INTERFACE SHEAR STRENGTH CHARACTERISTICS OF EMULSIFIED TACK COATS Nachiketa Patel Graduate Student Department of Civil & Environmental Engineering Louisiana Transportation Research Center Louisiana State University 51st Annual International Highway Engineering Exchange Program Conference September 27 - October 1, 2009 San Antonio, Texas
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INTERFACE SHEAR STRENGTH CHARACTERISTICS OF
EMULSIFIED TACK COATS
Nachiketa PatelGraduate Student
Department of Civil & Environmental EngineeringLouisiana Transportation Research Center
Louisiana State University51st Annual International Highway Engineering Exchange Program Conference
September 27 - October 1, 2009San Antonio, Texas
Presentation Outline
IntroductionPurpose of Applying Tack CoatsBackgroundObjectivesScopeMethodologyDiscussion of ResultsSummary and Conclusion
What is a Tack Coat?A light application of asphalt on an existing non absorptive surface
Three TypesAsphalt emulsionCutback asphaltAsphalt cement
Ensures bond between surface being paved and the overlying course
Why Tack Coat is used?Monolithic structurewithstand/transfer shear stresses from traffic loading
Lack of bond between the wearing and binding layersCause slippageactivate distress mechanisms and rapidly lead to total failure
Background
Experience and empirical judgmentSelection of tack coat material type, application rate, and placement
Quality control and quality assurance testing
rarely conducted resulting in the possibility of unacceptable performance at the interface, premature failure.
BackgroundNational Co-operative Highway Research Program Project 9-40
Optimization of Tack Coat for HMA PlacementStudy the influence of tack coat type and application rate on the bond strengthBonding characteristics testingDirect Shear Test
Objectives
Evaluate the interface shear strength of emulsified tack coats under a wide range of testing conditions commonly encountered in field applications
effect of emulsified tack coat type;effect of application rate; effect of dust;effect of wetness (rain).
ScopePavement surface types:
existing HMA, new HMA, milled HMA, and PCCSurface Condition:
Influence of Material/Application RateSurface Condition: Clean/Dry
Confinement: 0 psi
0102030405060708090
100In
terf
ace
Bond
Str
engt
h, p
si
0.031 0.062 0.155Residual Application Rate, gsy
CRS-1SS-1hTrackless
Influence of Material/Application RateSurface Condition: Dirty/Dry
Confining Pressure: 0 psi
0
10
20
30
40
50
60
70In
terf
ace
Bo
nd
Str
en
gth
, p
si
Clean Dirty Clean Dirty Clean Dirty
Cleanliness
DryWet
0.031 gsy 0.062 gsy 0.155 gsy
Influence of Surface ConditionTack Coat Material: SS-1h
Confinement: 0 psi
0
10
20
30
40
50
60
70In
terf
ace
Bo
nd
S
tre
ng
th,
psi
Dry Wet Dry Wet Dry Wet
Wetness
CleanDirty
0.031 gsy 0.062 gsy 0.155 gsy
Influence of Surface ConditionTack Coat Material: SS-1h
Confinement: 0 psi
0
10
20
30
40
50
60In
terf
ace
Bo
nd
S
tre
ng
th,
psi
0.031 0.062 0.155
Residual Application Rate, gsy
CleanDirty
Influence of Surface Condition/Application RateTack Coat Material: CRS-1
Surface Condition: Dry
Confinement: 0 psi
0
20
40
60
80
100
120In
terf
ace
Bo
nd
S
tre
ng
th,
psi
0.031 0.062 0.155
Residual Application Rate, gsy
CleanDirty
Influence of Surface Condition/Application RateTack Coat Material: Trackless
Surface Condition: Dry
Confinement: 0 psi
ConclusionEffect of Tack Coat Material on Interface Shear Strength
Trackless is strongest followed by SS-1h and CRS-1All residual application rates
Effect of Application Rate on Interface Shear StrengthHighest strength exhibited at high rate
All materials
Effect of Dirt on Interface Shear StrengthPresence of dirt exhibits greater interface strength than clean conditions Some cases, no difference statistically
Effect of Wetness on Interface Shear StrengthNo statistical difference between dry and wet conditions Some cases, wetness exhibits higher strength
NCHRP– Project 9-40
» Optimization of Tack Coat for HMA Placement– Technical Review Panel