Materials Selection Chapter 3

Seal existing pavementSeal existing pavement ̶ More binder the longer the seal will protect underlying HMA Bond to aggregateBond to aggregate Bond to pavementBond to pavement

Skid resistanceSkid resistance Limit polishingLimit polishing Control abrasionControl abrasion Protects the binder from trafficProtects the binder from traffic

Minimize risk of overheating Minimizing heat loss Minimizing heat loss Seek advice from your supplier!!! Seek advice from your supplier!!!

Aggregate Defines: Seal Type Binder Binder Construction Procedures Construction Procedures

United States AvailabilityAvailability TransportationTransportation ̶ Method ̶ Cost Favor local sources Favor local sources Emphasize Lower Cost Emphasize Lower CostOverseas Life Cycle Analysis Transportation Transportation ̶ Up to 500 miles Performance Performance Longevity Longevity Emphasize Quality Emphasize Quality

Grading / Particle Size:Grading / Particle Size: Determines mixture physical characteristics that affect fatigue resistance Cleanliness:Cleanliness: Dusty aggregates causes adhesion problems in chip seal.

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

Dense Graded Single Size

SIEVE SIZE, inches PERCENT PASSING dense graded single sized

Advantages of Single Sizing More uniform heightMore uniform height Weighs less per cubic footWeighs less per cubic foot ̶ 47% passing the # lbs/ft 3 ̶ 8% passing the # lbs/ft 3 More room for binderMore room for binder ̶ Increased Voids

Dense Graded (FA-3) $22.80 ton 18.5 lbs/yd 2 needed = $0.21 per yd lbs/yd 2 needed = $0.21 per yd 2 Single Sized 14.5 lbs/yd 2 needed = $0.16 per yd 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.

Best Performance when: Single sized Minimum fines Minimum fines Clean Clean Free of clay Free of clay Cubical Cubical Crushed faces Abrasion < 30% Abrasion < 30% Binder compatible Binder compatible Damp for emulsions Damp for emulsions Dry for hot binders Dry for hot binders

Sieve Analysis: <1% passing No.200Sieve Analysis: <1% passing No.200 ASTM D3319: Polished Stone Value (PSV) 44 to 48ASTM D3319: Polished Stone Value (PSV) 44 to 48 ASTM C131: LA Abrasion Test <30%ASTM C131: LA Abrasion Test <30% Percent Fracture: 75% with at least 2 fracture faces.Percent Fracture: 75% with at least 2 fracture faces.

TypeNorth AmericaAU, NZ, SA, UK Limestone37%13% Quartzite13%38% Granite35%38% Trap Rock13%25% Sandstone10%25% Natural Gravel58%25% Greywacke, Basalt4%88%

Asphalt must preferentially wet, and bond to aggregate surfaceAsphalt must preferentially wet, and bond to aggregate surface Poor compatibility leads to:Poor compatibility leads to: ̶ Stripping ̶ Disintegration ̶ Stone loss No reliable chemical indicators for strippingNo reliable chemical indicators for stripping

No bleeding when applied properlyNo bleeding when applied properly Fluid enough to cover surfaceFluid enough to cover surface Viscous enough to prevent puddling or pavement runoffViscous enough to prevent puddling or pavement runoff Develop adhesion quickly and retain aggregateDevelop adhesion quickly and retain aggregate

Standard Paving AsphaltStandard Paving Asphalt Aged Residue (AR) grade Asphalt EmulsionAsphalt Emulsion (modified, unmodified, rejuvenating) Polymer-Modified AsphaltsPolymer-Modified Asphalts Including PBA grades CMCRACMCRA Chemically-Modified Crumb Rubber Asphalt and Modified Binder (MB) grades CutbacksCutbacks

62% Residual

85% Residual

Influenced by: Surface TemperatureSurface Temperature AggregateAggregate Construction ClimateConstruction Climate Performance CharacteristicsPerformance Characteristics

Advantages Open earlier to traffic Appropriate for high surface temperatures Good stone retention Can be reheated or stored at high temperatures w/o adverse effectsDisadvantages High temperatures High energy consumption Safety concerns Sensitive to aggregate moisture

Emulsions “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) “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.”

Anionic -Anionic - Cationic +Cationic +

Particles coalesce to form larger particles Particles begin to stick together (Flocculation)

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 distressesDisadvantages Timing the “break” with aggregate spreading Improper and prolonged storage may result in phase separation, coalescence Longer cure time than hot applied cements

Temperature Flocculation and coalescence may occur if too coolFlocculation and coalescence may occur if too cool If too hot, water will evaporate prematurely resulting in coalescence and premature breakingIf too hot, water will evaporate prematurely resulting in coalescence and premature breaking Binder Suppliers are best source of heating information!Binder Suppliers are best source of heating information!

Circulate slowly at regular intervalsCirculate slowly at regular intervals Circulation frequency depends on weather and storage timeCirculation frequency depends on weather and storage time Flush pumps after use but not into tankFlush pumps after use but not into tank Warm lines and pumps as necessaryWarm lines and pumps as necessary Do not leave lines partially-filled w/emulsionDo not leave lines partially-filled w/emulsion

More “forgiving”More “forgiving” Allow for thicker residual asphalt filmAllow for thicker residual asphalt film Minimize asphalt runoffMinimize asphalt runoff Penetrate dust coatings (<5% fines)Penetrate dust coatings (<5% fines) Promote good bonding with aggregatePromote good bonding with aggregate Good for situations where available aggregate is very dirtyGood for situations where available aggregate is very dirty Must be allowed to skin overMust be allowed to skin over

Polymers typically utilizedPolymers typically utilized Reduce temperature susceptibilityReduce temperature susceptibility ̶ CRS-2 softening point 108º F ̶ CRS-2p softening point 128º F Better adhesionBetter adhesion ̶ Increased application rate by up to 15 % Increased stone retention / flexibilityIncreased stone retention / flexibility Early opening to trafficEarly opening to traffic Recommended for high traffic roadsRecommended for high traffic roads

Large molecules which enhance performanceLarge molecules which enhance performance Solid or liquid in formSolid or liquid in form PropertiesProperties ̶ Plastomeric (adds stiffness) ̶ Elastomeric (adds flexibility)

Properties Affecting Adhesion: MechanicalMechanical (dust, aggregate porosity) ChemicalChemical (moisture content, binder temperature) ElectrostaticElectrostatic (binder and aggregate should have opposite charges)

Questions?