Sustainable Pavement Construction Utilizing Engineered ... · Aggregate Fine-grained subgrade soil...

2nd Int. Conf. on Transportation Geotechnics, Sapporo, Hokkaido, Japan – Sept. 10-12, 2012

Sustainable Pavement Construction Utilizing Engineered Unbound

Aggregate Layers

Erol Tutumluer, Professor of Civil EngineeringPaul F. Kent Endowed Faculty [email protected] of Illinois at Urbana-Champaign

2nd Int. Conf. on Transportation Geotechnics, Sapporo, Hokkaido, Japan – Sept. 10-12, 2012 2nd Int. Conf. on Transportation Geotechnics, Sapporo, Hokkaido, Japan – Sept. 10-12, 2012


Aggregates In High Demand• As the transportation infrastructure continues to age and

grow and the need for repairs, reconstruction and new construction grows, the demand for aggregates expands– The worldwide demand for construction aggregates is estimated to

be rising by 4.7 percent annually– In the US alone, nearly 1.9 billion metric tons were produced in

2009 at a value of approximately $17.2 billion (www.nssga.org)– Approximately 27% of the crushed stone and 23% of the total sand

and gravel produced annually in the US are used in pavement base construction


Role of Aggregate Base

Aggregate

Fine-grained subgrade soil

Wheel

Asphalt Concrete

Load Distribution

In unpaved roads, thinly surfaced low to moderate volume roads and thicker airport pavements, Unbound Aggregate Layers serve as major structural components of the pavement system


OWNERSHIP BITUMINOUS

/FUNCTIONAL UNPAVED SURFACE OR RIGID TOTAL

SYSTEM TREATMENT SURFACE

Total Rural 1,369,503 178,826 1,459,896 3.008,225

Total Urban 50,521 71,192 940,949 1,062662

Total Rural and Urban 1,420,024 250,018 2,400,845 4,070,887

Road System in the US by Surface Type (miles)

Public Roads46,893 mi of Interstate Highway116,573 mi of other National Highway System roads3,907,420 mi of other roads


Unbound Aggregate Layers Constructed by Transportation Agencies

96%

65%

24%

46%

(44)

(30)

(11)

(21)

0 10 20 30 40

0% 20% 40% 60% 80% 100%

Base course

Subbase course

Open graded drainagelayer

Pavement workingplatforms for subgrade

stability applications

Number of Responses

Percentage of Survey Respondents

46 survey respondents

Unbound Aggregate Pavement Base / Subbase Applications (46 respondents –NCHRP Synthesis 43-03 -2012)


Sustainable Practices Target• Better characterizing and utilizing unbound aggregate

layers by incorporating recent advances in materials characterization– Stress-dependent modulus behavior– Directional dependency (anisotropy) of layer stiffness– Moving wheel load effects

University of Illinois – FastCell


Resilient Modulus (MR) Distributions in the Base

Dep

th (i

n.)

0 20 40 60 80 100

4

10

15

20

25

30

Radial distance (in.)

AC Modulus = 400 ksi0

Subgrade

- Nonlinear

10000 psi 15000 20000 25000 28000

Subgrade MR = 6 ksi

10000

10000

10000

15000

1500020000

2800025000

MR 2318 0.64d

0.065


Anisotropic Moduli from UI-FastCell Testing

High Quality Aggregate Base

Tutumluer and Seyhan (1999) TRB Record No. 1687

Vertical Modulus

Horizontal Modulus


Sustainable Practices Target• Limiting the thicknesses of energy-intensive bound layers

– availability and cost of asphalt & Portland cement– high CO2 emissions

• Using of aggregates as a lower cost, green alternative (CO2 emissions – 4 for aggregates: 50 for HMA /ton AC)

• Using the highest quality materials in thinner layers

• Using local aggregates to reduce:– noise and air pollution– human disturbance– transport costs and transport energy requirements


Best Value Granular Material for Road Foundations

Minnesota DOT Research Project, 2008 - 2011

18.81

21.76

14.66 14.47

7.77 6.82

0

5

10

15

20

25

Base Subbase

Equi

vale

nt M

R(k

si)

