Assessment of Bond Behavior of UHPC and Prestressing Strands

Abstract

Ultra High Performance Concrete - UHPC is a relatively new type of composite material with outstanding features (high compressive strength, high tensile strength and high durability). Also the bond strength between steel reinforcement and UHPC is better than that in ordinary concrete. This fact needs to be quantified, because no standard prescribes the bond behavior of UHPC and design of UHPC in general. The main aim of the experimental research was to determine the average bond stress between prestressing strands and different types of UHPC. The second aim was to show very significant increase of the average shear stress in bond of UHPC compared to that of ordinary concrete. In order to determine the bond capacity, two types of experimental specimens – parts of prestressed girders and specimens prepared according to standard, were tested in the laboratory. The specimens were prepared for pull out test, in which the prestressing strand is pulled out from the cube or part of girder made from UHPC. The tensile force in strand and slip of the end of reinforcement were measured and then the average bond stress was examined. The influence of different material properties and different anchorage lengths of prestressing strands to bond behavior of UHPC was examined and results were compared to these phenomena of ordinary concrete. The results of bond test led to the conclusion that the application of UHPC can significantly reduce the anchorage length of reinforcement compared with that in ordinary concrete.