Railway sleepers made of fiber-reinforced stoneware with angled layering

Abstract

Railway sleeper made of several layers of stone and fiber material, which are bonded together with the aid of resin, characterized in that at least one of the fiber layers is firmly bonded to the stone at at least one end with a defined radius of the stone geometry by approximately 90° over a defined distance.

Description

[0001] 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.

[0002] The challenge in the structural implementation of parts that could previously be produced from wood using relatively simple means now requires that they be made from artificial materials, as wood is becoming scarce as a mass-produced material due to the now undisputed climate change.

[0003] 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.

[0004] 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.

[0005] 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 finish also play a crucial role, not only for cleaning purposes, but also because of its color and visual appearance, which 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.

[0006] 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 would allow the harmful CO2 to be permanently removed from the atmosphere over appropriate periods and bound permanently in the carbon material itself.

[0007] 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 themselves 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.

[0008] The surface finishes are formed by a layer of stone to protect against weathering. Ideally, the threshold 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 (3) for easy prestressing. An intermediate layer of carbon can be inserted between these stones to further stiffen the rigid core. Currently, epoxy resins are well-suited for bonding the fiber to the stone, especially if the stone's porosity allows for resin penetration.

[0009] 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.

[0010] Since the finished stone sleeper is now prestressed, it can absorb dynamic compressive and tensile forces, utilizing granite's excellent self-damping properties to quickly dissipate vibrations within the system. Granite, which weighs only slightly more than aluminum, is transformed into a high-tech composite material with the addition of fibers. This composite material possesses the compressive strength of steel, while the necessary tensile strength is achieved through prestressing using, for example, thin layers of carbon fibers (2a) and (2b), 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.

[0011] Tests have shown that while a sleeper coated with carbon fibers can withstand high loads, the carbon coating is no longer sufficient to prevent hairline cracking in the area of ​​the rail bearing above a load of approximately 150 kN, especially if the sleeper is thinner than conventional concrete sleepers. Simply increasing the number of carbon layers is not effective, as this creates such high stiffness that deflection of the sleeper leads to detachment of the carbon layer from the stone surface. Fracture tests have shown that the peeling process typically begins at the ends of the carbon layer and progresses from there.

[0012] The invention therefore relates to measures that prevent or at least delay the initiation of the peeling process at the ends of the carbon layer. A first measure consists of staggered termination of the carbon layers ("shafting") with a pyramidal transition, which makes the end regions of the coating less rigid. A difference in length of just a few millimeters is sufficient for this shafting of the carbon layer.

[0013] As a newly introduced, more efficient measure, a roughly 90° rounding of the stone surface at the end of the sleeper is proposed. The carbon fibers are guided at an angle over this rounding and firmly bonded to the surface. By redirecting the tensile forces into compressive forces over a well-defined radius, local stress peaks caused by shear forces at the fiber ends are reduced, and the load is partially converted into horizontal compressive stress across a large area of ​​the stone from the side. This reduces the shear forces at the stone-carbon interface at the end of the sleeper, where they are greatest, thus effectively delaying or completely preventing the onset of peeling.

[0014] One of the many possible embodiments of the invention shows in Fig. In vertical section, a stone block (1) approximately 60–120 mm thick is bonded to top plates made of a less rigid stone (3) and prestressed with an upper carbon fiber layer (2a). A lower layer of carbon fibers (2b) is used to increase the tensile strength on the underside. The fiber layers (2a) and (2b) are bent at their respective ends at the top and bottom in an approximately 90° arc and bonded along the stone surface with a sufficiently large radius to be covered with final stone layers (5). This prevents the carbon layer from peeling due to the high tensile forces under load on the threshold, which would lead to failure of the entire system and allow the full tensile strength of the fiber layer to be utilized. All layers of stone and fibers are bonded with epoxy resin, which fills the gaps shown in the schematic drawing. Fig.The stone is filled. In particular, the deflected ends of the fiber layers are carefully encased in pressure-resistant stone for securing, and then bonded tightly and without creases to the stone. This process can also be carried out under high pressure to prevent air pockets from weakening the strong bond. The steel rails (4) are mounted onto the stone layers (3). Mounting details, not shown here, are achieved using holes and dowels in the stone, into which corresponding fastening screws are securely seated. QUOTES INCLUDED IN THE DESCRIPTION

[0000] 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

[0000] EP 29 25 929

[0007]

Claims

[1] Railway sleeper made of several layers of stone and fibrous material bonded together with resin, characterized by , that at least one of the fiber layers is firmly bonded to the stone at at least one end at a defined radius of approximately 90° to the stone geometry over a defined distance. [2] Arrangement according to claim 1, characterized by that the angle of the angled fiber layer is 90°. [3] Arrangement according to claims 1 and 2, characterized by that several or all fiber layer ends are glued at a preferably 90° angle. [4] Arrangement according to claims 1 to 3, characterized bythat 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 other - possibly carbonized - plant fiber, steel fibers and other fibers or a mixture of these fibers, which are bonded to the stone in layers with the help of resin. [5] Arrangement according to claims 1 to 4, characterized by that the matrix consists of hardening resins, for example epoxy resins, thermoplastic resins, synthetic resins, resins made from regenerative plant materials, e.g. algae, or resins produced from other sources. [6] Arrangement according to claims 1 to 5, characterized by that the stone consists of natural hard rock or other natural stone such as granite, marble, basalt, gabbro, sandstone, slate or artificial stone such as concrete, resin-bound quartz or stone flours or ceramic or other stoneware. [7] Arrangement according to claims 1 to 6, characterized by, that the fiber matrix of the fiber-stabilized stone slab contains different fibers in several different layers. [8] Arrangement of claims 1 to 7, characterized by , that at least one intermediate layer of fiber composite material is provided between the stone and one or more layers of preferably unidirectional carbon fiber layer, the elastic modulus of which lies between that of the stone body and that of the carbon fibers, wherein the intermediate layer is preferably made up of several thin layers of different fiber types with graduated stiffness, the stiffness decreasing in the direction towards the base body. [9] Arrangement of claims 1 to 8, characterized bythat the intermediate layer consists of several superimposed layers of different fiber types, wherein the layers preferably have a decreasing stiffness towards the stone-like base body and the fibers are selected from less stiff carbon, ceramic, basalt, glass or aramid. [10] Arrangement according to claims 1 to 9, characterized by , that the carbon fiber matrix of the fiber-stabilized stone slab has a cascaded structure in the area of ​​maximum bending moments in the different layers, with the outer layers, facing away from the stone, preferably becoming progressively shorter in order to minimize the expensive and energy-intensive carbon content. [11] Arrangement according to claims 1 to 10, characterized by , that the coefficient of expansion of the fiber matrix is ​​smaller overall than that of the stone to be stabilized. [12] Arrangement according to claims 1 to 11, characterized bythat the fiber layers hold the composite inside under prestress under load. [13] Arrangement according to claims 1 to 12, characterized by that the angled fiber layers on the surface are fixed on both sides by gluing to further sufficiently stiff stone slabs and thus kept in a straight shape.

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