

This dual-layer quality assurance system is a model for CIR projects. The contractor’s mobile lab provided immediate feedback for process adjustments, while agency inspectors verified that the finished product met specification requirements. Having an experienced crew who understood the CIR process and could respond to test results quickly was identified as a key success factor.

Paving, Compaction, and Surface Finish Optimization

The final quality of any CIR project depends on the paving and compaction phases. The BR-381 project featured several equipment modifications and procedural innovations that contributed to the smooth, durable surface finish achieved on the highway.

Paver Modifications for CIR Material

Brown Brown modified the paver hopper to increase its capacity. The larger hopper reduced the frequency of material transfer cycles, allowing for longer continuous paving runs. Keeping the hopper full added weight to the paver, improving screed stability and reducing the tendency for the machine to ride up or settle. Sloped diverters in the hopper corners prevented cold asphalt from building up in dead zones.

The paver screed was set with a slight incline on the leading edge, which pushed down on the cold asphalt and generated a smooth surface. Center augers on the paver were switched to convey inward rather than outward, preventing centerline separation. The result was a pavement surface with no visible signs of centerline separation, ripples, or dips.

Compaction Protocol for Rapid-Break Emulsion

Because the emulsion was designed to break quickly after the paver passed, the compaction train had to follow immediately.

1. The steel roller compactor followed closely behind the paver for initial breakdown compaction while the cold asphalt was still workable
2. The rubber tire compactor provided the final rolling pass, sealing the surface and achieving target density
3. Each compactor made six passes over the entire pavement width
4. No vibratory compaction was used, relying instead on static weight and kneading action

The absence of vibratory compaction is notable. In CIR applications, vibration can cause the emulsion and fine aggregate to separate, leading to a rich binder layer at the surface and a lean mix below. The static roller and pneumatic tire roller combination provides adequate densification without this segregation risk.

Key Advantages of the Direct-Feed Configuration

An important design feature of the BR-381 CIR train was that material from the pugmill was directly deposited into the paver, similar to how a material transfer vehicle feeds a paver in hot mix operations. This configuration, noted by Roadtec field service technician Mike Fischer, generates an improved surface finish on the new pavement compared to systems that discharge into a window for the paver to pick up.

The direct-feed approach provides several benefits: it maintains a consistent material temperature (important even for cold mix, as temperature affects workability), reduces the potential for aggregate segregation during material handling, and keeps the paver hopper continuously supplied for steady production. The BR-381 results validated this configuration, producing a highway surface that met the demanding requirements of a major trucking corridor in a challenging tropical environment.

For construction professionals evaluating rehabilitation strategies for heavily trafficked highways, the BR-381 project demonstrates that cold-in-place recycling, when executed with proper emulsion chemistry, surface preparation, and compaction protocols, can deliver pavement quality suitable for primary highway applications while reducing material costs and environmental impact compared to traditional reconstruction.