TECHNICAL FIELD

The present invention relates to acoustic noise abatement panels, particularly but not exclusively for transport corridors such as rail side or roadside use.

BACKGROUND TO THE INVENTION

Transport corridor noise is well understood as a significant issue for the construction of new roads and transport links, and the refurbishment of existing roads. Nearby residents are concerned that the increase in ambient acoustic noise associated with the road is kept to a minimum.

Noise abatement barriers are commonly constructed along roads, the objective being to attenuate the road noise produced by traffic. It is generally understood that roadside noise is relatively broadband, with the majority of acoustic energy in the 250Hz to 4kHz range, although the lower part of the range may be as low as 50Hz.

The generalities of construction of such barriers, particularly as used on highways and the like in Australia, has standardised to an extent. Steel H-beams are fixed in place at 2.4 to 6.0m intervals as support posts, with a foundation formed from concrete. Barrier panels are fixed to the flanges of these posts.

The required characteristics, both for noise attenuation and for impact resistance, are typically provided in such documents as the 'Main Roads Technical Standard MRTS15 for Noise Fences' (issued by the Queensland Government, but this typifies similar standards across all Australian States and Territories), the contents of which are hereby incorporated by reference.

One existing type of barrier panel which meets these standards is formed from reinforced or autoclaved aerated concrete. Although it performs adequately, it is expensive and labour intensive to install requiring mechanical fixings to the steel columns, and inconvenient to transport and handle, because of the very large associated weight. It also performs poorly over the lifetime of the fence which is often measured in decades. The concrete or painted surface deteriorates and the mechanical fixings rust and decay. It is an object of the present invention to provide an improved panel and panel construction/assembly system for noise abatement panels.

SUMMARY OF THE INVENTION

In a broad form, the present invention provides a panel formed from a sandwich of polystyrene between layers of a magnesium oxide cement board, (MgO Board). The completed panel then can be optionally finished in a range of coatings including an applied render type coating of sand glued to the MgO board, or suitable paint finishes. In a preferred form, the panel includes a set of recesses formed within the polystyrene layer, so as to increase acoustic attenuation, particularly at low frequencies.

According to one aspect, the present invention provides a noise abatement panel, including a first rigid board, a polystyrene layer, and a second rigid board, the first and second rigid board being formed from MgO board.

According to another aspect, the present invention provides a method of constructing a noise abatement barrier, including the steps of constructing a series of structural support members, and inserting one or more noise abatement panels as defined above between pairs of said members. BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments of the present invention will now be described with reference to the accompanying figures, in which:

Figure 1 is an exploded view, illustrating the construction according to one embodiment;

Figure 2 illustrates another embodiment of the present invention, with peripheral groves of 50mm wide x 20mm deep on each side of the polystyrene and offset to each other;

Figure 3 illustrates an individual barrier constructed using a panel;

Figure 4 illustrates an assembled barrier using panels according to implementations of the present invention;

Figure 5 is a view in section showing the construction of panel and associated member in accordance with one aspect of the present invention; Figures 6, 7, 8 and 9 illustrate on cross section alternative profiles for the polystyrene layer;

Figure 10 is a graph illustrating sound attenuation at frequencies for a first implementation; and

Figure 11 is a graph illustrating sound attenuation at frequencies for a second implementation.

DETAILED DESCRIPTION

The present invention will be described with reference to particular illustrative examples, in the field of roadside noise barrier construction. However, it will be appreciated that the present invention may be applied more widely to noise barriers for other purposes, for example at public amusements, railways, sporting arenas, and the like. It will be understood that the examples are intended to be illustrative and not limitative of the general inventive concepts disclosed herein.

The general construction of a panel 10 accordingly to an illustrative embodiment of the present invention is shown in figure 1. According to this embodiment, a central portion of polystyrene foam 14 is sandwiched between layers of an MgO board 13, 15. The board is then preferably coated 11, 12 with a suitable costing, for example glued sand which can then be painted, or a paint finish applied directly to the MgO board.

