Bridge Expansion Joint for Bridges with Expansion Joints in Asphalt Overlays

Asphalt overlays on bridge decks require expansion joints that are compatible with the overlay material and that prevent reflection cracking of the overlay at the joint location. The joint design must accommodate the movement of the deck while maintaining the integrity of the overlay. Reflection cracking occurs when the movement of the expansion joint causes cracks to propagate through the asphalt overlay above the joint. The cracks allow water to infiltrate the overlay and the deck structure, accelerating deterioration. Preventing reflection cracking is the primary design challenge for expansion joints in asphalt overlay bridges. Joint type selection for asphalt overlay bridges depends on the movement range and the overlay thickness. For small movements (less than 20 mm), an asphalt plug joint installed in the overlay is the simplest solution. For larger movements, a recessed strip seal or modular joint that is flush with the overlay surface is required. Overlay thickness at the joint location must be sufficient to provide adequate structural support for the traffic loading. The overlay must be at least 40 mm thick at the joint location to prevent cracking under traffic loading. Thicker overlays provide better protection against reflection cracking but add more dead load to the bridge. Tack coat application to the existing deck surface improves the bond between the overlay and the deck. A strong bond prevents the overlay from sliding on the deck surface, which can cause reflection cracking at the joint location. The tack coat must be applied to the clean, dry deck surface and allowed to cure before the overlay is placed. Maintenance of asphalt overlay expansion joints requires annual inspection for reflection cracking, debonding, and shoving. Any cracks in the overlay at the joint location must be sealed promptly to prevent water infiltration. Significant cracking or debonding requires removal and replacement of the overlay at the joint location.