SprayApplied Asphalt Seals 2001 Asphalt Institute Pavement Preservation

Spray-Applied Asphalt Seals 2001 Asphalt Institute Pavement Preservation Seminars Asphalt Institute

ASPHALT INSTITUTE Types of Surface Seals • Fog Seals – rejuvenators • • • Sand Seals Chip Seals Slurry Seals Microsurfacing Combinations – E. g. , cape seals To be reviewed in this session

ASPHALT INSTITUTE Purposes of Seal Coats/ Surface Treatments • Preventive maintenance – keep air and water out of existing pavement • Resurfacing – improve skid resistance through aggregate qualities and coarse texture • Initial surface – provide wearing surface for light-duty pavements • Interlayer – seal existing pavement, enhance bond between overlay and existing pavement

Fog Seals ASPHALT INSTITUTE • Light application of diluted, slow-setting asphalt emulsion without aggregate cover • SS-1, -1 h; CSS-1, -1 h diluted 39: 1 applied at ~0. 10 gal/sy Purpose – Seal the pavement – Inhibit raveling – Enrich hardened/oxidized asphalt – Provide delineation with shoulder • For pavements in good condition • Not generally recommended on high-speed roadways with dense or fine-textured surfaces

ASPHALT INSTITUTE Performance of Fog Seals • Most effective on pavements in good condition – Minor cracks – Some raveling or oxidation • Performance life is typically 1 to 2 years • Effectiveness improves with repeated applications • Typical cost: $0. 10 -0. 15/sy

ASPHALT INSTITUTE Coal Tar-Based Products • Resistant to damage from fuels and lubricants • Best applied where there is routine exposure to fuels or lubricants • Different coefficient of thermal expansion than asphalt – Results in shrinkage cracks in the seal

Rejuvenator/Sealer

ASPHALT INSTITUTE Asphalt Rejuvenators • Soften the asphalt binder • Reduce raveling • Close and delay surficial cracks

ASPHALT INSTITUTE Cost and Performance of Rejuvenators • Cost $0. 35 – $0. 50/SY • Performance 3 -5 Years (GA airports) • Not recommended for high-speed traffic conditions!!!

ASPHALT INSTITUTE Seal Coat Materials • Aggregate • Asphalt binder • Proportions (design)

ASPHALT INSTITUTE Aggregate Properties • Mineral Type • Particle size • Particle shape • Cleanliness • Toughness • Unit weight

ASPHALT INSTITUTE Example Gradations: Standard and Modified Grade 3 -modified #10 1/4 3/8 1/2 5/8 3/4 Sieve Size 0. 45

ASPHALT INSTITUTE Aggregate Particle Shape • Angular (crushed) particles – min. 85% w/ 2 or more crushed faces – Tex-460 -A, Part I • Cubical shape • Minimize flat/elongated particles – ASTM D 4791 – Flakiness index, TEX-224 -F – Maximum FI=17

ASPHALT INSTITUTE Contrasting Particle Shapes

ASPHALT INSTITUTE Flakiness Index Test Board Flat & Elongated Apparatus Flakiness Index Flat & Elongated

ASPHALT INSTITUTE

ASPHALT INSTITUTE

ASPHALT INSTITUTE Cleanliness Unwashed Grade 3 Washed Grade 3

ASPHALT INSTITUTE Aggregate Properties Cleanliness • 2% max soft particles/ deleterious material (TEX 217 -F, Part I) • 1% max dust/silt/clay (TEX-217 F, Part II)

ASPHALT INSTITUTE Aggregate Properties Toughness & Soundness • 5 -cycle Mg. SO 4 soundness less than 25% loss • LA Abrasion below 35% loss • Micro Deval (Tx. DOT is evaluating)

ASPHALT INSTITUTE Aggregate Unit Weight • Necessary to determine spread rate • Loose unit weight, AASHTO T 19 • ASTM C 29, TEX-201 -F (Gb)

ASPHALT INSTITUTE Aggregate Sampling • Obtain samples from jobsite!!! • Sampling stockpiles – Front end loader blending – Avoid segregated materials • Sample at various locations in the pile • Use a board when sampling to avoid further segregation during sampling

ASPHALT INSTITUTE Aggregate Sampling Procedures • Sampling locations • Minimum number of locations • Sample size

ASPHALT INSTITUTE Sampling Locations

ASPHALT INSTITUTE Aggregate Sampling and Testing • Based on maximum nominal aggregate size Nominal Size 37. 5 mm (1 -1/2”) 25. 0 mm (1”) 19. 0 mm (3/4”) 12. 5 mm (1/2”) 4. 75 mm (No. 4) Min. Sample, kg (lb) 75 (165) 50 (110) 25 (55) 15 (35) 10 (25)

ASPHALT INSTITUTE Asphalt Binders for Chip Seals Hot-applied Asphalt Emulsions Application Temp: 275 o- 350 o. F • AC-5 • AC-10 • AC-5, 10+2% latex • AC-15 P • AC-15 -5 TR Application Temp: 110 o - 160 o F • HFRS-2 P • CRS-2, -2 h • CRS-2 P • CRS-1 P Cutbacks: MC-2400, MC-2400+latex, MC-3000 @ 225 -275 F

