PowerPoint Presentation

Ryan G. Kernes, Amogh A. Shurpali, J. Riley Edwards, Marcus S. Dersch, David A. Lange, and Christopher P.L. BarkanInternational Concrete Crosstie & Fastening System SymposiumUrbana, IL6-8 June 2012

Investigation of the Mechanics of Rail Seat Deterioration (RSD) and Methods to Improve the Abrasion Resistance of Concrete SleepersSlide #Investigating Rail Seat DeteriorationPart of larger tie and fastener research program sponsored by FRA1OutlineObjectivesRail seat deterioration (RSD) backgroundLarge scale abrasion testEvaluation of frictional propertiesSmall scale abrasion resistance testResultsConclusions and future work

Slide #Investigating Rail Seat Deterioration2ObjectivesUnderstand the mechanics of the most critical failure modesInvestigate parameters that affect abrasion mechanismCharacterize frictional forces between rail seat and rail padPropose methods of mitigating the critical failure modesQuantify abrasion resistance of various concrete mix designs, curing conditions, and surface treatments

Slide #Investigating Rail Seat DeteriorationThrough industry surveys and focused discussions with industry expertsUnderstand mechanics by experimentation or modeling

3Rail Seat Deterioration (RSD)Degradation of concrete material under rail and padIncreases maintenance costs Shortens service life of the concrete crosstieLeads to track geometry defects

Feasible mechanisms:AbrasionCrushingFreeze-thaw damageHydro-abrasive erosionHydraulic pressure cracking

Slide #Investigating Rail Seat DeteriorationTrack geometry defects could result in an unstable rail condition4Abrasion Mechanism of RSDAbrasion is a progressive failure mechanism that occurs when:Frictional forces act between two surfaces in contactRelative movement occurs between the surfacesHarder surface cuts or ploughs into softer surface

Progression of abrasion at the rail seatCyclic motion of rail base induces shear forcesShear forces overcome static frictionPad slips relative to concreteStrain is imparted on concrete matrix

Abrasion involves 3-body wear: two interacting surfaces (rail pad and rail seat) and abrasive slurry (water and fines)

Slide #Investigating Rail Seat DeteriorationNot 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.5Large Scale Abrasion Resistance Test Experimental Setup

Vertical ActuatorHorizontal ActuatorAbrasion PadConcrete SpecimenSlide #Investigating Rail Seat DeteriorationHorizontally mounted actuator produces displacements of a pad relative to a fixed concrete specimen A static normal force is applied with a vertically mounted actuatorObjectives:Isolate abrasion mechanismMaintain representative contact mechanicsUnderstand effect of variables on abrasion rateLoad magnitude, displacement, load rate, water, sandEstablish most abrasive parameters to evaluate rail seat materials and surface treatmentsTest Setup:Nominal pressure: up to 900 psiDisplacements: 1/16 1/86 x 6 concrete specimens, f(c) > 7000 psi4 x 3 stock pad materials, Nylon 6/6 (unreinforced), Polyurethane (95 Shore A)Contaminates: laboratory sand, water

6Large Scale Abrasion Resistance Test ResultsConsistently able to cause deterioration of concrete due to abrasionConcrete deterioration initiates near pad edges and propagates inwardHeat build up in pad materials at local contact points leads to softening and adhesion to concrete surfaceDifficulty in correlating severity of abrasion to input variablesContact angle and pressure distributionHeterogeneity of concrete surface

Slide #Investigating Rail Seat DeteriorationDue 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?

7Experimental Evaluation of FrictionMagnitude of static frictional force is directly related to the normal force between the two bodies by the coefficient of friction ()Experimental frictional coefficient measured during test calculated by: = ||/where F is the force required to initiate lateral sliding under vertical normal load P400 loading cycles to simulate single unit train pass5,000 pound normal vertical load (420 psi), 1/8 lateral displacement, 3 cycles/second, no abrasive fines or water added

Slide #Investigating Rail Seat DeteriorationBecause 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.8

Mean Coefficient of Friction per Loading CyclePolyurethaneNylon 6/6Slide #Investigating Rail Seat DeteriorationEach line on graph represents an average of 4 repetitions of a single pad on a concrete specimen.Overall trendsDiff in Poly vs Nylon 6/6 based, changes based on modulus and thermal effectsNylon 6/6 experimental modulus is about 44 KSIPoly experimental modulus is about 30 KSI

Overall trend of decreasing COF due to contact films

9

Effect of Environmental Conditions on Nylon 6/6

Slide #Investigating Rail Seat DeteriorationAverage of 16 trials

10Effect of Environmental Conditions on Concrete Abrasion

Polished surface with no sandAbrasion initiated with sandSlide #Investigating Rail Seat Deterioration

