ZEMCH 2015 - International Conference Proceedings | Page 779

investigations, carried out by the authors, with different types of RSF. It was also considered the
need of suitable solutions to improve the final properties of the concrete in the perspective of an
industrial application of the proposed material. In this context is well recognized that the workability is strongly influenced by the particular type of fibre used. Using fibres derived from ST, the
characteristic high dimensional variability is the main cause of their balling tendency within the
mixture that consequently, reduces the workability of the mix.
As can be noted in Fig.1, RSF are characterized by different geometrical dimensions and they also
present many irregular wrinkles. Thus, a geometrical characterization analysis of the fibres was
performed on a sample of 1.000 specimens, randomly extracted after the shredding process of
the tires. The analysis is essential to evaluate the scatter of the lengths and diameters of the fibres,
which affects the tendency of a fibre reinforced mixture to produce balling of fibres in the freshly
mixed state. The fibre diameters varied between 0.11 mm and 1.71 mm and the class with the higher frequency was 0.20-0.25 mm (21.8%), as shown in Fig. 2.

Figure 2: Diameters frequency

The average value of the diameter was 0.33 mm with a C.O.V. equal to 41.34%. The length of the
reinforcement is referred to the distance between the outer ends of the fibres (Fig. 3). The class
including the major number of fibre length was 5-15 mm (65.3%), as shown in Fig. 4. The average
value of the fibre length was 12.63 mm with a C.O.V. of 61.36%.

Figure 3: Equivalent length definition

Application of steel fibres derived from scrap tires as reinforcement in concrete

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