An Investigation of a Suitable Shear Friction Interface between UHPC and Normal Strength Concrete for Bridge Deck Applications
Start date: 07/01/10
End date: 06/30/14
Sponsor(s): Iowa Department of Transportation
About the research
Today there are over 160,000 bridges in the nation that are structurally deficient or obsolete with more than 3,000 new bridges added to this list each year (Bhide 2001). Cracking in bridge decks is a common problem in the United States and the deterioration of the bridge deck is a leading cause for the obsolete or deficient inspection rating of the bridges. Exposure of bridge deck steel to a combination of moisture, temperature and chlorides from de-icing salts through surface crack leads to concrete deterioration and loss of serviceability. Nationwide, billions of dollars have been spent replacing bridge decks deteriorated by the effects of cracking. Federal, State and municipal bridge engineers are seeking alternative ways to build better bridges, reduce travel times, and improve repair techniques, thereby reducing maintenance costs. Additionally, owners are challenged with replacing critical bridge components, particularly bridge decks, during limited or overnight road closure periods. Therefore, there is an impending need to develop and implement longer-lasting bridge deck systems that may use advanced materials, innovative technologies and safe and fast construction practices, resulting in high quality bridges and highways. Ultra High Performance Concrete (UHPC) is a high strength concrete with high durability and a dependable tensile strength (nearly 1.73 ksi) when compared to normal strength concrete (NC) used in today's bridge decks. This helps in controlling deck cracking commonly seen in current day practice. Hence, UHPC is gaining significant interest among numerous State Departments of Transportation (DOTs) and the Federal Highway Administration (FHWA) for bridge applications to increase longevity and reduce maintenance costs. A recent experimental study at Iowa State University funded by FHWA's Highways for LIFE program has shown excellent structural characteristics of a full depth precast waffle deck system for bridge applications. The cost of UHPC material is significantly higher than the normal strength concrete which may hinder the routine use of UHPC in bridge decks. Given that deck deterioration occurs due to formation of crack on the top surface, a most cost-effective yet highly durable bridge deck could be formed through a composite bridge deck by overlaying a thin Ultra High Performance Concrete (UHPC) layer over a Normal Strength Concrete (NC) slab. However, a dependable shear friction for the UHPC and NC interface and the factors influencing its behavior needs to be investigated to make this concept a reality for field applications. This proposal focuses on the structural characterization of different shear friction interfaces that may be appropriate for overlying UHPC on NC slabs and identifying the most suitable interface for this connection with due consideration to constructability and the benefits of strength and durability characteristics of heat treated UHPC. The project will also address the factors influencing the shear friction behavior and proposes a possible UHPC-NC composite deck system. The broad objective of this proposal is to characterize the shear friction behavior between the UHPC and NC surfaces and establish suitable details needed to realize the UHPCNC composite deck system. The proposed research will also evaluate the practicality and the effects of different textures of surface preparations, concrete strength and precast/prestressed operations on the shear friction behavior of the composite deck.