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Moisture Damage andBenefits of
Liquid Anti-stripping Additives (LAS)
by
Sundaram Logaraj and James N Anagnos
June 23, 2005
More of a problem in recent years
Moisture Damage or Strippingin Asphalt Pavements
Moisture Damage SurveyGary Hicks -1985
34 States…..yes
12 States…..no
4 States…..no response
Survey – Gary Hicks &Tim Aschenbrener* – 08/2002
Problem Hicks 1985
Aschenbrener 2002
Yes 34 44
No or Rarely 12 9
No Response 4
*Colorado DOT
Tim Aschenbrenner Survey, CODOT - 2002
Treatment
Lime Lime or liquidsLiquidsLiquids seldomNo or rarely
Factors to Minimize Moisture Damage*
1. Good Mix Design- Specifications- Aggregates- Testing for moisture damage
and suitable treatment
Moisture Sensitivity Subcommittee,Asphalt Institute 2002
Factors to Minimize Moisture Damage*
2. Field and Construction Practices– Avoid stockpile segregation– Proper drying of aggregate– Proper compaction to required densities
– Adequate pavement drainage
Moisture Sensitivity Subcommittee,Asphalt Institute 2002
Premature Failure of Asphalt Overlays From Stripping:
Case Histories
ByPrithvi S. Kandhal
Ian Rickards
Pennsylvania Turnpike (Cumberland County)
• Work performed (Nov. 1994)– existing pavement milled to 40 mm depth– replaced with 9.5 mm size dense HMA
• Premature distress observed (early 1995)• Pavement inspected (July 1996)
Interstate 40 in Oklahoma
• Work performed (October 1990)– 90 mm cold milling– placed 70 mm thick Type “F” mix (25 mm
top size) in both EB and WB lanes
Interstate 40 in Oklahoma
– placed 19 mm thick OGFC in EB lanes– placed 25 mm thick dense “E” mix in WB
lanes because “F” mix was taking in water• Potholing observed in EB lanes• Pavement inspected in September 1991
Will Rogers Pkwy in Oklahoma
• Work performed (June 1992)– mill existing 20 mm thick OGFC– replace with 25 mm thick dense
HMA (Type B)
Will Rogers Pkwy in Oklahoma
• Potholing observed in July 1992• Inspected in July 1992
Hume Highway in NSW, Australia
• Overlay work performed (June 1993)– 80 mm thick dense HMA (25 mm mix)– 35 mm thick dense HMA (12.5 mm
mix)–30 mm thick OGFC
Hume Highway in NSW, Australia
• Potholing observed in SB lanes (February 1995)
• No potholing in NB lanes (?)
Adhesion and Stripping
• What are Adhesion and Stripping• Contributing factors• What are Anti-stripping Additives• How do they prevent stripping• Adhesion Vs Cohesion• What is being measured by various stripping
tests
Adhesion and Active Adhesion
Adhesion:"The process of forming chemical bond between the
asphalt film and the aggregate surface”
Active adhesion:"Coating and formation of chemical bond
in the presence of water”
Stripping
Aggregate
"Stripping is the breaking of the bond betweenaggregate and asphalt by the action of water.”
