Synthesis of Bridge Approach Slab Behavior, Design, and Construction Practice

Elimination of expansion joints between the bridge deck and approach slabs in an integral abutment bridge (IAB) decreases the potential for water and salt damage to a bridge’s superstructure and bearings. However, the lack of expansion joints in an IAB can lead to complex interactions between the superstructure/approach slabs and the substructure, which may have unintended consequences. In particular, cracking and settlement of structural concrete approach slabs have occurred at IABs in Illinois, so the Illinois State Toll Highway Authority (ISTHA) initiated a research project to study approach slabs at IABs. Field investigations indicated that approach slab cracking exhibits significant variability, but two general observations are (1) approach slabs with skews larger than 30° tended to have diagonal cracks that extend out of the obtuse corners and across the acute corners, and (2) longitudinal cracks (in the direction of traffic) were common among approach slabs that have little or no skew. This paper documents a synthesis of prior work and existing approach slab cracking, as well as a transportation agency survey related to design, construction, and performance of approach slabs.