1 HOT MIX ASPHALT IN BALLASTED RAILWAY TRACK

1 HOT MIX ASPHALT IN BALLASTED RAILWAY TRACK LUV SEHGAL Graduate Research Assistant, Rail. TEC, UIUC AMIT GARG, Graduate Research Assistant, Rail. TEC, UIUC and Chief Engineer, Indian Railways VIJAY SEHGAL Chief Administrative Officer (Construction), WCR Dr WILLIAM BUTTLAR Professor, Department of Civil and Environmental Engineering, UIUC

HOT MIX ASPHALT IN BALLASTED RAILWAY TRACK • • • Why the study? Existing railway track structure International Practices Types of models Kentrak 4. 0 analysis

Why the study? Increase in maximum railway speeds Increase in demand of high speed rail Increase in maximum axle loads Increase in trailing loads Very tight maintenance tolerances to ensure safety All these have led to high maintenance costs and have necessitated development of new low maintenance structural solutions University of Illinois Urbana Champaign 3

4 Track super & sub structure for HSR Super structure: Rail, rail pad, ties, ballast Sub structure: Sub ballast , subgrade University of Illinois Urbana Champaign

Railway line % Tunnels % Bridges or Total Viaducts Main Track Type (Ballasted/ Slab) 5 Japanese high-speed lines Tokaido: Tokyo–Osaka (515 km) 13 33 46 Ballasted Sanyo: Osaka–Hakata (554 km Tohoku: Tokyo–Morioka (497 km) 51 24 38 71 89 95 Slab Joetsu: Tokyo–Niigata (270 km) 40 60 100 Slab 1. 5 5. 8 11. 9 29. 7 26 27. 3 5. 3 11. 2 Ballasted slab Ballasted European high-speed lines Paris–Lyon (480 km) TGV Atlantique (280 km) Valence–Marseille (295 km) Hannover–Würzburg (326 km) Köln–Frankfurt (177 km) Roma–Napoli (220 km) Madrid–Sevilla (471 km) University of Illinois Urbana Champaign Madrid–Lleida (481 km) . 8 4. 7 5. 1 19. 3 22. 6 11. 4 1. 9 5. 4 . 7 1. 1 6. 8 10. 4 3. 4 15. 9 3. 4 5. 8

6 Focus should be back on optimizing ballasted HSR track structure as a means to reduce operating costs without large increase in construction costs. Railway research has shown that efforts in respect to optimization of track design for low maintenance will have two a pronged strategy- 1. the importance of having a stiff subgrade and 2. reducing to the extent possible the stiffness of the rail pad or that of the rail–sleeper–ballast. University of Illinois Urbana Champaign

7 Search for new solutions University of Illinois Urbana Champaign Heavier , wear resistant rails Concrete ties Thermoplastic rail pads (between rail and tie) with higher stiffness High strength ballast Improved stiffness characteristics of sub ballast Alternative to conventional granular sub ballast (in the form of asphalt layer)

8 Advantages of bituminous sub ballast Reduced track settlement , because of enhanced stiffness Reduced vertical stiffness variations , because of track structure homogenization, thus reducing differential settlements Improved ballast behavior, because of increased and consistent support by the underlayer without deformities, thus reducing vertical accelerations and displacements. HMA being completely water resistant, offers advantage over the granular solution regarding long term performance. Subgrade life increase Smoothening out variations in vertical stiffness variations. The track deterioration in transition zones is 5 -7 times more than regular track spans. Use of HMA underlayer reduces abrupt vertical stiffens variations due to its stiffness and high modulus. University of Illinois Urbana Champaign

9 Types of Track structures with HMA Asphalt Underlayment Asphalt Combination Ballastless Asphalt Combination University of Illinois Urbana Champaign

Country Slab/ Ballasted Layer 1 Layer 2 Layer 3 Japan Slab & Ballasted Slab thickness (19 cm), Ballast 30 cm) Asphalt concrete slab (15 cm), Asphalt concrete (5 cm) Crushed stone well 10 subgraded (15 cm), crushed stone layer )15 -60 cm) Italy Ballasted Ballast (35 cm) Asphalt mix 12 cm, 200 Supercompatto layer MPa) (30 cm, 80 MPa) Subgrade (40 Mpa) Spain Ballasted Ballast (35 cm) Asphalt concrete (1214 cm) Frost protection layer (30 -40 cm) Subgrade (80 Mpa) Germany Ballasted slab Asphalt Base (20 cm) Asphalt base multilayer Subbase (50 -65 cm) France Ballasted Ballast (30 cm) Asphalt layer (14 cm) Adjustment layer (20 cm) Subgrade Ballasted Ballast (20 -30 cm) Asphalt layer (12. 5 -15 cm) No subballast Subgrade Ballasted Ballast (20 -30 cm) Asphalt layer (12. 5 -15 cm) Sub ballast Subgrade Ballasted Ballast (30 cm) Blanket layer (upto 100 Sub ballast cm) Subgrade USA India University of Illinois Urbana Champaign Layer 4

