Patent Application
20060226247
This invention relates to structural elements, and more particularly relates to composite structural elements, and elements for use as railway ties, and a process for forming such composite structural elements.
Over the years, the area under forest cover has decreased steadily as people have been clearing trees to meet agricultural and industrial demands for the ever-growing population. Particularly to meet the demands of the construction industries, hardwood forests have been depleting steadily. A large number of structural elements such as railway ties, telephone poles, guard rails, fences, decks, and retaining walls, just to name a few, are constructed from wood. Although efforts have been made to conserve our forests and many industrialized countries have developed recycling programs to reduce the need of cutting down trees for use in construction, the amount of recycled timber suitable for use in construction is very limited. Furthermore, the recycled timber used in construction typically needs to be chemically treated before use, and thus renders it toxic.
In the railway transportation industries, for instance, railway ties, which are used to support railroad track rails on a ballast or concrete roadbed, are typically made of wood. Wood railway ties have been generally preferred in North America, since they can withstand climatic change, and are relatively easy to install and replace. However, given the scarcity of hardwoods, it would be desirable to replace wood with other materials.
In North America and in most civilized and developing countries of the world, rail transportation of both freight cars and passenger cars is an important part of each country's economic infrastructure. Given the large geographical areas of United States and Canada, and the sprawl of developing suburban areas in these countries, thousands of miles of railway tracks are needed to link these areas together. Accordingly, a staggering number of wood railway ties are needed each year for use in the building of new railway lines and also to replace those which have worn out over time.
Although wood railway ties provide durability and can carry the static and dynamic loads of freight and passenger trains traveling at various speeds, including relatively high speeds, perhaps well in excess of one hundred miles per hour, wood railway ties are susceptible to attack from such microorganisms as fungi and insects, which will weaken and eventually deteriorate the railway ties. It has been known that by treating the wood railway ties with creosote, the life span of the wood railway ties may be prolonged. However, the use of creosote as a preservative suffers the disadvantage that it is a toxic substance and a suspected carcinogen. Creosote treated railway ties therefore result in potential environmental hazards both during the treatment process of the manufacturing of the railway ties and the possibility of the creosote leaching into the surrounding soil or water table in the region of the railway. Furthermore, wood railway ties that have been chemically treated present a disposal difficulty, given the environmental concerns over the hazardous chemical preservatives. Thus, it is difficult and expensive to dispose of wood railway ties. Although wood railway ties can withstand the North American climate, they are, nevertheless, susceptible to damage from harsh weather conditions and excessive sunlight. As a result of these drawbacks, wood railway ties require frequent monitoring and maintenance so as to prevent failure due to splits, shakes (separation along the grain), decay, or warps. The costs in the materials, labor and disposal of these railway ties can be quite substantial as a staggering number of railway ties are used each year.
Concrete railway ties are popular in Europe and Japan, where the availability of hardwood is limited. However, concrete railway ties have several disadvantages associated with them. First, they are relatively expensive and can crack or spall over a number of years when used in areas of dramatic climatic change. Most significantly, they can suffer from rail to tie erosion under the heavier rolling stock loads in North America as compared to the lighter and smaller locomotives and passenger and freight cars used in Europe.
Steel railway ties have been employed, however, they realize only limited use in North America and other parts of the world. Susceptibility to rust and a high noise level during use, which is unacceptable on passenger trains, limits their acceptability. In addition, steel railway ties can shift within the ballast. Moreover, in places where the steel railway rails are also used to send electrical signals along the railroad rightof-way, and must therefore be electrically isolated one from the other, the use of electrically conductive railway ties between the rails is precluded.
It can be seen that there are many economic and environmental disadvantages associated with existing railway ties, whether they are made of wood, concrete or steel.
Attempts have been made to manufacture railway ties from other materials, such as recycled tires. However, the cost associated with recycling tires is high, and thus, such railway ties have not found broad commercial application. In addition, it has been found that railway ties manufactured from recycled tires lack stiffness and an adhesive is required to bind the granulates of recycled tires together, which further contributes to the high manufacturing costs.
Plastic polymers and plastic composite materials have also been used to manufacture railway ties as an alternative to wood. Manufactured plastics composites can exhibit the necessary stiffness strength, as well as increased resistance to degradation from moisture, excessive sunlight and attacks by microorganisms and insects. However, the cost of raw materials is a disadvantage of plastic polymers and plastic composites. Virgin polymer resins can be quite expensive thereby making their use economically unfeasible. In addition, plastic polymers can potentially release toxic materials if they are burned (e.g. in a tunnel file).
