3

Seal and Thin Surfacing Technology

TRB WORKSHOP 153SOUTH AFRICAN HIGHWAY TECHNOLOGY AND PRACTICE

Photo

Mr Gerrie van ZylDirector

PD Naidoo & Associates

Definition

• A Single Surfacing seal is:– product of application of a SPRAYED

bituminous binder– and application of SINGLE SIZED

aggregate to the pavement”– to

• provide a durable, all weather riding surface with sufficient skid resistance

• Seal, protect, waterproof the base

Seal process

Spray bituminous binder

Spread single-sizedaggregate

Rolling

SCOPE

• South African situation• Surfacing seal types• Development of design methodologies• Design• Labour intensive surfacings• Ultra-thin Surfacings• Way forward

South African Surfaced Road Network

• Total (754 000)

• Surfaced (114 000km)

• Seals = > 80%

Introduction

BACKGROUND

TRAFFIC DISTRIBUTION

PROCLAIMED SURFACED RURAL ROADS

(South Africa)

02000400060008000

100001200014000

0-20

020

0-50

050

0-10

0010

00-2

000

2000

-400

040

00-6

000

6000

-100

0010

000-

2000

020

000-

5000

0

5000

0-10

0000

>100

000

VEHICLES PER DAY(both directions)

km

AsphaltSeals

Road Pavements in South Africa

pavementstructure

side walk

FILL OR IN SITU MATERIAL

kerbbituminoussurfacing

(3mm – 50mm)

base (>90% granular)

sub-base (granular or cemented)

selected (granular)

single seal

double seal (1.5)

cape seal

double seal

Typical Seals used in SA

Typical Seals used in SA

geotextile seal

split seal

choked seal

inverted seal

BACKGROUND

Typical Seal Types

graded aggregate/ Otta seal

grit/ sand seal

slurry seal

Seal Type DistributionWestern Cape annual seal programme

(6 – year average)

Slurry Seals, 7%

Rejuvenation, 13%

Asphalt, 2%Double seals,

5%

Single seals, 51%

Sand seals, 22%

Development of Seal design methodologies

• Formal designs - Late 1930s• Hansen’s theory of filling voids (1935)• NDOT, 4 Provinces – each own

method• Significant research 70s

– Relating embedment to Ball penetration– Rational seal design method (Not well

accepted by practitioners)– TRH3 (1984) – compendium of designs

• Ad hoc studies – improvements to own methods

• Appropriate standards for low volume roads – 1993 (SABITA)

• TRH3 (1998)

30%Min

Development of Seal design methodologies

• TRH3 (1998)– Road authorities’ and consultant’s experience incorporated

– Improvements to rational design method

– Modified binders incorporated

Traffic

Binderapplication

Low

High

Minimum

Maximum for target texture

Road authorities’ recommended applications

30%Min

Max

Development of Seal design methodologies

• Numerical behavioural model (T Milne)– Loading on a textured surface

Introduction

Run 3 : SBS : Round Stone : Bitumen InterfaceDisplacement Top of Centre Stone

-2.00

-1.00

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

1 22 43 64 85 106 127 148 169 190 211 232 253 274 295 316 337 358 379 400 421 442 463 484 505 526 547

Time Step Of Front And Back Axle

Dis

plac

emen

t (m

m)

Displacement Lateral Displacement Longitudinal Displacement Vertical

Ru n 3 : SBS : Rou n d Ston e : Bitu me n Inte rfac eDisp la ce me nt T op of Cen tre Sto n e

-2.00

-1.00

0 .00

1 .00

2 .00

3 .00

4 .00

5 .00

6 .00

7 .00

1 2 2 43 64 85 106 127 148 169 19 02 11 232 253 274 295 31 63 37 358 379 400 42 14 424 63 484 505 526 54 7

Ti me Step O f F ro nt A nd B ack A xl e

Disp

lace

men

t (mm

)

D isp lace me nt Lat eral D ispl acement Longi t udin al Di spl acement V er ti cal

Ru n 3 : SBS : Rou n d Ston e : Bitu me n Inte rfac eDisp la ce me nt T op of Cen tre Sto n e

-2.00

-1.00

0 .00

1 .00

2 .00

3 .00

4 .00

5 .00

6 .00

7 .00

1 2 2 43 64 85 106 127 148 169 19 02 11 232 253 274 295 31 63 37 358 379 400 42 14 424 63 484 505 526 54 7

Ti me Step O f F ro nt A nd B ack A xl e

Disp

lace

men

t (mm

)

D isp lace me nt Lat eral D ispl acement Longi t udin al Di spl acement V er ti cal

Run 3 : SBS : Round Stone : Bi tumen In terfa ceDisp lac em en t Top o f Ce ntre Stone

