Recycled Tire Rubber

A tire is a composite of complex elastomer formulations, reinforced with plies of fibers and steel
fiber [29]. The number of tires being discarded is an environmental problem in all the world.
Every year nearly 1 billion tons of waste tires are discarded and only a small amount is recycled
[30]. Recycled tires have been extensively studied since the end of previous century to use in
asphalt pavement, waterproofing systems, membrane coating, among others [31].
Although rubber has excellent properties (e.g., high strength, great elasticity and durability), it
may affect several properties of concrete. For instance, cement mixed with coarse or fine
aggregate of waste tire rubber may generate concrete with lower specific density and lower
compressive and tensile strength as well as higher toughness and ductility and more efficient
sound insulation [32]. The variations of the physical and mechanical properties of this concrete
type may depend on replacement ratio and the size of the tire particles added to concrete. Asutkar
et al. [32] measured several physical and mechanical properties of rubber concrete using
different percentage of replacement of rubber aggregates. The aggregates were obtained by
shredding the vehicles scrap tire rubber, achieving a size range between 10 and 20 mm. They
determined that the optimum percentage of replacement of rubber aggregates can be up to 15%.
Even in these conditions rubber waste decreases the concrete compressive strength. Therefore,
they recommend the use of rubber waste aggregates in concrete for construction components
such as partition walls, road barriers, pavements, sidewalks and some other secondary elements
that do not require high compressive strength of concrete. Table 1, Table 2 and Table 3 depict the
mix proportion, physical properties of materials and results of the compressive strength and
density of rubber concrete [32].
Table 1. Mix proportion (kg/m3) of the rubber concrete [32]. Copyright© 2017, Elsevier B.V.
Table
Table 2. Physical properties of materials used as aggregates in the concrete [32]. Copyright©
2017, Elsevier B.V.
Table
Table 3. Compressive strength and density of concrete [32]. Copyright© 2017, Elsevier B.V.
Table
The feasibility of using crumb rubber tire in high strength concrete was studied by Thomas and
Gupta [33]. They investigated that compressive, flexural tensile and pull-off strength of high
strength concrete have a low decrease when the replacement percentage of crumb rubber is less
than 10%. A compressive strength close to 60 MPa was measured for this concrete mixed with
0% to 12.5% crumb rubber. Other mechanical properties such as water absorption, depth of
abrasion and depth of water penetration showed good results for mixes with up to 12.5% crumb
rubber. For these reasons, these authors recommended using high strength concrete with crumb
rubber aggregates for hydraulic structures like tunnels and dam spillways. Therefore, it is very
important to limit the content of aggregates of waste rubber tire in concrete to avoid a high
 reduction of its mechanical properties such as the compressive and tensile strength. Other
mechanical properties such as durability, abrasion and water absorption may be improved when
the percentage of rubber tire waste increases. Thus, recycled tire rubber may be used for normal
and high strength concrete mainly in secondary construction elements.
The steel fibers from waste tires can be mixed with tire rubber to be used as aggregates of
concrete combined with steel fibers from waste tires. Flores-Medina et al. [34] presented
experimental results of thermal and mechanical properties of sustainable concrete. These
concrete incorporated aggregates based on crumb rubber (CR) and steel fibers coated with rubber
(FCR). The rubberized concrete with FCR had better bending and compressive strengths in
comparison to concrete with crumb rubber. Furthermore, the concrete with FCR registered higher
both energy of fracture and toughness than the concrete with crumb rubber. In addition, thermal
conductivity showed the same decrement with waste rubber as aggregate with and without steel
fibers. For these reasons, Flores-Medina et al. [34] proposed using fibers coated with crumb
rubber for precast flat-roofs. Table 4 shows weight analysis of the main components of the two
types of recycled rubber used in [34]. In addition, Table 5 indicates the mix proportions of the
different concrete mixtures considered in [34]. Finally, Table 6 depicts the bulk density, bulk
porosity, compressive strength, Young’s modulus, bending strength, toughness and toughness
index (TI) of concrete specimens with CR an FCR. Deviation factor (%) is indicated between
brackets.
Table 4. Weight analysis of the main components of the two types of recycled rubber [34].
Copyright© 2017, Elsevier B.V.
Table
Table 5. Mix proportions of the different concrete mixtures [34]. Copyright© 2017, Elsevier B.V.
Table
Table 6. Bulk density, bulk porosity, compressive strength, Young’s modulus, bending strength,
toughness and toughness index (TI) results of concrete samples with CR an FCR. Deviation
factor (%) is indicated between brackets [34]. Copyright© 2017, Elsevier B.V.
Table
Although several studies have been carried out with rubberized concrete, more investigations are
necessary that consider its microstructure and influence in corrosion behavior of reinforcement
steel bars [35]. Furthermore, the mechanical behavior of rubberized concrete depends on the size
range and percentage of the rubber particles. Figure 3 shows a comparison of several tire rubber
particles with different size ranges and other aggregates used in rubberized concrete by [35]. It
depicts small and large rubber particles from car tires with size up to 10 mm and 20 mm,
respectively.
 Applsci 11 00629 g003 550Figure 3. Comparison of tire rubber particles with other aggregates
used in concrete mix. Reprinted with permission from [36]. Copyright© 2019, Elsevier B.V.

https://www.mdpi.com/2076-3417/11/2/629

The use of pulverized plastic bottles mixed into concrete construction has gained attention as a
potential sustainable building practice in recent years. This approach involves recycling plastic
bottles by grinding them into small particles or fibers and incorporating them into concrete
mixtures. Here, I'll provide an overview of this concept:

1. Plastic Bottle Recycling: To utilize plastic bottles in concrete construction, the bottles are
typically collected, cleaned, and then pulverized into small pieces or fibers. This process
contributes to reducing plastic waste and promotes recycling.

2. Enhancing Concrete Properties: The addition of pulverized plastic bottles to concrete can offer
several benefits:

Improved Insulation: Plastic particles in concrete can enhance its insulation properties, making
buildings more energy efficient.

Reduced Weight: Concrete with plastic additives can be lighter than traditional concrete, which
may be advantageous in some construction applications.

Increased Flexibility: Plastic fibers can increase the flexibility and crack resistance of concrete,
making it more durable.

Potential Cost Savings: In some cases, using recycled plastic bottles can be more cost-effective
than traditional concrete additives.

3. Environmental Benefits: Incorporating recycled plastic bottles into concrete helps reduce the
demand for new construction materials, such as sand and gravel, which can have environmental
 impacts when extracted in large quantities. It also diverts plastic waste from landfills or the
natural environment.

4. Challenges and Considerations: Despite the potential benefits, there are challenges and
considerations when using plastic bottles in concrete construction:

Engineering and Structural Integrity: The incorporation of plastic materials must be carefully
engineered to ensure the structural integrity and safety of the concrete.

Quality Control: Maintaining consistent quality in the concrete mixture with plastic additives can
be challenging and requires proper quality control measures.

Environmental Impact: While recycling plastic bottles is beneficial, the overall environmental
impact of concrete production, including emissions from cement manufacturing, remains a
concern.

5. Ongoing Research and Innovation: Researchers and construction industry professionals

continue to explore and refine the use of recycled plastic bottles in concrete. New technologies
and methods are being developed to optimize the performance, strength, and sustainability of
such concrete mixtures.

In conclusion, the use of pulverized plastic bottles in concrete construction represents an

innovative approach to recycling plastic waste and improving the sustainability of building
materials. While there are challenges to address, ongoing research and development in this field
offer the potential for more environmentally friendly and efficient construction practices.
Specific projects and studies related to this topic can provide more detailed information and data.