High QualityMedium QualityLow Quality


MnDOT Project Research ObjectiveDemonstrate that locally available materials can be economically efficient in the implementation of the available mechanistic based design procedures in Minnesota through

MnPAVE Mechanistic-Empirical Pavement Design Method

Benefits(i) proper material selection & utilization (ii) aggregate layer thickness optimizations during

the design process based on mechanistic material properties related to performance

(iii) more economical use of the locally available aggregate materials in Minnesota


MR & Strength Values Linked to Quality

21.22 21.73

16.73 14.48

9.397.08

0

5

10

15

20

25

Base Subbase

Equi

vale

nt M

R(k

si)

6-in. AC


18.8121.76

14.66 14.47

7.77 6.82

05

10152025

Base Subbase

Equi

vale

nt M

R(k

si)

8-in. AC


29.65

22.6222.85

15.8113.18

8.28

05

101520253035

Base Subbase

Equi

vale

nt M

R(k

si)

4-in. AC


(Average MR)Unit: ksi

In some cases, the granular subbase moduli were higher!!!


MnPAVE Sensitivity Analysis MatrixCL

Wheel load = 9 kipType pressure = 80 psi

PG 58-34

High, Medium & Low QualityUnstabilizedAggregate Base

High, Medium & Low QualityAggregate Subbase

AsphaltConcrete

Base

Subbase

Subgrade - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Engineered Soil

Undisturbed Soil

3”- 6” - 9” -12”

6”- 12” - 18”

12” - 36”

(AC)4”- 6”- 8”

1 in. = 25.4 mm

Beltrami&

Olmsted

E = 2, 4, 7, 10 ksi

50% * E

20-year ESALs = 0.2, 0.6, 1.5, 3, 6 Million


Effect of Aggregate Material Quality

Subbase material quality significantly impacts rutting performance

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

5 10 15 20 25 30 35 40 45 50Pavement Service Life (Years)

H-H - Rutting

H-L - Rutting

L-H - Rutting

L-L - Rutting

L-HH-L

TRB Paper 11-3462 by Xiao, Tutumluer and Siekmeier

Base-Subbase

Base-SubbaseBase-SubbaseBase-Subbase

RuttingPerformance


Aggregate Quality Is Important!

Courtesy Texas DOT


UIUC Aggregate Image Analyzer

0 100 200 300 400 500Angularity Index

Fric

tion

Ang

le (o

)4041424344454647

Crushed 436

Gravel 200

50/50 Blend322

Shear Strength Properties From Rapid Shear Triaxial Tests

Aggregate Shape, Texture & Angularity

Rao, Tutumluer and Kim (TRB 2002)


Effects of Angularity & Surface Texture on MR

Pan, Tutumluer and Anochie Boateng (2006) TRB Record No. 1952

y = 152281e0.001x

R2 = 0.86

175000

200000

225000

250000

275000

200 300 400 500 600Composite AI Index

Res

ilien

t Mod

ulus

MR (

kPa)

Crushed granite-uncrushed gravel blendsCrushed limestone-uncrushed gravel blendsCrushed gravel-uncrushed gravel blendsSlag-uncrushed gravel blendsSandstone-uncrushed gravel blendsUncrushed gravel only

y = 166430e0.1848x

R2 = 0.91

175000

200000

225000

250000

275000

0.50 1.00 1.50 2.00 2.50 3.00

Res

ilien

t Mod

ulus

MR

(kPa

)

Composite ST Index

Crushed granite-uncrushed gravel blendsCrushed limestone-uncrushed gravel blendsCrushed gravel-uncrushed gravel blendsSlag-uncrushed gravel blendsSandstone-uncrushed gravel blendsUncrushed gravel only

• No fines, dry, and same gradation • All the specimens tested at the same voids content of 41%


Need for Sustainable Practices in Illinois• Illinois Subgrade Stability Manual and Illinois DOT (IDOT)

pavement design procedures do not differentiate between aggregate properties when recommending layer thickness

