3. Mechanical properties

#### 3.1. Compressive strength

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


50 mm

versus fine rubber particles indicate that coarse and fine rubber particles are more effective at substitution ratios of less and more than 25%, respectively [14]. Using larger sizes of TDA, also known as tire chips, provides an opportunity to keep the steel belt wires after shredding in order to lower the costs, even though, they may not provide any specific advantage for the mix [25]. On the same line, application of fiber reinforcement by adding polypropylene fibers has

Reference Rubber aggregate Replaced conventional aggregate Specimen type/

Son et al. [19] Crumb rubber particles 1 mm Total aggregate weight (coarse & fine) Cylinder 100∅

Crumb rubber 600 μm River sand fine aggregate Cube 100 mm

4–16 mm

Large rubber particles 2.2 mm Limestone coarse aggregate Cylinder 150∅

19 mm

Crumb Rubber 6 mm Gravel coarse aggregate 12 mm Cylinder 100∅

31.5 mm

31.5 mm

Crushed limestone coarse aggregate

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

Crushed stone coarse aggregate

Crushed stone coarse aggregate

Mohammed et al. [18]

Topcu and Avcular [21]

Xue and Shinozuka [23]

Topcu [20] Rubber particles from mechanical grinding 6 mm

Zheng et al. [24] Crushed rubber with steel belt wires 4–15 mm

Zheng et al. [25] Ground rubber 2.6 mm and crushed

Table 1. Summary of selected research on rubberized concrete.

rubber with steel belt wires 4–15 mm

size

http://dx.doi.org/10.5772/intechopen.74313

200 mm

300 mm

200 mm Lumped Mass Columns

Cube 150 mm 60-day Beams 100 160 1000 mm

Cylinder 150∅ 300 mm

Cylinder 150∅ 300 mm

139

Cylinder 100∅ 200 mm Beams 100 100 350 mm

Similar to conventional concrete, application of supplementary cementitious materials such as silica fumes has shown to be effective on increasing the compressive strength of TDA concrete containing high water-to-cement ratios [11]. Replacing 7% of cement with silica fume has shown to increase the compressive strength between 3 and 7 MPa [23]. Tire-derived aggregates are also applicable to self-compacting concrete, which utilizes fine filler materials, admixtures such as superplasticizers, and viscosity modifying agents. Combination of shredded tire and crumb rubber has the potential to replace nearly 20–30% of the sand with a similar grain size [9]. Further, it is also possible to replace cement with ground rubber. Substitution of 5% of cement has shown to reduce the compressive strength by 5% [10]. Tire-derived aggregate concrete with enhanced characteristics due to admixtures and supplementary cementitious materials has

shown to be effective in reducing crack propagation due to shrinkage [12].

Toutanji [22] Tire chips 12.7 mm Crushed stone coarse aggregate


Table 1. Summary of selected research on rubberized concrete.

Reference Rubber aggregate Replaced conventional aggregate Specimen type/

Shredded tire chips 11–22 mm Crushed limestone coarse aggregate

Crumb rubber 1 mm Sand fine aggregate Cylinder 100∅

4–16 mm

Scrap and crumb tires 0.05–2 mm Fine aggregate sand 0–4 mm Cube 150 mm

Chipped rubber 25 mm Crushed siliceous coarse aggregate Cube 150 mm

Rubber strip fibers 8.5–21.5 mm No material removed Cylinder 150∅

Crumb rubber (similar to sand used) Crushed sand Cylinder 150∅

Khaloo et al. [14] Coarse tire chips Crushed stone gravel 20 mm Cylinder (50-day

Liu et al. [17] Crumb tire rubber 0.178 mm River sand fine aggregate 5 mm Cubes 150 mm

Crumb rubber Coarse lightweight expanded shale

aggregate

Natural sand 4 mm and crushed limestone 20 mm replaced equally

Tire shreds 20 mm w/ Steel Fibers

Large rubber 13 mm and crumb rubber

Crumb rubber similarly graded to sand

Tire chips from mechanical shredding 10–

and tire chips 10–40 mm

Included

#10-20

50 mm

Li et al. [16] Truck & car tire chips and fibers with and w/o steel belt 25–51 mm

Aiello and Leuzzi [5]

138 Cement Based Materials

Al-Tayeb et al.

