Enhanced flexural performances of cementitious composite beams with continuously graded steel fiber distribution

[Display omitted] •Successive vibrating treatment can produce graded fiber-reinforced beams.•Fibers tend to orient in one direction and become more concentrated due to vibrating.•Total porosity and critical pore size decrease with the vibrating time.•Graded fiber-reinforced beams show superior ductility and enhanced fiber efficiency. This paper focuses on improving the flexural behavior of steel fiber-reinforced beams with continuously graded structure. Successive vibrating after casting is assumed to be a feasible way to produce graded fiber-reinforced beams (GFRBs), resulting in fibers purposefully distributed in the tensile region. The fiber orientation and distribution are quantified through X-ray computed tomography (XCT). The porosity and pore size distribution are evaluated on the basis of XCT images and mercury intrusion porosimetry. Influences of fiber re-arrangement and microstructure on the compressive strength, the first-cracking strength, the ultimate flexural strength and the flexural toughness index are then investigated. The results show that: (1) the fibers deflect towards the longest side of the beam, and distribute more concentrated at the beam bottom, i.e. more fibers are available to withstand tension, due to the successive vibrating treatment; (2) the high vibration time does not induce a negative influence on the mortar matrix, but rather refines its microstructure with lower porosity and smaller pore size; (3) the flexural behavior is enhanced for fiber re-arrangement and microstructure improvement, revealing that the designed GFRB is capable of sustaining higher flexural strength and energy absorption capacity than the typically vibrated beam with the same fiber content.