• IDOT Experimental Feature IL 03-01 indicated aggregate properties have a significant effect on their performance in subgrade replacement and subbase applications– 203-mm crushed aggregate layer performed as well as 305-mm. of

the same material– 203-mm crushed aggregate performed better than a 305-mm gravel

More economical (SUSTAINABLE) use of aggregates by either Reducing Layer Thickness

or Avoiding Aggregate Failures


ICT R27-1 Research Project Performances of crushed gravel, dolomite, & limestone aggregates studied in Illinois Engineered properties & studied behavior

% fines, plasticity of fines, aggregate shape/angularity, & moisture state

2006-2009


ICT R27-1 Lab Test Matrix• Aggregate type: (1) dolomite, (2) limestone, (3) gravel

• Particle shape & angularity quantified via imaging

• Fines content: 4%, 8%, 12%, & 16% passing sieve No.200

• Plasticity of fines: 0% (non-plastic mineral filler) & ~10%

• Moisture-density (compaction) condition: At optimum moisture content (OMC), 90% of OMC, and 110% of OMC (Standard Proctor Procedure, AASHTO T99)

4x2x3 factorial studied for each aggregate material


(3) gravel

(1) dolomite

(2) limestone

typical midrange IDOT CA-6 gradations

4%, 8%, 12%, & 16% fines

Engineered Gradations


ICT R27-1 Project Findings• The most important parameter at low fines contents was

found to be the aggregate type/angularity (crushed vsuncrushed)– Crushed aggregates showed higher tolerance to accommodate

increasing %fines (16-17% for crushed vs 12-14% fines for gravel)

• The second most important parameter to affect aggregate behavior was plasticity of fines

• High amounts of plastic fines at wet of optimum moisture conditions created the worst combination and destroyed the load transfer matrix, resulting in excessive permanent deformations

ICT R27-1 Study –Tutumluer, Mishra and Butt (2009)


y = 7.8302x0.5477R² = 0.9882

y = 12.61x0.5222R² = 0.9755

0

50

100

150

200

250

300

350

400

450

0 100 200 300 400 500 600 700 800

Axial R

esilien

t Mod

ulus (M

pa)

Bulk Stress (KPa)

Comparing Limestone and Gravel at 4% Fines, Wopt

G_0_NP_OptL_0_NP_Opt

Crushed Limestone Shows Consistently Higher MR values compared to Uncrushed Gravel

Effects of Crushed vs Uncrushed on MR

Mishra & Tutumluer (GeoShanghai 2010)


y = 4.2282x0.6477R² = 0.9835

y = 3.2801x0.6532R² = 0.9707

0

50

100

150

200

250

300

350

0 100 200 300 400 500 600 700 800

Axial R

esilien

t Mod

ulus (M

pa)

Bulk Stress (kPa)

Effect of % Fines on MR of Gravel with Non‐Plastic Fines

Higher fines results in lower MR and lower rate of stress hardening

16 % Fines 90% Wopt

4 % Fines 90% Wopt

Effects of Percent Fines on MR

Mishra & Tutumluer (GeoShanghai 2010)


More Drastic Effect on Permanent Deformation than Resilient Modulus

Comparing Dolomite specimens with 4% and 16% Nonplastic Fines Tested at Std Proctor Optimum Moisture Content



0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 100 200 300 400 500 600 700 800 900 1000

Perm

anen

t Def

orm

atio

n (m

m)

Number of Cycles

4% Fines8% Fines12% Fines16% Fines

Dolomite with NP fines at Wopt

D – 8% NPD – 4% NP

D – 12% NP

D – 16% NP

% Fines on Permanent Deformation p


Stabilizing effects


0

0.1

0.2

0.3

0.4

0.5

0.6

0 100 200 300 400 500 600 700 800 900 1000

Perm

anen

t Def

orm

atio

n (m

m)

Number of Cycles

Gravel with NP fines at 90% Wopt

G – 4% NP

G – 8% NPG – 12% NP

G – 16% NP

% Fines on Permanent Deformation p


No stabilizing effects


0

0.1

0.2

0.3

0.4

0.5

0.6

0 100 200 300 400 500 600 700 800 900 1000

Perm

anen

t Def

orm

atio

n (m

m)