11 Design of HMA Layer Train Wheel Speed Max load in in mph Moment Deflection (lbs) Tons in rails in Inches Stress between Tie and Ballast in psi Stress between Ballast and Subgrade psi N/ sq cm Heavy Haul 40, 000 20 Conventional 32875 16. 4 Freight 50 50 431367 354530 0. 149 0. 122 29. 22 23. 92 22 18 15. 16 12. 4 HSR slow 250 50 301557 130718 0. 089 0. 039 17. 44 7. 65 13. 13 5. 75 9 4 16000 University of Illinois Urbana Champaign 8

Design philosophy for Superpave Mix design method 12 Similar to a bottom layer of a perpetual highway pavement HMA layer is insulated from sharp temperature variations, direct wheel loads and direct rain Recommended parameters: Medium modulus Fatigue resistant ( to accommodate high strains without cracking) Low void Fine grade mix ( for moisture resistivity) Fine grained binder Durability – The Biggest Concern University of Illinois Urbana Champaign

Track model for FE analysis Proposed inputs which can be adopted for a Superpave HMA design: 1. Grade: Fine graded dense mix 2. Modulus: Low to Medium 3. Max size of aggregates: 25 mm 4. Air voids: 1 -3% University of Illinois Urbana Champaign Parameter Name Wheel Load (pound force) Distance between Loads (inch) Ballast Modulus (psi) Subballast Thickness (inch) Subballast Modulus (psi) Poisson’s Ratio for Subballast Parameter Values Poisson’s Ratio for HMA Volume of Voids for HMA(%) Temperature for HMA (°F) Subgrade Thickness (inch) Poisson’s Ratio for Subgrade Poisson’s Ratio for Bedrock Traffic Volume (MGT) 0. 45 3 50 (spring) 77 (summer) 37 (autumn) 20 (winter) 698000 (spring) 372000 (summer) 1250000 (autumn) 2260000 (winter) 200 0. 4 0. 5 32 Ballast Thickness (inch) HMA Thickness (inch) Subgrade Modulus (psi) 12 in 4 -6 3000 -15000 HMA Modulus (psi) Two@72000 70 47000 4 20000 0. 35 13

KENTRAK 4. 0 Analysis 14 The KENTRACK program is a finite element based railway trackbed structural design program that analyzes trackbeds having various combinations of all-granular and asphalt-bound layered support. It is applicable for: 1. Calculating compressive stresses at the top of subgrade, indicative of potential long-term trackbed settlement failure. 2. For trackbeds containing asphalt layer, for calculating tensile strains at the bottom of the asphalt layer, indicative of potential fatigue cracking. 3. Predicting trackbed service lives University of Illinois Urbana Champaign

15 Variation of Dynamic Complex Modulus University of Illinois Urbana Champaign

16 KENTRAK ANALYSIS University of Illinois Urbana Champaign

17 Design Life DESIGN LIFE VS LOAD REPITITION All Granular-Compressive stress-Design life Variation of Design life 90 80 70 60 50 40 30 20 10 0 Asphalt Underlayment. Compressive stress-Design life Asphalt Combination. Compressive stress-Design life Asphalt Underlayment. Tensile strain- Design life 0 50000 100000 150000 200000 Load Repitition (1 Rep = 4 Axles) University of Illinois Urbana Champaign 250000 Asphalt Combination. Tensile strain- Design life

18 Conclusions Long term maintenance costs of the two options are being studied. Austria has used it in large stretches and have concluded a 17 -25% long term savings. Design life increased Height of track structure reduced Homogeneity in track structure Research for ideal PG Binder grade, Aggregate gradation, air voids is going on University of Illinois Urbana Champaign

ACKNOWLEDGEMENT : Prof Bill Buttlar Mr Vijay Sehgal Mr Sharda Mr MK Gupta 19 Thank You