The foam material 14 is formed of expanded polystyrene (EPS). EPS comes in a range of class grades relating to the material's average density. The selection of appropriate class of grade for the purpose of the panel construction can vary depending upon the environmental factors and standard requirements for the location in which the panel is to be erected. Ideally, the higher density class grades should be employed, i.e. having an average density of 19-28 kg/m ³ . Boards formed of EPS can be sourced from Poly-Tek Australia Pty Ltd. An ideal thickness of the EPS material has been found to be approximately 126mm, providing an overall panel thickness of 150mm for insertion into a standard 180UB column. However the elegance of this implementation of the present invention is that the EPS thickness can be easily adjusted for panel fit into variable column sizes without unduly affecting its acoustic or structural performances. At this thickness, the overall panel exhibits sufficient characteristics to satisfy impact tests and can be allow an overall thickness dimension which would fit within the slots of a standard H-Beam.

The board material 13, 15 is formed from an MgO board. In general, such boards are formed from cured magnesium oxide cement, with the addition of materials such as fibre glass reinforcement sheets, fillers and other additives. Such boards are widely used in China as construction materials, and exhibit excellent strength, weight, wear and stability characteristics. In order to satisfy the performance requirements of a road side barrier, the MgO board needs be of a sufficient strength to satisfy both the impact test and the wind loading criteria of the product (as will be further explained below) and of a sufficient density to satisfy the noise abatement criteria of the product when used as a 'system' with the steel columns.

The MgO board 13, 15 may be made of any suitable thickness, preferably in the range of 10mm to 12mm and most preferably 12mm. It should be at a density suitable to provide the requisite acoustic attenuation, being approximately 20kg / m2. A suitable MgO board product called INEX>BOARD is commercially available from The UBIQ Company. Any other MgO board which is able to fulfil the requirements may be used.

While a coating is not essential, it is suggested that a render style or paint finish is applied for aesthetic reasons. For example, this may be a mixture of sand and paint, of a type adapted to adhere to the board. Patterns, images or the like may be applied.

The polystyrene 14 and MgO board 13, 15 board layers may be joined by an adhesive fit for purpose and suitable for long term durability of the panel. Normal construction approaches for composite panels may be used. Typically, panels are formed by applying an adhesive between the MgO board and the polystyrene, so as to adhere the polystyrene between the sheet materials. The selection of suitable adhesive is dependent upon the styrene material and the sheet material, and the appropriate manufacturer should be consulted to ensure that the adhesive will be suitable. This is a factor of not only the materials, but the intended application and environmental conditions. It is preferred that the adhesive cover the entire face of the core material, to ensure complete bonding to the sheet material. Generally, pressure should be applied using a suitable clamp or other system, in accordance with the adhesive manufacturer's instructions, to ensure that a good bond is achieved. Depending upon the size and scale, the adhesive may be applied via a roller or the like, manually or using an automated system.

Appropriate polyurethane adhesives have proved suitable, as they provide effective wetting of the surfaces, interact well with the substrate, and provide effective adhesion. One suitable adhesive is Daltobond YG 10004, available commercially from Huntsman Polyurethanes Australia Pty Ltd.

Typically, it is envisaged according to this implementation that the panels 10 would be supplied in up to 6.0m lengths, with heights of 0.6, 0.9 and 1.2 metres. The panels may have surface decoration of any suitable type painted, embossed, moulded or otherwise provided on the surface. For example, in figure 3 it can be seen that a series of grooves 16 are formed on the surface. These grooves not only provide a desired appearance but also improve acoustic attenuation performance.

In another form, illustrated in figure 2, the panel 10 includes channels cut into each side of the polystyrene layer. The function of this is to reduce the surface to surface contact between the polystyrene and the MgO Boards to improve the acoustic attenuation of the panels. The channels in this implementation are approximately 50mm wide and 20mm deeps, at 100mm centres and offset from each other on each side.

