About the research
The current National Bridge Inventory database lists the concrete bridge deck deterioration, in the form of reinforcement corrosion or concrete distress, as one of the leading causes of structural deficiency. The combination of aging infrastructure, growing number of structurally deficient or obsolete bridges, and continuous increase in traffic volume in the United States demands rapid improvements to the nation’s bridge infrastructure with an emphasis on increasing bridge longevity. A recent Highways for LIFE project sponsored by the Federal Highway Administration (FHWA) entitled Full Depth UHPC Waffle Bridge Deck Panels confirmed the significant benefits of ultra-high performance concrete (UHPC) deck systems in terms of excellent structural performance, durability, and ease of construction. However, the initial capital cost of this deck system is comparatively higher than the traditional, normal strength concrete decks, which may hinder the wider usage of UHPC waffle decks in bridges. In order to overcome this challenge and to improve longevity of bridge decks, this project explores the possibility of using a thin layer of UHPC overlaying a normal strength concrete (NC) deck.
The behavior of the interface connection will have a significant impact on the overall structural and durability performance of the UHPC-NC composite deck system. Consequently, an integrated experimental and analytical study was conducted at Iowa State University to understand the influence of several variables, such as normal concrete strength, interface roughness, and curing condition on the shear transfer behavior across the interface between UHPC and NC. The laboratory testing was performed in two phases, including slant shear testing in Phase I and flexural testing of composite deck specimens in Phase II. A total of sixty test units with five different surface textures and three different concrete strengths were loaded to failure. Then, five 8 in. thick, 2 ft wide, and 8ft long deck specimens with 1.5 in. thick UHPC overlays were tested to failure. With the interface texture being the main variable, the composite deck sections were subjected to a combined monotonically increasing flexure and shear loading. The slant shear test results demonstrated that the shear transfer across the interface for all five different textures is adequate for overlay applications, which was later confirmed by the composite deck sections tests. Based on the experimental results, the researchers found that the current AASHTO 2010 guidelines provide a conservative estimate for the UHPC-NC interface shear strength.