Microsurfacing contractors face a persistent challenge on highway and road projects: pavement width rarely stays uniform from one section to the next. Lane widths narrow at bridges, widen at intersections, and shift through curve transitions. Traditionally, crews stop the paver, manually adjust the spreader box, restart, and accept a cold construction joint at every width change. Bergkamp Inc., based in Salina, Kansas, addressed this problem with its Variable Width Spreader Box (VSB), a system that expands and contracts while paving continues. This technology allows operators to match changing road geometries without stopping production, eliminating unnecessary joints and improving final ride quality. For contractors looking to increase efficiency and pavement durability, understanding how variable-width paving equipment works is essential to modern microsurfacing operations. For more foundational knowledge on small-commercial paving applications, read our article on Paving Utility Cuts Paths and Parking Lots Best.
How the Variable Width Spreader Box Works
The VSB is designed as a drop-in replacement for standard spreader boxes on microsurfacing pavers. It connects to the paver frame using the same mounting points as conventional equipment, so retrofitting an existing machine requires no structural modification. Once installed, the box connects to the paver hydraulic system, and the operator controls width adjustments using levers mounted on the handrails of the box itself.
Auger Configuration and Material Distribution
The VSB uses four hydraulically driven ribbon augers with a 12-inch pitch. The first two augers feed material toward the center of the box, while the outer two distribute the mix evenly across the full placement width. As the box expands or contracts, the augers remain equally spaced from one another, ensuring consistent material distribution at any width setting. This even spacing is critical for producing a uniform mat with no thin spots or material segregation.
A particularly useful design feature is that the auger blades never touch each other, even when the box is set to its narrowest width. This clearance prevents microsurfacing material from building up between the blades, which significantly reduces cleanup time between jobs. Contractors who switch between multiple mixes in a single day will appreciate the reduced downtime for box cleaning.
Strike-Off and Joint Control
Both the primary and secondary strike-offs use a patented sliding design. They move within a guide tube as the box expands or contracts during active paving, maintaining consistent profile control across the full width range. Inboard runners produce clean longitudinal joints at each pass, reducing the need for handwork at lane edges. The combination of sliding strike-offs and inboard runners gives the operator precise control over mat thickness and edge quality regardless of the paving width selected.
Available Models and Width Configurations
Bergkamp offers the VSB in three standard size ranges, with an additional custom option for wider applications. Each model covers a continuous width range, meaning the operator can select any intermediate width between the minimum and maximum without stopping to install mechanical extensions or remove pin-locked sections.
| Model | Minimum Width | Maximum Width | Best For |
|---|---|---|---|
| VSB-813 | 8 ft | 13 ft | Standard highway lanes, two-lane roads |
| VSB-914 | 9 ft | 14 ft | Interstate lanes with wider shoulders |
| VSB-1015 | 10 ft | 15 ft | Major highways with variable shoulder widths |
| Custom Order | — | Up to 16 ft | Specialized wide-section paving |
Each model allows the operator to set any width within its range on the fly by actuating hydraulic cylinders using the handrail-mounted valves. This on-the-fly adjustability means the paver never needs to stop for a width change, which directly eliminates cold construction joints at width transition points. For a closer look at precision asphalt paving techniques on demanding projects, see our case study on Precision Asphalt Paving How Ajax Paving Industries Met.
Operational Benefits and Quality Improvements
The primary benefit of the variable-width approach is the elimination of construction joints at every width transition. When a conventional paver stops for a manual adjustment, the material at the end of the previous pass cools, creating a weak bond with the freshly placed material after the restart. These cold joints are common failure points where water infiltration, raveling, and crack formation begin. By keeping the paver moving continuously, the VSB produces a monolithic mat with no cold joints across variable-width sections.
Key Advantages Over Fixed-Width Paving
- Continuous production — The paver never stops for width changes, maintaining a steady paving speed and consistent material delivery from the support truck.
- Elimination of cold joints — No restart marks or cold seams at width transitions, which extends pavement service life.
- Improved ride quality — Smooth width transitions produce a better final surface profile compared to stepped width changes.
- Reduced labor — No crew members need to manually adjust mechanical width stops or install extensions while the paver is stopped.
- Faster project completion — Eliminating stop-start cycles at every width change reduces total paving time on variable-width projects.
Surface Quality and Consistency
Because the augers maintain even spacing at every width setting, material distribution remains uniform regardless of whether the box is fully extended or fully retracted. This consistency prevents the common problem of thin edges or heavy centers that can occur when a fixed-width box is used outside its optimal design range. The continuous ribbon auger design also reduces the risk of aggregate segregation, which is a frequent quality issue in microsurfacing applications where mix design includes a broad gradation of aggregate sizes.
