2. Uluslar arası Raylı Sistemler Mühendisliği Sempozyumu (ISERSE’13), 9-11 Ekim 2013, Karabük, Türkiye
POLYMERIC COMPOSITE RAILWAY SLEEPERS
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a, *
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Amir GHORBANİ , Seçkin ERDEN
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Ege University, Mechanical Engineering Department, Izmir, Turkey, [email protected]
Ege University, Mechanical Engineering Department, Izmir, Turkey, [email protected]
Özet
Demiryolu traversleri, demiryolu sisteminin en önemli elemanlarındandır. Ahşap traversler hala en
yaygın malzeme sayılsa da, beton ve çelik malzemelerin kullanımı da artmaktadır. Ayrıca, geri
dönüştürülebilir malzemelerden üretilen traversler de son zamanlarda ilgi çekmektedir. Plastik atıkların
geri dönüştürülmesiyle hem çevre temizliği, hem de para tasarrufu hedeflenmektedir. Kompozit
traversler sağlam, dayanıklı ve güvenilir olduğundan, yaygın traverslere göre daha az bakım gerektirir
ve daha uzun ömürlüdür. Bu nedenle, düşük maliyetli ve uzun vadeli bir çözüm olarak görülebilirler.
Bu çalışma, alternatif bir demiryolu travers malzemesi olan polimerik kompozitlerle ilgili son gelişmeleri
gözden geçirmektedir. Yenilikçi kompozit traversler üzerine yürütülen araştırma ve geliştirme
faaliyetleri sunularak avantaj ve dezavantajları sıralanmıştır.
Anahtar kelimeler: Polimerik kompozit malzeme, Demiryolu traversleri.
Abstract
Railway sleepers are one of the most important elements of the railway track system. Although timber
sleepers are still the most common, use of pre-stressed concrete and steel materials is also
increasing. In addition, ties produced using recycled materials are of interest, recently. By recycling
plastic waste, considerable amount of money can be kept from ending up in the landfills. As composite
ties are strong, durable, and reliable, they require less maintenance and have longer life than common
railroad ties. Therefore, they can be an excellent, cost-effective and long-term solution.
This paper presents a review of recent developments on polymer composites as an alternative
material for railway sleepers. An overview of on-going research and development on innovative fiber
composite railway sleepers with investigation on their advantages and disadvantages are also
presented.
Keywords: Polymeric composite material, Railway sleepers.
1. Introduction
Railway sleepers are one of the most important elements of the railway track system. They are the
beams/ties laid underneath the rails to support the track[1]. Their function is to transfer the loads to the
ballast, transversely secure the rails to maintain the correct gauge-width and to resist the cutting and
abrading actions of the bearing plates and the ballast material [2]. Sleepers also resist the lateral and
the longitudinal movement of the rail system.
Different kinds of materials are used in sleeper production. Hardwood timber is the most widely used
sleeper material. There are more than 2.5 billion timber sleepers installed in the railway track
throughout the world [3]. In order to have a reliable track system and maintaining the quality of the
track system to a specified service level and ensuring. The safe track operation, a wide range of
ingredients should simultaneously be considered. Strength and durability of the sleepers is one of
those ingredients that play an important rule in track system.
Beside wood, concrete and steel were widely applied in sleepers but recently the use of polymericcomposite, because of their remarkable properties was also increased.
This paper presents an overview of advantages and disadvantages of the aforementioned materials
and also introducing the polymeric composite as an alternative material for railway sleepers.
Ghorbani A., Erden S.
2. Sleeper Materials
Sleeper materials currently in use and researched as potential alternatives are grouped here as nonpolymeric and polymeric sleepers, which are also sub-grouped to give additional information.
2.1. Non-polymeric sleepers
There has already been a vast research and development effort into materials for sleepers since
railways were introduced. Timber sleepers are still the most common, however, use of pre-stressed
concrete and steel sleepers is also increasing. The advantages and disadvantages of these railway
materials will be discussed in the following sections. Additionally, a comparison of their properties is
given in tabular form (Table 1).
2.1.1. Timbers
Timber sleepers have been widely used during recent decades. Like the others, it has advantageous
and disadvantageous. The main advantage of the timber is their adaptability as it can be fitted with all
types railway track. On the other hand while the cost of their maintenance is low in comparison to the
other kinds, its application seems to be a little bit more alternative [3]. Fungal decay and splitting at the
ends of the timbers are the most common types of sleeper failures. The first one mostly refers to the
environmental situation [4] and the second one refers to the very large transverse shear loading
exerted to the sleepers [5].
2.1.2. Softwood timbers
Softwood is wood from gymnosperm trees such as conifers, evergreen trees are often called
softwoods. Softwood timber does not offer the resistance of hardwood sleeper to gauge spreading and
spike hole enlargement [6]. In addition, softwood sleepers are not as effective in transmitting the loads
to the ballast as the hardwood sleepers do, thus they should not be mixed with hardwood sleepers on
the railway track.
