1. International Concrete Crosstie & Fastening System Symposium
Investigation of the Mechanics of Rail Seat Deterioration (RSD) and Methods to Improve the Abrasion Resistance of Concrete Sleepers
International Concrete Crosstie & Fastening System Symposium
Urbana, IL
6-8 June 2012
Part of larger tie and fastener research program sponsored by FRA
Ryan G. Kernes, Amogh A. Shurpali, J. Riley Edwards, Marcus S. Dersch, David A. Lange, and Christopher P.L. Barkan

2. Outline Objectives Rail seat deterioration (RSD) background
Large scale abrasion test
Evaluation of frictional properties
Small scale abrasion resistance test
Results
Conclusions and future work

3. Objectives Understand the mechanics of the most critical failure modes
Propose methods of mitigating the critical failure modes
Investigate parameters that affect abrasion mechanism
Quantify abrasion resistance of various concrete mix designs, curing conditions, and surface treatments
Characterize frictional forces between rail seat and rail pad
Through industry surveys and focused discussions with industry experts
Understand mechanics by experimentation or modeling

4. Rail Seat Deterioration (RSD)
Degradation of concrete material under rail and pad
Increases maintenance costs
Shortens service life of the concrete crosstie
Leads to track geometry defects
Feasible mechanisms:
Abrasion
Crushing
Freeze-thaw damage
Hydro-abrasive erosion
Hydraulic pressure cracking
Track geometry defects could result in an unstable rail condition

5. Abrasion Mechanism of RSD
Abrasion is a progressive failure mechanism that occurs when:
Frictional forces act between two surfaces in contact
Relative movement occurs between the surfaces
Harder surface cuts or ploughs into softer surface
Progression of abrasion at the rail seat
Cyclic motion of rail base induces shear forces
Shear forces overcome static friction
Pad slips relative to concrete
Strain is imparted on concrete matrix
Abrasion involves 3-body wear: two interacting surfaces (rail pad and rail seat) and abrasive slurry (water and fines)
Not an intrinsic property but a system property. Therefore, pads, environmental characteristics, must be investigated.
In order to investigate this complex phenomena, we have developed a laboratory setup at the University of Illinois.

6. Large Scale Abrasion Resistance Test Experimental Setup
Vertical Actuator
Abrasion Pad
Horizontal Actuator
Horizontally mounted actuator produces displacements of a pad relative to a fixed concrete specimen
A static normal force is applied with a vertically mounted actuator
Objectives:
Isolate abrasion mechanism
Maintain representative contact mechanics
Understand effect of variables on abrasion rate
Load magnitude, displacement, load rate, water, sand
Establish most abrasive parameters to evaluate rail seat materials and surface treatments
Test Setup:
Nominal pressure: up to 900 psi
Displacements: 1/16” – 1/8”
6” x 6” concrete specimens, f’(c) > 7000 psi
4” x 3” stock pad materials, Nylon 6/6 (unreinforced), Polyurethane (95 Shore A)
Contaminates: laboratory sand, water
Concrete Specimen

7. Large Scale Abrasion Resistance Test Results
Consistently able to cause deterioration of concrete due to abrasion
Concrete deterioration initiates near pad edges and propagates inward
Heat build up in pad materials at local contact points leads to softening and adhesion to concrete surface
Difficulty in correlating severity of abrasion to input variables
Contact angle and pressure distribution
Heterogeneity of concrete surface
Due to the difficulties in correlating abrasion severity, we decided to shift gears with the testing protocol.
Due to physical setup of the testing equipment where we can constantly monitor both lateral and vertical loads throughout the test, we are able to gain information related to the friction at the contact interface. So why is friction important?

8. Experimental Evaluation of Friction
Magnitude of static frictional force is directly related to the normal force between the two bodies by the coefficient of friction (μ)
Experimental frictional coefficient measured during test calculated by:
μ = |𝑭|/𝑷
where F is the force required to initiate lateral sliding under vertical normal load P
400 loading cycles to simulate single unit train pass
5,000 pound normal vertical load (420 psi), 1/8” lateral displacement, 3 cycles/second, no abrasive fines or water added
Because friction is not understood, we devised an experimental protocol to measure the friction at the pad – rail seat contact interface.
Pads allowed to cool to original temperature in between tests.

