Bridge Expansion Joint for Bridges with Expansion Joints in Deck Slabs on Blast Furnace Slag Fill

Blast furnace slag is a byproduct of iron production that can be used as a fill material for bridge approaches. Granulated blast furnace slag (GGBS) has latent hydraulic properties that allow it to gain strength over time when activated by alkali. Blast furnace slag near existing expansion joints requires careful planning to minimize the effects on the joints. GGBS properties include low density (1000-1200 kg/m3), latent hydraulic properties, and good drainage. GGBS requires an alkali activator (lime or cement) to develop its strength. When activated, GGBS gains strength over time, providing a stable fill material. GGBS placement involves mixing the GGBS with lime or cement and water, spreading the mixture in layers, and compacting it with a roller. The GGBS must be placed at the correct moisture content to achieve the required compaction. The GGBS must be covered with a geotextile separator to prevent migration of fines into the adjacent soil. Environmental considerations for GGBS fills include the potential for leaching of alkali from the lime or cement activator. The fill must be designed to prevent leaching of alkali into the groundwater. The pH of the leachate must be monitored to verify that it is within the acceptable range. Settlement of GGBS fills is minimal due to the self-cementing behavior. The settlement depends on the GGBS density and the applied load. Settlement monitoring is recommended during and after GGBS placement near existing joints. Post-installation inspection of existing expansion joints must verify that the GGBS 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.