Area of technology related to the invention

This invention is related to concrete noise protection panels whose absorbing layer is made of rubber pellets obtained by car tyre recycling, and which are the main element of concrete noise barriers. According to the international patent classification (IPC), the invention belongs to the area marked as E01F 8/00 (2010.01).

Technical problem

Noise is one of main causes of a reduced quality of living. Higher noise levels mostly result from road and railway traffic, and operation of industrial plants. The most frequent and safest way to lower propagation of noise is the use of noise barriers. Various materials are nowadays used to build such barriers: concrete, wood, aluminium, transparent materials, and natural materials. Over the past three years, concrete has been the most often used material, both in Croatia and worldwide, for the construction of noise barriers. Principal elements of each noise barrier are: foundations, posts, and panels that are installed in between the posts. In case of concrete barriers, panels are realized as two-layered elements consisting of the reinforced-concrete plate which is used as a support, and of an absorbing layer, made of a porous lightweight concrete. This absorbing layer is installed on the side facing the source of noise, and its role is to absorb the noise. The absorbing layer has so far been realized by adding wooden fibres, or ball-shaped expanded-clay pellets. This invention offers a technical solution for realization of the concrete panel absorbing layer made of rubber pallets that are obtained by recycling used car tyres. In this way, two benefits for environment are gained: a) controlled waste management, and b) noise protection. Rubber pellets are obtained during the used tyre recycling process, and then these pellets are used to make a new product - concrete noise-protection barriers with recycled rubber in the absorbing layer.

State-of-the-art

Noise protection panels are the main element of each noise barrier. Noise barriers placed immediately next to transport facilities (roads or railways), and next to industrial plants/installations are the most frequent and safest way for reducing propagation of noise. The use of barriers of adequate height and length enables an efficient noise level reduction, to the level specified in the design, immediately after installation.

There are two main types of noise barriers: reflective noise barriers and absorbtive noise barriers, and their noise reduction properties are primarily dependent on the properties of panels that are used for building such barriers. Reflective panels reflect sound waves without reducing their intensity, and absorptive panels "soak up" most of the sound wave energy, while only a small portion of such energy is reflected. Reflective panels are made of nontransparent and transparent materials, while absorptive panels are normally realized as nontransparent and contain porous material elements used as fill (e.g. mineral wool), which absorbs the sound. Compared to reflective panels, absorptive panels are more frequently used. Noise protection panels must comply with requirements relating to: adequate sound insulation Rw and adequate sound absorption Δία. Panels made of various materials are currently available on the market: wood, aluminium, tra nsparent materials, concrete.

Wood panels are principal elements of wooden barriers that are similar to garden fences and, in rural areas; they fit with their design quite well into the surrounding landscape. These barriers are rarely used in urban areas, although even there they can sometimes blend in well will such surroundings. If they are used in town in immediate vicinity of residential and pedestrian zones, wooden panels should be decorated with natural and lighter colours, or should be combined with transparent panels, which results in better illumination and visibility. Wooden barriers realized on longer stretches may be monotonous and should therefore be combined with transparent panels, embellished with some vegetation, or in another way. Furthermore, they should be avoided on viaducts and bridges as, even if they meet all acoustical requirements, they do not blend in with the concrete or steel structure of such facilities. The main disadvantage of wooden panels is their poor resistance to atmospheric influences.

Aluminium panels may be either absorptive or reflective. External vertical faces of aluminium panels are made of profiled aluminium sheeting 1.3 mm in thickness, while the interior space is filled with mineral wool or another absorbing material. External lining sheets of absorbing panels are perforated. External faces of aluminium panels can be painted in a wide variety of colours. In weather zones with high temperatures, vegetation planting, as a means to break barrier monotony, should be avoided. Finished panels are supplied to the construction site where they are easily installed in between steel posts, mostly made of HEA profiles. The main deficiency of these panels is the possibility of their damage by vehicles (along roads and railways), and by vandalistic behaviour (in urban areas).

