Impact Resistance Research and Performance Characterization of Hybrid Fiber–Reinforced UHPC in the Anchorage Zone of Bridge Expansion Joints

Abstract

Ultrahigh-performance concrete (UHPC) holds tremendous potential in addressing the issues of short service life and lack of reasonable impact resistance characterization in the anchorage zone of bridge expansion joints, due to its exceptional mechanical properties and durability. This study explores an innovative approach by introducing polyvinyl alcohol fibers, polypropylene fibers, polyethylene fibers, and polyoxymethylene fibers as replacements for steel fibers in the preparation of hybrid fiber–reinforced ultrahigh-performance concrete (HFUHPC), with a total fiber content of 2% vol. The specimens were subjected to construction properties, basic mechanical properties, and repeated drop-weight impact tests at different impact heights. These specimens were divided into four groups including HFUHPC, UHPC with only steel fibers, UHPC without fibers, and C50 fiber–reinforced concrete. The results indicated that the impact resistance of concrete in the anchorage zone of expansion joints should be characterized by the durable crack width impact number at 50 cm impact height for standard impact testing. The best impact resistance (characteristic impact number) of HFUHPC was obtained when the volume substitution rate was 10% (i.e., 0.2% vol by content for synthetic fibers). The service life of various types of fiber-reinforced concrete in the anchorage zone of bridge expansion joints was accurately predicted, and a formula for the characteristic impact number of UHPC based on the characteristic values of fiber and impact height was proposed.