Note about cohesive failure – Pore pressure
Asphalt
General Asphalt Composition- Mixture of Hydrocarbons- Also contain small amounts of acidic and basic
Acid value (mg KOH/g)
Base value (mg KOH/g)
Naphthenic bitumen (Asphalt) 1.5 to 5 0 to 1
Paraffinic bitumen (Asphalt) 0 to 1 0 to 1
Morgan, P., Mulder, A., The Shell Bitumen Industrial Handbook, p 86-88, 1995
organic compounds
Aggregate Type
SurfaceProperties
AsphaltProperties
Quartzite Acidic
Granite AcidicBasic ingredientsusually present
in lesser amountsSandstone Acidic
Limestone Alkaline AcidicIngredients
Aggregate and Asphalt Properties
• Aggregates with a high CaCO3 content will not pass polish test• Fines are siliceous material (sand) and the stripping in the fines
is more of a problem
Stripping in Asphalt PavementsCoating without chemical bonding
Moist Aggregate Dry Aggregate
Osmosis of Water Through Asphalt
• Film thickness• Viscosity• Pressure• Composition of asphalt
Morgan, P., Mulder, A.,The Shell Bitumen Industrial Handbook, 1995
Stripping
Static immersion test at 60°C
Ways to Improve Surface Interaction (Adhesion)
Aggregate
Asphalt
Interaction of Acidic Aggregates and Asphalt With Alkaline Amine
Components - LAS--SiOH + RNH2 --SiO- RN+H3
Polar End Non-Polar Hydrocarbon ChainGroup
H
HN
Asphalt Aggregate Interaction in the Presence of Suitable Compounds in Asphalt
Aggregate
AsphaltChemicalBonding
OH+H2 NSiAnti-StrippingAgentSilicious
Aggregate
Si O H3 N- +
Coating with chemical bonding
Boil Test Results
Aggregate (siliceous)– 20% Type C Gifford Hill– 40% Type D Gifford Hill– 24% Screenings GH– 13% Sand GH– 3% Fines Smithstone
Asphalt– 4.7% Coastal AC-20
Control 0.5% LAS0
20
40
60
80
100% Retained coating
• Mechanical Test– Indirect Tensile Strength
• 50 mm/min. displacement rate• Peak Load at Failure
Tensile Strength
Tensile Strength Ratio Test Results
Control 0.5% LAS0
20
40
60
80
100
120 Dry Str. psi Wet Str. psi%TSR
90% Saturation
Hamburg WheelHamburg Wheel--Tracking TestTracking Test
Material Mix Additive, Cycles Def, BinderID Type % of Asphalt mm
(Granite)Control C ---- 16,000 12.90 PG 76-22LAS C 0.75 20,000 6.40 PG 76-22
(Granite)Control C ---- 14,300 12.50 PG 70-22SLAS C 0.75 20,000 5.60 PG 70-22S
Hamburg WTT Results PavTex Engineering
Typical Test Results, AASHTO T-283
Nova Scotia Granite
0.6
0.7
0.8
0.9
1
1.1
1.2
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Dosage (% by weight of mix)
TSR
LAS 1 LAS 2 Lime
Important test methods for Hot-mixAnd Possible properties evaluatedby various tests
Test Methods Observed Properties
Boil test, Static immersion
Surface interaction betweenaggregate and asphalt (Adhesion)
Lottman type testsAnd Wheel Tracking
tests
Surface interaction (Adhesion)+
Hardening effect of the asphalt and mix (cohesion?)
Observations1. Asphalt Aggregate interaction (Adhesion and
Stripping) depends on the type of aggregate and asphalt composition
2. There is a lack of interaction (Adhesion) in most mixes and can be improved by proper treatment
3. Adhesion and stripping is a surface phenomenon
4. Maybe a combination of stripping tests should be used to evaluate both surface interactions and the mix properties (cohesion?)
AC TO DRUM MIXER
LIQUID ANTI-STRIP LINE
ANTI-STRIP PUMP
HEAT TRANSFER OIL LINES
LAS Injection System
Field System
AC LINE
CUTOFF VALVE
INJECTOR PORT STATIC MIXER
HEATING OIL
HEATING OILFLOWMETER
ANTI-STRIPSTORAGETANK
TEMP.REGULATOR
HEATING OIL
HEATING OIL
STRAINER
Block Diagram
Anti-Stripping Additive Cost Per Ton of Hot Mix
Bitumen, lbs 100
Additive, % 0.5
Additive, lbs/Ton 0.5
Additive cost, $/Ton ~$0.35/TonLAS additive cost a small fraction compared to the
cost of HM (~ 1% of the cost of Hot-Mix)
Benefits of LiquidAnti-Stripping Additives
1. Effective and prolong the life of the pavement
2. Allow wider selection of aggregates3. Inexpensive4. Easy to use
Thank You!
Questions???