Railways form the backbone of all economies, transporting goods, and passengers alike. Sleepers play a pivotal role in track performance and safety in rail transport. This study rigorously reviews the recent developments on composite sleepers and identifies the critical barriers to their widespread acceptance and applications. Currently the composite sleeper technologies that are available ranges from sleepers made with recycle plastic materials which contains short or no fibre to the sleepers that containing high volume of fibres. While recycled plastic sleepers are low cost, the major challenges of using this type of sleepers are their limited strength, stiffness and dynamic properties which in most cases, are incompatible with those of timber. On the other hand, the prohibitive cost of high fibre containing sleepers limit their widespread application. Moreover, limited knowledge on the historical long-term performance of these new and alternative materials restricts their application. Potential design approaches for overcoming the challenges in the utilisation and acceptance of composite sleeper technologies are also presented in this presentation.

1. COMPOSITE RAILWAY
SLEEPERS
RECENT DEVELOPMENTS, CHALLENGES AND
FUTURE PROSPECTS

2. Introduction:
 Sleepers: Members which are generally laid transverse to the
direction of rails, on which the rails are fixed and supported
through fasteners.
 Traditional materials used in sleepers:
a. Timber
b. Cast iron
c. Steel
d. Concrete
e. Prestressed Concrete
2

3. Timber Sleepers
 More than 2.5 billion timber
components have been
installed worldwide.
 Adaptable, easy to handle,
excellent dynamic, electrical
and sound-insulating
properties.
3
Figure 1. Timber sleepers. Adapted from
“UK Sleepers”, retrieved from
https://www.uksleepers.co.uk/UserFiles/
productImages/untreated-planed-and-
bevelled.jpg

4. Disadvantages:
 Mechanical wear and tear
and natural decay.
 Fungal and termite attack
 Transverse shear loads
Splits at the ends.
4
Figure 2. Decayed timber sleeper.
Adapted from “SSS Technologies”,
retrieved from
https://4.imimg.com/data4/MQ/WP/MY
-21679432/railway-wooden-sleepers-
500x500.jpg

5. Cast Iron Sleepers
 Service life of 50-60 years.
 Can be remoulded and has
high scrap value.
 Provides significant bearing
area and stronger at the seat
of rails.
5
Figure 3. Cast iron sleeper. Adapted from
“The Narrow Gauge Railway Museum”,
retrieved from
http://www.narrowgaugerailwaymuseum.
org.uk/wp-content/uploads/DQ016-1.jpg

6. Disadvantages:
 Gets corroded at a faster rate
and not recommended for
coastal areas.
 Many fastening elements.
 Cannot absorb shocks.
 Derailment
Damage
High replacement costs
6
Figure 4. Rusted cast iron sleeper.
Adapted from “ Shree Om Steel
Corporation”, retrieved from
https://5.imimg.com/data5/QU/IP/MY-
4218402/cast-iron-500x500.jpg

7. Steel Sleepers
 Free from decay and vermin.
 Better and simple connection
between rail and sleeper.
 Superior lateral rigidity,
resistance to creep and high
scrap value.
7
Figure 5. Steel sleepers. Adapted from
“Anshan Xiyida Metallurgy Co. Ltd”,
retrieved from
http://p.globalsources.com/IMAGES/PDT
/B1061518833/Railway-Track-rail-Steel-
Sleeper-at-Good-Price.jpg

8. Disadvantages:
 Salty regions makes susceptible
to corrosion.
 Not useful for all sections of
rails and used only with stones
as ballast.
 Derailment
Damage
High replacement costs
8
Figure 6. Rusted steel sleepers. Adapted
from “Daily Civil”, retrieved from
http://www.dailycivil.com/wp-
content/uploads/2018/02/slide_foto1.jpg

9. Concrete Sleepers
 Service life 50 years.
 Most durable.
 Heavyweight
Exceptional lateral stability
 Corrosion resistant, efficiency
in controlling creep, resist
termite attack, suitable with
almost all kinds of soil.
9
Figure 7. Concrete sleepers. Adapted
from “Alamy stock photo”, retrieved from
https://www.alamy.com/stock-photo-
extracted-old-concrete-sleepers-in-stock-
old-rusty-used-concrete-railway-
163645365.html

10. Disadvantages:
 Rigid nature difficult to
handle.
 Less adaptability.
 Inability to withstand the
cyclic nature of loads.
10
Figure 8. Broken concrete sleeper.
Adapted from “Photobucket”, retrieved
from
http://i225.photobucket.com/albums/dd
281/ainsworth74/Rail/Photo-0001.jpg