Figure 3 illustrates a panel 10 inserted within two H-beam sections 21, 22. It will be appreciated that an important advantage of the present invention is that the panels are much lighter than a Portland cement based product, and as such can be installed without the need for heavy or expensive cranage. It is preferred that a sealant, for example silicone, is provided within the groove of the H-beams to enhance sealing, and improve the noise attenuation of the panels.

To install the roadside barrier, firstly a series of vertical structural H-beams are provided along the proposed length. The H-beams are spaced apart in accordance with the length of the panels, being typically 3m to 4m. The H-beams have their bases buried in the ground with a concrete foundation. The height of the H- eams is selected depending upon the desired height of the barrier. Once the H-beams are erected, panels are then slotted in place from the top of the H- beams and guided by the channels on adjacent H-beams. After placing the panels, a silicone sealant may be added to the joints between the panels and the H-Beam and between the panels themselves to increase the acoustic performance if required, however the panel has been tested to demonstrate a satisfactory acoustic performance without any joint sealing. A required number of panels are stacked on one another between two H-beams until the required height of the barrier is achieved. The panels can be lifted into place by use of a crane hoist.

Figure 4 illustrates a finished section of noise abatement barrier, it can be seen that the use of different patterns on the panels provides an interesting aesthetic effect as well as provide improved noise abatement.

It will be apparent that the thickness of the manufactured panels should be commensurate with the gap between the arms of the H beam.

Of course, it will be appreciated that while this is a preferred construction for the road side barriers using panels implementing the present invention, other structural approaches could be used. Where the panels are used for other purposes, the thickness, dimensions and methods of fixing and retaining may be varied.

Experiments have found that the panel according to this implementation exhibits sufficient strength and acoustic abatement characteristics to meet standards and requirements for a roadside fence.

A panel formed of 126mm EPS and 12mm MgO board layers was subjected to testing.

A standard impact test was conducted on the panel. The test requires dropping a 4kg steel ball from a height of 3m onto the panel's surface. The MRTS15 dictates a maximum depth of deformation of 4mm and maximum area of deformation of 20mm. The panel satisfied the test by exhibiting only 12.5% of maximum depth deformation and less than 80% of allowable area of deformation.

Acoustic testing of the panel was conducted in accordance with standard AS 1191. According to MRTS15 the panel must exhibit a minimum sound reduction index (Rw) of 30dB. Testing was conducted with the panel in place between the structural posts. The panel measured an Rw of 34dB with solid EPS and an Rw of 36dB with triangle cut out polystyrene EPS (as shown in figure 5, which will be further described below). Both these tests were undertaken without any joint sealing and further testing has demonstrated an improved Rw of 4dB when the joints are sealed.

Structural tests concerning limits on bending, shear and axial loading were found to satisfy requirement for suitability in construction and capable of withstanding standards set out in MRTS15 for wind conditions throughout Australia.

Figure 5 illustrates an alternative implementation of the present invention.

In this implementation, the MgO sheets 13, 15 are as in the earlier example. However, the polystyrene layer 30 includes large cut out portions 31, 32 from each face.

The foam sections of implementations of the present invention are designed so as to reduce the ability for sound to propagate directly along the cell boundaries within the foam structure, by providing recesses within the foam structure. Additionally, such recesses act to reduce the rigidity of the foam structure. In preferred forms, as will be explained further below, the recesses alter the mechanical structure of the foam, so that it is less rigid, and in some cases has hinge like structures within the foam. Further, the removal of some material is believed to act to reduce the rigidity of the foam structure as a whole, which is turn acts to reduce the efficiency of sound transport within the foam. As a consequence, the attenuation of sound across the foam, and hence across the panels as a whole, is greatly improved, particularly in the low frequency portion of the sound signals. This is particularly important when considering road noise, as the low frequency components are important.

One disadvantage of polystyrene is that it suffers from what is known as a 'polystyrene signature' in the acoustic performance. This is usually a significant dip in acoustic attenuation performance in the frequency region of about 250 to 1000Hz, and a similar effect is apparent for any type of rigid or semi-rigid foam core.