Atahan and Sevim [7]

Atahan and Yucel [8]

Bignozzi and Sandrolini [9]

Ganjian et al. [10]

Guneyisi et al. [11]

Hernandez-Olivares et al. [12]

Issa and Salem

Khatib and Bayomy [15]

Miller and Tehrani [4]

[13]

[6]

size

200 mm Beams 100 50 400 mm

200 mm

Beams 250 250 900 mm

Cylinder 150∅ 300 mm Full Scale Barriers 1000 450 250 mm

Beams 100 100 500 mm

Cube 150 mm Cylinder 150∅ 300 mm (90-day strength)

300 mm Beams 150 150 600 mm

300 mm

strength)

300 mm Beams 152 152 50 mm

300 mm

Cylinders 35∅ 70 mm (SHPB Impact)

Cylinder 150∅ 300 mm Beams 152 152 50 mm

Coarse aggregate 12.5–20 mm Cube 150 mm

Crushed Stone 19 mm and Sand Cylinder 100∅

Coarse aggregate gravel Cylinder 150∅

Coarse aggregate gravel Cylinder 150∅

versus fine rubber particles indicate that coarse and fine rubber particles are more effective at substitution ratios of less and more than 25%, respectively [14]. Using larger sizes of TDA, also known as tire chips, provides an opportunity to keep the steel belt wires after shredding in order to lower the costs, even though, they may not provide any specific advantage for the mix [25]. On the same line, application of fiber reinforcement by adding polypropylene fibers has shown to be effective in reducing crack propagation due to shrinkage [12].

Similar to conventional concrete, application of supplementary cementitious materials such as silica fumes has shown to be effective on increasing the compressive strength of TDA concrete containing high water-to-cement ratios [11]. Replacing 7% of cement with silica fume has shown to increase the compressive strength between 3 and 7 MPa [23]. Tire-derived aggregates are also applicable to self-compacting concrete, which utilizes fine filler materials, admixtures such as superplasticizers, and viscosity modifying agents. Combination of shredded tire and crumb rubber has the potential to replace nearly 20–30% of the sand with a similar grain size [9]. Further, it is also possible to replace cement with ground rubber. Substitution of 5% of cement has shown to reduce the compressive strength by 5% [10]. Tire-derived aggregate concrete with enhanced characteristics due to admixtures and supplementary cementitious materials has

rubber aggregates suggest that using tire chips have more impact on the reduction of elastic modulus than using waste tire fibers do [16]. However, there are also evidences that the

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

http://dx.doi.org/10.5772/intechopen.74313

141

Further, using tire chips containing steel belts increases the stiffness of TDA concrete [16, 24, 25]. In addition, application of fly ash and silica fume can also enhance the modulus of elasticity [11, 23].

Figure 4 indicates how increasing the rubber content reduces the splitting tensile strength. However, existing research agrees that capacity of rubber in absorbing energy enhances the toughness of the TDA concrete [6, 16, 20]. Application of fiber reinforcement using polypropylene fibers has shown to improve the toughness further [12]. Comparison of results for compressive and tensile strengths suggests that the rate of reduction for split-tensile strength is less than the same rate for compressive strength [11]. Further, there are reports indicating that specimens with ground tires perform better in tension than specimens containing large

The relationship between flexural strength and TDA content is similar to other mechanical properties (Figure 5). However, there are variations in this relationship. Studies generally indicate that reduction of flexural strength parallels an increase in the ductility of specimens [22]. Some research indicates that the rate of reduction for the flexural strength is much steeper than other mechanical properties, particularly at lower rubber contents [15]. Application of smaller rubber particles improves the observed flexural strength [5, 10]. Adding polypropylene fibers has also shown to be effective in crack control, but not necessarily in enhancement of

Figure 4. Selected reported relative changes in the split-tensile strength of rubberized concrete.

reduction of modulus of elasticity is only a function of the rubber content [10].

