WO2020008482A1

WO2020008482A1 - Sound absorbing and sound insulating layer for anti-noise barriers

Info

Publication number: WO2020008482A1
Application number: PCT/IT2018/000093
Authority: WO
Inventors: Andrea Demozzi; Giovan Battista LANDRA
Original assignee: Afv Acciaierie Beltrame S.P.A.
Priority date: 2018-07-02
Filing date: 2018-07-02
Publication date: 2020-01-09

Abstract

The present invention can be seen as a solution of two problems, each of them important, even if considered individually. The main field of application of the invention concerns the construction of anti-noise barriers. However, in addition to indicating a solution to create noise barriers particularly efficient for use in the road and rail sectors, the taught solution was inspired by a different need: in fact, it is actually a solution that allows the efficient recycling of materials that, until now, have been considered waste materials. These are the so called "black slags" of steel casting. The present invention, in fact, indicates an anti-noise barrier which can be made using the slag produced in the rolling processes of the steel obtained by electric arc furnaces (EAF). The invention consists in exploiting the particular properties of such "black slag", employing it directly, i.e. without the need for expensive treatments. In a nutshell, a material, mainly composed of a mixture of "black slag" coming from the fusion of carbon steel, is used to constitute a sound-absorbing and sound-insulating layer; and said layer is integrated into structures suitable for creating anti-noise barriers, being suitably oriented so that it opposes the prevalent propagation direction of the sounds to be contained.

Description

TITLE:

SOUND ABSORBING AND SOUND INSULATING LAYER FOR ANTI-NOISE BARRIERS

DESCRIPTION

Technical field of application

The present invention can be seen as a solution of two problems, each of them important, even if considered individually.

The main field of application of the invention concerns the construction of anti-noise barriers. However, the taught solution was inspired by a different need: in fact, it is actually a solution that allows the efficient recycling of materials that, until now, have been considered waste materials.

The problem of the efficient recycling of a material, which, according to the prior art, must be disposed of, and therefore entails pure costs, is a problem of great importance in itself; therefore, solutions that allow a suitable recycling to generate potential gains are much sought after.

Prior Art

There are numerous cases in which it is important to have anti-noise barriers that can be effective to protect some places from noise that may cause, to the people who occupy them, from the simple annoyance to real damage to the psycho-physical health.

A particularly topical example consists of road noise barriers. In fact, there are many roads, even fast-flowing, that pass near homes or, more generally, near places where people are stationed. It is common experience that the continuous noise generated by road traffic is extremely annoying and, especially at relatively small distances, even very intense. For this reason, at the sides of a growing number of roads and motorways, high barriers are gradually erected, with the aim of containing the noise generated by the transit of vehicles.

It is clear that anti-noise barriers are useful (if not essential) also in other contexts, such as for isolating the noise of trains along sections of railway that pass near inhabited areas or, in general, also in construction, to achieve buildings where you want to preserve adequate acoustic comfort inside them.

In order to better illustrate both the invention and the known art, some physical characteristics which must be present in an anti-noise barrier are briefly summarized.

The sound, as is known, propagates very well in the air. However, it also propagates through other means and, in general, a sound wave in the air, when it invests a medium discontinuity, it separates into a sound wave that continues also through the new medium and into a reflected wave that propagates to backwards.

In general, then, a part of the energy associated with the wave is dissipated during its propagation (generating heat on the crossed medium).

When the discontinuity of medium consists of an anti-noise barrier, the part of the wave that propagates in the middle, obviously, goes beyond the barrier: and this is precisely the effect that a noise barrier must limit as much as possible. The part of the reflected wave, on the other hand, produces a reverberation in the noisy environment: and, obviously, this effect is undesired too. Ultimately, the optimal behavior of an anti-noise barrier should be to dissipate as much as possible the energy of a sound wave that invests the barrier itself.