The use of cut outs in the styrene material operates to improve the flexibility of the polystyrene core. The optimum shape, spacing, depth, and overlap may vary for different applications and materials, and the suitability for particular systems and applications can be optimised by comparative attenuation testing. It will be appreciated that care needs to be taken to understand the required mechanical properties of the finished composite panel when designing or selecting the modified foam profile. The removal of material will be expected to reduce the rigidity of the panel, whether this is significant in particular cases needs to be taken into account. The shape and configuration of the removed material may also have an impact on the structural characteristics of the overall composite panel. The more material which is removed, in principle, the higher degree of loss of rigidity in the foam and hence in the overall composite panel would be expected. Appropriate shaping and structuring can optimise the mechanical performance of the modified foam structure.

Figures 4 to 13 illustrate possible profiles, incorporating shaped recesses or grooves extending through both faces of a generally planar sheet of foam material. Considering figure 6, it can be seen that the layers of sheet material 13, 15 are provided, and that the polystyrene core 26 includes a series of grooves 24 extending from either face of the polystyrene core 26. Grooves 26 extend for a considerable depth into the surface of the polystyrene core 26. It is preferred that their depths are such that they overlap - that it, that both extend so that their depths are co-extensive within the foam. It is preferred that their depths are more or less the same, however, implementations with different depths are possible, it is preferred that there is an overlap between the grooves on opposite faces, more preferably in the range of about 20 to about 85% of the thickness of the foam, most preferably about one third of the thickness of the foam core. In a most preferred form, each groove has a depth of about 2/3 the thickness of the foam sheet. The size and depth of the slits represents a balance between acoustic performance and structural capability. Acoustically, the deeper and wider the slits, and the more closely spaced, the better the attenuation. However, as more material is removed, the structural capacity of the foam and hence the overall composite tends to be reduced.

Many different shapes and configurations of c-ut outs are possible in the polystyrene sheet. For example, figure 7 illustrates a form in which rounded teeth extend from each face. Figure 8 illustrates a form with triangular cut outs of much lesser relative depth than figure 5. In figure 9, the grooves extend at an angle to the faces of the polystyrene sheet. Many other configurations and shapes are possible.

Figure 10 is a graph illustrating the outcomes of an acoustic test conducted using an implementation of the present invention with 12mm INEX board and a solid 126 mm thick polystyrene layer. The test was designed to determine the airborne sound transmission loss of the panel without any sealing of the joints. This provided an Rw value of 34, with a frequency specific -attenuation as shown in figure 10.

Figure 11 is a similar graph to figure 10. In this case, the panel was 12mm

INEX board with a 126mm polystyrene layer, with extensive triangular cut outs as in figure 5 (again without and sealing of the joints). The panel was 2960 mm long, with the cut outs at 133.33 mm centres. Each extended 75 mm into the core, so that the overlap between the points of the cut-outs from opposite faces was 24mm. The same test was conducted in essentially the same conditions in the same facility. In this case, an Rw value of 36 was achieved, with a frequency specific attenuation as shown in figure 11. It is noted that the improvement of Rw of 2dB was achieved wholly within the 200Hz to 630Hz range, being that frequency range of most vehicle noise.

Accordingly, implementations of the present invention provide significant advantages over prior acoustic panels. Panels can be constructed according to the present invention which are much lighter in weight than existing panels, but still provide the necessary impact resistance, noise attenuation and mechanical and durability characteristics required for applications such as roadside noise abatement. Further, this panel construction avoids the need for a specialised bracket system to affix the panels.

A further characteristic of embodiments of the present invention is that because they can be formed from already existing components, the lead time for manufacture is greatly reduced compared to existing products. It is also possible to adapt the shape and size to novel situations if required. For example, the thickness of polystyrene can be readily changed so as to fit a required recess. Change to lengths can be readily for panels according to the present invention, relative to a pre-formed concrete panel. Whilst a series of specific layers are referred to, the present invention encompasses the use of additional layers or coatings. For example, an additional board or other layer could be disposed within the structure, or additional coatings, protective layers, and the like applied.