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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., [email protected]
Michael Genduso, E.I.
Florida Atlantic University, Boca Raton, FL, U.S.A., [email protected]
Vivek Tandon, PhD., P.E.
The University of Texas at El Paso, El Paso, TX, U.S.A., [email protected]
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Rehabilitating Deteriorated PCC Slabs
Deteriorated PCC becomes a stable sub-baseEliminates removal/delivery of fillCost effective and efficient
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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
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Additional Concerns- Rutting -
Causes of Rutting BehaviorHeavy vehicle loadsSlow, stopping, and standing trafficCompounded by high temperatures
EffectsUneven road surfacePonding of waterAccelerated deterioration
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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
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Test Equipment
Computer controlled MTS machineTime, load, number of cycles, and vertical deformation recorded by MTS systemDigital video acquisition focused on area of deformation
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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
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Specimen Preparation
Samples created in two lifts
Steel mold
Hand roller compaction
Bulk specific gravity of 2.08
20.4 kN/m3
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Materials Used
Coarse Aggregate – rhyolite with chert and limestone
Fine Aggregate – arroyo sand
Superpave PG-64-22 Binder
Tensar Biaxial Geogrid (BX 1500)
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Types of Samples and Placement Configuration
All specimens created in 2 liftsUnreinforced control samplesTacked to bottomEmbedded in bottomEmbedded in middle
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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
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Failure Criteria
Cif initial – Cycles to initial crack formation
Cmf mature – Cycles to mature crack formation
Ctf terminal – Cycles to terminal crack formation
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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
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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)
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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
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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
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Effects of Placement Location
Tacked samples performed poorlyDeeper embedment provides a stronger physical connectionProper embedment enables the materials to behave as a composite
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Physical Mechanisms
Tacked specimenFrictional resistance onlyDebonding occurs early
Embedded specimenDirect resistance to tensionFrictional resistanceGeogrid remains effective longer
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Quantification of Effects
Fabric Effectiveness Factor (FEF)Useful in quantification of both cracking and PD performance
)edunreinforc(
)reinforced(
tf
tf
c
cFEF
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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
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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
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AcknowledgementsDr. Khaled SobhanDr. Vivek TandonFlorida Atlantic University
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Questions?