55 Bonded Wearing Course A Bonded Wearing Course (BWC) is a high-performance, thin overlay that combines a polymer-modified asphalt emulsion with high-quality, gap-graded aggregate. This pavement preservation method is applied to existing pavement surfaces to provide a new, durable, skid-resistant wearing surface. It’s designed to seal the existing pavement from water and air intrusion, improve the ride quality and extend the service life of the road. The BWC process typically involves the following steps: 1. Surface Preparation: The existing pavement is cleaned to remove any dirt, debris or loose particles to ensure a strong bond with the overlay. 2. Tack Coat Application: A tack coat of polymer-modified asphalt emulsion is applied to the pavement surface to enhance the bond between the old and new layers. 3. Aggregate Application: Immediately after the tack coat application, a layer of gap-graded aggregate is placed on top of the emulsion. The aggregate is chosen for its cleanliness, angularity and durability. 4. Compaction: The aggregate is then compacted into the emulsion using pneumatic or vibratory rollers to ensure proper embedment and to achieve a dense, interlocked wearing surface. 5. Curing: The newly applied BWC must cure properly before being opened to traffic. The curing time depends on factors such as temperature, humidity and the type of emulsion used. The benefits of a Bonded Wearing Course include: • Improved Skid Resistance: The gap-graded aggregate provides excellent skid resistance, enhancing roadway safety. • Rutting and Reflective Cracking Resistance: The polymer-modified emulsion and gap-graded aggregate create a flexible layer that can resist rutting and slow the propagation of reflective cracking. • Waterproofing: BWC seals the existing pavement surface, protecting the underlying layers from water infiltration and associated damage. • Noise Reduction: The open texture of the aggregate can lead to reduced tire‑pavement noise. • Quick Traffic Return: BWC application allows for a relatively quick return to service, minimizing disruption to traffic. • Long Service Life: When properly applied, a Bonded Wearing Course can significantly extend the life of the pavement. BWC is appropriate for both asphalt and concrete pavements and is often used on high-volume roads and highways due to its durability and performance benefits. It is a cost-effective solution for treating surface distress and improving ride quality without the need for a thicker traditional hot mix asphalt overlay.
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