Effect of Increasing Normal Load on Nylon 6/65 kips 3 kips 10 kips Slide #Investigating Rail Seat DeteriorationAverage of 8 trials at 3 and 10 kips5 kip data is average of 44 trials12Small Scale Abrasion Resistance Test (SSART): Test SetupIn general, similar to other standard abrasion testsConsists of powered rotating steel wheel with 3 lapping rings Lapping rings permitted to rotate about their own axisVertical load applied using the dead weightsAbrasive sand and water dispensed during testing

Slide #Investigating Rail Seat DeteriorationLap 12 in; Rings 6 in. by 1.5 inch (depth) ; dead weight 4.5 lb

Hanging words (more than one)

Ottawa sand standard for testing13Test ProtocolEach test can evaluate 3 specimens Multiple tests are run to evaluate more than 3 specimensSpecimen dimensions: 4 inch (diameter),1 inch (thickness)Duration: 120 minutes Wear depth measurements taken every 20 minutesSpeed: 60 revolutions per minuteAbrasive fine: Ottawa 20-30 sand

BeforeAfter

Slide #Investigating Rail Seat Deterioration20-30: Passing through 841 microns retained on 596 micronsAverage wear depth: 2.5-6.0 mm/test Average weight loss: 75-100 gm/test.

14Test VariablesAdmixturesSilica fume: 5%,10%Fly ash: 15%, 30%

Curing ConditionMoistSubmergedOven dryAir

Surface TreatmentUV epoxyPolyurethaneGrindingFiber Reinforced Concrete (FRC) PolyurethaneSteel

Slide #Investigating Rail Seat DeteriorationLapping machine not a representative test, thats the reason for large scale which is15Effect of Mineral Admixtures

Slide #Investigating Rail Seat DeteriorationCompressive strength 1-2 specimensART: 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.

16Effect of Fiber Reinforcement

Slide #Investigating Rail Seat DeteriorationCompressive strength 1-2 specimensART: 3 ASTM 231 Pressure method

17Effect of Curing Conditions

Slide #Investigating Rail Seat DeteriorationComparison of Techniques to Increase Abrasion Resistance

Slide #Investigating Rail Seat DeteriorationAdditional Tests Conducted Objective: to obtain specimens batched by industry concrete crosstie suppliersSilica fume and epoxy coated specimens testedSaw-cut surface of control specimens considered analogous to ground surface and tested

GrindingEpoxy coatingSlide #Investigating Rail Seat DeteriorationSaw cut (Sustersic et al 1991)20Effect of Surface Treatments

Slide #Investigating Rail Seat DeteriorationConclusions Large scale testing:Confirmation of abrasion as a feasible RSD mechanismFrictional coefficient is affected by temperature, water, sand, normal forceSSART:Successfully compared 13 approaches to improving abrasion resistance of rail seat through material improvementsImprove abrasion resistance of concrete with:Optimal amounts of fly ashProper curing conditionAddition of steel fibersGrinding cement paste

Slide #Investigating Rail Seat Deterioration22Future WorkDetermining the optimal frictional properties at each interface of multi-layer rail pads (top, bottom, and between layers) could:Reduce movement at critical interfacesInfluence load path and location of slipDelay the onset of abrasive wear and extend rail seat lifeExtend to other fastening system componentsSSART: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 seatUse of Statistical Analysis Software (SAS) to model abrasive wear of concrete specimensOptimize concrete mix design and surface treatments to mitigate abrasion

Slide #Investigating Rail Seat Deterioration23AcknowledgementsFunding for this research has been provided byAssociation of American Railroads Technology Scanning ProgramNEXTRANS Region V Transportation CenterEisenhower Graduate FellowshipFor providing direction, advice, and resources:Amsted Rail - Amsted RPS: Jose Mediavilla, Dave Bowman, Brent Wilson, BNSF Railway: John Bosshart, Tom Brueske, Hank LeesAREMA Committee 30: Winfred Boesterling, Pelle Duong, Kevin Hicks, Tim Johns, Steve Mattson, Jim Parsley, Michael Steidl, Fabian Weber, John ZemanTTCI: Dave Davis, Richard ReiffPandrol Track Systems: Bob Coats, Scott TrippleUIUC: Tim Prunkard, Mauricio Gutierrez, Don Marrow, Darold MarrowFor 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

Slide #Investigating Rail Seat DeteriorationQuestionsRyan KernesResearch EngineerRail Transportation and Engineering Center - RailTECemail: rkernes2@illinois.edu

Amogh A. ShurpaliGraduate Research AssistantRail Transportation and Engineering Center - RailTECemail: ashurpa2@illinois.edu

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