Materials Selection Chapter 3 Chip Seal Binders Seal
Materials Selection Chapter 3
Chip Seal Binders • Seal existing pavement More binder the longer the seal will protect underlying HMA • Bond to aggregate • Bond to pavement
Chip Seal Aggregate • Skid resistance • Limit polishing • Control abrasion • Protects the binder from traffic
Binder Storage Considerations • Minimize risk of overheating • Minimizing heat loss • Seek advice from your supplier!!!
Aggregate Selection Aggregate Defines: • • • Seal Type Binder Construction Procedures
Aggregate Selection Factors United States • Availability • Transportation • • Method Cost Favor local sources Emphasize Lower Cost Overseas • • Life Cycle Analysis Transportation • • • Up to 500 miles Performance Longevity Emphasize Quality
Aggregate Physical Properties • Grading / Particle Size: Determines mixture physical characteristics that affect fatigue resistance • Cleanliness: Dusty aggregates causes adhesion problems in chip seal.
Aggregate Physical Properties Hardness / Abrasion Resistance: Must resist crushing, polishing, degradation, and maintain skid resistance Particle Shape and Surface Texture: Cubical, not elongated for better interlock and internal friction Absorption: Excessive absorption of binder can result in raveling
Flat Chips
Flat Chips
Dense Graded Vs. Single Size! Dense Graded Single Size
Dense Graded Vs. Single Size! 100 PERCENT PASSING 90 80 70 60 dense graded single sized 50 40 30 20 10 0 0 0. 1 0. 2 0. 3 0. 4 SIEVE SIZE, inches 0. 5 0. 6
Single Sized Aggregate Advantages of Single Sizing • More uniform height • Weighs less per cubic foot 47% passing the #4 95. 7 lbs/ft 3 8% passing the #4 84. 5 lbs/ft 3 • More room for binder Increased Voids
Single Sized Aggregate Advantage Dense Graded (FA-3) $22. 80 ton • 18. 5 lbs/yd 2 needed = $0. 21 per yd 2 Single Sized • 14. 5 lbs/yd 2 needed = $0. 16 per yd 2 Can pay $6. 30 a ton more for single sized aggregate at the same square yard cost as dense graded aggregate.
Aggregate Performance Best Performance when: • • • Single sized Minimum fines Clean Free of clay Cubical • • • Crushed faces Abrasion < 30% Binder compatible Damp for emulsions Dry for hot binders
Aggregate Testing • Sieve Analysis: <1% passing No. 200 • ASTM D 3319: Polished Stone Value (PSV) 44 to 48 • ASTM C 131: LA Abrasion Test <30% • Percent Fracture: 75% with at least 2 fracture faces.
Aggregate Types Type North America AU, NZ, SA, UK Limestone 37% 13% Quartzite 13% 38% Granite 35% 38% Trap Rock 13% 25% Sandstone 10% 25% Natural Gravel 58% 25% Greywacke, Basalt 4% 88%
Aggregate-Asphalt Compatibility • Asphalt must preferentially wet, and bond to aggregate surface • Poor compatibility leads to: Stripping Disintegration Stone loss • No reliable chemical indicators for stripping
Binder Properties • No bleeding when applied properly • Fluid enough to cover surface • Viscous enough to prevent puddling or pavement runoff • Develop adhesion quickly and retain aggregate
Types of Binders • Standard Paving Asphalt Aged Residue (AR) grade • Asphalt Emulsion (modified, unmodified, rejuvenating) • Polymer-Modified Asphalts Including PBA grades • CMCRA Chemically-Modified Crumb Rubber Asphalt and Modified Binder (MB) grades • Cutbacks
Hot Asphalt Cement
Asphalt Emulsion 62% Residual
Cut Back Asphalt 85% Residual
Binder Selection Influenced by: • Surface Temperature • Aggregate • Construction Climate • Performance Characteristics
Asphalt Cement Binders Advantages • Open earlier to traffic • Appropriate for high surface temperatures • Good stone retention • Can be reheated or stored at high temperatures w/o adverse effects Disadvantages • • High temperatures High energy consumption Safety concerns Sensitive to aggregate moisture
Emulsion Terminology “Emulsions lie between solutions and suspensions. An asphalt emulsion is asphalt particles dispersed in water. It is not a solution because the oil and water are susceptible to separation. The oil is stabilized with an emulsifier to keep it dispersed. ” “Breaking (curing) is used to describe the process by which the asphalt expels the water and dries to an integral film / layer on the aggregate. ”
Types of Asphalt Emulsions • Anionic • Cationic +
Emulsion Particle Coalescence Particles begin to stick together (Flocculation) Particles coalesce to form larger particles
Emulsion Break & Cure Stages
Asphalt Emulsion Binders Advantages • Lower energy use • Low application temperatures • Reduced emissions • More amenable for use at remote sites • Lower cost per increase in useful service life • Suitable for treating a wide array of distresses Disadvantages • Timing the “break” with aggregate spreading • Improper and prolonged storage may result in phase separation, coalescence • Longer cure time than hot applied cements
Emulsion Handling Temperature • Flocculation and coalescence may occur if too cool • If too hot, water will evaporate prematurely resulting in coalescence and premature breaking • Binder Suppliers are best source of heating information!
Emulsion Tank Storage • Circulate slowly at regular intervals • Circulation frequency depends on weather and storage time • Flush pumps after use but not into tank • Warm lines and pumps as necessary • Do not leave lines partially-filled w/emulsion
High Float Emulsions • • • More “forgiving” Allow for thicker residual asphalt film Minimize asphalt runoff Penetrate dust coatings (<5% fines) Promote good bonding with aggregate • Good for situations where available aggregate is very dirty • Must be allowed to skin over
Modified Binders • Polymers typically utilized • Reduce temperature susceptibility CRS-2 softening point 108º F CRS-2 p softening point 128º F • Better adhesion Increased application rate by up to 15 % • Increased stone retention / flexibility • Early opening to traffic • Recommended for high traffic roads
Polymers • Large molecules which enhance performance • Solid or liquid in form • Properties Plastomeric (adds stiffness) Elastomeric (adds flexibility)
Aggregate-Binder Compatibility Properties Affecting Adhesion: • Mechanical (dust, aggregate porosity) • Chemical (moisture content, binder temperature) • Electrostatic (binder and aggregate should have opposite charges)
Questions?
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