2.1.3. Concrete
Concrete, because of its natural weakness in tension is not used in sleeper’s products. Pre-stressed
concrete is a method for overcoming this matter. It can be used to produce beams, floors and bridges
with longer span. In this case the mentioned method is applied in timbers production by concrete.
Pre-stressed concrete sleepers have become widely and successfully accepted for railway sleeper
usage especially in high speed lines. Their economic and technical advantages are the results of
longer life cycles and lower maintenance costs. With their great weight, concrete sleepers assure
optimal position permanence and stability even for traffic at high speeds. In fact, many pre-stressed
concrete sleeper technologies have now been developed. Mono-bloc and twin-bloc pre-stressed
concrete sleepers are most commonly use concrete sleepers. Twin-bloc, because of its less weight
could attract more attention. Twin-bloc sleeper is made up of two concrete parts supported by steel
reinforcements. Although, it has a prominent disadvantageous as it has tendency to twist when lifted
which makes it difficult to handle an install these kinds of sleepers.
Concrete sleepers, beside their advantageous like more life-time and strength, have some
disadvantageous too. Such these disadvantageous are their heavy weight which required specialized
machinery during laying and installation and also their production casts, while their initial cost is almost
double that of hardwood timber sleepers. The investigation to the timber and concrete sleepers, reveal
that the concrete sleepers higher sleepers have high stiffness characteristics and the design requires
higher depth than the existing timber sleepers.
2.1.4. Steel
Australia has developed a world reputation in technology related to the design and performance of
steel railway sleepers.
Ghorbani A., Erden S.
The Institute of Railway Technology at Monash University is working to minimize cost and ensure
superior performance of steel sleepers [7]. Currently, steel sleepers account for over 13% of the
railway sleepers used within Australia. Steel sleepers can be interspersed with the existing track but in
a fixed interspersing pattern to reduce the variation in the track geometry and prevent the early inservice failure of sleepers. A steel sleeper weighs less than timber sleeper which makes it easy to
handle as well as having a life expectancy known to be in excess of 50 years. However, steel sleepers
are being used only on more lightly travelled tracks and are regarded as suitable only where speeds
are 160 km/h or less [8].
Steel sleepers require extra care during installation and tamping due to their inverted through profile
which makes them difficult to satisfactorily pack with ballast. Observations of rail deflections under
imposed vehicle track loading have shown that the steel sleepers settle a greater amount than the
timber sleepers, indicating that the steel and adjacent timber sleepers are not carrying an even
proportion of the imposed wheel loading [9]. Furthermore, steel sleepers are expensive and are used
only in minimal number because of the fear of corrosion. Another problem with steel sleepers is fatigue
cracking in the fastening holes caused by moving trains [10].
Table 1. Comparison of current materials for railway sleepers [11]
Properties
Adaptability
Workability
Handling and installation
Durability
Maintenance
Replacement
Availability
Cost
Fasteners
Tie ballast interaction
Electric conductivity
Impact
Weight (kg)
Service life (years)
Hardwood
Easy
Easy
Easy
Low
High
Easy
Low
High
Good
Very good
Low
High
60-70
20-30
Softwood
Difficult
Easy
Easy
Low
High
Easy
High
Low
Poor
Good
Low
High
60-70
20
Concrete
Difficult
Difficult
Difficult
High
Low
Difficult
High
Very high
Very good
Very good
High
Low
285
60
Steel
Difficult
Difficult
Difficult
Low
High
Difficult
High
Very high
Poor
Poor
Very high
Medium
70-80
50
2.2. Polymeric composite sleepers
Recent developments in fiber composites now suggest their use as alternative material for railway
sleepers. These developments can be subdivided into new railway sleepers produced by combining
other materials with fiber composites and the strengthening of existing sleeper materials with fiber
composite wraps. One of the earliest composite sleeper technologies developed in Australia is made
of polymer concrete and glass fiber reinforcement (Figure 1) that was used as replacement for timber,
steel and concrete sleepers.
Figure 1. Glass fiber reinforced polymer concrete sleeper weighing 61 kg [11].
Ghorbani A., Erden S.
2.2.1. Glue-laminated fiber composite sandwiches
Composite sandwich structure made up of glass fiber composite skins and modified phenolic core
material [12]. The results suggest that the glue-laminated composite sandwich beams have the
strength and the stiffness suitable for turnout sleeper. In glue-laminated sandwich beams, it was found
that the fiber wraps had minimal effect on the bending stiffness and strength but has a more
pronounced effect on the shear strength, Wich an almost 7% higher strength for specimen with wraps
than their unwrapped counterpart.
2.2.2. Polyurethane materials composite
Sumika Bayer Urethane Co. Ltd have developed composite sleepers FFU (fiber reinforced foamed
urethane) made from Baydur® 60 grade reinforced with long glass fibers. These Sleepers looks like
wood and combines all positive attributes of the natural product with those of a modern composite
material. These sleepers have a low linear coefficient of thermal expansion and low thermal
conductivity values. The sleepers have high compressive and tensile strength Due to the fiber
reinforcement material.