There are simple physical characteristics that make it possible to provide a first evaluation of the performance of a medium with respect to the propagation of a sound wave inside it, or with respect to reflection.

In general, it can be said that the propagation of a sound wave through a new medium, in correspondence with a discontinuity, is all the more reduced the greater the mass of the medium invested. Moreover, propagation inside means of high mass is more rapidly attenuated than propagation on light means, such as air. Heavy materials are therefore suitable for creating "sound-insulating" barriers that significantly attenuate the sound that crosses them, therefore the noise beyond the barrier is generally much less intense than the noise present before the barrier.

As for the reflection, instead, the physical characteristics to be considered are geometric. In particular, porous (or very rough) materials are not very reflective. This is also intuitively understandable, since it is possible to imagine that the sound wave incident a porous surface propagates in part inside the cavities due to the porosity of the material itself, so that the various reflections remain trapped inside the material which, in this case is called "sound-absorbing". Ultimately, ideal noise barriers must be "sound-insulating" and "sound-absorbing". Therefore, a first requirement that can be highlighted consists in the fact that materials having a high mass and an accentuated porosity are recommended to be used.

Other requirements, on which it is not necessary to dwell, concern constructive aspects in which the general shape of the barrier is cured, so that it can effectively intercept and convey the propagation of sound waves avoiding as much as possible that noise propagates on undesired pathways, which could get around the barriers themselves.

As already mentioned, a very topical application of these noise barriers is constituted by the barriers to be implemented to contain the noise generated by vehicular traffic in general.

It is clear that the extension of the network of roads, highways and railways of a populated and developed country extends for dozens, if not hundreds, of thousands of kilometers, and therefore there is a problem of abnormal costs. Given the number of barriers that should be installed, a gradual, but continuous and sustained installation of noise barriers is expected, generating a very interesting and lasting market for this type of infrastructure.

A first factor to take care of, in terms of cost containment, consists in the development of technologies that are easy to install, based on the use of modular panels, in order to obtain prefabricated barriers with low production and installation costs.

The noise barriers, however, must have the desired acoustic performance, and therefore the materials must have appropriate physical characteristics, mass, porosity and workability: these characteristics, as mentioned above, are indispensable.

The prior art, in cases of anti-noise barriers in which isolation and absorption are simultaneously treated, proposes various solutions. Among the most efficient, from the economic point of view, the barriers made of expanded clay are mentioned; this kind of barriers can be considered a benchmark, to evaluate the performances of the other materials used in these applications.

The various subjects active in this sector evidently use a number of variations of materials, with which they make anti-noise barriers. Often, the materials used are mixtures based on expanded clay, with the presence of heavy cements, optionally mixed in turn with other powders with suitable properties. Frequent is also the use of panels made of various layers, in which a base of concrete, which gives mass and strength, is coated with other mixtures, always based on cement or clay, which give the porosity. Moreover, the surfaces are often shaped so as to obtain suitable grooves aimed at reducing the effects of the reflection.

Other solutions include the use of structures that can be filled with heavy earth, or structures suitable to accommodate some vegetation.

We do not dwell further on the analysis of the materials used to create noise barriers according to the known art; however, it can be concluded that the total cost of an anti-noise barrier installed on the edge of a road or a railway necessarily entails significant costs due to materials. Therefore, precisely on this aspect, it would be desirable to introduce innovations to achieve further optimizations.

One way to reduce material costs is to use waste materials that can be recycled efficiently. In fact, a waste material is theoretically available at negligible costs.

It is noted, however, that the general limit of any policy for the recycling of materials is in the processes that recycling requires. In fact, if on the one hand it is true that waste is always made up of materials that are theoretically reusable, or even usable in other areas, it is also true that the processes for the recovery of materials, in a form that allows their reuse, are often complex processes that sometimes make recycling unseemly.

