Railway sleepers made of fiber-reinforced stoneware

Abstract

Railway sleeper made of several layers of stone and fibrous material bonded together with resin, characterized in that the sleeper has a rigid middle layer of hard stone, which is coated on the top or bottom with a rigid stone slab, wherein at least one of these two slabs is prestressed with the aid of fibers which contain alternating different fibrous materials in different layers at different locations.

Description

The present invention relates to the development of railway sleepers, which are required for laying railway tracks, for example railway tracks, and for fastening them. The challenge in the structural implementation of parts that could previously be produced from wood using relatively simple means is that they increasingly have to be made from artificial materials, as wood is becoming scarce as a mass-produced material in light of the now undisputed climate change. Newer construction methods have shifted to concrete that must be prestressed using structural means – for example, with threaded rods embedded in the concrete. Before the concrete hardens, these rods are tensioned at the ends using nuts, thus providing the hardened concrete with the necessary tensile strength through a fixed prestress reserve. The disadvantage is that such steel reinforcements rust and, over time, lose some of their prestress due to continuous stress. The concrete can then become brittle and cracked; moisture, frost, and the natural changes in the concrete over time further contribute to the deterioration of the concrete sleeper. The goal is to build a threshold that conserves timber resources, is more durable than concrete, and, most importantly, has a low CO2 footprint during its own production, or is carbon-negative. The production of concrete and steel requires a lot of energy, which unfortunately is currently associated with a large amount of CO2 emissions. Furthermore, the aim is to develop a universal new concept that can be used worldwide in diverse climatic conditions. Minimum and maximum temperature values, humidity, and weather influences such as water, frost, and atmospheric chemistry must not damage the materials used, ensuring a sustainable and long-lasting solution that can be manufactured virtually anywhere. Weight, strength, workability, and finally, the type of surface also play a crucial role, not only for cleaning purposes, but also because its color and visual appearance determine the suitability of a solution and its adaptation to specific conditions, whether in nature or in more enclosed spaces such as train stations or open platforms. The proposed idea here is to configure a sandwich of materials that solves several problems simultaneously. The aim is to optimize long-term load-bearing capacity and strength values, vibration damping, ease of processing with regard to rail connection, crack-free long-term durability of the component itself, surface durability, and the possibility of integrating further functionalities. A crucial, further objective is to reduce the energy required to manufacture railway sleepers today. The approach proposed here is intended to demonstrate a new platform for the aforementioned advancements in such sleepers. Manufacturing such a sleeper from granite requires an order of magnitude less energy compared to a concrete sleeper.The energy-intensive part is the carbon fiber used to prestress the stone. In the future, the preferred carbon fiber, as well as the necessary matrix consisting of modern resin systems, can be obtained indirectly from CO2 in the atmosphere via renewable, plant-based raw materials. This harmful CO2 can then be permanently removed from the atmosphere over appropriate periods and bound permanently in the carbon material itself. The present invention accordingly describes a sandwich consisting of several natural stone slabs bonded together by means of an intermediate layer of fiber material and a bonding matrix – for example, epoxy resins or other adhesive-like crosslinking agents. In most cases, it will be advantageous to design this composite of stone, fiber material, and resin such that the fiber layers prestress the stone slabs, thus eliminating the need for complex prestressing with threaded rods. This prestress should preferably be generated by a type of fiber that retains this prestress. Carbon fibers and stone fibers have proven to be the most suitable for this purpose, as described, for example, in EP 106 20 92 and EP 29 25 929. Using several fiber-coated stone slabs, bonded together to create prestress in the stoneware, a high-performance threshold is produced from natural materials such as granite, basalt, or gabbro. The innovation of this invention lies in the use of different fiber materials at points of varying stress on the threshold body, thus optimizing costs. Only the top and bottom cover plates are prestressed through the coating process. The surface finish is ideally formed by a layer of stone to protect against weathering. Ideally, the sleeper consists of three stone slabs, with the middle slab being significantly thicker than the top and bottom slabs for mechanical reasons. The core slab should be made of the stiffest possible rock (1), for example, gabbro or basalt, and the prestressed, thinner slabs made of a softer granite (4) for easy prestressing, or vice versa, to place the more tensile-resistant stone at the bottom to prevent cracking. In this way, sleepers can be configured to meet different requirements, whether on straight track, curves, or bridges, where the requirements differ due to varying load profiles.An intermediate layer of carbon can be inserted between these stones to further stiffen the rigid core and protect it from any cracking. Currently, epoxy resins are well-suited for bonding the fiber to the stone, especially if the stone's porosity allows for resin penetration. Holes are drilled in the top of this plate assembly, into which the fixing pins of the support plate are screwed using dowels, the support plate being a conventional support plate which in turn allows screwing to the clamps that hold the rails. Since the finished stone sleeper is now prestressed at the top and bottom, it can absorb dynamic compressive and tensile forces, utilizing granite's excellent self-damping properties to quickly dissipate vibrations within the system. The granite, which weighs only slightly more than aluminum, is transformed into a high-tech composite material with the addition of fibers. This material possesses the compressive strength of steel, while the necessary tensile strength is achieved through prestressing with thin layers of carbon fibers (3), which are stronger than steel. Granite is abundant on Earth in virtually every country. As it becomes possible in the future to produce carbon fibers from atmospheric CO2, it will be possible not only to develop materials that require less energy to manufacture but are also capable—like wood before it—of binding harmful carbon.Gabbro (1) has a high weathering potential if the dust generated during cutting is spread on agricultural land, for example. Climate science refers to the process of binding CO2 in conjunction with water as Enhanced Rock Weathering (ERW), a type of carbonation that dissolves the rock minerals in water, making the soil more fertile and remineralizing it. The carbon from the CO2 remains bound in the carbonate and is transported via groundwater and rivers to the sea, where it remains permanently (CDR - Carbon Dioxide Removal), making the material carbon-negative. To reduce manufacturing energy and the CO2 footprint, carbon fibers are only used where the central bending stress occurs. This is in the rail bearing in the lower fiber layer below the rail bearing during the positive bending moment caused by the train wheel loads, and in the middle of the sleeper during the negative bending moment in the upper fiber layer. To increase the number of carbon layers with minimal use of carbon fibers (3), these are cascaded downwards like a pyramid in the lower fiber layer and in the upper fiber layer with a cascaded structure of carbon layers (3) upwards. The remaining areas are seamlessly filled adjacent to the carbon layers with glass fibers or, preferably, the stiffer stone fibers or basalt fibers (2). Since granite and other rocks are frost-resistant despite their relative water absorption capacity, there are no problems even at sub-zero temperatures.There is hardly a more durable material than granite or basalt. One of the many possible embodiments of the invention is shown in cross-section in Fig. 1 of an approximately 80 mm thick stone slab (1) which is connected to an upper (4) and lower cover plate made of a less rigid stone (4), each prestressed with a carbon layer (3). Further layers of carbon and glass or basalt fibers (2) are used to increase the tensile strength. The fiber layers are covered at the top and bottom with a final stone layer (5), preferably also made of gabbro. All layers of stone and fibers are bonded with epoxy resin. (1) shows stone: gabbro or basalt, 2,900 kg / m³, impregnated with epoxy resin to a depth of 0.1 mm at the contact surfaces, porosity 0.15 vol%. (2) shows glass fiber or basalt fiber 550g / m2 (60% vol) impregnated with epoxy resin (40% vol). (3) shows carbon fiber 400g / m2 (60% vol) impregnated with epoxy resin (40% vol). (4) shows stone: Rosa Beta granite, 2,690 kg / m3, impregnated with epoxy resin to a depth of 0.2mm at the contact surfaces, porosity 0.3 vol%. Fig. 2 shows an additional fiber layer (6), either aramid fiber or ceramic fiber or glass fiber or basalt fiber or a mixture thereof, impregnated with epoxy resin. QUOTES INCLUDED IN THE DESCRIPTION This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature EP 106 20 92

