The adjacent precast prestressed concrete box-beam bridge is the bridge of choice for short and short-to-medium span bridges. This choice is because of the ease of construction, favorable span-to-depth ratios, aesthetic appeal, and high torsional stiffness. However, this bridge is losing favor primarily because of persisting durability performance issues resulting from longitudinal deck cracking at the shear key locations. This project was initiated to develop practical recommendations for modifications to current adjacent precast prestressed box-beam bridge details, specifications, and methods used in Wisconsin with a goal of minimizing the potential for developing longitudinal deck cracking over shear keys.

A list of best practices was developed after conducting (i) an extensive review of state-of-the-art literature and highway agency manuals and guides and (ii) a survey of selected highway agencies and fabricators. In addition, the impact of using various wearing surface types of adjacent box-beam bridge superstructure durability performance was evaluated using NBI data. Based on the outcome of these activities, shear key detail and material and construction specifications were updated. The revised details and specifications were implemented on three bridges: one with traditional abutments and a 6 in. thick cast-in-place concrete slab, and the other two with Geosynthetic Reinforced Soil (GRS) abutments and 2 in. thick masonry overlays. Deck cracking over the shear keys was documented during the inspection conducted just after construction and after the bridges had been in service for five months. In addition to the cracking over shear keys, randomly dispersed short cracks were observed on these decks. This observation is consistent for all three bridges. Subsequent analysis was conducted using structural details of these bridges, and material property data recorded during construction shows that shrinkage and thermal gradient loads initiate cracking irrespective of the overlay types used on these bridges. Recommendations include continuing with updated details and specifications while exploring the use of crack resistant overlay types and revising details through additional research.