The ideal case, for efficient recycling, is the one in which the waste material is spontaneously produced in a form that is suitable for direct use. These recycling opportunities are not always easy to identify because, as it is easy to understand, they require skills in non-related technological fields. This is the case of the so-called "black slag” of steel casting, in particular the slag that is produced in the rolling processes of steel obtained by EAF (Electric Arc Furnaces).

The technologies of steel production are quite mature technologies and the recovery of iron has always been an important objective for the sector. In fact, the iron that can be used to make steel is often more conveniently available from scrap of abandoned artifacts, rather than from naturally occurring minerals that contain it. Therefore, the steel industry is historically attentive to the theme of recycling.

However, at the current state of the art, some carbon steel rolling processes produce a waste that is not conveniently recyclable in the iron and steel sector in which such waste is produced: it is precisely the "black slag", which it is produced by melting processes in EAF. This slag has a chemical composition which makes it uninteresting for uses in the sector from which it comes, it is formed on the surface of the melting bath, and it consists of a complex mixture of oxides and silicates, present in various stable forms.

Therefore, this "black slag" is disposed of as non-recyclable waste, and this disposal is a significant cost for the steel rolling industry.

Summary of the Invention

At this point, it is important to note some features of this "black slag” of steel casting. It is a material with a significant metal content, therefore with a considerable mass, and has a porosity, also significant, which is formed by the effect of rapid effusive solidification. This "black slag" is then collected downstream of the melting process, in the form of granules of different sizes, with dimensions that also depend on the type of processing from which they come.

The main object of the present invention, as mentioned in the first part of the present description, consists in indicating an anti-noise barrier with sound-insulating and soundabsorbing properties. And this main purpose must be able to be achieved so as to obtain acoustic performances in line with those obtained by the known technique, or better with the same costs.

Therefore, another fundamental object of the present invention consists in using waste materials, coming from other processes, in order to reduce the costs associated with the material.

A further object of the present invention is to provide an anti-noise barrier which can be made using waste materials from other processes in an efficient way, practically using them without having to undergo them to complex treatments, possibly using such materials according known methods of production of anti-noise barriers (i.e. methods already established in the known art).

The desired objectives can be achieved by creating anti-noise barriers comprising a sound-absorbing and sound-insulating layer oriented so as to oppose the prevalent propagation direction of the sounds to be contained, and said layer is characterized by being mainly composed of a mixture of "black slag” of steel casting.

Of particular interest is the“black slag” produced in the steel rolling processes carried out by using electric arc furnaces (EAF).

The main advantage of the present invention is given by the fact that an anti-noise barrier, made according to the teachings of the present invention, satisfies all the main purposes for which it was conceived.

Brief Description of the Drawings

This invention also has further advantages which will be made more evident by the attached claims which form an integral part of the description and by illustrating some practical embodiments, described below by way of non-limiting example, in which further details and variants are highlighted.

These examples are described below with the aid of the attached drawings in which:

/ Figure 1 schematically shows a steel rolling plant with electric arc furnace which is producing a "black slag" waste. ' Figure 2a, 2b and 2c represent some examples of anti-noise barriers in which the "black slag" is used to take advantage of its sound-insulating and sound-absorbing characteristics. Figure 3 shows a different processing of the "black slag" to create prefabricated panels for noise barriers

Detailed Description

In Figure 1 , with the number 200, a typical plant for the production of carbon steel is schematically depicted. Said plant 200 produces a sheet of steel, indicated in Figure 1 with the number 300, starting from scrap iron of various origins, which feed the plant 200, and which are indicated by the number 301. In Figure 1 , it is highlighted that the plant 200, is also fed by other materials, indicated by the number 302, which are called "fluxing agents", and which typically consist of calcium lime, dolomitic lime and coal.

