Chip Seal Design Chapter 2

North America (ranked by prevalence) Empirical / Past Experience No Design Method Own Method McLeod (1960’s) - Asphalt Institute Kearby (1953) - Modified Kearby Hanson (1934 / 1935) - Obsolete Source: NCHRP Synthesis 342, 2005

Earliest formal method Developed for liquid asphalt (cutback) Based on Average Least Dimension (ALD)

Binder rate based on average thickness, aggregate embedment and voids Recommended uniformly graded aggregates Embedment based on aggregate hardness (increase for hard, decrease for soft) Larger aggregates -less embedment (high ADT) Medium aggregates -more embedment (low ADT)

Officially adopted by Asphalt Institute in 1969 Based partially on Hanson (1953) Aggregate rate based on gradation, shape, specific gravity, waste correction factors Binder rate based on aggregate gradation, pavement condition, traffic volume, asphalt type (absorption) For years marked end of chip seal design research

Kearby and McLeod (1953) UK TRL Road Note 39 (1996) AustRoads (2001) New Zealand P/17 (Mod of Australia) South Africa TRH 3 (Hybrid of UK & Australia)

Binders selected based on viscosity Polymer modified binders encouraged Binder grade based on traffic, season Aggregate size based on traffic, pavement hardness, desired friction Binder rate based on aggregate, surface texture, embedment by traffic Aggregate rate based on size, shape, relative density

Performance-based method Binder and aggregate rates based on: ̶ Aggregate angularity ̶ Traffic volume ̶ Road geometry ̶ Aggregate ALD ̶ Aggregate absorption ̶ Pavement absorption ̶ Texture depth Aggregate one layer thick

Aggregate: ̶ Angularity ̶ Size ALD ̶ Absorption ̶ Embedment Traffic volume Road geometry Pavement Absorption Texture Depth Application immediacy (2 nd seal)

Surface texture Traffic conditions (ADTs, speed,% commercial) Chip seal type Aggregate selection Binder application rate

Surface Properties of Asphalt Pavement Not Quantitatively Used in N. America Overseas, (75% quantify) ̶ Sand Patch Method (ASTM E 965) Surface Hardness (expected embedment depth) Non-uniform Textures makes binder application rate problematic

Also known as the “Sand Circle Method” Method for determining pavement macro-texture Spread known volume of sand or glass beads Calculate volume of material that fills surface voids to determine surface texture The greater the texture depth, the greater the quantity of sand or glass beads that will be lost in the surface voids

Know local traffic conditions and volumes Heavy vehicles must be considered in addition to total volume Calculate ADT and use adjustment for heavy vehicles Intersections – starting, stopping, turning

Weather conditions Ambient and road surface temperatures Aggregate moisture content Apply chip seals in the earliest part of the construction season as possible!

CHIP SEAL DESIGN Chip Seal DESIGN PROGRAM Developed by: Minnesota DOT

Metro FA-3 Chip Seal 05

Design for FA-3 (3/8 inch) chip Aggregate –Without design: Avg. 30 lbs/yd² –With design: Avg. 17 lbs/yd² Emulsified Asphalt –Without design: Avg. Binder 0.30 gal/yd² –With design: Avg. Binder 0.42 gal/yd²

Chip Seal Designs and Proper Construction:Chip Seal Designs and Proper Construction: ̶ Allows more miles ̶ Uses less money ̶ Achieves better results

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Different seals require different designs Construction sequence Number of courses Variations in aggregate nominal size

Chopped Fiberglass Strands

Protects binder from traffic wear Establishes seal thickness Influences surface texture and impacts ride and noise Potential for windshield damage Cost issues - Life Cycle Analysis Compatibility with Asphalt

Maximum size: 3/8 inch Single size aggregate Cubical or pyramidal and angular < 1% passing No. 200 sieve ̶ No Clay if possible Abrasion < 30%

Single Chip Seals ⅜ inch (10 mm) Double Chip Seals ½ inch (12.5 mm) (1st App) ¼ inch (6.25 mm) (2nd App) The bottom layer should be twice as big as the top layer!

Design for each Aggregate Layer Combine binder requirements for both seals ̶ Normally recommend to apply 40 % of binder total first and large stone. ̶ Sweep then apply remaining binder and smaller stone. Other methods

where: V = voids as fraction of aggregate vol. W = loose unit weight of aggregate G = bulk specific gravity of aggregate Metric:English:

Achieve an even, single layer

The Goal: Achieve 70+% Aggregate Final Embedment

Considerations Initial embedment will vary by environmental region Avoid bleeding Avoid loose aggregate

Percentage of residual asphalt (RA) is critical Emulsion 65% RA average Cutbacks 85% RA average Hot applied AC 100% Fills existing pavement voids What seals and protects the HMA Holds aggregate in-place

Binder selection is critical Single size aggregate Uniform aggregate distribution 70+% final embedment of aggregate Apply to roads with low surface distress Characterize texture and surface hardness Racked-in seals for bleeding

Roadway needs to be structurally sound Two options Option #1: Prime and Chip Seal A.Prime with —Cutback like MC 70 (0.30 to 0.40 gal/yd²) —Penetrating Prime Emulsion (Formulate for aggregate type) B.Chip Seal - Use large chip

Option #2: Otta SealOption #2: Otta Seal A.Use emulsion like HFMS-2 (0.50 gal/yd²) B.Use surfacing gravel —5/8” – 1” (50 lbs/yd²) —Two applications —2 to 3 weeks apart

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