Performance of Bottom Ash Performance of Bottom Ash Asphalt MixesAsphalt Mixes

Symposium on Prediction of Symposium on Prediction of Pavement PerformancePavement Performance

June 24, 2004June 24, 2004Cheyenne, WYCheyenne, WY

Dr. Khaled KsaibatiGeorge Huntington, P.E.

University of Wyoming

OverviewOverviewBottom Ash: The Disposal ProblemBottom Ash: The Disposal ProblemMaterials and Laboratory TestingMaterials and Laboratory Testing–– Superpave Mix DesignSuperpave Mix Design–– Georgia Loaded Wheel Test (GLWT)Georgia Loaded Wheel Test (GLWT)–– Thermal Stress Restrained Specimen Test (TSRST)Thermal Stress Restrained Specimen Test (TSRST)–– Tensile Strength Ratio (TSR)Tensile Strength Ratio (TSR)

Field Test SiteField Test Site–– Construction MethodsConstruction Methods–– Falling Weight Falling Weight DeflectometerDeflectometer (FWD)(FWD)–– Pavement Condition Index (PCI)Pavement Condition Index (PCI)

EconomicsEconomics

Coal AshCoal Ash

78 million tons per year in the USA78 million tons per year in the USABottom Ash Bottom Ash –– 20%20%Fly AshFly Ash–– the other 80%the other 80%–– lighter material carried through the furnace lighter material carried through the furnace

and collected by precipitatorsand collected by precipitators

Bottom AshBottom Ash

Slag that builds up on the heat absorbing Slag that builds up on the heat absorbing surfaces of the furnace, then falls to the surfaces of the furnace, then falls to the bottom and is collected in a hopperbottom and is collected in a hopperMost Wyoming bottom ash is wet bottom Most Wyoming bottom ash is wet bottom ash, sometimes referred to as boiler slagash, sometimes referred to as boiler slag–– Material that falls from the furnace into water Material that falls from the furnace into water

in a molten statein a molten state

Power Plant

Coal

Pulverizer Boiler Ash or Slag

Sluiced withWater

Utilization

Disposal

Pyrite Removal

Holding Pond Air DryingDewatering

Reclaim

Dewatering Bin(Drying)

Sizing(Screening or

Grinding

BottomAsh

Product

Bottom Ash GradationsBottom Ash Gradations

0%

20%

40%

60%

80%

100%

Sieve (0.45 Power Curve)

Perc

ent P

assi

ng

DJJBLR

#200 #30 #4 1/2" 1"

Ash Source

Bottom AshBottom Ash

Coal Ash DisposalCoal Ash Disposal““It’s time to recognize coal plant waste It’s time to recognize coal plant waste

disposal facilities for what they are disposal facilities for what they are –– huge, huge, unregulated toxic dumps…Some of unregulated toxic dumps…Some of Pennsylvania’s dumps are nothing more Pennsylvania’s dumps are nothing more than abandoned strip mine pits and mine than abandoned strip mine pits and mine shafts where the waste pollutes the shafts where the waste pollutes the groundwater Pennsylvanians depend on groundwater Pennsylvanians depend on for drinking and agriculture.”for drinking and agriculture.”

Joseph Joseph MinottMinott, Executive Director, Clean Air Council, Executive Director, Clean Air Council

Bottom Ash UsesBottom Ash Uses

Structural fillsStructural fillsRoad bases and Road bases and subbasessubbasesAsphalt fillerAsphalt fillerRoofing granulesRoofing granulesSandSand--blasting gritblasting gritSnow and ice controlSnow and ice controlFiltrationFiltrationAggregate in concrete productsAggregate in concrete products

Research ObjectiveResearch Objective

Evaluate the performance and feasibility Evaluate the performance and feasibility of using Wyoming bottom ash in asphalt of using Wyoming bottom ash in asphalt mixesmixes–– Laboratory studyLaboratory study–– Field studyField study

WarlowWarlow Drive in Gillette, WyomingDrive in Gillette, Wyoming

Bottom Ash SourcesBottom Ash Sources

Dave Johnston Power Plant (DJ)Dave Johnston Power Plant (DJ)–– Glenrock, WyomingGlenrock, WyomingJim Bridger Power Plant (JB)Jim Bridger Power Plant (JB)–– Point of Rocks, WyomingPoint of Rocks, WyomingLaramie River Power Plant (LR)Laramie River Power Plant (LR)–– Wheatland, WyomingWheatland, Wyoming

AggregatesAggregatesLimestoneLimestone–– Coarse aggregateCoarse aggregate

Pete Lien, Sundance, WyomingPete Lien, Sundance, Wyoming–– Crushed finesCrushed fines