The plant 200 comprises, as its essential part, an EAF (Electric Arc Furnace), indicated in Figure 1 with the number 201. Said iron scrap 301 and said“fluxing agents” 302 are loaded into said EAF 201 where they are merged for subsequent processing of which the details are left out. Said “fluxing agents” 302 are essential in this melting process and, in particular the lime components, in large part become a waste slag. As a consequence, in addition to the useful product, consisting of the steel 300 (obtainable in various forms), the plant 200 necessarily also produces a waste product that cannot be eliminated in this type of processes, which are now widely widespread.

Therefore, the process for the production of steel 300 through the use of these electric arc furnaces, produces a waste material whose precise composition depends on the type of steel to be obtained. Typically, such waste material, indicated in Figure 1 with the number 100, is a compound of different oxides (mainly of iron, silicon, magnesium, manganese and calcium), and it is referred to as "black slag".

These substances are also found in the natural state, they are not toxic and give rise to stable compounds, inert in adverse environmental conditions (e.g. acid rain) or in conditions typical of the installation environment (for example, when using de-icing salts along the roads).

Said "black slag" 100 forms on the surfaces of the steel sheet and, in being discarded, cools quickly, giving rise to a porous (due to the rapid solidification) and granular material, characterized by an irregular and varied granulometry.

To some extent, the particle size of said "black slag" 100 can be controlled by adjusting the cooling temperature, or by selection mechanisms that are able to select and divide said "black slag" 100 depending on granulometry.

The granulometry that results from the typical rolling processes, is such as to produce a sound- absorbing material with excellent performance in the medium-low sound frequencies, i.e. the frequencies that are particularly important to attenuate in road and rail application contexts.

In any case, the possibility of having a certain control of the particle size of the "black slag" 100, allows to design ad-hoc mixtures for different types of noise (for example, rail and motorway), studying mixtures targeted to the type of noise to intercept.

Ultimately, the noise barriers realized according to the teachings of the present invention generally provide that said mixture of "black slag" of steel casting, with which the sound- absorbing layer is made, is an aggregate of particles of different granulometry, and the particle size composition is designed to optimize the absorption of specific sound frequencies.

Having ascertained such sound-absorbing and sound-insulating properties of the "black slag" material 100, it is worth highlighting how it can be practically used to create sound- insulating and sound-absorbing layers in anti-noise barriers. In fact, among the aims of the invention, there was not just that of recycling a waste material to create anti-noise barriers, but also the purpose of using it as much as possible in its original form, without requiring complex and potentially costly processes.

In Figures 2a, 2b and 2c, some anti-noise barrier modules are shown in an essential way, inspired in part to construction techniques present in the prior art, in which however the material "black slag" 100 is employed, which in itself, gives the barriers extremely good acoustic performance.

In Figure 2a, it is shown a modular element, which can be used to compose an anti-noise barrier according to the invention. The number 111 indicates a containing structure with a fairly flat shape, in the example of Figure 2a, a parallelepiped with one of the three dimensions significantly shorter than the other two. Said containment structure 111 is a gabion suitable for containing a mixture of "black slag" 100.

It is immediately evident that this modular panel uses the "black slag" 100 in a substantially direct way. The only operations possibly carried out on the "black slag" 100 may consist of a selection on a granulometric basis and a mixing with other materials to obtain a more cohesive and compact mixture: in typical examples, said mixture of "black slag" of fusion of the steel 100 is mixed with materials suitable to give mechanical stability, or to avoid possible transfers of unwanted elements or compounds into the environment.

As it is easy to understand, these are extremely simple operations, and in any case not essential, since the "black slag" 100 can theoretically be poured into the gabion containing structure 1 1 1 also as it results from the rolling process of the steel.

In fact, it is appropriate to repeat how the material "black slag" 100 presents, in itself, optimal acoustic characteristics, so much that it can also be used directly. The acoustic performance of said "black slag" 100 can be deduced from a qualitative analysis of the material (its characteristics of mass and porosity have already been highlighted), but they have also been confirmed with accurate laboratory tests, in which the performance of a layer of "black slag" 100 was compared with layers of other materials used in the manufacture of noise barriers.

