Concrete Nosing Expansion Joint Repair Mortar Specification and Application

Concrete nosing expansion joints rely on the integrity of the concrete nosing to provide a smooth surface for traffic and to protect the joint seal. When the nosing deteriorates, repair is required to restore the joint's function and prevent further damage. Repair mortar selection for concrete nosing joints must consider the required strength, bond to existing concrete, shrinkage, and resistance to traffic loading and deicing chemicals. Polymer-modified cementitious mortars are the most common choice, offering good bond strength, low shrinkage, and adequate durability. Epoxy mortars provide higher strength and chemical resistance but are more expensive and require careful temperature control during application. Rapid-setting repair mortars are preferred for bridge applications where traffic disruption must be minimized. Mortars achieving 30 MPa at 4 hours allow traffic reopening within a single working shift. Calcium sulfoaluminate (CSA) cement mortars and accelerated Portland cement mortars are the most common rapid-setting systems. The strength development curve must be verified by testing before use. Surface preparation for nosing repair follows the same principles as general concrete repair. All deteriorated concrete must be removed to a sound substrate. The repair area must be cleaned by water jetting or compressed air to remove dust and debris. A bonding agent compatible with the repair mortar must be applied to the prepared surface. Formwork is required for repairs to the vertical faces of the nosing. The formwork must be rigid and sealed to prevent mortar leakage. The mortar is cast through ports in the formwork, ensuring complete filling without voids. The formwork must remain in place until the mortar has achieved sufficient strength to be self-supporting. Curing of repair mortars is critical for achieving the specified strength and durability. Wet curing with hessian and polythene sheeting for a minimum of 7 days is recommended for standard mortars. Rapid-setting mortars may have different curing requirements specified by the manufacturer. In hot weather, additional measures to prevent rapid moisture loss are required.