-2.0 0

-1.0 0

0.0 0

1.0 0

2.0 0

3.0 0

4.0 0

5.0 0

6.0 0

7.0 0

1 22 43 64 85 106 127 14 81 69 190 211 232 2 53 274 295 316 337 35 8 379 400 421 442 46 34 84 505 526 547

T ime S tep O f Fron t A nd Ba ck Ax le

Disp

lace

men

t (mm

)

Di spla cement L ate ral Di spla cement L ongi tud inal D is plac ement V er ti cal

Ru n 3 : SBS : Rou n d Ston e : Bitu me n Inte rfac eDisp la ce me nt T op of Cen tre Sto n e

-2.00

-1.00

0 .00

1 .00

2 .00

3 .00

4 .00

5 .00

6 .00

7 .00

1 2 2 43 64 85 106 127 148 169 19 02 11 232 253 274 295 31 63 37 358 379 400 42 14 424 63 484 505 526 54 7

Ti me Step O f F ro nt A nd B ack A xl e

Disp

lacem

ent (

mm

)

D isp lace me nt Lat eral D ispl acement Longi t udin al Di spl acement V er ti cal

σ = Bulk Stress σ = Micro Stress

σ Microσ Bulk

TyreInflation Pressure

P

TyreInflation Pressure

P

FmicroTextured

seal stone surface

σ Bulk < σ MicroF Bulk = F Micro

FbulkSmooth or closely

packed asphalt surface

Condition Condition IndexIndex

00Time (years)Time (years)

5050

100100

VCIt

Rate of deterioration dependent on• Type of surfacing• Condition before treatment• Traffic etc.Immediate

improvement

Effectiveness = (Area above Effectiveness = (Area above –– Area beneath) x ADT x Length Area beneath) x ADT x Length

Current studies on PMS data

TRH 3 Guideline document

• Part of TRH document series– Technical Recommendations for Highways

• Collate existing South African practice– Guidelines (not specifications)– Aimed at the average engineer (80/20)– Applicable only within range of experience– Highlights limitations and risks

• TRH3 (2007) – final review– Available March 2007

TRH 3 (2007)

• Background to sealwork• Investigation & seal type selection• Pre-treatment• Design

– Conventional and modified binder– Sand seals, Single & Double seals, – Slurry and Cape seals– Fogspray and rejuvenators– Geotextile seals– Graded aggregate seals

• Construction and quality control guidelines• Labour intensive sealing• Maintenance

Scope of the document

Seal selection

• Initial seals– Traffic volume and actions

– Gradient, base type and quality of construction(urban / rural)

– Maintenance capability

– Social environment, cost and purpose

Seal selection

• Reseals (additional information)– Condition of existing

pavement and surfacing

– Climatic sensitivity– Pre-treatment

requirement

Rutting Severe cracking

or pumping

Binder Active Aggregate

Loss

Warning crackingor Surfacing

Failures

Skid

problems

Voids

< 10mm

Yes

Yes

Yes

Yes

Yes

Yes

No

No

No

No

No

No

No

No

Yes

Yes

Yes

Yes

Yes

Yes

No

NoNo

No

Texture

or Coarse

Dry

DE + Text +Stone

DE

DE + Text +Stone

DE

Text +Stone

Text

Text +Stone

Nothing

PotentialAgg. loss

No potentialAgg. loss

DE

Yes

No

DE + Text + Mod

Text + Mod Stone

Stone

Medium

Treatment

Minimum Temperature (Station 589591)

-5

0

5

10

15

20

25

1-Ja

n-03

15-J

an-0

3

29-J

an-0

3

12-F

eb-0

3

26-F

eb-0

3

12-M

ar-0

3

26-M

ar-0

3

9-A

pr-0

3

23-A

pr-0

3

7-M

ay-0

3

21-M

ay-0

3

4-Ju

n-03

18-J

un-0

3

Date

Deg

ree

C

EXISTING TEXTURE ADJUSTMENT

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

EXISTING TEXTURE DEPTH

AD

DIT

ION

AL

NE

T B

IND

ER

ONLY MODIFIED BINDERSOR SPLIT APPLICATIONS

<2000 elv

3000 elv

4000 elv

>10000 elv

5000 elv

TEXTURETREATMENT

RECOMMENDED

PRE-TREATMENT

• Outstanding routine maintenance– Patching– Crack sealing– Edge break repair

• Shape correction– Roughness– Rut filling

• Texture treatment

SEAL DESIGN

PRINCIPLES TO DETERMINE BINDER APPLICATION RATE

VOID LOSS DUE TO AGGREGATE WEAR

TEXTURE FORSKID RESISTANCE

MAXIMUM VOIDS TO BEFILLED

VOID LOSS DUE TOEMBEDMENT

TOTAL VOIDS

MINIMUMVOIDS TO BE FILLED

30 %

100

%

ALD

Design…

Design parameters for Rational Design Method

• Full rational design method– Equivalent layer thickness – ELT (tray test)– Wear (based on stone hardness)– Embedment (Corrected ball penetration)– Existing texture (Sand patch test)– Required texture