Attempts have also been made to construct composite building materials from recyclable waste, by mixing high-density polyethylene and a thermoplastic coated fiber material such as fiberglass. However, much of the available recycled waste not only contains high-density polyethylene but also a mixture of other less desirable plastics materials such as polyvinyl chloride. Thus, separation of the high-density polyethylene from other plastics materials is difficult and also contributes to the costs of manufacturing the composite building materials from the recycled waste. In addition, such ties often require expensive and specialized fastening systems.
U.S. Pat. No. 5,221,702 issued to RICHARDS on Jun. 22, 1993 teaches molded composite paving products such as blocks for use in paving roads, parking lots and driveways, and a process for manufacturing the same. The composite paving block is formed from asphalt, plastic such as polyethylene or phenolic resin, elastomeric material such as rubber or polyvinyl chloride, and fiber material such as nylon or rayon. The materials are heated and blended together into a relatively uniform mixture of composite material. The composite material is then molded into individual paving blocks.
U.S. Pat. No. 5,367,007 issued to RICHARDS on Nov. 22, 1994 teaches a multi-layer molded composite paving block and a process for manufacturing the same. The multi-layer molded composite paving block has a first layer formed from recycled asphalt, thermoplastic or thermosetting plastic, monofilament fiber material and elastic material, and a second layer formed from thermoplastic such as polyethylene or thermosetting plastic, and an aggregate material. During the manufacturing process, the plastic constituent in each of the layers are heated and pressure bonded to one another, so as to form a securely interlocked structural interface between the first and second layers, and to thereby form a single integral structure.
U.S. Pat. No. 5,609,295 issued to RICHARDS on Mar. 11, 1997 teaches a composite railway tie and a method of manufacturing the same. The composite railway tie comprises a main body portion made of a binding constituent and an aggregate material. The binding constituent is a plastic material, while the aggregate material is in the form of irregular multi-faceted pieces such as gravel, limestone, granite, and rocks. The binding constituent holds the aggregate material together. An inner strengthening core made from a material having high tensile strength may be included in the railway tie.
U.S. Pat. No. 5,722,589 issued to RICHARDS on Mar. 3, 1998 is a Continuation-In-Part of the above U.S. Pat. No. 5,609,295. The composite load bearing structure has a main body made of a binding constituent and an aggregate material. An inner strengthening member is disposed within the main body which may comprise reinforcing bars, rolled, drawn, or cast ferrous sections-, rolled, drawn, or cast composite alloy sections; plastic, metallic, and carbon based fibers-, wire mesh, and expanded metal mesh.
U.S. Pat. No. 5,789,477 issued to NOSKER et al. on Aug. 4, 1998 teaches the formation of composite building materials from recyclable waste. The composite material is composed of an extruded mixture of high-density polyethylene and a thermoplastic-coated fiber material such as fiberglass.
U.S. Pat. No. 6,191,228 issued to NOSKER el al. on Feb. 20, 2001 teaches the use of recycled plastics for preparing high performance composite railroad ties. The railroad tie is formed from a plastic composite material comprising a polystyrene component forming a first phase and a polyolefin component forming a second phase. The two phases, polystyrene and polyolefin, intertwine and remain continuous throughout the composite railroad ties.
U.S. Pat. No. 6,247,651 issued to MARINELLI on Jun. 19, 2001 teaches a composite railway crosstie, shaped like an I-beam, which is made from a combination of recycled materials. The composite crosstie is composed of recycled high-density polyethylene and polypropylene plastics, scrapped and granulated rubber tires and screener waste glass fibers.
It will be apparent from the foregoing prior art that the composite block or railway tie is made from plastics which has a high proportion of high-density polypropylene, rubber ties, waste glass fibers, aggregate materials such as gravel, limestone, granite, and reinforcing bars as strengthening core, and combinations and mixtures thereof.
It is an object of the present invention to provide a novel composite structural element, and a process for forming such composite structural elements which obviates or mitigates the disadvantages of the prior art.
In accordance with one aspect of the present invention, a composite structural element is provided. The composite structural element comprises asphalt in a proportion of about 15% to 95% by weight, and fiber-reinforced plastics and optionally plastics chosen from the group consisting of virgin plastics, recycled plastics, and combinations and mixtures thereof in which the total plastics component content is at least in a proportion of about 5 to 85% by weight.