[0007] EP 29 25 929

[0007]

Claims

Railway sleeper made of several layers of stone and fibrous material bonded together with resin, characterized in that the sleeper has a stiff middle layer of hard stone, which is coated on the top or bottom with a stiff stone slab, wherein at least one of these two slabs is prestressed with the aid of fibers which contain alternating different fibrous materials in different layers at different locations. Arrangement according to claim 1, characterized in that the hard stone slab in the middle consists of hard gabbro or basalt or softer granite. Arrangement according to claims 1 and 2, characterized in that the cover plates are made of hard gabbro or basalt or softer granite. Arrangement according to claims 1 to 3, characterized in that the tensile-stabilizing fiber is a glass fiber, carbon fiber, stone fiber, aramid fiber, natural fiber - such as flax, hemp, corn, cotton, wood, bamboo or any other - possibly carbonized - plant fiber, steel fibers and other fibers or also a mixture of these fibers, which are bonded to the stone in layers with the aid of resin. Arrangement according to claims 1 to 4, characterized in that the matrix consists of hardening resins, for example epoxy resins, thermoplastic resins, synthetic resins, resins produced from regenerative plant materials, e.g. algae. Arrangement according to claims 1 to 5, characterized in that the stone consists of natural hard rock or other natural stone such as granite, marble, basalt, sandstone, slate or artificial stone such as concrete, resin-bound quartz or stone flours or ceramic or other stoneware. Arrangement according to claims 1 to 6, characterized in that the fiber matrix of the fiber-stabilized stone slab contains different fibers in different layers. Arrangement according to claims 1 to 7, characterized in that the carbon fiber matrix of the fiber-stabilized stone slab has a cascaded structure of very stiff fibers in the different layers in the area of ​​maximum bending moments - below in the area of ​​positive moments of the rail supports and above in the middle area of ​​the netagive bending moment. Arrangement according to claims 1 to 8, characterized in that the coefficient of expansion of the fiber matrix is ​​overall smaller than that of the stone to be stabilized. Arrangement according to claims 1 to 9, characterized in that the fiber layers hold the stone cover plates under permanently installed prestress. Arrangement according to claims 1 to 10, characterized in that the stone slabs are made of weatherable material such as gabbro or basalt. Arrangement according to claims 1 to 11, characterized in that a further stiff fiber layer is installed between the prestressed cover plates and the core.

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