In particular, various non-trivial acoustic tests were carried out to characterize the mixture both in comparison with other industry-leading materials (expanded clay) and as an anti-noise barrier prototype, and the results showed that the performance determined by the presence of the "slag" black "100 are better in a generalized way.

The tests as anti-noise barrier prototype have been carried out referring to the UNI EN ISO 1793-5 and 1793-6 standards for the measurement of the reflection index (Rl) and of sound reduction index (SI). These rules are completely new for the barriers market, as they introduce a new way of assessing the acoustic characteristics: not only in diffuse sound field, like the previous rules, but also in direct sound field, with incidence almost orthogonal to the barrier (thus simulating a type of noise closer to the real one in the transport routes, which has a diffusion according to co-axial cylinders with energy levels decreasing with the distance from the axis).

To implement this verification method, the acoustic laboratory that carried out the tests had to build new support structures, as well as new instrumentation and software. As far as environmental characteristics are concerned, then, flowthrough samplings were carried out after rains, and methods / technologies were studied to fix any type of release in the environment of the material making up the barrier.

Figure 2b is substantially the same as Figure 2a; the difference consists in the fact that the containing structure, indicated in Figure 2b with the number 112, is not necessarily a gabion, but various materials suitable for containing the mixture of "black slag" 100 can be used. Thus, the walls of the module may comprise containing tarpaulins (of various materials), or it may be formed with shells of acoustic panels of different materials such as metal, plastic, wood or composite material.

In Figure 2c, a further type of anti-noise barrier is shown, inspired by the same concepts shown in Figures 2a and 2b. The difference presented in Figure 2c consists in the fact that the containment structure, indicated by the number 113, is not a prefabricated containing structure, but is made in situ, and the mixture of "black slag" 100 is poured, again while the work is in progress, into a specially created interspace. From a conceptual point of view, all Figures 2 have the same type of noise barrier in which the sound-insulating and sound-absorbing layer based on "black slag" 100 is simply contained in appropriate containment structures; Figures 2 are however useful for appreciating the number of possible embodiments.

In particular, in Figure 2c, the number 101 indicates the sound-absorbing and sound-insulating layer which is formed when the special interspace is completely filled with the mixture of "black slag" 100, and Figure 2c suggests how a sound-absorbing layer can therefore be obtained in any structure in which there may be a gap to be filled. For example, on the walls of a building where there are rooms with a high need for sound absorption, such as gyms, auditoriums, meeting rooms, schools.

Figure 3 shows in section a panel in which two layers are visible, and it is representative of a different constructive concept of soundproofing panels. The number 120 shows a layer with structural and support functions, typically made of concrete, although, obviously, it is possible to use other materials that can guarantee the same function. With the number 101 , on the other hand, the sound-absorbing and sound-insulating layer is indicated. In the case presented in Figure 3, the "black slag" is not contained in a containment structure, but it is made to adhere to the support structure 120. In this case, the“black slag” must be mixed with other substances, for example cements, mortars or glues, which may serve the purpose of applying the layer 101 on the support 120 and, once the dough dries, it remains fixed.

Evidently, this type of use of the "black slag" of steel casting can be applied both for the manufacture of prefabricated panels and for realizations in situ moreover, other layers may also be provided in addition to said essential layers: i.e. the support layer 120 and the sound- absorbing and sound-insulating layer 101. In particular, said sound-absorbing and sound-insulating layer 101 can be coated with other layers having a protective function or to fix possible unwanted releases of elements or compounds in the environment, such coatings can typically be made with a nanotechnological layer, for example silicone, to be applied by spraying or by wetting.

In short, therefore, the inventive concept underlying the present invention is summarized in the realization of a soundproofing layer to be obtained on elements constituting a noise barrier, so that this layer is oriented so as to oppose the sound propagation that is intended to be contained.

This layer essentially consists of a waste material such as the "black slag" of steel casting.