In one embodiment, the composite structural element further comprises an elastomer in a proportion of about 0 to 80% by weight. Preferably, the elastomer is in a proportion of between 0% to 25% by weight.
In another embodiment, the asphalt is in a proportion of about 65% to 85% by weight. Preferably, the asphalt is in a proportion of about 70% to 80% by weight.
In yet another embodiment, the total plastics component content is in a proportion of about 10 to 45% by weight. Preferably, the total plastics component content is in a proportion of about 15% to 40% by weight. More preferably, the total plastics component content is in a proportion of about 20% to 30% by weight. Still more preferably, the total plastics component content is in a proportion of about 25% to 30% by weight.
In one embodiment, the fiber reinforced plastics is in a proportion of about 25% to 75% by weight of the total plastics component content. Preferably, the fiber reinforced plastics is in a proportion of about 30% to 70% by weight of the total plastics component content. More preferably, the fiber reinforced plastics is in a proportion of about 40% to 60% by weight of the total plastics component content.
Typically the asphalt is sized such that more than 75% of the asphalt would pass through a screen having 0.75 inch square openings. More preferably, the asphalt is sized such that more than 50% of the asphalt would pass through a screen having 0.5 inch square openings.
Preferably, the plastics component is sized such that more than 75% of the plastics component would pass through a screen having 0.5 inch square openings.
Typically the elastomer is sized such that more than 75% of the elastomer would pass through a screen having 0.25 inch square openings. More preferably, the elastomer is sized such that more than 75% of the elastomer would pass through a screen having 0.125 inch square openings.
Further, the asphalt may be recycled asphalt. The fiber-reinforced plastics may be recycled industrial waste. The virgin plastics may be chosen from the group consisting of low density polyethylene (LDPE), high density polyethylene (HDPE), and polypropylene (PP). The recycled plastics component is composed of polymers chosen from the group consisting of polyvinyl chloride (PVC), low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET), and combinations and mixtures thereof. Still further, the elastomer may he recycled tire rubber.
In one embodiment, the composite structural element is a railway tie.
In another embodiment, the plastics component also includes a particulate filler.
In another aspect of the present invention, a process for manufacturing composite structural elements is provided, which comprises the steps of: (a) introducing asphalt, plastics, and fiber-reinforced plastics into a blender; (b) mixing and heating the materials of step (a) at a temperature in the range of about 250 to 380° F. until a homogenous blended mixture is obtained; (c) discharging the blended mixture and subjecting the blended mixture to one of the steps chosen from the group consisting of: (i) feeding the blended mixture into an forming device which molds and stabilizes the blended mixture conveying the blended mixture through subsequent cooling stages; and cutting the molded blended mixture into pre-determined lengths to form composite structural elements; and (ii) placing pre-determined quantities of the blended mixture into molds having predetermined sizes and shapes and molding the blended mixture under pressure into composite structural elements.
In one embodiment, step (a) of the process further includes the introduction of an elastomer into the blender.
In another embodiment, the plastics and the fiber-reinforced plastics are pre-mixed before mixing with the asphalt.
In yet another embodiment, the plastics, the fiber-reinforced plastics and the elastomer are pre-mixed before mixing with the asphalt.
In still another further embodiment, at least one of the asphalt, plastics, and fiberreinforced plastics is pre-heated before introduction into the blender in step (a).
Additionally, in another embodiment, the elastomer is pre-heated before introduction into the blender in step (a).
Typically, the materials are heated at a temperature in the range of 275 to 375° F. in step (b). Further, the forming device in step (i) functions at a temperature regime of 250 to 400° F. Still further, the blended mixture is molded under pressure in the range of 500 to 5000 psi.
It is contemplated that the composite structural element is economical to manufacture and that it poses less environmental concerns as recyclable and reclaimed materials may be used. Furthermore, the composite structural element of the present invention does not require the use of any reinforcing beams for strength.
The novel features which are believed to be characteristic of the present invention, as to its structure, organization, use and method of operation, together with further objectives and advantages thereof, will be better understood from the following discussion.
The present invention provides a composite structural element and a method of making the same. The composite structural element may be used as a railway tie that serves to anchor rails and keep them parallel to one another.
