compositerailwaysleepers-180926115325 - Copy.pptx

gj

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: Timber Cast iron Steel Concrete Prestressed Concrete 2

3. Disadvantages: Gets corroded at a faster rate and not recommended for coastal areas . Many fastening elements . Cannot absorb shocks . Derailment Damage High replacement costs 3 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

4. Disadvantages: Rigid nature difficult to handle . Less adaptability . Inability to withstand the cyclic nature of loads. 4 Figure 8. Broken concrete sleeper. Adapted from “ Photobucket ”, retrieved from http://i225.photobucket.com/albums/dd281/ainsworth74/Rail/Photo-0001.jpg

5. Prestressed Concrete Sleepers Longer life span . Can be used in high-speed tracks . Can withstand static and cyclic loads . 5 Figure 9. Prestressed concrete sleepers. Adapted from “ Agico group ”, retrieved from http://www.railway-fasteners.com/uploads/allimg/layingofconcreterailwaysleepers.jpg

6. Disadvantages: Rail seat deterioration: The most repeated type of failure in prestressed concrete sleeper. 6 Figure 10. Schematic diagrams for rail seat deterioration [1]

7. Centre-bound damage and longitudinal cracks: Sleepers develop tensile fracture while experiencing the high magnitude and high-frequency loads acting during the train movement. 7 Figure 11. Tensile cracks at the centre of sleepers. [1]

8. 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. 8

9. Potential Materials That Can Be Used: 9 Polymer composite Sleepers Geopolymer sleepers Fibre reinforced concrete Self-compacting concrete (SCC) Rubber Concrete

10. 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 . 10

11. 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. 11

12. 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. 12

13. 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 . 13

14. 14 Topcu (1995) Volume Replacement of fine aggregates (%) 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 (%) 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 (%) 25 50 75 100 Cylinder compressive strength(MPa) 30.77 6.36 1.22 0.81 0.55 Volume Replacement of coarse aggregates (%) 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]

15. 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 ) 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 . 15

16. 16 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]

17. 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) 17 Figure 13. Sekisui FFU synthetic sleeper [5]

18. 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 18 Table 5. Type-3 sleepers [4]

19. 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 . 19

20. Limited Information on Long-Term Performance Impact loading Fatigue loading UV radiation Moisture Aqueous solution Elevated temperature Fire Lateral track stability 20

21. 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. 21