ASPHALT INSTITUTE Asphalt Cements & Cutbacks • Best used in hot, dry weather • Must have dry, clean aggregate and surface – Precoated aggregates • (AC) Very effective in high traffic areas that can’t afford long cure time • Cutbacks require traffic control while curing

ASPHALT INSTITUTE Asphalt Emulsions • Can be used with damp ( up to 3 %) aggregates – Do not use precoated aggregates when using emulsions • Applied at temperatures generally below the boiling point of water • Eliminates fire hazard associated with cutbacks • Sets up more quickly than cutbacks

ASPHALT INSTITUTE Polymer Modified Binders • Needed for high volume traffic • Don’t deliver what can’t be used immediately • Better for large cover stone • More expensive

ASPHALT INSTITUTE Design Concept, Illustrated Average Least Dimension Aggregate Asphalt • Assume total void space (asphalt + air) = 20% • Asphalt should fill 60 -70% of voids • Prefer single-size, cubical aggregate particles

ASPHALT INSTITUTE Design Basis • Asphalt binder should fill 60 to 70 percent of the void space after particles have been fully oriented • Procedure developed by F. M. Hanson, New Zealand • References: – AAPT Supplement to Vol. 29, 1960 (N. W. Mc. Leod) – Asphalt Institute MS-13 (out of publication)

ASPHALT INSTITUTE Seal Coat Design • Tabulated ranges for different aggregate sizes (MS-19, Tables 6. 3, 6. 4 and 6. 5) • Calculated, based on volumetric proportions of solids, binder and air voids • Experience

ASPHALT INSTITUTE Effect of Changing Variables • Traffic: ADT from 1200 to 300 – Shot rate increases from 0. 32 to 0. 37 gal/sy • Flakiness Index: FI from 0 to 20% – Use ALD instead of M – Spread rate decreases from 22. 4 to 16. 6 lb/sy – Shot rate decreases from 0. 32 to 0. 24 gal/sy • Surface: Smooth, non-porous to slightly raveled-porous – Shot rate increases from 0. 32 to 0. 41 gal/sy

Two-Course Surface Treatments Asphalt, Percent by Weight & Volume ASPHALT INSTITUTE

ASPHALT INSTITUTE Construction Considerations • Existing pavement condition • Temperature/ambient conditions • Construction techniques

ASPHALT INSTITUTE Existing Pavement Condition • Areas of structural distress (alligator cracking, potholes, etc. ) should be patched in advance • Rutted or corrugated areas should be corrected by leveling or milling • Linear cracks more than 1/8 inch wide should be filled or sealed properly before placing seal coat-DO NOT USE EXCESSIVE CRACK SEAL MATERIAL • Clean the surface with a rotary broom or other approved method immediately before sealcoating

This is NOT a candidate!!!

ASPHALT INSTITUTE Yes No After sealing cracks Maybe?

ASPHALT INSTITUTE Construction Techniques • Uniform application of asphalt binder and cover stone • Aggregate must be spread and imbedded before asphalt cement cools and hardens, within ONE MINUTE of spraying • When emulsion is used, aggregate must be spread and imbedded before emulsion completely breaks • Do not excessively agitate emulsions

ASPHALT INSTITUTE First and last piece of equipment on the job!

ASPHALT INSTITUTE Temperature/Ambient Conditions • Surface temperature is critical, should exceed 70°F • During cool weather, allow time for surface to warm before allowing work to begin • Do not apply when the surface is wet or when the threat of rain is imminent • Control traffic speed during first 24 hrs. (max. 20 mph) • During hot weather, allow seal to “set” overnight before opening to traffic

ASPHALT INSTITUTE Check Equipment • Check distributor, components – Nozzles – Height of spray bar – Temperature • Check spreader

ASPHALT INSTITUTE Pressure Distributor

Self-Propelled Spreader

ASPHALT INSTITUTE Rollers • For single seal coats/one course surface treatments, use pneumatic (rubber tire) rollers • Only consider light (low pli) steel-wheel rollers for second course of double seal/two course surface treatment – rubber-coated steel-wheel rollers – “combi” roller (steel drum plus pneumatic tires), operated w/pneumatic in front

ASPHALT INSTITUTE Rollers for Surface Treatments

Calibrate Equipment • Spray Bar Height – prefer double or triple lap • Nozzle Angle – 15 -30° • Nozzle Type • Spray Bar Pressure • Bitumeter

ASPHALT INSTITUTE Spray Bar

Spread and Roll while Binder is Fluid

ASPHALT INSTITUTE

Rolling • Immediately after chipping • Pneumatic-tired roller – 50 to 60 psi • 12 -ton minimum • Stop after aggregates are set

Particle Arrangement: After Embedment Underlying Material • Note particle reorientation • Approx. 30% voids after rolling • Approx. 20% voids after traffic

ASPHALT INSTITUTE Seal Coat Performance Depends on: • • Quality of materials Design Condition of existing pavement Construction

ASPHALT INSTITUTE Fog Seals • Application of diluted, mixing grade emulsion to fill hairline cracks or bind loose particles • 3: 1 to 5: 1 dilution (water to emulsion), applied at 0. 10 -0. 15 gal/sy • Most effective on open-textured HMA or after final sweeping on chip seals