Number of Cycles

Dolomite Non-Plastic 90% Wopt

Dolomite Non-Plastic 110% Wopt

Dolomite Plastic 90% Wopt

16% Fines Content

Plastic Fines are Bad Even at Low Moisture Contents

D – NP 90% wopt

D – NP 110% wopt

D – Plas 90% wopt

Effect of Plasticity of Fines on p



0

0.5

1

1.5

2

2.5

3

0 100 200 300 400 500 600 700 800 900 1000

Perm

anen

t Def

orm

atio

n (m

m)

Number of Cycles

Gravel 12% Non-Plastic FinesDolomite 12% Non-Plastic FinesGravel 12% Plastic Fines

Effect of Plastic Fines on p - 110% Wopt

Plastic Fines with wet conditions create the worst problems

G – 12% Plastic

G – 12% NPD – 12% NP


Shear Failure!!!


Aggregate Layer Design ConceptsRutting due to

base compaction

AggregateSoil

Rutting due to shear in base

AggregateSoil

b

b/3

b

b/3

• Resist shear deformation within the aggregate base– Crushed, angular stone for higher stability/strength

– Proper compaction!!!


ICT R27-81 Research Project

Construct Engineered Aggregate Test Sections over Soft Subgrade

Evaluate Performance through Accelerated Testing Field Characterization

DCP, LWD, GeoGauge, Nuclear, and Handheld GPR


ATREL Full-Scale Test Sections

University of Illinois, ATREL Facility

Cell 3 Cell 4

Cell 2 Cell 5

Cell 1 Cell 6

Basin Flow Direction towards West

In total, 6 cells constructed in 3 test strips, 237.5 ft each

The test strips separated by 12 ft

Test Cells Constructed for APT Testing

Each Cell Had 3 Test Sections

122.5’ 22.5’10’10’ 15’ 15’ 15’

T T2 310’ 10’

130ft ATLASCrawlerPlacement

TransitionZoneTestSectionSpeedStabilizationZone

14” 14” 12” 8” 8”8” 12” UnboundAggregateLayer

CBR = 3 Subgrade top 12” (305 mm) tilled & compacted

18ft

Transversedrainsinstalled Test cell 5 had a subgrade of CBR 6 with aggregate layers of thicknesses 254 mm, 203 mm, and 152 mm respectively

Topview

Profileview


Subgrade Soil Characteristics

Soil is CL-ML

OMC = 10.2%MDD = 19.9 kN/m3 (126.6 pcf)

Standard Compactive Effort


Tilling Stage-I to mix soil from top 305 mm


Moisture Content Determination with Microwave


Adding Water to Achieve Target CBR


DCP Testing – CBR Profile

LOG (CBR) = 0.84 – 1.26 * LOG (PR)


Light Weight Deflectometer (LWD), GeoGauge, & Electrical Density Gauge (EDG) on Finished Subgrade


Asphalt Prime Coating for Moisture Retention


Subgrade Pressure Cell Installation along Wheel Path


Aluminum Paint & Foil at Subgrade Interface


Aggregate Placement & Compaction

Aggregate Bases Constructed

Cell Number Subgrade CBR Material Type Aggregate Layer Thickness (in.)

1 3 Uncrushed, HighFines, Non-Plastic 8, 12, 14

2 3Crushed, Low Fines, Moderately Plastic

8, 12, 14

3 3 Crushed, High Fines, Non-Plastic 8, 12, 14

4 3 Crushed, High Fines, Non-Plastic 8, 12, 14

5 6Crushed, Low Fines, Moderately Plastic

6, 8, 10

6 1 Large Aggregate topped with CA-6

12-in. thick large aggregate overlain

by 6-in. CA-6


Accelerated Testing & Loading System - ATLAS

10 kip (44 kN), Single Wheel Load - 110 psi (759 kPa)

Tire Pressure

22.5’ 22.5’Wheel Span = 85 feet

(constant Speed Achieved for 65 feet)



Rut Measurement at Different Passes


Investigation of Failure Modes by Trenching


Cell 1 Uncrushed Gravel Test Sections

Section1(14”‐356mm)