11. Prestressed Concrete Sleepers
 Longer life span.
 Can be used in high-speed
tracks.
 Can withstand static and
cyclic loads.
11
Figure 9. Prestressed concrete sleepers.
Adapted from “Agico group”, retrieved
from http://www.railway-
fasteners.com/uploads/allimg/layingofco
ncreterailwaysleepers.jpg

12. Disadvantages:
1. Rail seat deterioration:
◦ The most repeated type of failure in prestressed concrete
sleeper.
12
Figure 10. Schematic diagrams for rail seat deterioration [1]

13. 2. Centre-bound damage and longitudinal cracks:
◦ Sleepers develop tensile fracture while experiencing the high
magnitude and high-frequency loads acting during the train
movement.
13
Figure 11. Tensile cracks at the centre of sleepers. [1]

14. 3. Derailment and impact loading:
◦ Derailment usually damages them beyond repair.
◦ Infrequent loads have a dynamic impact effect and can result
in cracks, flat wheels and dipped rails.
◦ In the present international scenario, most guidelines deal
with only static and dynamic loads without much regard for
the impact loads.
14

15. Q. Why the railway industry uses a variety of
sleeper materials rather than a particular
one?
None of the traditional materials (timber, steel, concrete etc.) satisfies
all the requirements of a sleeper to resist mechanical, biological and
chemical degradation.
15
(a) Timber (b) Steel (c) Concrete
Figure 12. Example of diverse failure modes of sleepers during service life [2,3]

16. Potential Materials That Can Be Used:
16
 Polymer composite Sleepers
 Geopolymer sleepers
 Fibre reinforced concrete
 Self-compacting concrete (SCC)
 Rubber Concrete

17. Polymer composite sleepers
 Composites made of polymers have superior corrosion and
chemical resistance, better durability characteristics and high
specific strength.
 Ex. Fibre reinforced foamed urethane (FFU)
17
Properties FFU Australian hardwood
Life expectancy 50 years 10 years
Bending strength (MPa) 142 65
Hardness (MPa) 28 10
Shear strength (MPa) 10 6.1
Water Absorption (mg/cm2) 3.3 137
Impact Strength (MPa) 41 -
Table 1. Property comparison of FFU with Australian hardwood [Kaewunruen et al. (2013)]

18. Geopolymer sleepers
 Geopolymers rely on polycondensation reaction between alumina
and silica for strength gain.
 Strength attainment up to 80 Mpa in 24 hours.
 It requires reaction between a cementitious binder, aggregates,
and an alkaline activator solution (AAS) for efficient strength
attainment.
 Most of the mechanical properties of geopolymer concrete are at
par with the conventional concrete.
18

19. Fibre reinforced concrete
 Fibres of different types have been used in concrete for decades,
among them most sought after one is steel fibre.
 The addition of steel fibres only marginally increases the
compressive strength of concrete, but the split tensile strength can
be increased up to 40%.
 8% increase in the modulus of elasticity along with the ability of
fibres to bridge the gap when cracks start to develop, lead to
enhanced strength properties.
19

20. Self-compacting concrete (SCC)
 Evolved in Japan due to the necessity of finding a material that
could be used in heavily reinforced sections.
 Most of the properties are comparable or better than ordinary
concrete.
 Use of palm oil fuel ash as replacement of cement for up to 20% by
weight of cementitious materials improves acid and sulphate
resistance of SCC, along with the drying shrinkage property without
much change in the compressive strength.
 Fly-ash and blast furnace slag provide enhanced crack resistance
and relaxation pattern of SCC.
20

21. Rubber Concrete
 The addition of rubber in concrete as replacement of aggregates
(both fine and coarse) has been on for 40 years.
 The use of rubber in concrete forces a decrease in compressive
strength and split tensile strength of concrete.
 However, pre-treatment of crumb rubber with adhesives led to
more bonding of rubber with the concrete matrix and counter the
reduction in strength properties.
21

