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

Bottom ash is a byproduct of coal combustion that can be used as a fill material for bridge approaches. Bottom ash has different properties from fly ash and requires different design considerations. Bottom ash near existing expansion joints requires careful planning to minimize the effects on the joints. Bottom ash properties include low density (800-1100 kg/m3), angular particle shape, and good drainage. Bottom ash does not have the self-cementing properties of Class C fly ash, so it must be compacted to achieve stability. The angular particle shape provides good interlocking between particles, resulting in high friction angle. Bottom ash placement involves spreading the bottom ash in layers and compacting it with a roller. The bottom ash must be placed at the correct moisture content to achieve the required compaction. The bottom ash must be covered with a geotextile separator to prevent migration of fines into the adjacent soil. Environmental considerations for bottom ash fills include the potential for leaching of heavy metals and other contaminants. The bottom 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 bottom ash fills depends on the compaction level and the applied load. Properly compacted bottom ash fills have settlement characteristics similar to natural granular fills. Settlement monitoring is recommended during and after bottom ash placement near existing joints. Post-installation inspection of existing expansion joints must verify that the bottom 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.