2. An overview of constituent materials

Other than the inclusion of the rubber particles, the rubberized concrete mix is virtually the same as most other concrete including cement, fine aggregates, coarse aggregates, and water. Some researchers have incorporated super plasticizers, in order to achieve better workability. Others have experimented with the use of silica fume and fly ash in order to achieve enhanced strengths. Further, researchers have experimented with pretreating the rubber particles using chemical washes in attempts to develop better bonds between the rubber particles and the cementitious matrix. Following sections discuss individual components making up the rubberized concrete matrix.

#### 2.1. Tire-derived aggregate materials

TDA refers to the rubber particles, processed from multiple types of tires differing in composition and fiber type, used for replacing the mineral or rotary kiln expanded lightweight aggregates in many mixtures (Figure 1). Descriptive classification of rubber particles relies on the size and manufacturing processes of materials [3]. The first and largest classification of TDA is shredded tire chips, which are typically results of mechanical shredding. Resulting tire chips may be as large as 460 mm long by 230 mm wide to as small as 150 mm long. A combination of both primary and secondary shredding processes is also common to produce smaller shredded chips. The next classification is ground rubber; with a typical range of 19–0.1 mm in size. Ground rubber is subject to two stages of magnetic separation and Tire-Derived Aggregate Cementitious Materials: A Review of Mechanical Properties http://dx.doi.org/10.5772/intechopen.74313 137

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

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

#### 2.2. Mix design constituents

or coarse aggregate as a percentage of volume or weight. This application redirects a signif-

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

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

Other than the inclusion of the rubber particles, the rubberized concrete mix is virtually the same as most other concrete including cement, fine aggregates, coarse aggregates, and water. Some researchers have incorporated super plasticizers, in order to achieve better workability. Others have experimented with the use of silica fume and fly ash in order to achieve enhanced strengths. Further, researchers have experimented with pretreating the rubber particles using chemical washes in attempts to develop better bonds between the rubber particles and the cementitious matrix. Following sections discuss individual components making up the rub-

TDA refers to the rubber particles, processed from multiple types of tires differing in composition and fiber type, used for replacing the mineral or rotary kiln expanded lightweight aggregates in many mixtures (Figure 1). Descriptive classification of rubber particles relies on the size and manufacturing processes of materials [3]. The first and largest classification of TDA is shredded tire chips, which are typically results of mechanical shredding. Resulting tire chips may be as large as 460 mm long by 230 mm wide to as small as 150 mm long. A combination of both primary and secondary shredding processes is also common to produce smaller shredded chips. The next classification is ground rubber; with a typical range of 19–0.1 mm in size. Ground rubber is subject to two stages of magnetic separation and

icant amount of waste rubber from landfills to infrastructure industries.

rubber for use in concrete has continued to attract the attention of researchers.

such as traffic barriers and other impact-resistant systems.

2. An overview of constituent materials

berized concrete matrix.

136 Cement Based Materials

2.1. Tire-derived aggregate materials

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 ease of mixing and placing operations [4].