Transparent panels are made of laminated, hardened or reinforced glass, and also of plastics (acrylic or polycarbonate sheets, plexiglass). They enable partial of full penetration of light rays, thus providing a view to the surrounding landscape. Due to their visual neutrality, these materials do not impair the view of the surrounding area, and can therefore be used on a majority of locations. Transparent panels are in most cases reflective, and should be avoided in places where sound reflection could be bothersome to local population. Transparency is the main reason why transparent panels are nowadays almost the only panel type installed on bridges and viaducts. Transparent panels are often realized in combination with other panels, i.e. as elements that will break monotony of a repetitive material, as openings enabling passage of light, or as elements that will assist drivers by enabling better visibility and more adequate orientation. Realized as top parts of barriers made of another material, they make them seem lower and visually more acceptable. One of significant deficiencies of these panels is their insufficient resistance to vandalism. Damaged or destroyed panel profiles can not be repaired and must be fully replaced. As they may present danger to participants in traffic, new and stronger plexiglass panels have recently been introduced which will remain undamaged even when subjected to a strong dynamic impact, or will crack in such a way to remain compact and connected to other elements.

Concrete panels are nowadays often used for noise protection in cases when protection measures are implemented by means of concrete barriers. Concrete barriers are realized in two ways: using prefabricated panels (produced under controlled factory conditions and supplied ready-made to the construction site) or panels realized on the spot, which is now quite rare. According to acoustical properties, concrete panels can be either reflective or absorbtive. Absorptive panels are presently fabricated by adding wooden fibres or pellets in form of balls made of expanded clay. One way of building concrete barriers is to use absorptive blocs and fill the interior with concrete. The second way is much faster and simpler: it involves the use of two layered concrete panels composed of a concrete bearing layer, which acts as a support, and an absorbtive layer, placed on the side facing the source of noise, built of a porous lightweight concrete, and acting as noise a bsorber. The shortcoming of these concrete panels lies in the fact that the production of aggregate for lightweight concrete forming the absorptive layer of the barrier (wooden fibres or expanded clay pellets) is harmful to natural environment. To produce wooden fibres, wood has to be cut and processed, while clay must be excavated and thermally treated in order to produce expanded clay.

Presentation of the essence of the invention

The problem of noise protection by means of concrete barriers, the main element of which is the concrete absorptive panel, is solved according to this invention by applying rubber pellets in the absorptive layer of the panel. Rubber pellets of an appropriate diameter, which replace currently used wooden fibres or expanded clay pellets, are obtained by recycling used automobile tyres originating from various types of vehicles (passenger cars, trucks, buses, airplanes, and construction and agricultural equipment). This environmentally friendly and innovative product provides not only protection against noise, but also offers a great contribution to the disposal and management of waste (used car tyres) in a good-quality, efficient, innovative and cost- effective manner - through development of a new product. The necessary absorption coefficient is obtained by defining an appropriate proportion of rubber pellets in the absorptive layer (corresponding to the absorption coefficient requirement), and the shape of the absorption layer (trapezoidal, currogated, etc.). The use of this invention, based on tyre recycling for obtaining pellets used in the production of the porous lightweight concrete absorptive layer, enables a very simple resolution of two environmental problems: noise protection by means of concrete panels with an absorptive layer of recycled rubber, and an appropriate management of waste, i.e. used automobile tyres in this case.

Brief description of drawings

The drawings included in the description, which form an integral part of the invention description, are given to additionally explain basic principles of the invention.

Figure 1 Drawing showing positions of concrete barrier elements (foundations, posts, panels)

Position 10: Concrete panel with absorptive layer of recycled rubber

Position 11: Concrete post

Position 12: Concrete plank

Position 13: Concrete foundations

Position 14: Cement mortar

Figure 2 Detailed panel to panel connection (horizontal connection)

Position 20: Concrete bearing layer of the panel

Position 21: Absorptive layer of the panel made of rubber pellets

Position 22: Special sealer for filling the horizontal gap

Figure 3 Panel to concrete post connection detail (vertical connection

Position 30: Sealer for filling the vertical gap

Position 31: Special anchors for grasping and handling

Figure 4 Panel to steel post connection detail

Position 40: Steel HEA profile

Detailed description of at least one way in which the invention can be realized

The concrete noise protection panel with recycled rubber (10), concrete post (11), concrete plank (12), and concrete foundations (13), are the main elements of the concrete noise barrier, Figure 1. The concrete panel (10) is installed in between the posts that can be made either of reinforced-concrete or steel. If steel posts are used (40), then appropriate HEA profiles are applied, taking into account the wind zone in which the barrier is installed, Figure 4. If concrete posts (11) are used, then the use is made of prefabricated reinforced-concrete posts of an appropriate I profile, which are placed into a concrete foundation "cap" (13), while the space between posts and the foundation cap is filled with cement mortar (14). The concrete foundation can be realized on the spot or as a prefabricated element in which case it is just placed onto a previously prepared bedding. As the dominant load is the wind load, the selection of the type and dimensions of foundations depends not only on the bearing capacity of the foundation soil, but also on the wind zone in which the structure is located. Before installing concrete panels for noise protection, it is necessary to install concrete planks (12) by which concrete panels (10) are separated from the terrain, Figure 1. The horizontal connection between concrete panels is realized by the tongue and groove joint (Figure 2) and a special sealer (22), while vertical connection (post and panel connection) is realized using an appropriate neoprene sealer (30) whose dimensions and shape depend on the type of post, Figure 3. To facilitate handling of concrete panels (10) during the loading, transport and assembly, special anchors of sufficient capacity most be installed to enable proper attachment and handling (31).

