*2.3.6 Composite materials*

Composite materials for noise barriers can be defined as any product composed of two or more "basic" materials, for example, wood mixed with concrete and then placed on a concrete foundation. By combining basic materials, the characteristics of the final product (noise barriers) and its durability, and even in some cases safety, are altered.


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be involved.

*Innovative Approaches to Noise Reduction DOI: http://dx.doi.org/10.5772/intechopen.93056*

density of 20 kg/m2

1960s [17].

**3.1 Soundscape definition**

people, music and traffic noise.

**2.4 Noise barriers transmission loss (***TL***)**

find material testing reports from authorised laboratories.

is possible and of great interest to record current soundscapes.

and anthrophony [17], which is shown in **Figure 8**.

**3. A contemporary approach: soundscape**

Typical values of the noise barriers transmission loss (TL) parameter when looking at the A-weighted characteristic are from 10 dBA to 15 dBA. Noise barriers should be constructed of materials with a minimum density of 20 kg m<sup>2</sup>

materials (i.e. higher material density enables a thinner material). **Table 1** gives the approximate TL values for some common materials, tested for a typical A-weighted highway traffic frequency spectrum [16]. These values can be used as a rough guideline in designing noise barriers. For more accurate values, one would need to

The soundscape concept has been introduced to modify and complement the assessment of noise and its effects on humans. From the beginning, soundscape research has questioned the limits of existing acoustic measurements and the cultural dimension which Schafer included in his research for the first time in the

A particular soundscape includes all the sounds from a certain acoustic environment received by the human ear. The first idea of soundscape was introduced by Schafer, in his book *The New Soundscape* [17]. His primary idea was to record a soundscape of the world in a form of a map similar to geographical maps. However, extremely rapid changes in the soundscapes have made this idea impossible to implement. Soundscapes, among other things, change rapidly due to the growth of the human population, people's migration and traffic increase. On the other hand, it

The soundscape of a certain environment consists of various sound groups and sound sources. They can be divided into three major groups, biophony, geophony

Biophony are all the sounds produced by living organisms in their natural habitat (**Table 2**). It is by far the most complex feature of soundscape because it combines all biological sound sources, from microscopic to large fauna that live in a given environment for a certain period of time. In environments that are rich with different voices of living beings, organisms produce acoustic signals in different spatial relationships which can sound as one or more sound signals. Geophony are all-natural sounds coming from non-biological sources in a certain environment (**Table 2**). Generally, they can be divided into four types: the sound effects of wind, water, climate and geophysical forces. Anthrophony are all sounds generated by humans in any natural environment. This group includes sounds coming from

Bearing in mind all of the aforementioned, it can be concluded that the concept of soundscape as a field of research is extremely broad and requires a multidisciplinary approach. In studies and researches, apart from acoustic engineers, psychologists, physicians, builders, architects and sociologists should

**Table 2** shows sound sources or acoustic components and direct acoustic effects

of non-anthropogenic sound elements (biophony and geophony).

can be achieved by lighter and thicker or heavier and thinner

. A

#### **Table 1.**

*Approximate values of transmission loss parameter for different types of materials.*

*Noise and Environment*

to the interlayer.

*2.3.5 Plastic*

*2.3.6 Composite materials*

When such glass breaks, small granular fragments are formed which remain glued

Transparent panels are ideal for reducing or completely eliminating the visual impact of a noise barrier; however, their costs can be 20 times higher than those made of concrete or steel. The justification for their high cost can be found in improving safety in places where opaque noise barriers can have a negative effect on visibility. These types of panels are more sensitive to damage from flying debris and abrasive action as a consequence of the sandblasting effect that is inevitably due to

There are several types of plastic materials available and often used in the construction of noise barriers: polyethylene, PVC (polyvinyl chloride) and fibreglass. Plastic panels can be installed in almost any situation due to their extremely low mass, easiness to mould and weatherproof features. Bearing in mind all of the aforementioned, they are increasingly used for the construction of noise barriers, especially those of a more complex shape. The problem with plastic materials is a slightly lower structural strength and flammability, i.e. the smoke and gases pro-

Composite materials for noise barriers can be defined as any product composed of two or more "basic" materials, for example, wood mixed with concrete and then placed on a concrete foundation. By combining basic materials, the characteristics of the final product (noise barriers) and its durability, and even in some cases safety, are altered.

Concrete Block, 200 mm × 200 mm × 405 mm 200 151 34 Dense Concrete 100 244 40 Steel 1,27 10 25 Steel 0,95 7,3 22 Steel 0,79 6,1 20 Iron 0,64 4,9 18 Aluminium 1,59 4,4 23 Aluminium 3,18 8,8 25 Aluminium 6,35 17,1 27 Wood (Fir) 12 8,3 18 Wood (Fir) 25 16,1 21 Wood (Fir) 50 32,7 24 Plywood 12 8,3 20 Plywood 25 16,1 23 Glass 3,18 7,8 22 Plexiglas 6 7,3 22

**(mm)**

**Weight (kg/m2)** **Transmission loss (dBA)**

the swirling dust that is always present on the pavement layer.

duced by the combustion of plastics are very toxic.

**Material Thickness** 

*Approximate values of transmission loss parameter for different types of materials.*

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**Table 1.**
