Rehabilitation of reinforced concrete members using ultra high-performnace [sic] performance concrete (UHPC)

Abstract

This study consists of evaluating the efficiency of strengthening normal concrete (NC) beams using Ultra High-Performance Concrete (UHPC), since NC beams are often subjected to detrimental steel corrosion and excessive loads. For this purpose, two different types of beams, type I with weak shear reinforcement and type II with weak bending reinforcement, were prepared. For each type, a reference non-strengthened beam was compared with four other beams, one with discontinuous shear UHPC plates and a continuous bending plate, another with continuous shear and bending UHPC plates, and one with continuous shear UHPC plates. The strengthening method was done by attaching the UHPC plates using an epoxy adhesive. First of all, UHPC material was examined through a mix containing 1.5% steel fibers per mass of UHPC mortar. Results showed that UHPC can reach a high compressive strength of 108 MPa at 28 days. Then, the total eight beams were tested under two-point load, and the results were accordingly compared to investigate the efficiency of the strengthening material and method, the efficiency of the bottom UHPC plate placed in tension zone, and the difference between continuous and discontinuous shear UHPC plates. Results showed that all strengthened beams recorded a higher maximum load capacity and lower deflection than the control beams. The bottom plate was efficient when the reinforcement was weak in bending, however it did not contribute to any significant increase in load capacity when the reinforcement was strong. Moreover, the continuous plates performed better then discontinuous ones. On the level of the failure modes, non-strengthened beams showed shear cracks, but strengthened beams generated flexural cracks, which proves that shear plates may contribute to a better overall structural behavior of the beam (in both shear and bending). For future studies, it is recommended to investigate the same objectives on different reinforcement configurations and longer beam span lengths, to evaluate the consistency of UHPC plates and generalize them as an effective strengthening material and method for all reinforced concrete beams.