Pete Lien, Rapid City, South DakotaPete Lien, Rapid City, South Dakota–– Most test results availableMost test results available–– Field test section placed in 2002Field test section placed in 2002GraniteGranite–– Lewis and Lewis, Southwestern WyomingLewis and Lewis, Southwestern Wyoming–– Testing has begunTesting has begun

Asphalt and LimeAsphalt and Lime

AsphaltAsphalt–– PG 64PG 64--22 from the Sinclair refinery in 22 from the Sinclair refinery in

Casper, WyomingCasper, WyomingLimeLime–– 1% hydrated lime slurry1% hydrated lime slurry–– Pete Lien, Rapid City, South DakotaPete Lien, Rapid City, South Dakota

Aggregate TestingAggregate Testing

Aggregate and Bottom AshAggregate and Bottom Ash–– GradationGradation–– Specific GravitySpecific Gravity–– AbsorptionAbsorption–– Magnesium sulfate soundnessMagnesium sulfate soundnessCoarse aggregate Coarse aggregate –– LA Abrasion testsLA Abrasion tests

Mix DesignsMix Designs

8 Superpave Level I mix designs8 Superpave Level I mix designs–– 75 gyrations75 gyrationsControl and with 15% bottom ashControl and with 15% bottom ash–– Control, no bottom ashControl, no bottom ash–– 15% DJ (Dave Johnston) bottom ash15% DJ (Dave Johnston) bottom ash–– 15% JB (Jim Bridger) bottom ash15% JB (Jim Bridger) bottom ash–– 15% LR (Laramie River) bottom ash15% LR (Laramie River) bottom ashBlended to get similar gradationsBlended to get similar gradations4.0% Air Voids4.0% Air Voids

Aggregate Qualification Test ResultsAggregate Qualification Test Results

SpecificSpecificGravityGravity

SourceSource

coarsecoarse

finefine

combined

combined

SandSand

EquivalentEquivalent

FlatFlat

+ Elongated+ Elongated

Fine Fine

Aggregate

Aggregate

Angularity

Angularity

Fractured Fractured

FacesFaces

L.A.

L.A.

Abrasion

Abrasion

GraniteGranite 2.5842.584 2.5942.594 2.5862.586 7474 00 4747 100100 1818

LimestoneLimestone 2.6662.666 2.6082.608 2.6312.631 7979 55 4646 100100 2525

Limestone JMF (0.45 Curve),including 15% bottom ash

0%

20%

40%

60%

80%

100%

Sieve

Per

cent

Pas

sing

ControlDJJBLR

#200 1/2"3/8"#4#8#16

#30

#50#100

3/4"

Granite JMF (0.45 Curve),including 15% bottom ash

0%

20%

40%

60%

80%

100%

Sieve

Perc

ent P

assi

ng

ControlDJJBLR

#200 1/2"3/8"#4#8#16

#30

#50

#1003/4"

Mix Design Summary Mix Design Summary (4.0% Air Voids)(4.0% Air Voids)

MIXMIX

Asphalt

Asphalt

Content, %

Content, %

Bulk

Bulk

Density,

Density, pcf

pcf

Maxim

um

Maxim

um

Density,

Density, pcf

pcf

VM

A, %

VM

A, %

VFA

, %V

FA, %

Limestone ControlLimestone Control 4.64.6 150.5150.5 156.8156.8 12.612.6 68.868.8LS & 15% DJ BALS & 15% DJ BA 6.16.1 146.4146.4 152.4152.4 15.615.6 73.973.9LS & 15% JB BALS & 15% JB BA 5.25.2 144.8144.8 150.8150.8 15.315.3 83.383.3LS & 15% LR BALS & 15% LR BA 5.75.7 147.8147.8 154.0154.0 14.614.6 72.972.9Granite ControlGranite Control 5.55.5 144.6144.6 150.6150.6 15.315.3 74.074.0

GR & 15% DJ BAGR & 15% DJ BA 6.26.2 142.8142.8 148.9148.9 15.315.3 73.073.0GR & 15% JB BAGR & 15% JB BA 6.26.2 139.5139.5 145.8145.8 16.116.1 75.075.0GR & 15% LR BAGR & 15% LR BA 6.06.0 142.9142.9 149.4149.4 15.215.2 72.072.0

Laboratory Evaluation: Mix TypesLaboratory Evaluation: Mix Types

Lab mixed and Superpave gyratory Lab mixed and Superpave gyratory compacted specimenscompacted specimensPlant mixed and lab compacted Plant mixed and lab compacted specimensspecimensPlant mixed and field compacted Plant mixed and field compacted specimensspecimens

