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

A SPHALT I NSTITUTE 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

A SPHALT I NSTITUTE 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

A SPHALT I NSTITUTE Fog Seals 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 Light application of diluted, slow-setting asphalt emulsion without aggregate cover SS-1,-1h; CSS-1,-1h diluted 3- 9:1 applied at ~0.10 gal/sy

A SPHALT I NSTITUTE 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: $ /sy

A SPHALT I NSTITUTE 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

A SPHALT I NSTITUTE Asphalt Rejuvenators Soften the asphalt binder Reduce raveling Close and delay surficial cracks

A SPHALT I NSTITUTE Cost and Performance of Rejuvenators Cost $0.35 – $0.50/SY Performance 3-5 Years (GA airports) 3-5 Years (GA airports) Not recommended for high-speed traffic conditions!!!

A SPHALT I NSTITUTE Seal Coat Materials Aggregate Asphalt binder Proportions (design)

A SPHALT I NSTITUTE Aggregate Properties Mineral Type Particle size Particle shape Cleanliness Toughness Unit weight

A SPHALT I NSTITUTE Example Gradations: Standard and Modified Grade 3 #10 1/4 3/8 1/2 5/8 3/4 Sieve Size 0.45 Grade 3 Grade 3-modified

A SPHALT I NSTITUTE 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

A SPHALT I NSTITUTE Contrasting Particle Shapes

A SPHALT I NSTITUTE Flakiness Index Test Board Flat & Elongated Apparatus Flakiness IndexFlat & Elongated

A SPHALT I NSTITUTE

Cleanliness Unwashed Grade 3 Washed Grade 3

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

A SPHALT I NSTITUTE Toughness & Soundness 5-cycle MgSO4 soundness less than 25% loss LA Abrasion below 35% loss Micro Deval (TxDOT is evaluating) Aggregate Properties

A SPHALT I NSTITUTE Aggregate Unit Weight Necessary to determine spread rate Loose unit weight, AASHTO T 19 ASTM C 29, TEX-201-F (G b )

A SPHALT I NSTITUTE 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

A SPHALT I NSTITUTE Aggregate Sampling Procedures Sampling locations Minimum number of locations Sample size

A SPHALT I NSTITUTE Sampling Locations

A SPHALT I NSTITUTE Based on maximum nominal aggregate size Nominal SizeMin. Sample, kg (lb) 37.5 mm (1-1/2”)75 (165) 25.0 mm (1”)50 (110) 19.0 mm (3/4”)25 (55) 12.5 mm (1/2”)15 (35) 4.75 mm (No. 4)10 (25) Aggregate Sampling and Testing

A SPHALT I NSTITUTE Binder Requirements for Chip Seals Spraying: Fluid enough to apply uniformly, without draining or puddling Embedment: Fluid enough to develop rapid wetting and fast initial adhesion between binder and aggregate and underlying surface Performance: Viscous enough to retain the aggregate under traffic, ductile enough to stretch without tearing, adheres to aggregates

A SPHALT I NSTITUTE Binder Selection Criteria Temperature Traffic Aggregate –Cleanliness –Size –Type Experience

A SPHALT I NSTITUTE Asphalt Binders for Chip Seals Hot-applied Application Temp: 275 o o F 275 o o F AC-5 AC-10 AC-5,10+2% latex AC-15P AC-15-5TR Asphalt Emulsions Application Temp: 110 o o F HFRS-2 HFRS-2P CRS-2, -2h CRS-2P CRS-1P Cutbacks: MC-2400, MC-2400+latex, F

A SPHALT I NSTITUTE 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

A SPHALT I NSTITUTE 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

A SPHALT I NSTITUTE Polymer Modified Binders Needed for high volume traffic Don’t deliver what can’t be used immediately Better for large cover stone More expensive

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

A SPHALT I NSTITUTE 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. McLeod) –Asphalt Institute MS-13 (out of publication)

A SPHALT I NSTITUTE 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

Design Formulas Formulas have been derived for finding the amounts of : aggregate asphalt binder needed for a single surface treatment (seal coat) To use these formulas: sieve analysis (AASHTO T27) Flakiness Index (TEX-224F) loose unit weight (AASHTO T19)

A SPHALT I NSTITUTE Spread Modulus The mean particle diameter is calculated as the weighted average of the mean size of the largest 20 percent, the middle 60 percent and the smallest 20 percent M = 0.20 (b+a)/ (c+b)/ (d+c)/2

A SPHALT I NSTITUTE Spread Modulus where: M=Spread modulus a=100 percent passing aggregate size (inches) b=80 percent passing aggregate size (inches) c=20 percent passing aggregate size (inches) d=0 percent passing aggregate size (inches)

A SPHALT I NSTITUTE Spread Modulus DIAGRAM OF THE CONCEPT X X X Top 20% Middle 60% Bottom 20% a = 100%of ___ b = 80%of ___ c = 20% of ___ d = 0% of ___

A SPHALT I NSTITUTE Average Least Dimension Accounts for flat/elongated particles –Flakiness Index, Tex-224-F Adjustment to mean particle diameter using chart 3/8” 2” 1/4” 1½”1½”1½”1½”1” 5/32”

