In the high-elevation forests of California’s Sierra Nevada mountains, innovative road rehabilitation techniques are proving that infrastructure restoration can align with environmental stewardship. Pavement Recycling Systems (PRS), based in Mira Loma, California, undertook a remarkable project on Sherman Pass Road in the Sequoia National Forest, using a Wirtgen KMA 220 portable cold mixing plant to recycle failed pavement entirely on site. This approach eliminated the need for long-distance material hauling and demonstrated the viability of cold in-place recycling in challenging terrain. For construction professionals evaluating sustainable pavement solutions, understanding the interplay between equipment choice and site conditions is essential, much like evaluating whether Is Steam Heat Still a Viable Heating Choice depends on building-specific factors such as infrastructure age and retrofit costs.
The Sierra Nevada Project: Cold Recycling at 8,400 Feet
Sherman Pass Road, a former logging route now used primarily for recreational access to campgrounds and wilderness areas, had deteriorated significantly. The United States Forest Service identified the worst sections of this mountain road for rehabilitation, targeting a 6-inch-deep milling of failed pavement across 24-foot-wide sections. PRS mobilized its KMA 220 portable plant to a clearing at approximately 8,400 feet above sea level, amid towering conifers and sensitive alpine ecosystems.
Project Scope and Logistics
The scale of this rehabilitation effort was substantial, with crews processing between 18,000 and 20,000 tons of material over the course of the project. Marty Castaneda, Jr., superintendent for PRS, described a tightly coordinated operation where each day’s work began with milling approximately 1,000 feet ahead of the paver. Haul trucks transported milled material to a small crusher that reduced it to a 2-inch-minus gradation before feeding it into the KMA 220 for processing with cement and water.
The 45-Minute Workability Window
A critical constraint of cement-bound recycling is the rapid curing time of the material. PRS crews had approximately 45 minutes from the moment cement and water were mixed with the reclaimed aggregate until the material began to set. This required precise coordination across the entire operation:
- Milling crews stayed 1,000 feet ahead of the paver at all times
- Stockpiles at the KMA 220 were maintained at a manageable size to prevent material from sitting too long
- Trucks operated in continuous round-trip cycles, with one-way hauls reaching up to 14 miles
- The paver laid material in 500-foot segments before repositioning
Castaneda emphasized that the stockpile could not sit for more than a few minutes on the ground, as the material would lose too much moisture and begin curing prematurely. The daily production averaged 2,700 linear feet, demonstrating the efficiency of a well-orchestrated operation even under tight temporal constraints.
Technical Advantages of the Wirtgen KMA 220 Portable Cold Mix Plant
The centerpiece of PRS’s operation was the Wirtgen KMA 220, a self-contained portable cold mixing plant that builds on the success of its predecessor, the KMA 200. This machine represents a significant evolution in mobile recycling technology, combining portability with industrial-scale production capacity.
Key Technical Specifications
| Specification | Detail |
|---|---|
| Production Capacity | 220 tons per hour |
| Mixing Capacity | 220 tph (modified twin-shaft continuous mixer) |
| Engine Output | 175 hp (diesel-hydraulic drive) |
| Water Tank Capacity | 1,188 gallons |
| Axle Configuration | Three air-suspension axles with raising/lowering capability |
| Material Options | Emulsions, foamed asphalt, cement, lime, polymer additives, fly ash |
| Control System | Cockpit Graphics Center (CGC) |
Design Features for Mobility and Reliability
The KMA 220 was designed with transportability as a core requirement. Its three air-suspension axles, each with raising and lowering capability and automatic load-dependent all-wheel air brakes, allow the unit to be towed directly to project sites without special oversize permits in many cases. The loading conveyor folds for transport, and the operator cabin slews into its transport position at the end of the low-bed trailer.
Additional design elements that enhance field performance include:
- Hydraulically folding grids on top of material hoppers for easy cleaning
- Folding ramps on the sides of material hoppers to prevent contamination
- Fully diesel-hydraulic drive of all components, eliminating complex mechanical linkages
- The Cockpit Graphics Center (CGC) for precise monitoring and control of mix recipes
Environmental Benefits of In-Situ Pavement Recycling
The Sherman Pass Road project achieved 100 percent recycling of the existing road surface into a rebuilt, cement-bound pavement. While this might seem like an intentional green choice, PRS superintendent Castaneda noted that the remote location left few alternatives. The two-hour haul time through winding mountain roads made importing hot mix asphalt or concrete economically and logistically impractical. Recycling became the only viable option, and it delivered substantial environmental benefits as a result.