Section2(12”–305mm)

Section3(8”203mm)


Measured Subgrade Stress Levels (Cell 1: N = 2)

3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8020406080100120140160180200

Time(sec)

SubgradeStre

ss(kPa)

305mmAggregateLayer203mmAggregateLayer169.8kPa(24.6psi) 195.5kPa(28.4psi)


Excavated Trench Photos Showing Surface and Aggregate-Subgrade Interface Deformations

356-mm (14-in.) thick aggregate layer

Subgrade displacement laterally offset from wheel path

Gravel undergoing shear failure


Cell 1 Subgrade – LWD, GeoGauge & DCP

Section3subgradewassignificantlystrongerthantheothertwosections


Cell 1: Uncrushed Gravel Layer Moduli

GeoGuagemeasuredmodulishowsimilartrendasinsubgrade

LWDresultssignificantlyaffectedbysubgradeduetogreaterdepthofinfluence

Notethehighercompactionlevelsachievedonstrongersubgrade


Laboratory Assessment of Aggregate Behavior

ϕ=150mm;H=150mm

1000loadapplications

s =104kPa (15psi)

d =104kPa (15psi)

1d

s

s s

Uncrushed gravel underwent significantly higher permanent deformation


Custom Designed GPR Track for Rut- Measurement

Ground Penetrating Radar (GPR) Measurements Aggregate vs. Subgrade Rutting


Cell 4 - Limestone - 168 passes

Section 1 (14” 356 mm)



Rutting primarily in subgrade (wheel path directly corresponds to subgrade dip)


‐40 ‐30 ‐20 ‐10 0 10 20 30 40

‐40

‐20

0

20

40

60

80

100

120

LateralPosition(in.)N<<‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐>>S

RutDepth(mm)

Section1@N=1

Section1@N=10

Section1@N=55

Section1@N=100

Section1@N=168

Cell 4 – Limestone (356 mm) – Rut Development Due to Subgrade


‐40 ‐30 ‐20 ‐10 0 10 20 30 40

‐80

‐60

‐40

‐20

0

20

40

60

80

100

120

LateralPosition(in.)N<<‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐>>S

RutDepth(mm)

Section1@N=1

Section1@N=10

Section1@N=47

‐40 ‐30 ‐20 ‐10 0 10 20 30 40

‐40

‐20

0

20

40

60

80

100

120

LateralPosition(in.)N<<‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐>>S

RutDepth(mm)

Section1@N=1

Section1@N=10

Section1@N=55

Section1@N=100

Section1@N=168

Uncrushed Gravel

Crushed Limestone

Early and Sudden Shear Failure in the Gravel Layer

Progressive Failure of the Subgrade


Cell 3 – Dolomite Section 1 (356 mm)






Cell 6 - Large Sized AggregateConstructed on CBR =1 Subgrade

Mishra and Tutumluer (2nd ICTG, Hokkaido 2012)

2nd Int. Conf. on Transportation Geotechnics, Sapporo, Hokkaido, Japan – Sept. 10-12, 2012 2nd Int. Conf. on Transportation Geotechnics, Sapporo, Hokkaido, Japan – Sept. 10-12, 2012

-48 -40 -20 0 20 40 48

100

80

60

40

20

0

-20

-40

-48 -40 -20 0 20 40 48

100806040200

-20-40-60

Rut

Dep

th (m

m)

Lateral Position (in.)

1 Pass 10 Passes 33 Passes 63 Passes

Rut

Dep

th (m

m)

Lateral Position (in.)