3.3. Split-tensile strength

tire chips [10].

3.4. Flexural strength

the strength [12].

Figure 2. Selected reported relative changes in the compressive strength of rubberized concrete.

applications in hollow concrete blocks. The recommended rubber contents for loadbearing and non-loadbearing systems are 6.5 and 40.7%, respectively [18].

#### 3.2. Modulus of elasticity - static

Research shows that increasing the rubber content in concrete decreases the static modulus of elasticity [6–8, 19]. However, there is not much agreement on the amount of reduction at high rubber contents (Figure 3). Generally, Tire-derived aggregates influence the stress-strain relationship and enhance the ductility of the concrete [14]. Some comparative studies on the size of

Figure 3. Selected reported relative changes in the static modulus of elasticity of rubberized concrete.

rubber aggregates suggest that using tire chips have more impact on the reduction of elastic modulus than using waste tire fibers do [16]. However, there are also evidences that the reduction of modulus of elasticity is only a function of the rubber content [10].

Further, using tire chips containing steel belts increases the stiffness of TDA concrete [16, 24, 25]. In addition, application of fly ash and silica fume can also enhance the modulus of elasticity [11, 23].

#### 3.3. Split-tensile strength

Figure 4 indicates how increasing the rubber content reduces the splitting tensile strength. However, existing research agrees that capacity of rubber in absorbing energy enhances the toughness of the TDA concrete [6, 16, 20]. Application of fiber reinforcement using polypropylene fibers has shown to improve the toughness further [12]. Comparison of results for compressive and tensile strengths suggests that the rate of reduction for split-tensile strength is less than the same rate for compressive strength [11]. Further, there are reports indicating that specimens with ground tires perform better in tension than specimens containing large tire chips [10].

#### 3.4. Flexural strength

applications in hollow concrete blocks. The recommended rubber contents for loadbearing and

Research shows that increasing the rubber content in concrete decreases the static modulus of elasticity [6–8, 19]. However, there is not much agreement on the amount of reduction at high rubber contents (Figure 3). Generally, Tire-derived aggregates influence the stress-strain relationship and enhance the ductility of the concrete [14]. Some comparative studies on the size of

non-loadbearing systems are 6.5 and 40.7%, respectively [18].

Figure 2. Selected reported relative changes in the compressive strength of rubberized concrete.

Figure 3. Selected reported relative changes in the static modulus of elasticity of rubberized concrete.

3.2. Modulus of elasticity - static

140 Cement Based Materials

The relationship between flexural strength and TDA content is similar to other mechanical properties (Figure 5). However, there are variations in this relationship. Studies generally indicate that reduction of flexural strength parallels an increase in the ductility of specimens [22]. Some research indicates that the rate of reduction for the flexural strength is much steeper than other mechanical properties, particularly at lower rubber contents [15]. Application of smaller rubber particles improves the observed flexural strength [5, 10]. Adding polypropylene fibers has also shown to be effective in crack control, but not necessarily in enhancement of the strength [12].

Figure 4. Selected reported relative changes in the split-tensile strength of rubberized concrete.

but reduces the strength. This explains how some studies have shown a reduction of toughness because of increasing the rubber content, even though subjected specimens have shown significant increase in ductility [20]. Nevertheless, most reported data show a general increase in toughness with the increase in rubber content [5, 22]. Some research studies have also suggested that a maximum toughness value exist for the optimum rubber content and proper TDA gradation [14]. Measuring toughness from the brittleness index using the stress-strain hysteresis loops also confirms the positive effect of rubber on the toughness [25]. In addition, the toughness of TDA concrete subject to impact load also increases with the increase in strain rate [17]. Furthermore, application of fibers, particularly in tensile specimens, significantly enhances the