Said "black slag" of steel casting can be used as loose material to be contained in appropriate containment structures. In this case it is not necessary any processing of the raw material, at most a possible selection on a granulometric basis that can be carried out to optimize the absorption of specific sound frequencies, especially in the medium-low frequency ranges. Alternatively, said "black slag" of steel casting can be amalgamated with other materials suitable for the manufacture of noise barriers. For example, it can be incorporated in concrete castings, to form prefabricated panels or soundproofing structures in place; furthermore, it can be mixed with other stabilizing elements, such as cement or bitumen powder.

All the different variants will have the characteristic of not occluding the porosity of the mixture, or, in any case, they have to allow the passage of the incident sound waves and their absorption in the cavities of the material.

The invention described above can be applied to numerous variants, which may be related to future developments, both in terms of materials technologies, and in terms of the development of processes in the construction sector.

In particular, different materials can be used for containment structures or for support structures. Furthermore, new installation or construction methodologies can be developed and widely diffused, whereby new specific prefabricated elements could also be convenient for the construction of noise barriers, so that it cannot be excluded that new types of structures can be invented that can lead to variants or improvements of the present invention.

Such variants may offer further advantages with respect to those previously mentioned, and they may be introduced by the man skilled in the branch, without departing from the invention as it results from the present description and from the appended claims.

In addition to this, the invention itself can be carried out in a partial manner as well as many details described can be substituted by technically equivalent elements.

In particular, and as already mentioned above, the technologies concerning the use of specific materials, in addition to the "black slag" 100, are not a characterizing part of the present invention and therefore, if in the future they should be available materials more advantageous than those indicated in the preferred implementations, further improvements could be made in the realization of the present invention without modifying its inventive nature and the principles that inspired it.

Finally, the invention described can be used to incorporate and support further expedients for the construction of increasingly inexpensive noise barriers, with ever better performance, robust and capable of reproducing increasingly interesting aesthetic effects: such measures not treated in the present description may be described in further patent applications that can be associated with this invention.

Claims

1. Anti-noise barrier comprising a sound-absorbing and sound-insulating layer (101 )

oriented in such a way as to oppose to the prevalent propagation direction of the sounds to be contained, and said layer is characterized by comprising a mixture of“black slag” (100) of steel casting.

2. Anti-noise barrier according to claim 1, wherein said“black slag” (100) of steel casting results from rolling steel processing performed by using electric arc furnaces (201).

3. Anti-noise barrier according to claim 1 or claim 2, wherein said mixture of“black slag” (100) of steel casting is an aggregate of particles having a different granulometry, and the granulometric composition is designed to optimize the absorption of specific sound frequencies.

4. Anti-noise barrier according to claim 1 , 2 or 3, wherein said sound-absorbing and sound- insulating layer (101) is made by containing said“black slag” (100) of steel casting inside suitable containment structures.

5. Anti-noise barrier according to claim 4, wherein said containment structures are gabions designed to be modular elements of anti-noise barriers.

6. Anti-noise barrier according to claim 4, wherein said containment structures comprise containment tarpaulins.

7. Anti-noise barrier according to claim 4, wherein said containment structures are also formed with shells of acoustic panels of different material such as metal, plastic, wood or composite material.

8. Anti-noise barrier according to claims 1 , 2 or 3, wherein said mixture of“black slag” (100) of steel casting is mixed with materials suitable for conferring mechanical stability.

9. Anti-noise barrier according to claims 1, 2 or 3, in which said sound-absorbing and

sound-insulating layer (101) is coated with a layer consisting of nanotechnological substances.

10. Anti-noise barrier according to claim 1 , 2 or 3, wherein said sound-absorbing and sound- insulating layer (101) is deposited in situ on walls or on interspaces.

11. Anti-noise barrier according to claim 1 , 2 or 3, wherein said sound-absorbing and sound- insulating layer (101) is obtained on prefabricated concrete panels.

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