Elsevier

Cement and Concrete Research

Volume 36, Issue 9, September 2006, Pages 1686-1691
Cement and Concrete Research

Use of waste tire steel beads in Portland cement concrete

https://doi.org/10.1016/j.cemconres.2006.05.015Get rights and content

Abstract

Large quantities of waste tires are generated every year. The proper disposal of the tires creates an increasing problem that needs to be addressed. Many researchers have investigated the use of recycled tire products in several traditional Civil Engineering materials. The use of crumb rubber and tire chips in Portland cement concrete has been the subject of many research projects over the last years. This study is focusing on the use of steel beads, a by-product of the tire recycling process, in concrete mixtures. Different concrete specimens were fabricated and tested in uniaxial compression and splitting tension. The main variable in the mixtures was the volumetric percentage of the steel beads. The experimental results indicate that although the compressive strength is reduced when steel beads are used, the toughness of the material greatly increases. Moreover, the workability of the mixtures fabricated was not significantly affected.

Introduction

Because of the environmental threat associated with the waste tires, their proper disposal has attracted a lot of attention in the last years. In the United States alone, 290 million tires are generated per year along with an existing 275 million tires currently stockpiled throughout the nation [1]. In order to properly dispose of these millions of tires, the use of innovative techniques to recycle them is important. Without the proper disposal of these waste tires, the resulting stockpiles would cause major health risks for the public and the environment [2], [3], [4].

There has been an increased interest in using the recycled waste tire products. This interest is proven by a higher than 80% use of scrap tires produced in the United States for beneficial use, as opposed to only 25% in 1990 [1]. Thanks to Civil Engineering research, numerous uses of scrap tires have been introduced, including use in landfills, septic drain fields, subgrade fill, and chemically modified asphalt binder [1], [5]. Of particular interest is the use of waste tires in Portland cement concrete.

The two main products of the tire recycling are: (i) crumb rubber and (ii) tire chips (see Fig. 1a). Crumb rubber consists of ground rubber particles, while tire chips are larger shredded rubber pieces, which contain a relatively small quantity of steel wires. A byproduct of the recycling process is the waste steel bead. The beads in the passenger tires are made of high tensile strength steel wires (1500–1900 MPa) and are used to secure the tire in the rim. The recycled steel beads, being products of the magnetic separation, include short steel wires as well as wires covered by or embedded in rubber pieces (see Fig. 1b). The difference between the tire chips and the steel beads is that the steel beads contain a much smaller quantity and size of rubber pieces and larger quantity of steel wires, as indicated by the rubber and steel volume fractions shown in Table 1. As the steel beads are currently not being reused, it would be environmentally beneficial to study their potential use as a recycled material.

The use of crumb rubber and tire chips in concrete for recycling purposes has attracted a lot of attention [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17]. It has been reported that the replacement of coarse aggregate with waste tire chips in Portland cement concrete mixtures results in a significant increase of toughness and ductility [5], [6], [7], [8], [9], [14], [15]. On the contrary, losses in compressive strength of up to 85% have been reported when replacing the entire coarse aggregate fraction with tire chips [5], [6], [7], [8], [9], [10], [14], [15], [16], [17]. The type of tire that is used to replace the coarse aggregate plays a very important role in the performance of the concrete mixture. Tire particles from truck tires are much stiffer than those of car tires, leading to stronger and stiffer concrete mixtures [5], [7], [17]. Along with the reduction in compressive strength, significant losses in the stiffness of the specimens were reported [5], [6], [7], [8], [15]. The improved ductility and toughness could be very beneficial in several civil engineering applications. However, the large decrease of compressive strength makes the recycling of waste tire products in concrete unattractive. While the use of both crumb rubber and tire chips has been widely investigated, no study has explored the potential incorporation of waste steel beads. The purpose of the experimental work presented in this study was to investigate the use of waste tire steel beads in Portland cement concrete.

Since the steel beads contain a significant volumetric percentage of steel wires (30–70%), the recycled steel bead concrete (RSBC) could be considered as a relative material to steel fiber reinforced concrete (FRC). However, main differences between the FRC and the RSBC exist: (i) the existence of rubber in RSBC, which is absent in FRC, and (ii) the identical dimensions and properties of the steel fibers used in the FRC, compared to large variations in shape, length, diameter and mechanical properties of the steel bead wires. The addition of steel fibers in FRC results in improvement of most mechanical properties [18], [19], [20]. The ductility and toughness is reported to increase, while no reduction in compressive strength is reported. Although previous findings suggest that that the increase in tensile strength provided by steel fibers typically is high, the increase in compressive strength typically does not exceed 25% [18]. Furthermore, the increase in compressive strength can be considered negligible when the volume fraction of the fibers is small.

The authors believe that the RSBC will exhibit better mechanical properties compared to concrete made with the addition of other recycled tire products such as crumb rubber or tire chips. Based on a review of the effects that crumb rubber, tire chips and steel fibers have on the freshly mixed and hardened properties of concrete, the authors believe that the incorporation of steel beads in concrete could lead to a viable, environmentally friendly material with attractive properties.

Section snippets

Mix design and materials

The control mix of concrete was designed with a mix ratio of cement/water/sand/coarse of 1.0:0.45:1.2:2.0 by weight. This mix design yielded an average 28 day compressive strength of 40.92 MPa (5935 psi). In the concrete mix, a Type I/II Portland cement was used. The fine aggregate had a specific gravity of 2.7 and a fineness modulus of 2.8. The coarse aggregate had a specific gravity of 2.65 with a maximum aggregate size of 12.5 mm (1/2 in.).

The waste tire particles used consisted of steel

Analysis of results

Several properties of the RSBC mixtures were examined in this study. The properties are separated into two main categories: (i) freshly mixed concrete properties and (ii) hardened concrete properties. The effects of the steel beads on the concrete mixture properties are presented below.

Conclusions

Based on the results obtained and the observations made during testing of the specimens, the following conclusions can be made:

  • Concrete mixtures can be made containing small volume fractions of waste tire steel beads. The mixes are workable up to 4% volume fractions although there is a decrease in workability with an increase in steel bead content.

  • The inclusion of waste tire steel beads slightly reduces the density of a concrete specimen when compared to the control mix.

  • The addition of steel

Acknowledgments

This study was supported by the University of Massachusetts Dartmouth. The authors would like to thank Dr. D.A. Tata and Dr. William Edberg for their helpful comments, as well as students: Michael Rodrigues, Jonathan Novak, and Asa Mintz for their assistance.

References (28)

  • S.S. Singh

    Innovative applications of scrap-tires

    Wisconsin Professional Engineer

    (1993)
  • M. Nehdi et al.

    Cementitious composites containing recycled tire rubber: an overview of engineering properties and potential applications

  • Z.K. Khatib et al.

    Rubberized Portland cement concrete

    Journal of Materials in Civil Engineering

    (1999)
  • P.K. Mehta et al.

    Concrete, Structure, Properties, and Materials

    (1993)
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