Study of Hybrid Steel Fibers Effects on the Workability and Compressive Properties of Non-proprietary UHPC

Abstract

Non-proprietary ultra-high-performance concrete (UHPC) is renowned for excellent mechanical properties, especially high compressive strength which is generally above 150 MPa. Despite the high compressive strength, the failure mode of non-proprietary UHPC under axial loading is sudden, brittle, and explosive. The undesired compression failure mode is not ideal for structure design and undermines the engineering value of non-proprietary UHPC. This research targets to convert the compression failure mode of non-proprietary UHPC from brittle to ductile with hybrid steel fiber reinforcement and select the most effective reinforcing proportion. In this research, a ground granulated blast-furnace slag (GGBS) based non-proprietary UHPC mix is reinforced with five combinations of two steel fiber types with straight ends. The lengths of the two steel fibers are 6.5 mm and 13 mm. The total volume fraction of steel fibers is 2%. The 28-day compressive strengths and the failure modes of the reinforced samples are compared to select a hybrid steel fiber combination that transforms the failure mode of non-proprietary UHPC and strengthens the compression performance most effectively. The experiment results demonstrate that: (1) with steel fibers presented, non-proprietary UHPC is capable of continuously taking compressive load after matrix cracks; (2) instead of explosive brittle failure mode, fiber reinforced non-proprietary UHPC fails in a ductile behavior under axial compression load and the samples stay in integrity; (3) hybrid steel fiber reinforcement is more effective than single type steel fiber reinforcement in improving the compression performance of non-proprietary UHPC.