A Preliminary Study on the Fibre Recovery Potential of Steel Fibre Reinforced Concrete: Fid-Bau Portal

A Preliminary Study on the Fibre Recovery Potential of Steel Fibre Reinforced Concrete

Vandevyvere, Brecht / Pauwels, Hans / Vandewalle, Lucie

This experimental study investigates the fibre recovery of fibre reinforced concrete. Specifically, a total of 24 fibre reinforced concrete specimens, each containing 30 kg/m³ of 4D Dramix® 55/50 BG fibres, were subjected to different recycling techniques. Initially, the fibre reinforced concrete specimens were crushed using a jaw crusher at the company AC Materials (Ghent, Belgium) until a concrete fraction smaller than 15 cm was achieved. In the second stage, the company Centre Terre et Pierre (CTP), located in Doornik (Belgium), used an impact crusher to maximize the fibre release. The current study indicates that the impact crusher, operating at 40 Hz with a crusher opening of 9 mm, recovered 85% of the fibres from the original fibre reinforced concrete specimens. In contrast, a lower frequency (30 Hz) showed a 5x higher amount of unreleased concrete-fibre components. Moreover, increasing the frequency to 50 Hz did not substantially enhance the fibre recovery, making 40 Hz with 9 mm opening the optimal fibre recovery setting in this study. Due to the recycling procedure, the recovered fibres are distorted, and consequently, the residual tensile strength capacity is slightly reduced compared to the virgin 4D Dramix® 55/50 fibres. The test data clearly show that the reduction is mainly observed at higher crack mouth opening displacements. The average reduction in the f_R3-value is 0.7 MPa (relative decrease of 18%) with the incorporation of 30 kg/m³ recovered 4D Dramix® fibres. Besides a higher level of variability is observed in the test data. Nevertheless, these primary results clearly show the substantial fibre recovery potential and the feasibility of the existing constitutive tensile model in Eurocode 2 for the FRC mixture with recovered steel fibres.