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

http://dx.doi.org/10.5772/intechopen.74313

143

Some of the most beneficial properties of rubberized concrete include its behavior under dynamic loading, making the enhancement of these properties desirable in comparison with the brittle and rigid behavior of plain concrete. Research suggests that rubberized concrete may have practical applications as traffic barriers, vibration mitigation, and seismic force mitigation among others. There are various techniques for investigation of these behaviors. Figures 7 and 8 show two significant parameters, energy absorption and damping, respectively, measured for TDA concrete at different rubber contents. As shown in these figures, there are limited studies as the

The full-scale New Jersey-shaped safety barriers subject to non-severe impact loads indicate a gradual increase in the energy absorption when rubber content changes from 0 to 100% by volume [7]. These results are qualitatively comparable with similar collision testing studies [21]. However, impact testing on hybrid beams, containing a layer of TDA concrete on top of plain concrete has resulted in significant increase in energy absorption for only 20% rubber content [6]. Similar tests using falling weights confirms the effectiveness of TDA concrete in reducing the severity of the impact at only 20–40% rubber contents, even though, the pest

performance is achieved at rubber contents larger than 60–80% [8].

Figure 7. Selected reported relative changes in the damping ratio of rubberized concrete.

toughness [16].

3.6. Dynamic properties

basis for each of these relationships.

Figure 5. Selected reported relative changes in the flexural strength of rubberized concrete.

Rubberized concrete has also applications in composite floors. Research shows that floors with 10% rubber content have smaller failure load due to flexure in large spans, but nearly the same failure load caused by shear in short spans. The capability of TDA composite floors in withstanding larger deformations has a significant impact on the ductility of the system [26].

#### 3.5. Toughness

Figure 6 contains selected reported data on the relationship between toughness and rubber content in TDA concrete. Toughness is generally a measure based on the area covered by the load-deflection diagrams, thus, it relates to both ductility and strength. As a result, reported data points on toughness are scattered, as rubber contents increases the ductility,

Figure 6. Selected reported relative changes in the toughness of rubberized concrete.

but reduces the strength. This explains how some studies have shown a reduction of toughness because of increasing the rubber content, even though subjected specimens have shown significant increase in ductility [20]. Nevertheless, most reported data show a general increase in toughness with the increase in rubber content [5, 22]. Some research studies have also suggested that a maximum toughness value exist for the optimum rubber content and proper TDA gradation [14]. Measuring toughness from the brittleness index using the stress-strain hysteresis loops also confirms the positive effect of rubber on the toughness [25]. In addition, the toughness of TDA concrete subject to impact load also increases with the increase in strain rate [17]. Furthermore, application of fibers, particularly in tensile specimens, significantly enhances the toughness [16].

#### 3.6. Dynamic properties

Rubberized concrete has also applications in composite floors. Research shows that floors with 10% rubber content have smaller failure load due to flexure in large spans, but nearly the same failure load caused by shear in short spans. The capability of TDA composite floors in withstanding larger deformations has a significant impact on the ductility of the system [26].

Figure 5. Selected reported relative changes in the flexural strength of rubberized concrete.

Figure 6. Selected reported relative changes in the toughness of rubberized concrete.

Figure 6 contains selected reported data on the relationship between toughness and rubber content in TDA concrete. Toughness is generally a measure based on the area covered by the load-deflection diagrams, thus, it relates to both ductility and strength. As a result, reported data points on toughness are scattered, as rubber contents increases the ductility,

3.5. Toughness

142 Cement Based Materials

Some of the most beneficial properties of rubberized concrete include its behavior under dynamic loading, making the enhancement of these properties desirable in comparison with the brittle and rigid behavior of plain concrete. Research suggests that rubberized concrete may have practical applications as traffic barriers, vibration mitigation, and seismic force mitigation among others. There are various techniques for investigation of these behaviors. Figures 7 and 8 show two significant parameters, energy absorption and damping, respectively, measured for TDA concrete at different rubber contents. As shown in these figures, there are limited studies as the basis for each of these relationships.

