Service Life Design Guidance for UHPC Link Slabs
Friday, October 29 at 1:00pm to 2:00pmVirtual Event
Design for service life rather than just for strength against potential overload and fatigue failure is becoming a more common consideration for bridges. One aspect of design, and often bridge retrofit, with potential for a large impact is minimizing the number of transverse deck joints. Bridge deterioration can often be traced to poor performance of these deck joints due to failure of the joint seal allowing chloride laden water onto bridge girder ends, bearings, and substructure elements. Using link slabs over the piers allows for eliminating some interior joints and moving expansion joints to the end of the bridge while still maintaining typical bridge behavior. Link slabs allow the simply supported behavior expected for many bridges, yet still transmit deformations and forces to expansion joints and reduce potential penetrations in the bridge deck. Advanced materials, such as ultra-high performance concrete (UHPC) can simplify link slab details and substantially improve their durability.
UHPC link slabs are specifically relevant to accelerating bridge retrofit in that the short required debonded lengths can significantly reduce the required amount of demolition and the overall time required for the project. Debonded lengths for UHPC link slabs can be as small as 16 in. compared to several feet for conventional construction. While the concrete in the immediate area of the joint may be deteriorated and can be removed quickly, concrete further from the joint will often be sound and take substantial time and labor to remove. The hairline distributed cracks that form in a UHPC link slab limit pathways for water to penetrate to the bridge girders and substructure, and UHPC itself is inherently more durable than conventional concrete due to its very low permeability.
UHPC link slabs have been used successfully in the field by several state DOTs, several research studies have been carried out focused on link slabs, and appropriate design guidelines are available in the AASHTO LRFD Guide Specifications for Accelerated Bridge Construction (2018). However, more information is needed for quantifying the service life benefits of using UHPC link slabs compared to conventional construction.
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