Effect of magnetic field exposure time on mechanical and microstructure properties of steel fiber-reinforced concrete (SFRC)

Abstract

The present experimental study is an effort to investigate the effect of uniform magnetic field (UMF) exposure time on mechanical and microstructural behaviors of steel fiber-reinforced concrete (SFRC) with fiber volume fractions of 0.4, 0.7 and 1% by employing compressive and flexural strengths tests, and scanning electron microscopy (SEM) imaging. Following this, the brittleness index of SFRC specimens due to different exposure times was assessed. In addition, the ultrasonic test was employed to assess nondestructively the compressive strength of SFRC affected by the UMF for different times. For this purpose, ready-mixed SFRC specimens were exposed to the UMF of density 5000 Gauss, during the casting process, for three different time periods: 1, 2 and 3 min. The study also investigated the effect of UMF exposure direction on the compressive strength of SFRC specimens. Finally, an equation has been proposed to estimate flexural strength of SFRC exposed to the UMF based on compressive strength results. The obtained results demonstrated that the mechanical strength of SFRC increased as the UMF exposure time increased which is more obvious for specimens containing 0.7% steel fibers by volume of the concrete. Concerning this, compressive and flexural strengths of the specimens, exposed to the UMF for 3 min increased by about 21 and 27%, respectively. Furthermore, based on the SEM analysis, chemical reactions of cement hydration increased with increasing the UMF exposure time, leading to increasing bond between cement paste and steel fibers.