Finite element modeling (FEM) and field validation of approach slab and subgrade behavior

Approach slabs function as a transition between a roadway and a bridge deck. If not designed and constructed properly, approach slabs can cause drivers to experience rough roadway conditions and face other hazards such as traffic accidents, vehicle damage, and deterioration of the superstructure. Due to the exceptional mechanical properties observed in Ultra-High Performance Concrete (UHPC), the material is explored for use as an overlay to improve approach slab performance. This study presents a validated Finite Element Model (FEM) that demonstrates the cracking behavior of an approach slab incorporating an UHPC overlay. The model’s findings are validated using a field investigation, where a composite approach slab featuring a UHPC overlay is casted in New Jersey, USA. Strain gages are installed throughout the slab, confirming the results witnessed in the model. A parametric study is also presented, which determines the optimized thickness of a UHPC approach slab that is both fully supported by the subgrade soil and exposed to a 1.524 m (5 ft) sediment washout. By using a monolithic UHPC approach slab, it was found that the slab’s thickness can be reduced by up to 55.6% while still maintaining a safe and serviceable design. The results of this investigation are expected to facilitate the use of UHPC in approach slab design and construction.