Chip Seal Design Chapter 2 Chip Seal Design

Chip Seal Design Chapter 2

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

Hanson Method (1934 / 1935) • Earliest formal method • Developed for liquid asphalt (cutback) • Based on Average Least Dimension (ALD)

Kearby Method (1953) • 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)

Mc. Leod Method (1960’s) (Most Common) • 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

Overseas Seal Design Methods • Kearby and Mc. Leod (1953) • UK TRL Road Note 39 (1996) • Aust. Roads (2001) • New Zealand P/17 (Mod of Australia) • South Africa TRH 3 (Hybrid of UK & Australia)

UK TRL Road Note 39 (TRL = Transport Research Laboratory) • 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

Aust. Roads Design Method Australian Spray Seal • 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

New Zealand P/17 (P/17 = Performance Based Specification) Design Factors • Aggregate: • • • Angularity Size ALD Absorption Embedment Traffic volume Road geometry Pavement Absorption Texture Depth Application immediacy (2 nd seal)

Effects of Rolling on Chip Orientation

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

Surface Texture Evaluation • 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

Sand Patch Method • 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

Traffic Conditions • 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

Climate Considerations • 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

Example of Chip Seal 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

Benefit of a Chip Seal Design • Chip Seal Designs and Proper Construction: Allows more miles Uses less money Achieves better results

Chip Seal Design Program Download at: http: //www. dot. state. mn. us/materials/researchsealcoat. html

Selection of Seal Coat Type Different seals require different designs • Construction sequence • Number of courses • Variations in aggregate nominal size

Single Chip Seal

Double Chip Seal

Racked-in Chip Seal

Cape Seal

Inverted Seal

Sandwich Seal (Dry Matting)

Geotextile-Reinforced Seal

Fiber-Reinforced Seal Chopped Fiberglass Strands

Aggregate Selection • 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

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

Common Aggregate Sizes Single Chip Seals • ⅜ inch (10 mm) Double Chip Seals The bottom layer should be twice as big as the top layer! • • ½ inch (12. 5 mm) (1 st App) ¼ inch (6. 25 mm) (2 nd App)

Double Chip Seal Construction 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

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

Aggregate Application Achieve an even, single layer

Binder Application Rate The Goal: Achieve 70+% Aggregate Final Embedment

Binder Application Rate Considerations • Initial embedment will vary by environmental region • Avoid bleeding • Avoid loose aggregate

Binder Considerations 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

Design Best Practices • 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

Chip Seals to Surface Gravel Roads 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

Chip Seals to Surface Gravel Roads • Option #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

Otta Seal

Otta Seal

Otta Seal

Otta Seal

Questions?