Concrete Nosing Expansion Joint for Precast Concrete Bridges

Precast concrete bridges offer faster construction and better quality control than cast-in-place bridges, but the expansion joint must be designed to suit the precast construction method. Concrete nosing joints can be constructed using either precast nosing units or cast-in-place concrete. Precast nosing units are fabricated in a controlled factory environment, providing better concrete quality and dimensional accuracy than cast-in-place nosings. The units are cast with the steel edge angles and anchor bolts already in place, reducing site installation time. The units are delivered to site and installed in the joint gap, with the space between the unit and the precast deck filled with non-shrink grout. Cast-in-place concrete nosings are constructed on site after the precast deck units have been installed. The steel edge angles are positioned and the nosing concrete is cast around them. The concrete quality is more variable than for precast nosings, but the cast-in-place method allows more flexibility in the joint geometry. Bond between the nosing concrete and the precast deck is critical for the structural performance of the joint. The interface must be roughened by sandblasting or mechanical scarification to provide adequate bond. Bonding agents may be required for some concrete systems. The interface must be kept clean and free of contamination until the nosing concrete is cast. Shrinkage of the nosing concrete can cause cracking at the interface with the precast deck. Low-shrinkage or non-shrink concrete mixes should be used for nosing construction. Expansion joints within the nosing concrete may be required for long nosing sections to control shrinkage cracking. Inspection of precast concrete bridge joints should include checking the joint gap, the nosing concrete condition, and the steel edge angle condition. Any cracking or spalling of the nosing concrete should be repaired promptly to prevent further deterioration. The joint gap should be measured annually to verify that the bridge is moving within its design range.