Bond of Reinforcement in Ultra-High-Performance Concrete

Abstract

Ultra-high-performance concrete (UHPC) is a relatively new class of advanced cementitious composite materials, which exhibits high compressive (above 21.7 ksi [150 MPa]) and tensile (above 0.72 ksi [5 MPa]) strengths. The discrete steel fiber reinforcement included in UHPC allows the concrete to maintain tensile capacity beyond cracking of the cementitious matrix. The combination of the matrix and fiber performance allow for a reduction on the development length of reinforcing steel bar, thus providing the potential for a redesign of some structural systems such as field-cast connections between prefabricated bridge elements. The bond behavior of deformed steel reinforcing bar in UHPC is investigated in this study by conducting direct tension pullout tests. Over 200 tests were completed and the effect of embedment length, concrete cover, bar spacing, concrete strength, bar size, bar type, and yielding strength on bond strength were investigated. It was found that the bond behavior of deformed reinforcing steel in UHPC is different from that in traditional concrete in many aspects. In general, the reinforcing steel development length in UHPC can be significantly reduced. Guidance on the embedment of deformed reinforcing bars into UHPC is provided.