Laboratory Evaluation: Laboratory Evaluation: Performance TestsPerformance Tests

RuttingRutting–– Georgia Loaded Wheel TestGeorgia Loaded Wheel Test, GLWT, GLWTLow Temperature CrackingLow Temperature Cracking–– Thermal Stress Restrained Specimen TestThermal Stress Restrained Specimen Test, TSRST, TSRSTStrippingStripping–– Tensile Strength Ratio, TSR Tensile Strength Ratio, TSR ((LottmanLottman Test, 15 cycles)Test, 15 cycles)

Georgia Loaded Wheel Test (GLWT)Georgia Loaded Wheel Test (GLWT)

Cylindrical specimen 3” tall, 6” diameterCylindrical specimen 3” tall, 6” diameter100100## load on a pneumatic linear hose load on a pneumatic linear hose pressurized to 100 psipressurized to 100 psi1500 F inside the chamberthe chamberLoad applied by an aluminum wheel onto Load applied by an aluminum wheel onto the hose, which rests on the specimenthe hose, which rests on the specimenRut depths measured at preRut depths measured at pre--determined determined numbers of cyclesnumbers of cycles

Georgia Loaded Wheel TesterGeorgia Loaded Wheel Tester

Georgia Loaded Wheel TesterGeorgia Loaded Wheel Tester

Georgia Loaded Wheel TesterGeorgia Loaded Wheel Tester

GLWT 8,000 Cycle Rut Depths

0.00

0.02

0.04

0.06

0.08

0.10

0.12

Control DJ JB LR

Rut

Dep

th, i

nche

sLab Compacted Plant Mix Lab Compacted Lab Mix

Thermal Stress Restrained Thermal Stress Restrained Specimen Test (TSRST)Specimen Test (TSRST)

Evaluates low temperature crackingEvaluates low temperature crackingSpecimen is cooled, developing tensile Specimen is cooled, developing tensile stressesstresses

–– 10” long by 2” diameter specimen10” long by 2” diameter specimen–– Ends restrainedEnds restrained–– Specimen cooled at 16Specimen cooled at 16ººF/hrF/hr–– Temperature and load at failure recordedTemperature and load at failure recorded

Thermal Stress Restrained Thermal Stress Restrained Specimen TestSpecimen Test

Thermal Stress Restrained Thermal Stress Restrained Specimen TestSpecimen Test

TSRST Failure Temperatures

-40

-30

-20

-10

0Control DJ JB LR

ºFLab Mixed and CompactedPlant Mixed and Field Compacted

TSRST Failure Stresses

0

100

200

300

400

500

600

Control DJ JB LR

Tens

ile S

tress

, psi

Lab Mixed and CompactedPlant Mixed and Field Compacted

Indirect Tensile Strength TestIndirect Tensile Strength Test

LottmanLottman TestTest–– 15 cycles15 cyclesAASHTO T 283AASHTO T 283–– Modified Modified LottmanLottman–– Single cycleSingle cycle

Indirect Tensile Strength TestIndirect Tensile Strength Test

Specimens in subsetsSpecimens in subsets–– One tested dryOne tested dry–– One tested after conditioningOne tested after conditioningConditioningConditioning–– Vacuum out air and replace with waterVacuum out air and replace with water–– Leave in water at 140Leave in water at 140ººF for 24 hoursF for 24 hours–– Freeze at 5Freeze at 5ººF then back to 140F then back to 140ººF water F water

for 24 hoursfor 24 hours–– May repeat for multiple cyclesMay repeat for multiple cycles

Tensile Strength Ratio (TSR)Tensile Strength Ratio (TSR)Specimens compressed between Specimens compressed between bearing plates on the diameter of the bearing plates on the diameter of the specimen until cracks appear, specimen until cracks appear, indicating tensile failureindicating tensile failureTSR = STSR = Scc//SSddSScc = tensile strength of conditioned subset= tensile strength of conditioned subsetSSdd = tensile strength of unconditioned subset= tensile strength of unconditioned subset

WYDOT considers a TSR > 75% a passWYDOT considers a TSR > 75% a pass

Tensile Strength Retained: Lab Mixes

50%

60%

70%

80%

90%

100%

0 4 8 12 16Cycles

TSR

ControlDJJBLR

Tensile Strength Retained:Plant & Field Mixes

40%

50%

60%

70%

80%

90%

100%

0 4 8 12 16

Cycles

TSR

ControlDJJBLR

Field EvaluationField Evaluation

Hot PlantHot Plant

15% bottom ash added through its own 15% bottom ash added through its own cold feed bincold feed binLime slurry addedLime slurry added

ConstructionConstruction

Mill 3” of existing 8” of asphalt pavementMill 3” of existing 8” of asphalt pavementAdditional milling at wide cracksAdditional milling at wide cracks–– Place Place PavePrepPavePrep®® fabricfabric–– Place Place ¾”¾” hot mix and compacthot mix and compactTack and paving fabricTack and paving fabricPlace 3Place 3”” of plant mixof plant mixFour 800’ test sectionsFour 800’ test sections

