Bridge Expansion Joint for Bridges with Expansion Joints in Deck Slabs on Fly Ash Fill

Fly ash is a byproduct of coal combustion that can be used as a fill material for bridge approaches. Self-cementing fly ash (Class C fly ash) gains strength over time due to the pozzolanic reactions, providing a stable fill material. Fly ash near existing expansion joints requires careful planning to minimize the effects on the joints. Self-cementing fly ash properties include low density (900-1200 kg/m3), self-cementing behavior, and good drainage. Class C fly ash contains sufficient calcium to undergo pozzolanic reactions without the addition of lime or cement. The self-cementing behavior provides a stable fill that does not require compaction to achieve strength. Fly ash placement involves spreading the fly ash in layers and compacting it with a roller. The fly ash must be placed at the correct moisture content to achieve the required compaction. The fly ash must be covered with a geotextile separator to prevent migration of fines into the adjacent soil. Environmental considerations for fly ash fills include the potential for leaching of heavy metals and other contaminants. The fly ash must be tested for contaminant leaching before use as a fill material. The fill must be designed to prevent leaching of contaminants into the groundwater. Settlement of fly ash fills is minimal due to the self-cementing behavior. The settlement depends on the fly ash density and the applied load. Settlement monitoring is recommended during and after fly ash placement near existing joints. Post-installation inspection of existing expansion joints must verify that the fly ash installation has not caused any damage. The inspection should check the joint gap width, the concrete edge beam condition, and the anchor bolt torque. Any damage must be repaired before the bridge is returned to service.