TRAFFIC ENGINEERING STUDIES

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Effect of Anti-Stripping Agents in
Asphalt-Aggregate Interactions
by
Dr. Mohammad Nahid Siddiqui Prof. Mohammad Farhat
Ali Eng. Mirza Ghouse Baig
Department of Chemistry King Fahd University of
Petroleum Minerals Dhahran, 31261 Saudi Arabia
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Objective

• To Study the effects of antistripping agents
  on asphalt-aggregate mixtures using
  Adsorption-desorption and IR test methods.

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Presentation OutLine

• Introduction and Background
• Moisture Damage
• Anti-Stripping Additives
• Experimental
• Asphalt Aggregate Properties
• Adsorption-desorption Testing
• Results and Discussion
• Conclusions

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Moisture Damage
Significance A high degree of stripping was
detected in between 25 to 50 on various pavement
sites inspected in Saudi Arabia during late
1990.
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Moisture Damage
Main Focus To Improve aggregate asphalt bonding.
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Antistripping Additives

• Organic Small Molecules
• Amines, Silanes
• Polyamines, Amidoamines
• Inorganic Aggregate Treatments
• Hydrated Lime
• Portland Cement
• Polymeric Agents
• Functionalized Butadiene
• Styrene-Butadiene

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Introduction Background

• Asphalt-aggregate interactions in pavements
• directly affect the adhesion bond strength.
• Chemistry of asphalt surface chemistry of
• aggregates particularly affects the
  interactions.

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Asphalt-Aggregate Bonding
Aggregate
Asphalt

• Wettability
• Viscosity (temp)
• Composition (oxygen)
• Durability

• Surface chemistry (mineral composition)
• Surface texture
• Porosity
• Surface condition (cleanliness, moisture)

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Effect of Surface Film on Aggregate Coverage
(after Hubbard)
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Effect of Aggregate Surface on Texture Adhesion
(after Hubbard)
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Contact Angle in an Aggregate, Asphalt and Water
System (after pfeiffer).
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Asphalt-Aggregates Bonding
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Effect of Polarity on Adhesion (after Hubbard)
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Molecular Orientation (after Hubbard)
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Experimental Work

• Asphalts from Two Refineries
• Riyadh Refinery (RY)
• Ras Tanura Refinery (RT)
• Aggregates from Three different regions
• Taif
• Eastern Province (EP)
• Riyadh
• Three Anti-Stripping Agents
• Iterlene IN/400-S
• Cecabase 260
• Polyram L200

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Elemental Analysis (wt ) of RT and RY Asphalts
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Physical Characteristics of RT and RY
Asphalts
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Aggregates

• Limestone (Eastern Province)
• Basalt (granite) (Western Province, TAIF)
• Limestone (Riyadh Area)

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Properties of Aggregates
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Anti-Stripping Agents
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Chromatography Column
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Adsorption Equation
Ai VC (A1 A2)/50 A1
where,
Ai initial adsorption, mg/gm V volume of
solution in the column at the time A2 is
measured, ml 00.0 ml C initial concentration
of asphalt in solution, gm/l 1.2 g/l A1
first absorbance reading A2 second absorbance
reading after 6.5 hours
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Results Discussion
Initial and Net Adsorption Values for
Riyadh Asphalt with Cesabase-260
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Results
(Contd)
Initial and Net Adsorption Values for Ras-Tanura
Asphalt with Cesabase-260
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Results
(Contd)
Initial and Net Adsorption Values for Ras-Tanura
Asphalt with Iterlene 400-S
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Results
(Contd)
Typical Comparison on Riyadh asphalt-aggregate mix
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Results
(Contd)
Typical Comparison on Ras Tanura
asphalt-aggregate mix
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Conclusions

• Based on the results of this study following
  conclusions were drawn.
• Type of Aggregates has significant effect on
  absorption behavior.
• Different aggregate showed different adsorption
  for same asphalt.
• Moisture sensitivity for each asphalt-aggregate
  combinations depend on the type of antistripping
  agent used.

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Conclusions
(Contd)

• No single antistripping agent could work with all
  three aggregate types studied. Therefore,
  selection of proper antistripping agent will be
  unique for each project.
• Among the three antistripping agents studied
• Cecabase was found to be more effective with
  Riyadh asphalt mixtures.
• Iterlene was found to be more effective with Ras
  Tanura asphalt mixtures

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Recommendations

• More fundamental work is needed on the chemistry
  of asphalt-aggregate interaction for a better
  understanding of the chemical compositional
  factors that control asphalt properties..

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Thank you