1 1 –– Control, 3 Control, 3 –– 15% bottom ash15% bottom ash

RotomilledRotomilled SurfaceSurface

Milled Pavement and Milled Pavement and PavePrepPavePrep®®

Placing hot mix over Placing hot mix over PavePrepPavePrep®®

Compacting over patched areasCompacting over patched areas

Tack and Paving FabricTack and Paving Fabric

LaydownLaydown

CompactionCompaction

Finished PavementFinished Pavement

PostPost--Construction Field EvaluationConstruction Field Evaluation

FWD TestingFWD Testing–– Measure of structural integrity of the Measure of structural integrity of the

pavementpavement–– Tested before and after the overlayTested before and after the overlayPavement Condition Index (PCI)Pavement Condition Index (PCI)–– Measure of pavement performanceMeasure of pavement performance–– To be performedTo be performed

Falling Weight Falling Weight DeflectometerDeflectometer (FWD)(FWD)

FWD Load Plate Deflections

5

10

15

20

25

30

35

40

0+00 5+00 10+00 15+00 20+00 25+00 30+00 35+00

Def

lect

ion,

mils

DJ LRJB Control

Green: After Overlay

Red: Before Overlay

FWD 12" Sensor Deflections

02468

101214161820

0+00 5+00 10+00 15+00 20+00 25+00 30+00 35+00

Def

lect

ions

, mils

JB DJ LR Control

Green: After Overlay

Red: Before Overlay

Pavement Condition Index (PCI)Pavement Condition Index (PCI)

PCIPCI RatingRating100 100 -- 8585 ExcellentExcellent85 85 -- 7070 Very GoodVery Good70 70 -- 5555 GoodGood55 55 -- 4040 FairFair40 40 -- 2525 PoorPoor25 25 -- 1010 Very PoorVery Poor10 10 -- 00 FailedFailed

Pavement surface Pavement surface condition surveycondition surveyASTM D 6433ASTM D 6433

PCI: PCI: WarlowWarlow DriveDrive

SurveySurvey PCIPCIPavement Pavement

RatingRatingPrePre--Paving: Paving:

October 2002October 2002 5454 FairFair

6 months: 6 months: April 2003April 2003 9999 ExcellentExcellent

12 months: 12 months: October 2003October 2003 9090 ExcellentExcellent

Economic ConsiderationsEconomic Considerations

Increased asphalt costsIncreased asphalt costs–– 0.5% to 1.5% asphalt content increase0.5% to 1.5% asphalt content increaseReduced aggregate costsReduced aggregate costs–– 15% of aggregate replaced with bottom ash15% of aggregate replaced with bottom ash

Does higher asphalt content lead to Does higher asphalt content lead to improved durability?improved durability?–– Similar benefits to using fewer gyrations for Similar benefits to using fewer gyrations for

low volume roads during Superpave mix low volume roads during Superpave mix designdesign

Summary: Mix DesignSummary: Mix Design

Asphalt contents for bottom ash mixes are Asphalt contents for bottom ash mixes are 0.5% to 1.5% higher than for the control 0.5% to 1.5% higher than for the control mixesmixes

Summary: Performance TestsSummary: Performance Tests

GLWT indicates that the Control and LR GLWT indicates that the Control and LR sections should have better rut resistancesections should have better rut resistanceTSRST results are inconclusive in TSRST results are inconclusive in predicting thermal crackingpredicting thermal cracking–– The lab mix results indicate thermal cracking The lab mix results indicate thermal cracking

at higher temperatures for the bottom ash at higher temperatures for the bottom ash mixes, but this is not reflected in the field mix mixes, but this is not reflected in the field mix resultsresults

TSR indicates the JB bottom ash may be TSR indicates the JB bottom ash may be more vulnerable to strippingmore vulnerable to stripping

Summary: Field SectionSummary: Field Section

FWD results indicate better structural FWD results indicate better structural improvements for the JB and DJ mixes improvements for the JB and DJ mixes than for the control and LR mixesthan for the control and LR mixes

Evaluating the longEvaluating the long--term performance of term performance of the test sections should give an indication the test sections should give an indication of how bottom ash pavements performof how bottom ash pavements perform–– FWDFWD–– Pavement Condition Index (PCI)Pavement Condition Index (PCI)

ImplementationImplementationIf the performance of the bottom ash If the performance of the bottom ash pavements is similar to other pavements, pavements is similar to other pavements, initial material costs will dictate whether initial material costs will dictate whether bottom ash pavements are cost effectivebottom ash pavements are cost effective–– Bottom ash costBottom ash cost

PurchasePurchaseHaulHaulDisposalDisposal

–– Aggregate and asphalt costsAggregate and asphalt costsPurchasePurchaseHaulHaul

Questions?Questions?