Experimental study on a novel UHPC grout-filled pipe sleeve with mechanical interlocking for large-diameter deformed bars

Abstract Grouted sleeve splice is a competitive alternative to reinforcement connections of accelerated bridge construction (ABC). When it is used to connect large-diameter deformed bars, overlong development length is required, although the decreased amount of connected bars and increased construction tolerance can accelerate construction speed. This paper aims to develop a novel ultra-high performance concrete (UHPC) grout-filled pipe sleeve with bolts for large-diameter deformed bars. It is expected to shorten the embedded length and delay grout crushing and splitting caused by bolts using UHPC's high material properties. A direct tensile test was conducted on 21 specimens to validate the feasibility, investigate the design parameters' effects, and explore the working mechanism of the pipe sleeve. Results show that the proposed pipe sleeve is feasible to connect large-diameter deformed bars with an embedded length of 5db. There are four failure modes including grout bond failure without/with bolts as well as bar bond failure without/with bolts in this test. UHPC without steel fiber is a preferred grout for the pipe sleeve because steel fiber can weaken grout fluidity and reduce bar-grout bond strength as well as grout-pipe bond strength. The existence of bolts can significantly enhance bar-grout bond strength as well as grout-pipe bond strength. The grout-pipe bond performance is sensitive to the depth of bolts in grout, amount of bolts, and distance of bolts to the end. When the pipe sleeve is used for deformed bars with higher strength, bearing capacity is slightly increased and deformation capacity is markedly weakened for bar-grout bond behavior. A greater cross dimension of the steel pipe is a good choice to avoid grout bond failure.