Characterization of the bond strength between ultra high performance concrete bridge deck overlays and concrete substrates

The major factors that lead to the deterioration of the bridge deck include exposure to the severe environment, traffic loads, and deicing salts. The search for methods to extend the service life of bridges has resulted in several techniques that include the application of overlays, membranes, sealers, coated reinforcing bars, and many other solutions. The focus herein is limited to overlays. The main purpose of a bridge deck overlay is to extend the life of the structure by providing protection from the water and chemical penetration, and a durable wearing surface. The overlay also has to provide adequate bearing capacity, which is compatible with the loading of the bridge deck. The high compressive strength and improved durability characteristics suggest that the ultra high performance concrete (UHPC) could be used as an attractive alternative to conventional overlay materials and solutions if a strong mechanical bond is formed between the overlay and the substrate material. An experimental study was performed to evaluate the bond strength between UHPC overlay and a normal concrete substrate with different types of surface textures including, smooth, low roughness, and high roughness.;Slant shear test (ASTM C 882-99) and splitting prism test were performed to quantify the bond strength in compression and shear, and in tension. Additionally, third point loading tests (ASTMC 1018) were conducted to evaluate the performance of a bi-layer member in flexure. For the slant shear test, type III Portland cement mortar was used as the substrate. The mortar specimens used maintained a compressive strength more than 4,500 psi after 28 days of moist curing. For the splitting prism and flexure tests a concrete mix representative of MDOT bridge deck mix was used. Half specimens of mortar/concrete were cast and cured followed by preparation of surface roughness. UHPC layer was cast against the prepared surface and the composite specimens were cured under ambient air temperatures to mimic likely application conditions.;This study demonstrated that under compression loading (slant shear test), the bond strength is greater than the strength of substrate, provided that a proper surface roughness is used. However, in the case of no surface preparation, failure consistently occurs at the interface. For the bond strength under indirect tension (splitting test), results were not very sensitive to the surface roughness. Failure at the interface included corner breaks or chunk breaks in the concrete with no failure within the UHPC section. Analytical result shows, maximum stresses at the interface is less than the shear and tensile bond strength. So it could be assumed that there is no interface slip due to the flexure failure. Even though, further research is needed to understand the actual interface behavior.;Result from this study indicates that UHPC has the potential to be used as an overlay material; however further experimental investigation is needed to understand the impact of the long term cyclic performance on the bond strength and shrinkage behavior that causes debonding between the old concrete substrate and new overlay material.