Cementitious Composites Reinforced with Magnetically Oriented Steel Microfibers: Mechanical Properties, Deformability and Fracture Propagation

The aim of the manuscript is to analyze the influence of the magnetic orientation of steel microfibers (length 13 mm, diameter 0.2 mm) on the mechanical properties and fracture propagation of cementitious composites. The series varied in terms of the volumetric content of the fibers, 0%, 1% and 2% (<i>V_f</i>), and the orientation variant, random (S) or magnetic (S-M, <i>B</i> = 80 mT). Three-point bending tests were performed with force-deflection curve (<i>F-δ</i>) registration. The flexural tensile strength (<i>f_ct,_fl</i>), the flexural elastic modulus (<i>E_f</i>), the work of fracture up to a specified residual load level <i>(W_f</i>) and deflection level (<i>W_f*</i>), as well as the compressive strength (<i>f_c</i>) were determined. The improvement of the mechanical properties was noted for magnetically oriented fibers in reference to random arrangement (<i>f_ct,_fl</i>: 90-133%; <i>f_c</i>: 12-34%; <i>W_f*</i>: 98-146%). The efficiency factor (<i>η_X</i>) was introduced to determine the change in property per fiber content unit, which enabled comparison regardless of the fiber dosage. As the higher <i>η_X</i> values were determined for 1% content (e.g., <i>f_ct,_fl</i> equal to 133%/p.p for <i>V_f</i> = 1% and 45%/p.p for <i>V_f</i> = 2%), further increase in dosage was expected to cause reduced improvement. Different fracture mechanisms were noted for S and S-M composites by means of the Digital Image Correlation method.