Bridge Expansion Joint for Bridges with Expansion Joints in Deck Slabs on Controlled Low Strength Material

Controlled low strength material (CLSM), also known as flowable fill or controlled density fill, is a self-compacting, cementitious material used as backfill for bridge abutments and approach fills. CLSM near existing expansion joints requires careful planning to minimize the effects on the joints. CLSM properties include low strength (0.3-8.3 MPa), high flowability, and self-compacting behavior. CLSM is used as a replacement for compacted granular fill in areas where compaction is difficult, such as behind bridge abutments. The low strength allows CLSM to be excavated if future access is required. CLSM placement near existing expansion joints requires careful control of the placement rate and the hydrostatic pressure. The hydrostatic pressure from the fluid CLSM can affect adjacent expansion joints by applying lateral pressure to the joint components. The placement rate must be controlled to limit the hydrostatic pressure. Settlement of CLSM backfill is minimal because CLSM is self-compacting and does not require compaction. However, CLSM can shrink slightly as it cures, which can cause minor settlement of the backfill surface. Settlement monitoring is recommended during and after CLSM placement near existing joints. Post-placement inspection of existing expansion joints must verify that the CLSM placement 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. CLSM quality control requires testing of the CLSM mix to verify that it meets the specified requirements. Flow consistency tests verify that the CLSM is sufficiently fluid for self-compaction. Compressive strength tests verify that the CLSM has the required strength for the application. The test results are compared with the design requirements to verify that the CLSM is performing as intended.