This invention is related to the main noise barrier element, which is a two-layered concrete panel (10), and more precisely to its absorption layer (21) which is realized with rubber pellets made of old recycled tyres. Used tyres are previously collected at authorized disposal sites specialized for this type of waste, after which the recycling procedure is conducted. The initial phase of mechanical tyre recycling consists in removing steel components from the tyre, which is followed by tyre cutting into pieces, and by further tyre comminution at the recycling line. Various rubber pellet fractions can be obtained during the recycling procedure. For this invention, the use is made of an approximately single-sized fraction of rubber pellets and, at that, coarser single-sized pellets are used in cases when such two-layered panels have to meet special absorption requirements.

To enable production of the porous lightweight concrete absorptive panel layer, rubber pellets must previously be treated with an appropriate additive so as to ensure a continuous link between rubber pellets and the cement paste. The preparation of rubber pellets is followed by mixing with cement, water and the remaining single-sized stone aggregate. Appropriate absorptive and insulating properties of the barrier are obtained thanks to an adequate proportion of rubber in the porous lightweight concrete of the absorptive layer, and to its shape. This is explained by the fact that rubber as a material has good thermal and acoustic properties, while concrete, in which a part of the stone aggregate is replaced with recycled rubber, in this case with rubber pellets, has good absorptive and insulating properties. Concrete containing recycled rubber pellets is characterized by lower heat transfer and greater sound absorption, and is therefore suitable for noise protection. An appropriate level of absorption is also obtained by defining an adequate shape of the absorptive layer (which is most often undulating and trapezoidal) and, thanks to the geometry of irregularities (width and depth of waves), a greater overall area is obtained, Figure 3. A particular architectural shape of concrete panels can be obtained by varying the position of ribs (which can be either vertical, horizontal or inclined), and also by varying the colour of the absorptive layer. When needed, this type of concrete panels can be realized by placing the absorptive layer on both sides, and so a two-sided absorptive panel is obtained. The barrier panel production is based on the so called "inverse" principle. First the porous lightweight concrete of the absorptive layer, containing a specified proportion of rubber pellets, is placed in the moulds, and only then the concrete of the bearing part of the panel is placed. The concrete of the absorptive layer is placed in appropriate moulds (the thickness and external shape of the absorptive layer depends on absorption requirements set for a given panel), which is followed by positioning of reinforcing bars, and finally the concrete of the bearing layer, which assumes a static (load-bearing) function of the panel, is placed. The load bearing layer thickness depends of the wind zone in which all these elements will be installed. The panel length is defined based on the axis-to-axis distance between posts, and the panel height may be varied depending on the barrier height requirements specified in the design.

The way in which the invention will be applied

The technical solution, based on the noise-protection concrete panel with an absorptive layer of recycled rubber, can be used at all locations where noise protection by means of noise barriers is needed. Due to considerable mass of the concrete panel, concrete barriers are more stable when compared to other barrier types. It is a heavy-duty panel that is especially resistant to mechanical impacts. This panel is particularly appropriate for use along railway lines where a high air pressure is generated by passage of trains, along motorways, and near schools and in other areas with a high concentration of pedestrians.

These noise-protection concrete panels with recycled rubber are very simple to assemble. After realization of barrier foundation, installation of posts and bottom concrete planks (which is a normal procedure for all noise barriers), concrete panels are installed between posts by means of cranes. If this protection is realized along roads than the installation cal be done using truck-mounted cranes and, if the protection is realized along railway lines, the panels can be installed by means of an appropriate rail vehicle equipped with a crane.

Although it is related to the production of noise-protection concrete panels, this technical solution is not useful solely for noise protection. It also contributes to waste management as used car tyres are disposed of in a sustainable manner. In fact, the absorptive layer of these concrete barriers is fabricated using rubber pellets obtained through recycling of used tyres.