Experimental investigation of bond behavior of mild steel reinforcement in UHPC

Ultra-High Performance Concrete (UHPC) is a relatively new class of advanced cementitious composite material, which exhibits high compressive and tensile strengths. The discrete steel fiber reinforcement included in UHPC allows the material to maintain a tensile capacity beyond cracking of the cementitious matrix. The bond behavior of deformed reinforcing bar in UHPC is investigated in this study by conducting pull out tests and beam tests with lap splices. The rebar used for these tests are #4 (M13), #5 (M16) A615 grade 60 bars and # 6(M19), #7 (M22) A615 grade 80 bars. The embedment length and side cover for the pull out tests were varied from 6db to 8db (db = diameter of the rebar) and 1db to 3.5db, respectively. The beam tests were conducted under four-point loading and the clear cover for these tests was varied from 1db to 3db. The rebar for all beam specimens were spliced at mid-span for a length of 8db. The beam specimens were instrumented to capture the strains at different points along the splice length. 16 pull out and 12 beam tests were completed and the effect of embedment length, concrete cover, bar size and bar type on the bond strength were investigated. This paper presents the details of this experimental investigation and adds significant new data on the bond stress distribution along the development length. It was found that the development length of embedded reinforcement in UHPC can be significantly reduced when compared to normal concrete.