The Composite Structural Element
In accordance with the present invention, the composite structural element comprises asphalt, fiber-reinforced plastics and optionally plastics chosen from the group consisting of virgin plastics, recycled plastics, and combinations and mixtures thereof. Typically, the asphalt comprises between 15% and 95%, by weight of the composite element and the total plastics component content comprises between 5 and 85% by weight of the composite structural element. Although a minor amount of impurities may be present in the starting materials, such as moisture, the effect on the manufacturing process of the composite structural element is negligible.
Preferably, the asphalt comprises 65% to 85% by weight of the total weight of the composite structural element. More preferably, the asphalt comprises 70% to 80% by weight of the total weight of the composite structural element. Preferably, the total plastic component comprises 10% to 45% by weight of the total weight of the composite structural element. More preferably, the total plastic component comprises 15% to 40% by weight of the total weight of the composite structural element. Even more preferably, the total plastic component comprises 20% to 30% by weight of the total weight of the composite structural element. Still more preferably, the total plastic component comprises 25% to 30% by weight of the total weight of the composite structural element.
The fiber-reinforced plastics preferably comprises between 25% and 75% by weight of the total plastics component content. More preferably, the fiber-reinforced plastics comprises between 30% and 70% by weight of the total plastics component content. Still more preferably, the fiber-reinforced plastics comprises between 40% and 60% by weight of the total plastics component content.
While the composite structural component is typically formed from asphalt, fiber-reinforced plastics and other plastics, the composite structural element may further comprise an elastomer in a proportion of about 0 to 80% by weight. Preferably, the elastomer comprises between 0 and 25% by weight of the composite structural element.
Typically, asphalt used in the composite structural element of the present invention is recycled asphalt that has been crushed and subsequently screened for size. Asphalt is typically passed through a series of screens having progressively smaller square openings. Larger asphalt particles are caught in the first screens while finer particles are caught by later screens. Preferably, more than 75% of the asphalt would pass through a screen having 0.75 inch square openings. Even more preferably, at least 50% of the asphalt would pass through a screen having 0.5 inch square openings.
The virgin plastics of the composite structural element of the present invention may be chosen from the group consisting of low-density polyethylene (LDPE), high-density polyethylene (HDPE), and polypropylene (PP).
Although virgin plastics may be used to form the composite structural element of the present invention, it is preferable to use recycled plastics so as to reduce the amount of waste in our environment. The recycled community-collected plastics of the composite structural element of the present invention is composed of polymers chosen from the group consisting of polyvinyl chloride (PVC), low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET), and combinations and mixtures thereof. In fact, the recycled plastics may be post-consumer plastics or post-industrial plastics, or a combination of both. Typically, in post-consumer plastics, the proportion of highdensity polyethylene (HDPE) is low, with the plastics content being mainly composed of low-density polyethylene (LDPE) and polypropylene (PP). In post-industrial plastics, however, the proportion of high-density polyethylene (HDPE) is usually more significant. The fact that post-consumer plastics or post-industrial plastics or combinations of both may be used provides both economic and environmental advantages.
To prepare the plastics component for the manufacturing process of the composite structural element, the plastic component is also sized in a manner similar to the asphalt. Preferably, more than 75% of the plastics component would pass through a screen having 0.5 inch square openings. For post-consumer plastics, the plastics are typically a ground material. For post-industrial plastics, the plastics are typically in flakes. However, the post-industrial plastics may also have been shaved or chopped.
The fiber-reinforced plastics used in the composite structural element of the present invention are typically derived from recycled automobile bumpers. The automobile bumpers used in the composite structural element comprise typically comprise glass-filled polypropylene. Glass-filled polypropylene with a pre-determined proportion of glass is readily available commercially where the glass is intertwined with the polypropylene and is continuous throughout the polypropylene component. Other recycled industrial waste may also be used for the fiber-reinforced plastics. It has been found that by mixing virgin plastic and fiberglass together, clumps of materials are obtained, and not particularly favorable in the manufacturing of the composite structural element. Thus, it is desirable to use plastic that is reinforced with fiberglass, such as glass-filled polypropylene. It has been determined by the present inventors that the presence of the glass-filled polypropylene enhances the strength of the composite structural element. Other fibers (such as carbon fibers or silicon fibers) could instead be used to reinforce the plastics component.
Optionally, particulate fillers may also be added to the plastics component. Particulate fillers can enhance the strength of the plastic component. Examples of particulate fillers include carbonates (such as CaCO3 or chalk limestone), clay, mica, microspheres, minerals (silicates), agricultural waste products, silicons and talc.
