Bridge Expansion Joint for Bridges with Expansion Joints in Deck Slabs on Biogrouting

Biogrouting (microbially induced calcite precipitation, MICP) is an emerging ground improvement technique that uses bacteria to precipitate calcium carbonate in the soil voids, binding the soil particles together and increasing the strength and stiffness of the soil. Biogrouting near existing expansion joints requires careful planning to minimize the effects on the joints. MICP process involves injecting bacteria and a nutrient solution (urea and calcium chloride) into the soil. The bacteria hydrolyze the urea to produce carbonate ions, which react with the calcium ions to precipitate calcium carbonate. The calcium carbonate fills the soil voids and binds the soil particles together. Ground heave from biogrouting is minimal because the calcium carbonate fills the existing voids without displacing the soil. However, if the injection pressure is too high, the solution can fracture the soil and cause ground heave. The injection pressure must be monitored and controlled to prevent fracturing. Chemical effects of biogrouting on adjacent structures must be considered. The nutrient solution contains urea and calcium chloride, which can be aggressive to concrete and steel. The injection must be controlled to prevent the solution from reaching adjacent expansion joints or bridge structures. Post-grouting inspection of existing expansion joints must verify that the biogrouting 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. Biogrouting effectiveness is verified by comparing the soil properties before and after grouting. Unconfined compressive strength tests and permeability tests are performed before and after grouting to measure the improvement. The test results are compared with the design requirements to verify that the grouting has achieved the required improvement.