Failure modes of self-compacting concrete beams reinforced with discarded steel fiber under fire conditions

Abstract

This paper presents results from an experimental systematic study on the fire behavior of high-strength self-compacting concrete (HSCC) beams strengthened with discarded steel fibers (DSF). The current program focuses on the comparison between the structural behavior of tested beams at ambient temperature with (i) furnace-heated beams at the temperature of 600 °C for 60 min (steady-state), and (ii) beams exposed to combined thermo-mechanical loading (fire scenario). For unheated beams, it was found that using 1 % of the DSF converts failure mode from the shear into the flexural failure even in the absence of stirrups, indicating a significant enhancement in the shear strength. At 600°C, there was a clear decrease in the ultimate strength of test beams as they retained only about 69 % of the initial strength. Structural testing revealed that FRHSCC beams were able to sustain the applied load without failure for 85 min of fire exposure, even after the temperature at rebar exceeds 400°C. Finally, beams tested under thermo-mechanical loading showed a significant deterioration in flexural strength while the furnace-heated beams showed a greater loss in shear resistance under monotonic loading. In light of this, it was concluded that furnace-heated beams did not show the real behavior of the fire scenarios. In view of the results, it can be concluded that the strengthening of HSCC beams with DSF can be an effective solution, through increasing fire resistance by above 32 % and increasing residual strength by almost 25 % compared to the beams without fiber. However, it was found that elevated temperature (under fire conditions), beyond 600°C, significantly degrades the positive effect of fibers in improving the mechanical and structural properties of concrete.