9. Mean Coefficient of Friction per Loading Cycle
Polyurethane
Each line on graph represents an average of 4 repetitions of a single pad on a concrete specimen.
Overall trends
Diff in Poly vs Nylon 6/6 based, changes based on modulus and thermal effects
Nylon 6/6 experimental modulus is about 44 KSI
Poly experimental modulus is about 30 KSI
Overall trend of decreasing COF due to contact films
Nylon 6/6

10. Effect of Environmental Conditions on Nylon 6/6
Average of 16 trials

11. Effect of Environmental Conditions on Concrete Abrasion
Polished surface with no sand
Abrasion initiated with sand

12. Effect of Increasing Normal Load on Nylon 6/6
3 kips
5 kips
Average of 8 trials at 3 and 10 kips
5 kip data is average of 44 trials
10 kips

13. Small Scale Abrasion Resistance Test (SSART): Test Setup
In general, similar to other standard abrasion tests
Consists of powered rotating steel wheel with 3 lapping rings
Lapping rings permitted to rotate about their own axis
Vertical load applied using the dead weights
Abrasive sand and water dispensed during testing
Lap 12 in; Rings 6 in. by 1.5 inch (depth) ; dead weight 4.5 lb
Hanging words (more than one)
Ottawa sand standard for testing

14. Test Protocol Each test can evaluate 3 specimens
Multiple tests are run to evaluate more than 3 specimens
Specimen dimensions: inch (diameter),1 inch (thickness)
Duration: 120 minutes
Wear depth measurements taken every 20 minutes
Speed: 60 revolutions per minute
Abrasive fine: Ottawa sand
Before
20-30: Passing through 841 microns retained on 596 microns
Average wear depth: mm/test
Average weight loss: gm/test.
After

15. Test Variables Admixtures Surface Treatment Silica fume: 5%,10%
Fly ash: 15%, 30%
Curing Condition
Moist
Submerged
Oven dry
Air
Surface Treatment
UV epoxy
Polyurethane
Grinding
Fiber Reinforced Concrete (FRC)
Steel
Lapping machine not a representative test, that’s the reason for large scale which is…

16. Effect of Mineral Admixtures
Compressive strength 1-2 specimens
ART: 3
ASTM 231 Pressure method
Generated results that are in agreement with the prevalent literature related to fly ash and silica fume. This gives us confidence moving forward in evaluating other mixes that have not been tested before.

17. Effect of Fiber Reinforcement
Compressive strength 1-2 specimens
ART: 3
ASTM 231 Pressure method

18. Effect of Curing Conditions

19. Comparison of Techniques to Increase Abrasion Resistance

20. Additional Tests Conducted
Objective: to obtain specimens batched by industry concrete crosstie suppliers
Silica fume and epoxy coated specimens tested
Saw-cut surface of control specimens considered analogous to ground surface and tested
Saw cut (Sustersic et al 1991)
Grinding
Epoxy coating

21. Effect of Surface Treatments

22. Conclusions Large scale testing:
Confirmation of abrasion as a feasible RSD mechanism
Frictional coefficient is affected by temperature, water, sand, normal force
SSART:
Successfully compared 13 approaches to improving abrasion resistance of rail seat through material improvements
Improve abrasion resistance of concrete with:
Optimal amounts of fly ash
Proper curing condition
Addition of steel fibers
Grinding cement paste

23. Future Work
Determining the optimal frictional properties at each interface of multi-layer rail pads (top, bottom, and between layers) could:
Reduce movement at critical interfaces
Influence load path and location of slip
Delay the onset of abrasive wear and extend rail seat life
Extend to other fastening system components
SSART:
Perform image analysis to characterize the role of coarse aggregate in abrasion resistance
Study the effect of air entrainment and quality of aggregates on abrasion resistance of rail seat
Use of Statistical Analysis Software (SAS) to model abrasive wear of concrete specimens
Optimize concrete mix design and surface treatments to mitigate abrasion

24. Acknowledgements Funding for this research has been provided by
Association of American Railroads Technology Scanning Program
NEXTRANS Region V Transportation Center
Eisenhower Graduate Fellowship
For providing direction, advice, and resources:
Amsted Rail - Amsted RPS: Jose Mediavilla, Dave Bowman, Brent Wilson,
BNSF Railway: John Bosshart, Tom Brueske, Hank Lees
AREMA Committee 30: Winfred Boesterling, Pelle Duong, Kevin Hicks, Tim Johns, Steve Mattson, Jim Parsley, Michael Steidl, Fabian Weber, John Zeman
TTCI: Dave Davis, Richard Reiff
Pandrol Track Systems: Bob Coats, Scott Tripple
UIUC: Tim Prunkard, Mauricio Gutierrez, Don Marrow, Darold Marrow
For assisting with the research and lab work:
Josh Brickman, Ryan Feeney, Kris Gustafson, Steven Jastrzebski, Andrew Kimmle, Calvin Nutt, Chris Rapp, Amogh Shurpali, Emily Van Dam, Michael Wnek

25. Questions Ryan Kernes Research Engineer
Rail Transportation and Engineering Center - RailTEC
Amogh A. Shurpali
Graduate Research Assistant
Rail Transportation and Engineering Center - RailTEC