CHIP SEALING DESIGN AND PERFORMANCE

G. Holleran, Vice President, Valley Slurry Seal Company, USA
Jack Van Kirk, Director of Asphalt Technology, Basic Resources Incorporated, USA
Jeffery R. Reed, President Valley Slurry Seal Sacramento Ca USA

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• Definitions and aims
• Chip Seal Life Survey
• Failure Of Chip Seals
• Design relationships to failure
• Design Methods- Rational and Empirical
  • Australia
  • New Zealand
  • South Africa
  • USA
• Conclusions

• Chip Seal or spray seal is a surfacing
• It is used in many countries as a primary surfacing over granular pavements
• Chip Seal may be carried out with hot asphalt, emulsion, modified hot asphalt (polymer or AR)
• Properly done it’s a durable, skid resistant surface.

Materials

Aggregates: clean, single sized as possible,compatible with the binder, pre-coated preferred- especially for hot binders. Binder: Compatible with aggregate, spray able, high enough viscosity to stay on the road, low enough not to streak. Additives: precoats, polymers, rubber, anti stripping agents.

• SHRP SP5; >5 years
• Australia: 8-15 years
• New Zealand 8-15 years
• South Africa: 8-12 years

Failure of Chip Seals Stripping- stone loss early life Stripping- stone loss over time Flushing, bleeding Stone crushing Delamination Age Cracking

• Binder cohesive failure
• Insufficient binder
• Slow cure of emulsion
• Application problems- cold/broken binder, slow spreading, insufficient rolling, cold weather, dirty aggregate.
• Wrong binder

Stripping: Stone Loss with Time
	Premature Aging and Embrittlement Traffic combined with low binder High Stress Areas, corners Unusual traffic levels Snow ploughs Wrong binder Application problems such as streaking

• Heavier than expected traffic
• Binder level too high
• High shear levels on corners or hills
• Higher levels of slow moving trucks
• Wrong binder ( low RBSP)
• Poor binder distribution

 

Stone Crushing Unsound aggregate Steel rollers

• Surface too cold
• Binder too low
• Binder too cold
• Dirty Surface
• Poor spray distribution

 

Age Cracking Binder ages too fast Binder too low

How to Avoid Failures Design methods determine the correct binder Correct aggregate The right application conditions The right amounts for the conditions and traffic

After Compaction and Curing  

Two Coat Seal

• Base Binder Application / Rate for aggregate size
• Adjustments for existing surface
  • Embedment
  • Texture
  • Absorption
• Adjustments for traffic type
• Adjustments for topography
• Adjustments for aggregate absorption

• Rational design: Australia, South Africa
  Based on engineering properties
• Performance based using voids: New Zealand
  Based on Safety, Durability, waterproofing
  Environment
  Economics
  

• Chip Seals are 80% of the sealed network. 250,000km
• 300 million lires
• They are used for trunk roads, city roads, residential streets and interstates.
• They are both a primary surfacing and a preservation tool.
• Reseals are generally single coat and new work multiple coat.

 

Method: Single Coats

Theoretical aggregate spread rate:
TASR = (1000/ALD) X (1000-VL)/ (1000- VC)
(m2/m3)
Where VL = Void Vol in loose bulk agg
VC= Void Volume in compacted layer
ALD = average least dimension of aggregate

• Channelisation:
• Short Term effects
• Topography
• Untrafficked areas
• Traffic type

Surface Texture
Flushed-free binder
Black: near stone tops
Smooth: agg worn
Matte: texture 2/3 ALD
Hungry:<1/2 ALD
Very Hungry: <1/3ALD

Flushed	Black	Smooth
Matte	Hungry	Very Hungry

Embedment

	Traffic Volume (AADT per lane)
Surface Hardness	150 -300	300 -625	625 -1250	1250 -2500	>2500
Hard (Ball Value 1 - 2)	Nil	Nil	Nil	-0.1	-0.2
Medium (Ball Value 3 - 4)	Nil	Nil	-0.1	-0.2	-0.3
Soft (Ball Value 5 - 8)	-0.1	-0.1	-0.2	-0.3*	-0.4*
*Where embedment allowances of 0.3 L/m< sup> or more are indicated in the above table, consideration should be given to alternative treatments such as armour-coating with higher quality materials rolled into the surface of the base or the use of a primerseal/prime and seal with a small aggregate in order to provide a platform on which larger aggregate seal may be placed.

Absorption
Typically +0.1 Lt/m2

• Design first application using single application method but reduce the basic voids factor by 0.02
• Do not allow for whip off
• Design the second as for a single application don’t use any surface texture allowances

• Based On Factors that affect the mat
• Aggregate, Wear, Degradation, Skid, Embedment, Voids Filled with Binder

• Modified Plate Test: Bulk and Mat voids
• Embedment from traffic and ball penetrometer
• The traffic Volume and the hardness are used to determine the amount of in service wear and degradation.
• Spherical layer theory is used to calculate fractional void losses cause by embedment and wear
• Voids for minimum skid ( 0.64mm) are substracted to give voids for binder design
• Maximum binder rate is the filling of the remaining voids
• Minimum binder is that required to hold aggregate before wear and embedment
• An allowance is made to fill surface texture voids
• Computer program available. Used since 1986.

• Ball penetration: using a relationship determined.
• Measures the penetration of a 19mm ball when hit with a Marshall hammer, corrected to a std temp.
• Aggregate Strength: A wet dry test or crushing test.
• Modified Tray Test: Aggregate place d shoulder to shoulder and a loose fitting membrane placed over the top. Sand replacement is used to measure the mat thickness and the aggregate volume subtracted from the total mat volume to determine mat voids.

• Voids Design
• Performance assessment
• All roads
• Single reseals for maintenance or first construction, multiple coat seals rehabilitation and first construction.

 

New Zealand: Voids Design

Single Coat

Texture Depth

Sand Circle diameter (mm)	e (/m2	Sand Circle diameter (mm)	e (/m2
150	0.49	210	0.22
155	0.45	220	0.20
160	0.42	230	0.18
165	0.39	250	0.14
170	0.37	275	0.11
175	0.34	300	0.08
180	0.32	325	0.06
190	0.28	350	0.05
200	0.25	400	0.03
		500	0

Sand Patch

• Absorptive surfaces: inc 10%
• Soft surfaces: decrease 10%
• Steep grades” decrease 10%
• High stress 10-20% increase or use two coat system
• Urban: 10-20% increase

Two Coat Seals

Size Selection

• Principal performance requirements
• Min specs
• Tests
• Payment
• Proportional payment
• Contractor QA qualification

• Based on nominal design life
• Based on texture depth changes with time and traffic
• Skid, PSI, uniformity
• Noise, permeability, durability, stone retention
• High traffic volumes and smaller sealing chip chip life is controlled by flushing.
• Low traffic volumes and large chip its controlled by durability of materials

Texture Depth Change with Time
(after Patrick and Donbavand Transit NZ)

• Texture Uniformity (visual, sand patch 0.25mm max deviation)
• Uniformity of Pavement Hardness (ball penetrometer)
• Traffic Stress (design based on experience)
• Repairs

• ARRB test program
• South African, Australian, NZ
• Showed that all work fairly well

• Each site is different
• Attention to detail
• As rational as possible
• Qualified Contractors
• Design each seal