Mechanical behavior of hybrid steel-fiber self-consolidating concrete: Materials and structural aspects

• Hybrid steel FRC were investigated in the materials and structural scale.
• Rheological investigation indicated that the hybridization of fibers lead to an increase in viscosity.
• Fiber hybridization was effective in limiting the initiation and propagation of micro-crack thus increasing the first-crack and ultimate loads.
• Structural tests showed different cracking and failure mechanisms.

This work presents the preliminary results of an experimental investigation on the mechanical behavior of self-consolidating concrete reinforced with hybrid steel fibers in the material and structural scale. Straight and hooked end steel fibers with different lengths and diameters were used as reinforcement in fiber volume fractions of 1.0 and 1.5%. In the fresh state the concrete was characterized using the slump flow, L-box and V-funnel tests. To determine the effect of the hybrid reinforcement on the plastic viscosity and shear yield stress a parallel plate rheometer was used. Following, the mechanical response was measured under tension and bending tests. In the flexural test, the movement of the neutral axis was experimentally determined by strain-gages attached to compression and tensile surfaces. Furthermore, the mechanical response of the material under bi-axial bending was addressed using the round panel test. During the test the crack opening was measured using three linear variable differential transformers (LVDT’s). The cracking mechanisms were discussed and compared to that obtained under four point bending and direct tension. The obtained results indicated that the fiber hybridization improved the behavior of the composites for low strain and displacement levels increasing the serviceability limit state of the same through the control of the crack width. For large displacement levels the use of the longer fibers led to a higher toughness but with an expressive crack opening. Due to its structural redundancy the round panel test allowed the formation of a multiple cracking pattern which was not observed in the four point beam tests. Finally, the obtained material’s properties were used in a nonlinear finite element model to simulate the round panel test. The simulation reasonably agreed with the experimental test data.