Designing FullDesigning Full--Depth Depth ReclamationReclamationReclamationReclamationProjects for Urban AreasProjects for Urban Areas

W. Spencer Guthrie, Ph.D.Associate ProfessorAssociate Professor

Department of Civil and Environmental Engineering, Brigham Young Universityg g, g g y

INTRODUCTIONINTRODUCTION• Pavement engineers and managers arePavement engineers and managers are

focusing increasingly on preservation of existing roadwaysexisting roadways

• Availability of high quality aggregates is diminishing in many areasdiminishing in many areas

• Funding for road reconstruction remains li it d hil t l tilimited while costs are escalating

• Drivers have high expectations for pavement serviceability

ASCE Infrastructure Report CardASCE Infrastructure Report Card

FULLFULL--DEPTH RECLAMATIONDEPTH RECLAMATION• FDR consists of in-situ pulverization of a

typically failed asphalt layer with a portion of the underlying base to create a new basethe underlying base to create a new base layer

• FDR is most commonly used to rebuildFDR is most commonly used to rebuild structurally failed asphalt pavements generally exhibiting at least 20% fatigue

ki th 0 5 i f tticracking or more than 0.5 in. of rutting• FDR is both economically and

environmentally friendlyenvironmentally friendly

FullFull--Depth Reclamation: Depth Reclamation: Reclaiming the Asphalt PavementReclaiming the Asphalt PavementReclaiming the Asphalt PavementReclaiming the Asphalt Pavement

Schematic courtesy MN DOT

Advantages of the FDR ProcessAdvantages of the FDR Process• Uses in-place materials

gg

• Requires little or no material to be hauled offMaintains or improves• Maintains or improves existing grade

• Conserves virgin materialConserves virgin material• Saves cost by using

in-place “investment”in place investment• Saves energy by reducing

mining and hauls• Is a very sustainable

process

Economic Benefits of FullEconomic Benefits of Full--Depth Depth R l ti (f PCA)R l ti (f PCA)Reclamation (from PCA)Reclamation (from PCA)

Effect of RAP ContentEffect of RAP Content

• Blending with RAP can also 60

70

lead to reductions in structural 30

40

50

BR

(%)

structural quality of aggregate 10

20

30

CB

aggregate base materials

00 25 50 75 100

RAP Content (%)

B1 B2

Base Material PropertiesBase Material Properties

250

300

350

R (%

)_

150

200

250

ge B

ase

CBR

0

50

100

Ave

rag

Just beforeReclamation

Just afterReclamation

1 Year afterReclamation

Orem San Marcos South Jordan

Benefits of FDR Using CementBenefits of FDR Using Cementgg• Increased rigidity

f di t ib ti l dfor distributing loads• Elimination of rutting

below surfacebelow surface• Reduced moisture and

frost susceptibilityp y• Reduced fatigue

cracking• Thinner pavement

sections

Stress Distribution

Wheel Load

AsphaltTensile Strain -cracking p

U t t d

cracking

Untreated Base

SubgradeCompressive strain -i Subgraderutting

Stress Distribution

Wheel Load

AsphaltTensile Strain -cracking pcracking

CTB

SubgradeCompressive strain -i Subgraderutting

CementCement--Based Pavement Based Pavement M t i lM t i l

Roller-Compacted Conventional

MaterialsMaterialsPerviousp

Concrete ConcretePerviousConcrete

ent Soil-Cement

ent C

onte

Flowable Fill

Cement-Treated

Base

Cem

e Flowable Fill

Cement-ModifiedSoil

Full-DepthReclamation

Water Content

Soil

FDR Construction ProcessFDR Construction ProcessPulverize, Shape, Add Cement, Mix In Place,

Compact, and Surface

Bituminous New Surfacing

GranularBase

SurfacingPulverized

Pulverized Stabilized Stabilized

New Surfacing

Base

Subgrade Subgrade Subgrade Subgrade Subgrade

Existingroad

Pulverizationto desired

Removal ofexcess

Addition of cement,

Application of final surface

depth material (if necessary)and shaping

mixing, reshaping, and

compacting

final surface course

Failed PavementFailed Pavement

PulverizationPulverization

ReshapingReshaping

Spreading Cement SlurrySpreading Cement Slurry

Spreading Cement SlurrySpreading Cement Slurry

Cement UniformityCement Uniformity

Spreading Cement SlurrySpreading Cement Slurry

Spreading Cement PowderSpreading Cement Powder

Material BlendingMaterial Blending

CompactionCompaction

GradingGrading

CuringCuring

Minimal DisruptionMinimal Disruption

MicrocrackingMicrocracking

MicrocrackingMicrocracking

• Purpose is to minimize propagation of CTB shrinkage cracks into asphalt surface course

• Process involves providing moist curing for 2 to 3 days, rolling at maximum vibration and l d t t i k dslow speed to create microcracks, and

providing moist curing for another 2 to 3 daysR lli h ld t h th tiff f th• Rolling should stop when the stiffness of the layer decreases by 40 to 50%

MicrocrackingMicrocracking

Reflection Cracking from Reflection Cracking from Heavily Stabilized CTB LayerHeavily Stabilized CTB LayerHeavily Stabilized CTB LayerHeavily Stabilized CTB Layer

Photo Courtesy of Tom Scullion, TTI

CTB Field TestingCTB Field TestingCTB Field TestingCTB Field Testing

SurfacingSurfacing

PavementPavement AnalysisAnalysis• Service Life = 20 years• Design Equivalent Single Axle Loads =3 in. HMA • Design Equivalent Single Axle Loads =

15,000• Overall Standard Deviation = 0.45

Initial Serviceability 4 5New Surfacing8 in. CTB

• Initial Serviceability = 4.5• Terminal Serviceability = 2.0• Asphalt Structural Layer Coefficient =

