Ultra Thin Bonded Wearing Course (UTBWC): What It Is
An ultra thin bonded wearing course (UTBWC) is a thin layer of hot mix laid over a heavy, polymer-modified emulsion membrane in one pass. The membrane glues the thin layer to the old pavement and seals it, while the gap-graded mix gives a rough, quiet, skid-resistant surface. It is a preservation treatment for roads that are structurally sound but have surface wear.
Asphalt tonnage calculator →How it is built
A special spray paver does the work. It carries an emulsion tank and spray bar ahead of the screed.
- Clean the existing surface, and repair cracks and potholes.
- The spray paver applies a thick polymer-modified emulsion membrane.
- Within seconds, the screed places the hot, gap-graded mix over the membrane.
- The heat breaks the emulsion and the binder wicks up into the mix.
- Static steel rollers seat the mat with a few passes; vibration is generally avoided on such thin layers.
Because the membrane is never exposed to traffic, there is no tracking, and the layer bonds tightly.
Thickness and materials
- Thickness: typically about 3/8 to 3/4 inch.
- Aggregate: hard, crushed, gap-graded stone, often 1/4, 3/8 or 1/2 inch nominal.
- Binder: performance-graded binder in the mix, often polymer-modified.
- Membrane: heavy polymer-modified emulsion at a much higher rate than a normal tack coat.
Where it came from
The process was developed in France and introduced to the United States in the early 1990s under the Novachip name. Many agencies now specify UTBWC generically.
Benefits
- Seals the old surface while adding new texture and friction.
- Thin enough to avoid most curb, drainage and bridge clearance problems.
- Quick return to traffic.
- Quieter and less spray than a chip seal road surface.
Limits
- Not a structural treatment; it will not fix rutting deeper than its thickness or base failures.
- Needs a specialized spray paver.
- Costs more than chip seals or microsurfacing.
Preparing the surface
Badly rutted or rough surfaces may be leveled or micro milled first so the thin mat can be placed evenly.
Quantity example (made-up numbers)
A 3/4-inch UTBWC on a 24-foot by 1-mile road covers 126,720 square feet, or 14,080 square yards. Thin gap-graded mixes are often specified by spread rate; at an assumed 70 lb per square yard, that is about 493 tons. For comparison, see open-graded friction course. Use the asphalt tonnage calculator for your own area and depth.
Questions people ask
What is an ultra thin bonded wearing course?
A pavement preservation treatment made of a thin, gap-graded hot mix placed over a thick polymer-modified emulsion membrane in a single pass by a spray paver.
How thick is UTBWC?
Typically about 3/8 to 3/4 inch (roughly 10 to 20 mm), depending on aggregate size and agency specs.
What is a spray paver?
A paver with a built-in emulsion tank and spray bar that applies the bonding membrane just ahead of the screed, so the hot mix covers it within seconds.
Is UTBWC the same as Novachip?
Novachip is a proprietary brand of ultra thin bonded wearing course, originally developed in France. Many agencies now specify the process generically.
How long does UTBWC last?
Service life depends on traffic, climate and the existing pavement. It is a surface treatment, not a structural fix, so it works best on roads with sound structure.
Can UTBWC be placed at night?
Yes, and it can often be opened to traffic shortly after rolling, which suits busy roads.
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