The tracks for the Japanese high-speed train Shinkansen have been laid on polyurethane sleepers
and as part of a renovation project, the tracks on the Zollamt Bridge, Vienna in Europe have been laid
on these sleepers (Figure 2).
Figure 2. Glass fiber reinforced polyurethane sleepers [13].
2.2.3. Recycled plastic materials and fiber composite
A number of companies are selling railway sleepers manufactured using recycled plastic materials and
fiber composites. These sleepers are said to have high strength, be more durable and to weigh similar
to timber sleepers while otherwise exhibiting properties similar to their wooden counterparts in terms of
damping impact loads, lateral stability and sound absorption [14].
Ghorbani A., Erden S.
The Tie-Tek sleepers is one of these type of sleepers that were firstly used by Union Pacific Railroad.
These were composed of recycled HDPE, crumbled rubber, glass reinforcement, mineral fillers, and
some other patented items [13]. Indian Railways adopted these materials for use in bridge sleepers
[15], and they also made a comparison of fiber reinforced plastic sleepers with wooden and steel ones
(Table 2). Their composites consisted of E-glass woven fabric as the reinforcement and polyester as
the resin. Polyester resin was also mixed with accelerator, hardener, fire retardant, and UV Stabilizer.
Table 2. Comparison of some bridge sleepers [13]
Item
Durability (Years)
Weight (kg)
Replacement of
sleepers
Handling
Suitability for Track
circuited area
Cost per Sleeper with
fittings
Life Cycle cost
(Rs./Year)
Wooden
8-10
100-171
Type of Bridge Sleepers
Steel
15-20
110
Composite
40-50
54
Easy
Difficult
Easy
Not so easy
Difficult
Easy
Suitable
Problematic
Suitable
Rs. 3500/-
Rs. 9500/-
Rs. 19240/-
402/-
575/-
385/-
U.S. Plastic Lumber Corp. (USPL), manufactures plastic lumber, packaging and other products made
from recycled plastic. USPL produces its DuraTie recycled composite ties using its CycleX process, in
which plastic waste streams (such as milk cartons, plastic bags and industrial plastic waste) are
turning into durable products. Reinforcements, for example glass fiber, can be added during the
manufacturing process.
The Polywood Inc. manufacturers structural plastic lumber from post-consumer and post-industrial
recycled plastics and has patented technologies for this production. The company Produce ties “cocontinuous” immiscible post-consumer HDPE and PS scrap, which was initially developed at Rutgers
University, which negates the need for glass reinforcement in high load-bearing applications.
The Demer Corp. spent approximately 4 years on research and development of the railroad ties, which
are made from 60% recycled-gypsum filler and 40% post-consumer high density and low density
polyethylene and polypropylene.
The Polysum Technologies LLC received its first patent for a thermoplastic railroad cross tie. The
company’s thermoplastic railroad tie is available in two configurations: the Tuff-Tie and the Hi-Load tie.
Polysum’s Tuff-Tie made from HDPE with 50% virgin gypsum. To produce the ties, a corotating twinscrew extruder feeds 3,300 pounds per hour of gypsum-filled HDPR to an accumulator, which sends
melt into an e-foot long mold.
Axion International, who produced first thermoplastic composite bridges in the world, used their
Reinforced Structural Plastic Composite, which they also name as “thermoplastic”, in making
crossties, too. Their HDPE-based recycled material is reinforced with polypropylene coated glass
fibers. They made a replacement cost comparison of their railroad tie material with wood and concrete
(Table 3).
Table 3. Railroad ties – Cost per mile with installation, on a per cycle basis [16]
Replacement
Cost
Initial Cost
Wood
Concrete
Thermoplastic
$255,000
$375,000
$435,000
Cycle 2
Cumulative
Cost
$510,000
$750,000
$435,000
Cycle 3
Cumulative
Cost
$765,000
$1,125,000
$435,000
Cycle 4
Cumulative
Cost
$1,020,000
$1,500,000
$435,000
Total
Cumulative
Cost
$1,275,000
$1,875,000
$435,000
Ghorbani A., Erden S.
3. Conclusion
Polymeric composites may a good alternative for current railway sleepers as they have properties
such as corrosion and chemical resistance, environmental durability, and high specific strength. They
will create ecological benefits due to their recycleability, causing decrease of plastics in landfills, and
reduction in forest degradation.
Current trials of polymeric composites as railway sleepers have some succesful stories, which ended
up with commercial patented products as seen in Axion International, while some trials were not found
satisfactory as stated in reports of Indian Railways.
While traditional materials have all well established continuous production lines, cost of production on
industrial scale is still a question for polymeric composite sleepers. Hybrid structures to be obtained by
combination of composites and traditional materials also exhibited satisfactory properties, which make
them also an alternative.
Developments up to date suggest further research on such alternative materials with regard to their
advantages compared to existing railway sleepers.
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