A SPHALT I NSTITUTE Average Least Dimension

A SPHALT I NSTITUTE Asphalt Quantity T=Traffic factor ADT<99T= <ADT<500T= <ADT<1000T= <ADT<2000T= <ADTT=0.60 R= Residual asphalt content A = (1.122MT+V)/R A=Asphalt shot rate, gal/sy V=Absorption variable, gal/sy Flushed surfaceV=-0.03 Smooth, nonporousV=0.00 Slightly porousV=0.03 Slightly raveled, porousV=0.06 Badly raveled, porousV=0.09

A SPHALT I NSTITUTE Aggregate Quantity S = (0.80 MW)(1+E ) where: S = Aggregate spread (lbs/sy) M = Spread Modulus (or Average Least Dimension) W = Aggregate loose unit weight (AASHTO T19), lbs/ft 3 E = Waste factor, typically 5-10% ( )

A SPHALT I NSTITUTE Equations/units in SI S (kg/m 2 ) = 10MW(1+E) –M is determined in cm –W is loose unit wt in g/cm 3 A (l/m 2 ) = (2MT + V)/R –calculates asphalt rate to fill 20% volume of voids Multiply gal/sy times 4.53 to convert V to l/m 2

A SPHALT I NSTITUTE Surface Treatment Design Example Given Conditions: ADT = 1200 Existing surface - Smooth, nonporous Aggregate Unit Weight - 86 lbs /ft 3 Asphalt: CRS-2h, 0.70 residual Waste = 5% (0.05)

A SPHALT I NSTITUTE Gradation SieveOpening% Passing 5/8 in /2 in /8 in No No

A SPHALT I NSTITUTE Example Gradation Plot Sieve Size, in #10 #4 3/8 1/2 5/8 Plotted gradation

A SPHALT I NSTITUTE Spread Modulus: from sieve analysis: a = 100% passing aggregate size =.50 b = 80% passing aggregate size =.40 c = 20% passing aggregate size =.22 d = 0% passing aggregate size =.08 M = 0.10 (b+a) ( c+b) (d+c) = 0.10( ) ( ) ( )  M = 0.31 Surface Treatment Design Example

A SPHALT I NSTITUTE Aggregate Spread, lb/yd 2 S = 0.80 (MW) x (1+ E) M = 0.31, W = 86 lbs/ft 3, E (waste) = 0.05 S = 0.80[ (0.31)(86) ] x [1.05] = 22.4 lb/sy Asphalt Shot Rate, gal/yd 2 A = (1.122MT + V)/ R M = 0.31, ADT =1200, so T = 0.65 Smooth, nonporous surface: V = For CRS-2, R = 0.70 A = (1.122 (0.31)(0.65) ) / 0.70 = 0.32 gal/sy Surface Treatment Design Example

A SPHALT I NSTITUTE 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

A SPHALT I NSTITUTE Double Chip Seal Design Assumptions: Final thickness is same as top size of large aggregate Small aggregate fills upper voids in large aggregate Absolute volume of voids is 5-7%

A SPHALT I NSTITUTE Two-Course Surface Treatment Design Data: Bulk specific gravity (Gsb), AASHTO T85 Aggregate loose unit weight, AASHTO T19 Sieve analyses (AASHTO T 27) Average particle size and spread ratios Select desired asphalt volume for application

A SPHALT I NSTITUTE Two-Course Surface Treatment Determine average particle size (APS) for large and small aggregates –calculated from sieve analysis (spread modulus) using + #8 –measured (“board” test)

A SPHALT I NSTITUTE Two-Course Surface Treatment Find spread ratio for each aggregate –surface area covered by 1 cy of aggregate one particle thick –1:100 is 1 cy to 100 sy –calculate by dividing APS (in 64ths of an inch) into 2304 –Example: for ½ inch APS: spread ratio is 2304/32 = 1:72

A SPHALT I NSTITUTE Asphalt, Percent by Weight & Volume Two-Course Surface Treatments

A SPHALT I NSTITUTE Construction Considerations Existing pavement condition Temperature/ambient conditions Construction techniques

A SPHALT I NSTITUTE 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 DO NOT USE EXCESSIVE CRACK SEAL MATERIALLinear 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!!!

A SPHALT I NSTITUTEYes After sealing cracks Maybe? No

A SPHALT I NSTITUTE Construction Seasons for Seal Coats, Surface Treatments Plan to construct seal coats when average low temperatures are higher than 50F (10C) Correlates well with growing season for frost- tender vegetables Example: –Assume average dates of last and first frost are April 15 and October 15 –Average dates for min. 50F low temps are approximately May 1 to October 1

A SPHALT I NSTITUTE 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

A SPHALT I NSTITUTE First and last piece of equipment on the job!

A SPHALT I NSTITUTE 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

A SPHALT I NSTITUTE Check Equipment Check distributor, components –Nozzles –Height of spray bar –Temperature Check spreader

A SPHALT I NSTITUTE Pressure Distributor

Self-Propelled Spreader

A SPHALT I NSTITUTE 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

A SPHALT I NSTITUTE Rollers for Surface Treatments

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

A SPHALT I NSTITUTE Spray Bar

Spread and Roll while Binder is Fluid

A SPHALT I NSTITUTE

Rolling Immediately after chipping Pneumatic-tired roller – 50 to 60psi 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

A SPHALT I NSTITUTE Seal Coat Performance Depends on: Quality of materials Design Condition of existing pavement Construction

A SPHALT I NSTITUTE 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 gal/sy Most effective on open-textured HMA or after final sweeping on chip seals