Eliminating Long-Distance Material Transport
By processing material on site, the project eliminated dozens of truck trips that would have been required to bring virgin aggregate and asphalt from lower elevations or desert sources. This directly reduced diesel fuel consumption, traffic congestion on narrow mountain roads, and the carbon footprint of the rehabilitation work. Wayne Evans, Wirtgen vice president of business development, noted that locating a permit-free portable plant at or near a project site can cut dozens of trucks from long hauls.
Zero Emissions and Permit-Free Operation
Because the KMA 220 is a cold mixing plant that requires no heating of materials, it operates without visible emissions and does not require EPA operating permits. This makes it particularly well suited for environmentally sensitive areas such as national forests and wilderness boundaries. The machine can process 100 percent recycled materials, including reclaimed asphalt pavement (RAP), excavated road base, and crushed recycled concrete aggregate (RCA), into cold mix without generating the stack emissions associated with hot mix plants.
Construction projects in sensitive environments must account for a range of ecological factors. Understanding Environmental Considerations in Site Investigation helps contractors identify potential impacts before breaking ground. Similarly, a thorough Environmental Impact Assessment of Construction Projects provides the framework for evaluating whether proposed methods align with regulatory requirements and ecological preservation goals.
Cold Foam and Emulsion Stabilization Options
PRS operates its KMA 220 across a broad range of applications, using it equally throughout the year for cement, foamed asphalt, and asphalt emulsion stabilized bases. The machine had been employed on an emulsion project for the city of Palm Desert, California, immediately before the Sierra Nevada work, and it had previously been used in Yosemite National Park. This versatility allows contractors to select the most appropriate stabilization method for each project’s specific conditions, whether the goal is strength gain, moisture resistance, or flexibility.
Operational Considerations for High-Altitude Cold Recycling
Operating at 8,400 feet in the Sierra Nevada presented unique challenges that required careful planning and execution. The lessons from this project offer valuable guidance for contractors considering cold recycling in remote or high-elevation locations.
Mobilization and Site Setup
Transporting the KMA 220 to the project site required navigating narrow mountain roads with hairpin turns. Castaneda noted that while the move required some effort, the towable design of the plant made it manageable. Once on site, crews set up a cement silo and water system, with water continuously trucked in due to the remote location. The KMA 220’s 1,188-gallon water tank provided on-board storage, but the 5 to 6 percent water content added to the crushed material required a steady supply chain.
Workflow Optimization in Confined Spaces
Narrow roads and mountain switchbacks left crews with limited room to maneuver, requiring disciplined workflow management. The project used single-lane closures at active work sites, with traffic control managing the light recreational traffic accessing campgrounds in the area. Key operational strategies included:
- Keeping the KMA 220 stationary for the entire duration of the project, with trucks bringing millings and removing processed material regardless of their location relative to the plant
- Milling only the worst sections identified by the Forest Service, focusing resources on areas of maximum need
- Maintaining a rotating stockpile at the plant to ensure continuous truck circulation even when the paver was operating far from the processing site
- Coordinating truck cycles so that the same vehicles that delivered millings returned with processed material, maximizing equipment utilization
Material Mix Design for Cold Recycling
For the Sherman Pass Road project, PRS added 5 percent cement and 5 to 6 percent water to the crushed reclaimed material. The resulting cement-bound pavement provided a durable driving surface suitable for recreational vehicle loads while using the existing road material as the primary aggregate source. The 100 percent recycling rate eliminated the need for virgin material import, which would have been costly and disruptive given the remote mountain setting.
Cold recycling projects require careful evaluation of material properties and site conditions to achieve optimal results. Historical case studies, such as the Key Aspects of Love Canal Worst Environmental Tragedy of the US, demonstrate how inadequate site assessment and material handling can lead to long-term environmental consequences. Modern cold recycling practices incorporate lessons from past environmental challenges to ensure that infrastructure improvements do not create unintended ecological liabilities.
Economic Viability of Remote-Site Recycling
The economic case for the KMA 220 on Sherman Pass Road was driven less by environmental idealism and more by hard logistics. Castaneda stated directly that the distance from any hot mix asphalt or concrete plants made recycling the most advantageous option, eliminating the logistics of moving large quantities of material from lower elevations. The machine’s 225-ton-per-hour production capacity made the economics work, with the cost-effectiveness of on-site recycling outweighing the alternative of trucking material over two hours each way through mountain terrain.
This project demonstrates that environmental benefits and economic efficiency can converge when the right technology is applied to the right conditions. Cold in-place recycling using portable plants like the KMA 220 offers a compelling model for road rehabilitation in remote, environmentally sensitive, or logistically constrained locations, turning the challenge of distance and elevation into an opportunity for sustainable infrastructure practice.