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???