Effects of Geosynthetic Reinforcement on the Propagation of Reflection Cracking

and Accumulation of Permanent Deformation in Asphalt Overlays

Khaled Sobhan, PhD

Florida Atlantic University, Boca Raton, FL, U.S.A., sobhan@civil.fau.edu

Michael Genduso, E.I.

Florida Atlantic University, Boca Raton, FL, U.S.A., mgenduso@fau.edu

Vivek Tandon, PhD., P.E.

The University of Texas at El Paso, El Paso, TX, U.S.A., vivek@utep.edu

Rehabilitating Deteriorated PCC Slabs

Deteriorated PCC becomes a stable sub-baseEliminates removal/delivery of fillCost effective and efficient

Problems Associated With AC Overlays- Reflection Cracking -

Causes of Reflection CrackingLoad-induced differential movementsHorizontal movementsCurling and warping of PCC slabs

EffectsPoor road surfaceWater infiltrationSusceptibility to further deterioration

Additional Concerns- Rutting -

Causes of Rutting BehaviorHeavy vehicle loadsSlow, stopping, and standing trafficCompounded by high temperatures

EffectsUneven road surfacePonding of waterAccelerated deterioration

Objectives

Quantify the effects of geosynthetic inclusion on fatigue life as well as permanent deformation behaviorIdentify the physical mechanisms involved with geosynthetic reinforcementMake recommendations for future testing

Test Equipment

Computer controlled MTS machineTime, load, number of cycles, and vertical deformation recorded by MTS systemDigital video acquisition focused on area of deformation

Test Specimen Setup

457.2 mm x 152.4 mm (18” x 6”)76.2 mm (3”) thick overlay13.3 mm (1/2”) plywood w/ 10 mm (0.4”) gap100.6 mm (4”) neoprene rubber base

Specimen Preparation

Samples created in two lifts

Steel mold

Hand roller compaction

Bulk specific gravity of 2.08

20.4 kN/m3

Materials Used

Coarse Aggregate – rhyolite with chert and limestone

Fine Aggregate – arroyo sand

Superpave PG-64-22 Binder

Tensar Biaxial Geogrid (BX 1500)

Types of Samples and Placement Configuration

All specimens created in 2 liftsUnreinforced control samplesTacked to bottomEmbedded in bottomEmbedded in middle

Test Procedure

Static TestsMonotonically increasingAvg Load Value of Cif was 1110 N

Cyclic/Fatigue Tests2 hzLR 0.2 – 1.2

Established static strength criteria

Sinusoidal loading to simulate field conditions

Failure Criteria

Cif initial – Cycles to initial crack formation

Cmf mature – Cycles to mature crack formation

Ctf terminal – Cycles to terminal crack formation

Fatigue Behavior

Reinforced samples lasted many more cycles to terminal cracking at all LR’sEmbedded samples showed the most significant performance improvement in terms of fatigue life

Analysis of PD

At LR up to 0.4 reinforced samples accumulated less PD over a longer lifeAbove LR of 0.4, reinforced samples accumulated slightly more PD over a significantly increased life

Cycle s

0

0.4

0.8

1.2

1.6

2

Per

man

ent D

eform

atio

n [c

m]

Cycle s

0

0.4

0.8

1.2

1.6

2

Per

man

ent D

eform

atio

n [c

m]

Cycle s

0

0.4

0.8

1.2

1.6

2

Per

man

ent D

eform

atio

n [c

m]

Cycle s

0

0.4

0.8

1.2

1.6

2

Per

man

ent D

eform

atio

n [c

m]

888 N Tests(LR = 0.8)

444 N Tests(LR = 0.4)

1110 N Tests(LR = 1.0)

1332 N Tests(LR = 1.2) S P E C IME N ID

U nreinforcedTackedEm beddedBottomEm beddedM iddle

Cycle s

0

0.4

0.8

1.2

1.6

2

Perm

anent D

efo

rmatio

n [cm

] 222 N Tests(LR = 0.2)

LR < 0.4

Performance of Reinforced Samples

1E+001

1E+002

1E+003

1E+004

1E+005

1E+006

1E+007

Cycle s

0

0.4

0.8

1.2

1.6

2

Pe

rma

ne

nt

De

form

atio

n [

cm] 222 N Tests

(LR = 0.2)

1E+002

1E+003

1E+004

1E+005

1E+006

1E+007

Cycle s

0

0.4

0.8

1.2

1.6

2

Per

man

ent D

efo

rmat

ion

[cm

]

444 N Tests(LR = 0.4)

S P E C IM E N IDU nreinforcedTackedEm beddedBottomEm beddedM iddle

Lasted at least one order of magnitude longerSustained about 40% less permanent deformation

LR > 0.4

Sustained 2 – 3 times more permanent deformationLasted up to 2 orders of magnitude longer

1E+002

1E+003

1E+004

1E+005

1E+006

1E+007

Cycle s

0

0.4

0.8

1.2

1.6

2

Per

man

ent D

efo

rmat

ion

[cm

]

888 N Tests(LR = 0.8)

1E+001

1E+002

1E+003

1E+004

1E+005

1E+006

1E+007

Cycle s

0

0.4

0.8

1.2

1.6

2

Per

man

ent D

efo

rmat

ion

[cm

]

1110 N Tests(LR = 1.0)

1E+001

1E+002

1E+003

1E+004

1E+005

1E+006

1E+007

Cycle s

0

0.4

0.8

1.2

1.6

2

Per

man

ent D

efo

rmat

ion

[cm

]

1332 N Tests(LR = 1.2)

S P E C IME N IDU nreinforcedTackedEm beddedBottomEm beddedM iddle

Performance of Reinforced Samples

Effects of Placement Location

Tacked samples performed poorlyDeeper embedment provides a stronger physical connectionProper embedment enables the materials to behave as a composite

Physical Mechanisms

Tacked specimenFrictional resistance onlyDebonding occurs early

Embedded specimenDirect resistance to tensionFrictional resistanceGeogrid remains effective longer

Quantification of Effects

Fabric Effectiveness Factor (FEF)Useful in quantification of both cracking and PD performance

)edunreinforc(

)reinforced(

tf

tf

c

cFEF

ConclusionsSpecimens with embedded geosynthetic reinforcement outperformed non-reinforced samples in terms of both fatigue life and rutting behaviorProper embedment is required to realize the benefits of geogridEmbedded geogrid provides physical reinforcement as well as energy absorptionDebonding, or the separation of geogrid from the AC layer, is the failure mechanismWith embedded specimens, this separation occurs gradually as shown by consistent rates of crack propagation and rutting

Recommendations for Future Testing

Investigate feasibility of various placement techniques used in practiceEvaluate and simulate the most efficient techniques in the labPerform a cost benefit analysis

AcknowledgementsDr. Khaled SobhanDr. Vivek TandonFlorida Atlantic University

Questions?