Strength and Behavior of Reinforced Concrete Bridge Deck Slabs Overlaid with Ultra High-Performance Concrete

Ultra-High Performance Concrete (UHPC) has appeared in the past two decades. It is a relatively new type of concrete that exhibits mechanical properties that are far superior to conventional concrete. All around the world, many bridges have been built but are structurally deficient before reaching their design services. Because bridges are subject to high live loads due to traffic volume, they are usually overlaid with materials like NSC, bituminous, etc., which cause damage due to their weak resistance to tension force and permeability. Generally, deterioration starts with cracking on the top surface of bridge decks; over time, this damage goes through the substructures, and those structurally deficient bridges require a very high budget to replace. Applying a thin layer of UHPC on top of normal concrete bridge decks has been proposed as a potential treatment in a prior study. Because UHPC has a high compressive and tensile strengths, which mainly result from the addition of steel fibers that enhance durability and long-term stability properties.
In this study seventeen simply supported reinforced concrete flat plate
slabs 1500x500x140 mm were casted and tested, loaded through two-line loads along the short span direction, to investigate the strength and behavior of reinforced concrete bridge deck slabs overlaid with UHPC.
The main variables studied in this investigation were:
• Overlay thickness 20-50 mm.
• Reinforced UHPC overlay with reinforcement ratio 0-1.31 %.
• Interface patterns rough, horizontal groove, vertical groove, cross-hatch groove, and diagonal groove.
• Substrate material compressive strength 20-40 MPa.
• Three types of material evaluated for overlay application NSC, HPC,
and UHPC.
• The addition of a mechanical connector with a rough surface pattern
evaluated zero until three rows of an anchor.
Results indicated that using UHPC overlay can double the ultimate
strength carried by the composite slab compared with the HPC overlay. The thin layer of UHPC as the wearing surface increases the life of the existing structure and reduces the maintenance cost twice compared with HPC. Also, the addition of embedded rebar at the UHPC layer tends to conclude shear stress at the interface and normal stress at the UHPC overlay by about 30 %. Moreover, ultimate strength increases with an increase in the degree of interface roughness between two layers of concrete, and an adequate bond can be attained with all interface patterns. The ultimate strength increases with an increase in substrate material compressive strength due to adhesion and cohesion properties at the interface. For bridge deck slabs overlaid with UHPC the mode of failure is governed through the substrate while the adequate bond strength is provided by good surface preparation, otherwise, top concrete crush and splitting of the composite structure take place with HPC and NSC. Test results also indicated that the addition of a mechanical connectors with rough surface preparation leads to an increase strength by 50 %. With the use UHPC overlay, the characteristics of the slab were entirely enhanced. The central deflection increased by about 50% compared with HPC. Overlay failure never happened with UHPC overlay. The concrete compressive and tensile strains are increased by a considerable amount (for the same load level). UHPC overlay with proper surface preparation leads to composite structure behaving monolithically and failure load goes through the substrate.