1 Pass 10 Passes 33 Passes 63 Passes 100 Passes 159 Passes

Section 2Manteno (3-5 in. size)

North Wheel Path(without Geotextile)

South Wheel Path(with Geotextile)

Effect of Woven Geotextile

Mishra and Tutumluer (2nd ICTG, Hokkaido 2012)

New ICT R27-124 Research Project(8/2012 – 7/2014) Evaluation of “Aggregate Subgrade” Materials Used as Pavement Subgrade/Granular Subbase “Aggregate Subgrade” materials – Large-sized virgin aggregates,

recycled concrete aggregate (RCA), reclaimed asphalt pavement (RAP), or combinations

Develop characterization techniques Evaluate field performances through accelerated full-scale testing

Unsurfaced working platform application Asphalt surfaced low volume pavements


Mechanisms contributing to failure of unsurfaced pavements change significantly based on aggregate quality

Uncrushed gravel with high fines underwent internal shear failure

Pavement sections with crushed aggregates failed primarily due to shear movement of the subgrade

Effect of compactive effort was critical to layer stability when crushed aggregates lad low (< 5%) fines content

ICT R27-124: Lessons Learned


Benefits to Illinois DOT• Anecdotal evidence based on years of experience with

the different types of aggregate available throughout the state suggests that IDOT uses approximately 1.7 million metric tons of aggregate in improved subgrade applications annually

• With an average cost per metric ton of $14, IDOT spends approximately twenty-nine million dollars per year for aggregate improved subgrades

More economical (SUSTAINABLE) use of aggregates by either Reducing Layer Thickness

or Avoiding Aggregate Failures


• replacing conventional aggregates with more marginal natural materials where possible

• replacing conventional aggregates with waste / by-product / residue / recycled materials (RAP, RCA, etc.)

Sustainable Practices Target

67.4% 80.4%

21.7%4.3%

Reclaimed AsphaltPavement (RAP)

Recycled ConcreteAggregates (RCA)

Other (BlastFurnace Slag, GlassCullet, etc.)

None of these

Unbound Aggregate Pavement Base /Subbase Applications (46 respondents –NCHRP Synthesis 43-03 -2012)

http://ict.illinois.edu

ICT R27-27 Research Project

TRB 2010 Paper by Deniz, Tutumluer & Popovics 2nd Int. Conf. on Transportation Geotechnics, Sapporo, Hokkaido, Japan – Sept. 10-12, 2012

Target Sustainable Aggregate Production

• Research that leads to advances in aggregate technology and innovative products and applications needed to target specific transportation projects

– matching future regional needs with availability of resources – conservation of water and energy in aggregate production and

applications – making beneficial use of micro-fine material – a byproduct

of quarry operations

New ICT R27-125 Research Project(8/2012 – 7/2014) Sustainable Aggregates Production -- Green Applications for Aggregate By-products Investigate and develop a method(s) to utilize product fractions currently

being wasted (approximately 8% of mined & less than ¼ in.) to lower overall costs to IDOT and extend the use of natural aggregate resources

Modify existing specifications or Develop new specifications/mixes to utilize “higher fines materials” PHASE I: STUDY OF ILLINOIS AGGREGATE BY-PRODUCTS PHASE II: GREEN APPLICATIONS FOR AGGREGATE BY-PRODUCTS


Sustainable Practices Also Target• Adapting and utilizing best practices of road

construction in European and other foreign countries, i.e. South Africa, Australia, etc.

Example: South African Inverted Pavements

High Quality Well Graded Crushed Stone (G1)

• Plasticity Index zero toslightly plastic

• Compacted utilizing a finalslushing process to adensity specification of 86to 88% of “solid density”(~ 100 to 105% ModifiedProctor – AASHTO T180)


Subgrade

Cement Treated Subbase (3-5% cement)

High Quality Crushed Aggregate Base

Asphalt Concrete3-5 cm

15 cm

FHWA Report FHWA-PL-03-001http://international.fhwa.dot.gov/paveprestech/techdoc.htm

15-20 cm

South African StrategyInverted Pavement Design



• Need to do more with less $ while maintaining performance

• Inverted Pavement Systems are green and sustainable Make optimum use of the compressive

characteristics unbound aggregates Better compaction of aggregate placed over

stabilized Less cracking & improved fatigue life due to

lower tensile stresses at bottom of asphalt layer Minimize reflective cracking potential of lightly

(3-5%) cement stabilized subbase Protect subgrade from wheel load stresses Result: Improved Pavement Performance

Why Inverted Pavements?


Thank you!..

Sustainable Pavement Construction Utilizing Engineered ... · Aggregate Fine-grained subgrade soil...

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