Subgrade

0.40• Cement-Treated Base Structural Layer

Coefficient = 0.18Final

Pavement St t • Drainage Coefficient = 1.0

• Subgrade Resilient Modulus = 15 ksi

Structure

Cost = 20% Less than Traditional ReconstructionCost = 20% Less than Traditional ReconstructionCost = 20% Less than Traditional ReconstructionCost = 20% Less than Traditional ReconstructionReliability = 99%Reliability = 99%

Material SamplingMaterial Sampling

Determining Asphalt Determining Asphalt ThicknessThicknessThicknessThickness

Material SamplingMaterial Sampling

Material SamplingMaterial Sampling

CalciumCalcium--Induced Heave of Induced Heave of SulfateSulfate Bearing SoilBearing Soil (ASTM C1580)SulfateSulfate--Bearing Soil Bearing Soil (ASTM C1580)

CalciumCalcium--Induced Heave of Induced Heave of SulfateSulfate Bearing SoilBearing Soil (ASTM C1580)SulfateSulfate--Bearing Soil Bearing Soil (ASTM C1580)

Soil Classification and Selection Soil Classification and Selection of Trial Cement Contentsof Trial Cement Contents

ASTM C136ASTM D4318ASTM D4318

Determining RAPDetermining RAP--Base RatioBase RatioDetermining RAPDetermining RAP Base Ratio Base Ratio for Material Weighfor Material Weigh--OutsOuts

FDR layer thickness should generally not exceed 8 to 10 in forFDR layer thickness should generally not exceed 8 to 10 in. for single-lift construction

Slurry PreparationSlurry Preparation

Slurry PreparationSlurry Preparation

Slurry Aging and Slurry Aging and Proportioning for AggregateProportioning for Aggregate

Mixing Slurry with AggregateMixing Slurry with Aggregateg y gg gg y gg g

Selecting Compaction Selecting Compaction Standard and DeterminingStandard and DeterminingStandard and Determining Standard and Determining

MoistureMoisture--Density CurveDensity Curve

ASTM D558

Optimum Moisture ContentOptimum Moisture Contentpp7.5

6 5

7.0

)

6.0

6.5

OM

C (%

5 0

5.5

5.00 25 50 75 100

RAP Content (%)

49

( )

R1-B1 R1-B2 R2-B1 R2-B2

Maximum Dry DensityMaximum Dry Densityy yy y140

130

135

t3 )

120

125

MD

D (l

b/ft

110

115

120M

1100 25 50 75 100

RAP Content (%)

50

( )

R1-B1 R1-B2 R2-B1 R2-B2

Compacting and CuringCompacting and CuringCompacting and CuringCompacting and Curing

Conditioning in Vacuum Conditioning in Vacuum Saturation TestSaturation Test (ASTM C593)Saturation Test Saturation Test (ASTM C593)

• Specimens are conditioned for 30 minutes in a vacuum h b d 24 i (11 8 i) d h k dchamber evacuated to 24 in. Hg (11.8 psi) and then soaked

for 60 minutes in de-aired, de-ionized water• UCS is immediately measured with specimen in soaked statey p• Conditioning requires less than 2 hours

44--hr Underwater Soakhr Underwater Soak44 hr Underwater Soakhr Underwater Soak

Capping and 7Capping and 7--day Unconfined day Unconfined Compressive Strength TestingCompressive Strength TestingCompressive Strength TestingCompressive Strength Testing

Strain rate of 0.05 in./minute

Materials Materials Engineering and Engineering and Pavement DesignPavement DesignPavement DesignPavement Design

• Specify cement stabilization only if p y ysoluble sulfate concentration is below 3000 ppm

• Specify cement content corresponding to 7-day UCS of between 400 and 500

fpsi after appropriate curing and conditioningU l ffi i ( ) f 0 16• Use a layer coefficient (a2) of 0.16 to 0.20 in structural pavement design or a corresponding moduluscorresponding modulus

Pavement Pavement ContructionContruction

• Complete compaction before substantial p phydration occurs so that cementitious bonds are not broken during densification– Allowable compaction delay time depends upon

wind speed, air temperature, relative humidity Provide a moist curing period of between 4• Provide a moist-curing period of between 4 and 7 days

• Specify microcracking of the CTB layer if an• Specify microcracking of the CTB layer if an asphalt surface course will be placed

Quality Control and QualityQuality Control and QualityQuality Control and Quality Quality Control and Quality AssuranceAssurance

• QC/QA on FDR projects can be difficult because the OMC and target dry densitybecause the OMC and target dry density depend upon RAP content, which can greatly vary across a projecty p j

• Profile milling can be utilized to improve uniformity of asphalt thickness prior to FDR so that RAP contents are more constant

Quality Control and QualityQuality Control and QualityQuality Control and Quality Quality Control and Quality AssuranceAssurance

• In the field, nuclear density gauges have limited utility because relative density is notlimited utility because relative density is not correlated to relative strength for CTB materials

• Stiffness testing is recommended• UCS testing of field-mixed Proctor samples isUCS testing of field mixed Proctor samples is

recommended

CONCLUSIONCONCLUSION• FDR in conjunction with cement stabilization

is an effective method for reconstructing failed flexible pavementsfailed flexible pavements

• Cement slurry can be utilized in urban, residential areas to eliminate fugitive dust problemsproblems

• Cement content should be determined through laboratory testingg y g

• Microcracking should be utilized to minimize development of reflection cracking in asphalt surface coursessurface courses

THANK YOUTHANK YOU

W. Spencer Guthrie, Ph.D.D t t f Ci il d E i t lDepartment of Civil and Environmental

EngineeringBrigham Young UniversityBrigham Young University

801-422-3864guthrie@byu eduguthrie@byu.edu