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. 2021 Oct 15;14(20):6111.
doi: 10.3390/ma14206111.

Residual Strength and Drying Behavior of Concrete Reinforced with Recycled Steel Fiber from Tires

David Revuelta  1 , Pedro Carballosa  1 , José Luis García Calvo  1 , Filipe Pedrosa  1   2
Affiliations

Residual Strength and Drying Behavior of Concrete Reinforced with Recycled Steel Fiber from Tires

David Revuelta et al. Materials (Basel). .

Abstract

Fiber reinforcement of concrete is an effective technique of providing ductility to concrete, increasing its flexural residual strength while reducing its potential for cracking due to drying shrinkage. There are currently a wide variety of industrial fibers on the market. Recycled steel fibers (RSF) from tires could offer a viable substitute of industrialized fibers in a more sustainable and eco-friendly way. However, mistrust exists among users, based on fear that the recycling process will reduce the performance, coupled with the difficulty of characterization of the geometry of the RSF, as a consequence of the size variability introduced by the recycling process. This work compares the behavior of RSF from tires compared with industrialized steel or polypropylene fibers, evaluating the fresh state, compressive strength, flexural residual strength, and drying behavior. The concept of Equivalent Fiber Length (EFL) is also defined to help the statistical geometrical characterization of the RSF. A microstructural analysis was carried out to evaluate the integration of the fiber in the matrix, as well as the possible presence of contaminants. The conclusion is reached that the addition of RSF has a similar effect to that of industrialized fibers on concrete's properties when added at the same percentage.

Keywords: drying shrinkage; fiber reinforced concrete; flexural residual strength; polypropylene fibers; recycled fibers; steel fibers.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Figures

Figure 1
Figure 1
“Balling” effect of recycled steel fibers from tires (Picture by authors).
Figure 2
Figure 2
Recycled steel fibers from tires used in this paper.
Figure 3
Figure 3
Common industrial fibers used in this paper: (a) polypropylene fibers; (b) steel fibers.
Figure 4
Figure 4
Examples of RSF length characterization: (a) from [32]; (b) used in this paper.
Figure 5
Figure 5
Definition of an Equivalent Fiber Length (EFL).
Figure 6
Figure 6
Concrete rings made to ascertain cracking resistance according to ASTM C1581 [57] (Picture by authors).
Figure 7
Figure 7
Test set up to ascertain flexural tensile strength according to EN 14651 [58] (Picture by authors).
Figure 8
Figure 8
Histograms of geometrical characteristics: (a) Equivalent Fiber Length; (b) diameter.
Figure 9
Figure 9
Slump-test cones from EN 12350-2 [51] test method: PPF-CC (a), RSF-CC (b), SF-RS (c), and RSF-RS (d). (Pictures by authors).
Figure 10
Figure 10
Inner ring strains recorded with the ASTM C1581 [57] test for cracking control evaluation: PPF-CC mix (a) and RSF-CC mix (b).
Figure 11
Figure 11
Load vs. CMOD curves according to EN 14651 [58] for determining flexural residual strength: SF-RS (a), RSF-RS (b), and average curves (mean of the three specimens per mix) for both mixes (c).
Figure 12
Figure 12
Location of the crack at the center spam in one of the tested beams (Picture by authors).
Figure 13
Figure 13
Recycled steel fiber (elements with spherical or elliptical shape in in light gray color) in the cementitious matrix.
Figure 14
Figure 14
Detail of the fiber-matrix interface and appearance of the matrix component phases.
Figure 15
Figure 15
Detail of the surface of the recycled steel fiber embedded in the cementitious matrix.
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References

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