22. 22
Topcu (1995)
Volume Replacement of fine aggregates (%) 0 15 30 45
Unit Weight(Kg/dm3) 2.30 2.22 2.14 2.01
Cylinder compressive strength(MPa) 23.48 24.22 19.70 14.77
Cube compressive strength(MPa) 29.50 18.80 16.90 12.90
Split tensile strength 3.21 2.17 1.53 1.13
Volume Replacement of coarse aggregates (%) 0 15 30 45
Cylinder compressive strength(MPa) 23.50 16.18 12.62 9.90
Cube compressive strength(MPa) 29.50 14.60 8.91 12.20
Split tensile strength 3.32 1.50 1.06 0.82
Table 2. Mechanical properties of rubber concrete as reported by [Topcu]
Khaloo et al.(2008)
Volume Replacement of fine aggregates (%) 0 25 50 75 100
Cylinder compressive strength(MPa) 30.77 6.36 1.22 0.81 0.55
Volume Replacement of coarse aggregates (%) 0 25 50 75 100
Cylinder compressive strength(MPa) 30.77 6.52 1.49 0.65 0.37
Table 3. Mechanical properties of rubber concrete as reported by [Khaloo et al. 2008]

23. Recent Developments on Composite
Sleepers
 Sleepers with short or no fibre reinforcements (Type-1)
 Reinforcement in the longitudinal direction (Type-2)
 Reinforcement in longitudinal and transverse directions (Type-3)
1. Sleepers with short or no fibre reinforcements (Type-1)
 It consist of recycled plastic or bitumen with fillers.
 Do not improve the structural performance required for
heavy duty railway sleeper application.
 Ease of drill and cut, good durability, consumption of waste
materials, reasonable price, and tough.
 It suffers from low strength and stiffness, limited design
flexibility, temperature, creep sensitivity and low fire
resistance.
23

24. 24
Materials Country Applications Designed shape
TieTek
85% recycled plastic (tyres, waste
fibreglass)
USA
Mainline sleeper, turnout bearers
and bridge transoms
Axion
100% recycled plastic (plastic bag,
bottles etc.)
USA
Mainline sleeper, turnout bearers
and bridge transoms
IntegriCo
Landfill-bound 100% recycled plastic
materials
USA Commuter, industrial and mining
I-Plas
100% domestic and industrial
recycled plastic
UK Timber replacement
Tufflex
Mix of recycled polypropylene and
polyethylene
S. Africa
Underground rail track and narrow
gauge line
Natural
rubber
Natural rubber Thailand Narrow gauge line
KLP 100% recycled plastic materials Netherland
Mainline sleeper, turnout bearers
and bridge transoms
MPW
Polymer, mixed plastic and glass fibre
waste
Germany Timber replacement
Wood core Plastic reinforced with wooden beam USA Timber replacement
Table 4. Available Type-1 sleeper technologies [4]

25. 2. Reinforcement in the longitudinal direction (Type-2)
 Reinforced with long continuous glass fibre reinforcement in
the longitudinal direction and no or very short random fibre in
the transverse direction.
 Easy to drill and cut, good durability, superior flexural strength
and modulus of elasticity.
 low shear strength and shear modulus, limited design
flexibility, marginal fire resistance and costly.
 Ex. Fibre reinforced foamed urethane (FFU)
25
Figure 13. Sekisui FFU synthetic sleeper [5]

26. 3. Reinforcement in longitudinal and transverse directions
(Type-3)
 Reinforced in both longitudinal and transverse directions and
consequently both the flexural and shear behaviour are
dominated by fibres.
 The structural performance of this sleeper can be engineered
through the adjustment of the fibre reinforcements in each
direction according to the specified performance
requirements.
 Non-ductile behaviour of glass fibre reinforced polymer
sleeper can be overcome by including some steel
reinforcement bars, which is very important when sleepers
are installed in bridges.
 Excellent design flexibility, good flexural and shear strength,
easy drilling and good fire performance.
26

27. Name Materials Country Applications Designed shape
Sandwich
Glue laminated
sandwich composite
Australia
Mainline sleeper, turnout bearers
and bridge transoms
Hybrid
Geopolymer concrete
filled pultruded
composite
Australia
Mainline sleeper, turnout bearers
and bridge transoms
27
Table 5. Type-3 sleepers [4]

28. Challenges Of Using Composite Sleeper
 Inferior Strength and Stiffness Properties Compared To Timber
Sleeper.
28
Performance measurement
AREMA specification
Type-1 Type-2 Type-3
Oak Softwood Glue Lam
Density (kg/m3) 1096 855 960 850–1150 740 1040–2000
Modulus of elasticity (GPa) 8.4 7.4 12.0 1.5–1.8 8.1 5.0–8.0
Modulus of rupture (MPa) 57.9 49.3 66.9 17.2–20.6 142 70–120
Shear strength (MPa) 5 4 4 4 10 15–20
Rail seat compression (MPa) 4.6 3 3.9 15.2–20.6 28 40
Screw withdrawal (kN) 22.2 13.3 N/A 31.6–35.6 65 >60
Table 6. Performance comparison of different types of composite sleeper [4]
AREMA - American Railway Engineering and Maintenance-of-Way Association

