1. Introduction

Investigation of rubberized concrete has received considerable attention since late twentieth century, when exploration of the idea of adding rubber particles to the concrete matrix began. The intriguing idea for many has been the combination of an ultra-flexible material to an ultra-rigid material to enhance ductile performance of the composite material. In addition, the idea of incorporating a waste material that may otherwise end up in a landfill is attractive for sustainable development. The main constituent of rubberized concrete is tirederived aggregate (TDA), incorporated in a cementitious matrix through replacement of fine

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

or coarse aggregate as a percentage of volume or weight. This application redirects a significant amount of waste rubber from landfills to infrastructure industries.

The idea of repurposing a waste material for use in concrete has roots in concerns regarding the amount of waste tires in landfills. The United States alone generates 289 million scrap tires on an annual basis as of 2006 [1]. The Environmental Protection Agency (EPA) identifies stockpiled tires as an "ideal incubator for mosquito larvae" and connects this to the spread of the West Nile Virus from 1999 to 2005 [1]. As of 2012, tires were being recycled at a rate of 44.6% with rubber and leather contributing 6.18 million tons of waste after accounting for recycling and recovery [2]. The idea of reducing the number of waste tires that accumulate in landfills through recycling rubber for use in concrete has continued to attract the attention of researchers.

The general focus of research on rubberized concrete is the evaluation of mechanical properties of the concrete. The basic properties include compressive, tensile, and flexural strengths. The performance of TDA concrete subject to dynamic loading is another essential property of TDA concrete. In addition, application of supplementary cementitious materials and admixtures, such as silica fume and fly ash, has potentials to enhance various characteristics of TDA concrete. Research seems to be in support of the fact that the lower strength and enhanced dynamic properties of the TDA concrete mixtures are valuable in certain practical applications such as traffic barriers and other impact-resistant systems.

screening to remove the steel fibers from the rubber particles. The smallest classification of TDA is crumb rubber, obtained through micro-milling, cracker-milling, and granular processes. Crumb rubber particle sizes range from 4.75 to 0.075 mm. Another method is a cryo-

Tire-Derived Aggregate Cementitious Materials: A Review of Mechanical Properties

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The common fine aggregate used in most research studies on rubberized concrete is natural sand with a gravel coarse aggregate. The cement used is either Type 1 or Type 2 cement, with no significant evidence suggesting one type of cement performing better. Other admixtures incorporated into rubberized concrete include the addition of silica fume and fly ash by replacement of cement. This enhances the strength of rubberized concrete and bond between the rubber and cement. Further, rubber particles may also replace lightweight aggregates (LWA), such as rotary kiln expanded shale, clay, and slate, in various lightweight concrete materials, where, the similarity between the volume weights of TDA and LWA enhances the

Table 1 lists selected research projects and their characteristics. Existing literature indicates that an increase in rubber content results in a systematic decrease in the compression strength of the concrete material (Figure 2). The substitution of mineral aggregates with TDA is generally between 0 and 100% of the total aggregate volume in increments of 20%. The relationship between the compressive strength and rubber content in the mix is not linear [22]. Further, the size of the particles has an impact on this relationship. While, inclusion of 100% crumb rubber may reduce the compressive strength by more than 90% [8], substitution of fine aggregates by less than 25% appears to have no significant impact on this strength [13]. In particular, research has shown that application of fine crump rubbers has less negative impact on the compressive strength of the mix [5, 6, 15, 20]. A comparison between applications of coarse rubber particles

genic method, in which the rubber is frozen using nitrogen and then shattered [3].

Figure 1. Crumb rubber manufactured through mechanical shredding of recycled tires.

2.2. Mix design constituents

ease of mixing and placing operations [4].

3. Mechanical properties

3.1. Compressive strength