In addition to the asphalt, fiber-reinforced plastics and other plastics materials, the composite structural element may further contain an elastomer. The elastomer is preferably tire rubber that has been recycled from sources such as scrap tires. The preferred process for producing such recycled rubber is a cryogenic process, which is well known in the industry. The rubber that is produced by a suitable cryogenic process or a suitable ambient reduction process, is preferably crumb rubber that is free from other materials found in the tires. Preferably, at least 75% of the elastomer would pass through a screen having 0.25 inch square openings. Even more preferably, at least 75% of the elastomer would pass through a screen having 0.125 inch square openings.
As is apparent from the compositions of the composite structural element of the present invention, the composite structural element would be resistant to attack by microorganisms such as fungi and insects, and also would not need to be treated with chemical preservatives. The composite structural element of the present would also be able to withstand harsh environmental conditions such as strong ultraviolet light, and freezing climates.
Since the composite structural element of the present invention is constructed from reclaimed or recycled materials, the costs for manufacturing the composite structural element may be reduced significantly. At the same time, by using reclaimed or recycled materials in the formation of the composite structural element, waste is also reduced and it is beneficial for the environment.
Test Results
A composite block comprised of 60% asphalt, 20% LDPE and LDPE 20% glass-filled polypropylene underwent compression and bending tests to determine its strength. The glass-filled polypropylene contained 15% by weight of fiberglass.
A 1.4″×1.9″×3.8″ block underwent a compression test. The modulus of elasticity was found to be greater than 150,000 psi. The compressive strength was found to be in excess of 3000 psi.
A 8″×4″×2.4″ block of the same composition as the block above underwent a 4-point bending test. The modulus of rupture was found to be 1600 psi.
These results indicate that the material used for the composite block is sufficiently strong for use in a variety of applications, including use as a railway tie.
Method of Manufacture
The composite structural element can be made by either a continuous process or a batch process. First, the asphalt, plastics, and fiber-reinforced plastics are introduced to a blender. The materials are then mixed and heated at a temperature in the range of about 250 to 380° F. until a homogenous blended mixture is obtained.
The blended mixture is then discharged and subjected to one of two processes. The first process is a continuous process in which the blended mixture is fed into a forming device that molds and stabilizes the blended mixture. The molded mixture is then passed through subsequent cooling stages. Finally, the molded mixture is segmented or cut into pre-determined lengths to form composite structural elements.
Alternatively, the blended mixture is subjected to a batch process in which predetermined quantities of the blended mixture is placed into molds having predetermined sizes and shapes and molding the blended mixture under pressure into composite structural elements.
In the embodiment where the composite structural element is additionally composed of an elastomer, the elastomer is typically introduced into the blender with the asphalt, plastics and fiber-reinforced plastics.
Typically, the plastics and the fiber-reinforced plastics are pre-mixed before mixing with the asphalt. In another embodiment, the plastics, the fiber-reinforced plastics and the elastomers are pre-mixed before mixing with the asphalt. Further, in another embodiment of the present invention, at least one of the asphalt, plastics, and fiberreinforced plastics is pre-heated before introduction into the blender. In yet another embodiment, the elastomer is pre-heated before introduction into the blender.
Preferably, the materials is heated in the blending stage at a temperature in the range of 275° F. to 375° F. Temperature control in the manufacturing process is crucial as at extreme temperatures, combustion of the plastics material may occur which is extremely dangerous. A high proportion of polyvinyl chloride in the plastics component is not desirable, as a by-product of the combustion of polyvinyl chloride is chlorine gas, which is extremely toxic.
Typically, the forming device used in the continuous process functions at a temperature between about 250° F. to 400° F. The blended mixture in the batch process is typically molded under pressure in the range of 500 psi to 5000 psi.
Typically, the forming device is a mold that shapes the mixture into a ribbon or other shape. The ribbon may then be segmented or cut into components.
While only specific combinations of various features and components of the present invention have been discussed herein, it will be apparent to those skilled in the art that desired subsets of the disclosed features and components and/or alternative combinations of these features and components can be utilized, as desired.
Throughout this specification and the claims which follow, unless the context requires otherwise, the word ‘comprise’, and variations such as ‘comprises’ or ‘comprising’, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not to the exclusion of any other integer or step or group of integers or steps.