29.  Price of Composite Sleeper
◦ 85 to 105 USD per sleeper (Type-1 excluding installation).
◦ 70 to 200 USD per sleeper (Type-1 including installation).
◦ 5–10 times higher than that of a standard timber sleeper (Type-
2 and Type-3).
◦ However, its lower life cycle cost is anticipated to offset its high
initial cost.
 Low Anchorage Capability
◦ Hardwood timber sleeper has a screw-spike resistance of 40 kN.
◦ Modern design requires a screw-spike resistance of 60 kN.
◦ Type-1 poor performance.
◦ Type-2 & Type-3 more quality and high performance.
29

30.  Formation of Material Voids
◦ Once the moulds are filled, the cooling process starts, and
during this period, there is a high possibility of voids being
formed inside the materials.
◦ This problem can be obtained during the production of any
material depending on their manufacturing techniques.
 Creep Deformation
◦ Among all the traditional sleeper materials, concrete and steel
are prone to creep.
◦ Fly-ash based geopolymer concrete tends to have significant
problem with creep and shortening effect.
◦ The long-term performances of plastic sleepers (Type-1) are
becoming a critical issue as their continuous service over time
has a significant effect on their mechanical properties.
◦ However, sufficient information have not been found on the
creep deformation for Type-2 and Type-3 sleepers.
30

31.  Limited Information on Long-Term Performance
◦ Impact loading
◦ Fatigue loading
◦ UV radiation
◦ Moisture
◦ Aqueous solution
◦ Elevated temperature
◦ Fire
◦ Lateral track stability
31

32. Future Prospects
 The major challenges of using Type-1 composite railway sleepers
are their limited strength, stiffness and dynamic properties which,
in most cases, are not compatible with those of timber.
 The limitations of low structural performance in Type-1 sleeper
have been overcome in Type-2 and Type-3.
 But their high prices compared to standard sleeper materials are
still remaining a big challenge.
 Moreover, the lack of knowledge on their long-term performances
and the unavailability of design guidelines restrict their widespread
applications and utilisations.
32

33. Properties and performances Type-1 Type-2 Type-3
Flexural strength and stiffness Low Good Good
Shear strength Low Medium Good
Anchorage capacity Low Good Good
Drilling and cutting Easy Easy Moderately easy
Price Low High High
33
Table 7. Comparison of different types of composite sleeper [4]
The following approaches are proposed to overcome the current
limitations of composite sleepers.
• Improving Structural Performance
• Optimal Material Usage and Improve Manufacturing Techniques
• Short and Long Term Performance Evaluation
• Design Recommendations and Standards

34. Conclusion:
 The high maintenance costs and environmental problems of
traditional sleepers motivates researches to make composite
sleepers.
 The primary obstacles - low strength and stiffness, low anchorage
capability, formation of voids, permanent creep deformation,
temperature variations, insufficient lateral resistance and high cost.
 FFU sleepers are superior to the standard hardwood bearers. SCC
can improve the bond between concrete and steel. Rubber
concrete sleepers 3 times better than normal prestressed concrete
sleepers.
 However more significant research needs to be conducted.
34

35. References:
[1] Raj A, Nagarajan P, Shashikala A P. A review on the development of new materials
for construction of prestressed concrete railway sleepers. IOP Conf. Series: Materials
Science and Eng. 330 (2018) 012129 doi:10.1088/1757-899X/330/1/012129.
[2] Manalo A, Aravinthan T, Karunasena W, Ticoalu A. A review of alternative materials
for replacing existing timber sleepers. Compos Struct 2010;92:603–11.
[3] Ferdous W, Manalo A. Failures of mainline railway sleepers and suggested remedies
– review of current practice. Eng Fail Anal 2014;44:17–35.
[4] Ferdous W, Manalo A, Van Erp G, Aravinthan T, Kaewunruen S, Remennikov A. A
review of composite railway sleepers – recent developments, challenges and future
prospects. Compos Struct 2015;134:158-168.
[5] Koller G. The use of sleepers made of FFU synthetic wood in Europe; 2009. p. 28–32.
35

36. MD SAIF AHMED
B151061CE
NIT CALICUT
Prepared by
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