The full-scale New Jersey-shaped safety barriers subject to non-severe impact loads indicate a gradual increase in the energy absorption when rubber content changes from 0 to 100% by volume [7]. These results are qualitatively comparable with similar collision testing studies [21]. However, impact testing on hybrid beams, containing a layer of TDA concrete on top of plain concrete has resulted in significant increase in energy absorption for only 20% rubber content [6]. Similar tests using falling weights confirms the effectiveness of TDA concrete in reducing the severity of the impact at only 20–40% rubber contents, even though, the pest performance is achieved at rubber contents larger than 60–80% [8].

Figure 7. Selected reported relative changes in the damping ratio of rubberized concrete.

to present characteristics of TDA concrete, which was simplified to ten parameters in the

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

http://dx.doi.org/10.5772/intechopen.74313

145

Numerical simulations using finite element analysis are also available to model mechanical properties of TDA concrete. The basis for these simulations is generally an elastoplastic model for the behavior of materials. Successful modeling of beam specimens has been reported using hexahedron elements with standard shape functions [6]. Using a two-phase composite material helps to define the dispersion of TDA in the cementitious matrix. This

Figure 9 shows a comparative view of the relationships between mechanical properties of TDA concrete and the TDA content volume. This figure suggests that developing a simple model for practical design of TDA concrete elements may be possible, as various strengths follow similar

In this model, SRF is the "strength reduction factor"; R is the rubber content as a volumetric ratio by the total volume of aggregates; and a, b, and m are modeling parameters. This equation is equal to unity at a rubber content of 0% and reaches an asymptote at higher rubber content values. The m parameter indicates the degree of curvature of the reduction and is a function of the particle size. In addition, parameters a and b must satisfy the relationship a þ b ¼ 1. Table 2 contains suggested modeling parameters from

Figure 9. Selected reported relative changes in the dynamic properties of rubberized concrete (marked data) and their

SRF <sup>¼</sup> <sup>a</sup> <sup>þ</sup> <sup>b</sup>ð Þ <sup>1</sup> � <sup>R</sup> <sup>m</sup> (1)

model utilized three-node triangular elements to simulate split-tensile tests [16].

Eq. (1) presents a proposed model to find the strength reduction factor [15]:

modified form [17].

4.2. Suggested strength reduction factors

trends in respect to TDA content.

past studies.

general trends (trend-lines).

Figure 8. Selected reported relative changes in the absorbed energy of rubberized concrete.

Similarly, the damping ratio of TDA concrete measured by elastic wave method showed a moderate increase because of the increase in the rubber content in concrete [24]. However, the shake-table studies on TDA concrete columns indicated much higher damping ratios [23]. These comparisons indicate how TDA becomes more effective in post-peak performance of concrete specimens. Further, same shake table studies have shown that increasing rubber content in the TDA concrete reduces the natural frequencies and the response acceleration by 28 and 27%, respectively [23].

Non-destructive tests using ultrasonic pulses confirm that rubber reduces the velocity of waves, which is in correlation with lower dynamic modulus of elasticity [14]. Dynamic compression tests confirm the capability of TDA concrete in dissipating energy and show that increasing the load frequency or strain rate increases the dynamic modulus of elasticity [12, 17]. However, the age of the specimens has an adverse impact on the energy dissipation [12].

#### 3.7. Thermal conductivity, electrical conductivity and sound absorption

Nonstructural mechanical properties of TDA concrete have been subject to studies for specific applications. Non-loadbearing wall elements often require proper thermal and electrical insulation as well as sound absorption. Studies indicate that TDA improves the sound absorption of concrete, reduces the thermal conductivity coefficient, and increases the electrical resistivity [13, 18, 27].