The ability to pave at any intermediate width also means the contractor can match exact project specifications without over-paving or under-paving. On projects where the pavement width varies by only a few inches across a long section, the VSB can follow the precise road geometry rather than leaving strips of unpaved surface that require a second pass or handwork.
Selecting the Right Spreader Box for the Job
While the VSB is Bergkamp’s flagship variable-width product, the company offers several other spreader box configurations designed for specific microsurfacing and slurry seal applications. Understanding the options helps contractors select the right tool for each job type.
Hydraulic Spreader Box
Designed for microsurfacing and quick-set slurry seal mixes, the Hydraulic Spreader Box uses pin-adjusted width settings rather than continuous on-the-fly adjustment. Once the pins are removed, the width adjusts hydraulically in 6-inch increments from 8 to 14 feet. Widths up to 16 feet are available by special order. This box is a good middle-ground option for contractors who want hydraulic adjustment capability but do not require the continuous variable-width feature of the VSB on every job.
Slurry Seal Box
For conventional slurry seal applications, Bergkamp offers a box available with or without augers. Width adjustment is manual, using pin-and-hole settings in 6-inch increments from 9 to 14 feet, with special orders up to 16 feet. The augerless configuration is suitable for thinner slurry applications where gravity-fed material flow is sufficient, while the auger-equipped version provides positive material distribution for thicker applications or faster placement speeds.
Rut Box for Wheel-Path Filling
Rut filling is a specialized microsurfacing application that requires precise material placement in wheel-path depressions without wasting material on the surrounding surface. Bergkamp’s Rut Box uses two independently adjustable V-shaped screeds that channel larger aggregate to the deeper part of the rut, matching the mix design to the rut depth profile. Available in 5-foot and 6-foot widths, the Rut Box minimizes material waste and produces a more uniform surface after the rut is filled and the final microsurfacing layer is applied.
Selecting the correct spreader box for each application depends on project conditions, mix type, and production requirements. For a broader overview of paving equipment categories and selection criteria, refer to our equipment guide on Pavement Construction and Asphalt Equipment a Complete Guide and Road Construction and Asphalt Paving Equipment Machinery for.
Compatibility and Retrofitting
As the first variable-width spreader box of its kind, the VSB was originally designed for Bergkamp microsurfacing pavers. However, Bergkamp offers customization options to adapt the VSB for other paver brands. The mounting interface and hydraulic connections can be modified to suit different paver models, making the technology accessible to contractors who operate mixed fleets. The quick-change design means the VSB can replace a standard box in the field without special tools, allowing the same paver to swap between variable-width and fixed-width work as needed.
Crew Training and Daily Maintenance
Operators need to learn the handrail-mounted valve controls and develop a feel for making smooth width adjustments while the paver is in motion. The learning curve is generally short because the control action is intuitive push-to-expand, pull-to-contract. The key skill is anticipating width changes ahead of time and making gradual adjustments rather than abrupt corrections, which could produce visible width marks in the finished mat.
- Inspect hydraulic hoses and fittings daily for wear, especially at the moving interfaces where the box expands and contracts.
- Check auger drive chains or hydraulic motors for consistent operation across the full width range.
- Clean the sliding strike-off guide tubes after each shift to prevent material buildup that could restrict smooth movement.
- Verify that the inboard runners are not worn below specification, as worn runners reduce joint quality.
- Lubricate all pivot points and sliding surfaces according to the manufacturer schedule, with extra attention during high-production periods.
When Variable Width Makes the Biggest Impact
The VSB delivers the greatest return on investment on projects with frequent width changes, such as rural highways where shoulder widths vary at culverts and bridge approaches, urban arterials with turn lanes and bus bays that create width transitions at regular intervals, interchange ramps where taper sections require gradual width changes over short distances, and resurfacing projects on older roads built to varying width standards over multiple construction eras. On straight, uniform-width projects such as long interstate sections, a standard fixed-width box remains an efficient choice.
Cost-Benefit Analysis
- Production rate increase — Eliminating stops at width changes typically recovers 10 to 15 minutes per transition. On a project with ten transitions, that is nearly two hours of additional paving time per shift.
- Material savings — Eliminating cold joints reduces the material needed for tack coat and joint treatment at each transition point.
- Quality premium — Projects specified with smoothness incentives reward the continuous mat produced by variable-width paving.
- Reduced crew fatigue — Fewer stops and manual adjustments mean the crew expends less physical effort per shift, improving safety and productivity.
By matching equipment capability to road geometry, Bergkamp’s Variable Width Spreader Box gives microsurfacing contractors a practical tool for improving both production efficiency and pavement quality on variable-width projects.