Simplified design charts

• Accept ELT is a function of ALD• Accept stone within national

specification– Hardness (10% FACT > 210kN)

Design…

DESIGN PARAMETERS

• Traffic – Equivalent light vehicles per lane per day (1 Heavy = 40 Light )

• Average least dimension (ALD)• Embedment potential (Ball penetration)• Preferred texture depth• Adjustments

– existing texture– slow traffic / gradients– climate (macro and micro climates)– preferred aggregate matrix– modified binder adjustment– cold to hot binder Design…

Simplified design charts

Note: Risk - Too much binder for target texture, yet too little to prevent whip-off

ALD 10 mm SINGLE

0

5000

10000

15000

20000

25000

30000

35000

40000

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0

Embedment (mm)

Tra

ffic

(elv

/lane

/day

)

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0

Embedment (mm)

Net

t col

d bi

nder

(lit

res/

m2)

1.0 mm

0.5 mm

Minimum

0.7 mm

1.5 2.0 2.5 3.0 4.0

Corrected Ball Penetration (mm) 0.0 - 1.0

• ALD = 10mm• Traffic (ELV = 10 000) • Corrected BP = 1mm

• Min binder required= 1.15 l/m2

• Max binder for 1mm texture = 1.25 l/m2

ALD 10 mm SINGLE

PRACTICAL ADJUSTMENTS

• Additional binder for existing coarse texture

EXISTING TEXTURE ADJUSTMENT

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

EXISTING TEXTURE DEPTH

AD

DIT

ION

AL

NE

T B

IND

ER

ONLY MODIFIED BINDERSOR SPLIT APPLICATIONS

<2000 elv

3000 elv

4000 elv

>10000 elv

5000 elv

TEXTURETREATMENT

RECOMMENDED

Design…

PRACTICAL ADJUSTMENTS

• Reduction in binder for slow-moving vehicles and channelisation

• Up to 10%

Design…

PRACTICAL ADJUSTMENTS

• Adjustment for specific climate– Reduction in hot

humid areas– Increase in hot dry

areas

• Not applicable to modified binders

Design…

PRACTICAL ADJUSTMENTS

• Adjustment for preferred aggregate matrix

• Designs based on shoulder-to-shoulder matrix

• Open textures require adjustmentNote: experience required

Design…

PRACTICAL ADJUSTMENTS

• Adjustment : conventional to modified binder

• Several contributing factors– Less orientation (more

voids)– Binder properties e.g.

viscosity– Traffic

• Guidelines based on traffic and binder type

• Factors dependent on modified binder type

S-E1 Conversion Factors

1.01.01.1>20000

1.01.01.210000 - 20000

1.11.01.35000 - 10000

1.21.11.4<5000

SplitDoubleSingleTraffic ELV

Design…

PRACTICAL ADJUSTMENTS

• Adjustment cold to hot binder• Designs based on residual

binder (net cold binder)• Typical conversions• Some products – supplier

specific

1.07Bitumen Rubber

1.08Polymer Modified

1.5565% emulsion

1.19MC 3000

1.0980/100 pen bitumen

Cold to hotBinder type

Design…

Aggregate Spread rates

• Function of – Aggregate size – Shape– Purpose and seal

type

• Guidelines provided• Specification after

trials on site

Design…

Aggregate Spread Rate

50

70

90

110

130

150

170

190

210

230

4 5 6 7 8 9 10 11 12

ALD (mm)

First layer

Second layerCape Seal

Spr

ead

rate

m2 /

m3

Place

SpreadLevel

Roll static

Protectkerbs

Labour intensive seals(Slurry bound Macadam)

Apply slurry

Protect Vibratory roll

Smooth slush marks

Labour intensive seals(Slurry bound Macadam)

Cut back to full penetration

Check penetration at edges and repair

Apply final slurry

Drag burlap

Labour intensive (Slurry bound Macadam)

Ultra-thin Surfacings (UTFC)

• Paver-laid seal• Asphalt design principles apply• Proprietary products• Excellent initial performance (16 – 20mm)• Agrement certification required• Cost (16mm - similar to large aggregate double

seal)• Considerations

– Maintenance– Long-term performance– Turning actions

Way Forward

• Continuous feedback on TRH3 guidelines• Ongoing research • Learn from experience elsewhere• Regular updates

– Updates available on NDOT and SANRAL websites

THE END

Thank you very muchfor your attention!

TRB WORKSHOP 153SOUTH AFRICAN HIGHWAY TECHNOLOGY AND PRACTICE

gerriev@pdna.co.za