South African Seal Design & Practice
description
Transcript of South African Seal Design & Practice
South African Seal Design &
Practice
Trevor Distin
Overview
• Introduction– Use of seals
• Design– Parameters used in
SA seal design
• Construction– Pushing the
operational limits of seals
Acknowledgement
• CAPSA07 papers on consolidating best practice in surfacing seals– Gerry Van Zyl– Douglas Judd
• AAPA for sponsoring my trip
Introduction…
Area (Sq km) 1,219,912 7,686,850
Population 44 million 20 million
Road Network 750,000km 810,000km
Surfaced Roads 150,000km 337,000km
Bitumen Consumed 310,000T 800,000T
• 80% of roads sealed with a surfacing seal
• Less than 2600km carry ADT > 10,000 in both directions
Introduction…
Road Pavements in South Africa
pavement structure
side walk
FILL OR IN SITU MATERIAL
kerb
bituminous
surfacing
Base (+90 % Granular)
Sub-base (granular or cemented)
Selected (granular)
Seals > 80%(3mm – 20mm)
Introduction…
fog spray optional
stone
tack coat
existing substrate
fog spray optional
stone
tack coat
existing substrate
fog spray optional
tack coat
existing substrate
1st layer - stone
2nd layer - stone
penetration coat
fog spray optional
tack coat
existing substrate
1st layer - stone
2nd layer - stone
penetration coat
fog spray optional
tack coat
existing substrate
1st layer - stone
2nd layer - stone
penetration coat
fog spray optional
tack coat
existing substrate
1st layer - stone
2nd layer - stone
penetration coat
fog spray optional
tack coat
existing substrate
1st layer - stone
2nd layer - stone
penetration coat
tack coat
existing substrate
1st layer - stone
2nd layer - stone
penetration coat
tack coat
existing substrate
stone
fine slurry (1 or 2 layers)
fog spray
tack coat
existing substrate
stone
fine slurry (1 or 2 layers)
fog spray
tack coat
existing substrate
sand or grit
tack coat
existing substrate
sand or grit
Common seals
• Single seal
• Double seal
• 1 ½ seal
• Cape seal
• Sand seal
Introduction…
Less common seals
• Geofabric seal
• Split seal
• Choke seal
• Inverted seal
• Graded seal (Otta)
stone
tack coat
existing substrate
thin layer of aggregate
penetration coat
stone
tack coat
existing substrate
thin layer of aggregate
penetration coat
tack coat
existing substrate
1st layer stone
penetration coat
2nd layer - stone
3rd layer - stone
tack coat
existing substrate
1st layer stone
penetration coat
2nd layer - stone
3rd layer - stone
tack coat
existing substrate
1st layer stone
2nd layer - stone
tack coat
existing substrate
1st layer stone
2nd layer - stone
tack coat
existing substrate
1st layer stone
2nd layer - stone
penetration coat
tack coat
existing substrate
1st layer stone
2nd layer - stone
penetration coat
tack coat
existing substrate
graded aggregate
sand
tack coat
tack coat
existing substrate
graded aggregate
sand
tack coat
Introduction…
Seal design process
• Site investigation • Define uniform sections• Sample and test material• Select appropriate seal and binder type• Measurement and interpretation of Measurement and interpretation of
design input parametersdesign input parameters• Calculate binder application rates• Determine aggregate spread rates• Monitor conditions on site and early
performance and make adjustmentsDesign…
Principles for the determination of the 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 3
0 %
10
0 %
AL
D
Design…
Design and construction of surfacing seals TRH 3:2007
Design input parameters• Basic Design Parameters
– Traffic volume in Traffic volume in ELVs/lane/dayELVs/lane/day
– Corrected Ball Corrected Ball Penetration ValuePenetration Value
– Preferred texture depthPreferred texture depth• Adjustment Factors
– Existing textureExisting texture– Slow moving heavy Slow moving heavy
vehicles/ gradientvehicles/ gradient– Macro & Micro climates– Aggregate SpreadAggregate Spread
• Conversion Factors– Hot applied modified
binders– Cold to hot application
Design…
Corrected ball penetration
Determine potential embedment And void loss
Embedment…
Corrected ball penetration
TMH6 Method ST4
Pen T0 = Pen T1 – K (T1 – T0)
Where
T0 = Design Surface temperature
T1 = Measured Surface temperature
K = Temperature-susceptibility based on seal type
Temperature isotherms
Embedment…
NORTHERN PROV.
MPUMULANGAJHB
NAMIBIA ZIMBABWE
BLOEMFONTEIN
CAPE TOWN
MUSSINA
55.0
50.0
40.0
40.0
45.0
CHIPINGE
FRANCISTOWN
KEETMANSHOOP
LESOTHO
EASTERN CAPE
WESTERN CAPE
NORTHERN CAPE
FREE STATE
NORTH WEST
KWAZULUNATAL
NAMIBIA
BOTSWANA
MOCAMBIQUE
DURBAN
GABORONE
WINDHOEK
PORT ELIZABETHMOSSEL BAY
55.0
MAPUTO
WALVIS BAY
BEIRA
EAST LONDON
50.0
50.0
50.0
45.0
45.0
45.0
45.0
45.0
40.0
40.0
45.0
NORTHERN PROV.
MPUMULANGAJHB
NAMIBIA ZIMBABWE
BLOEMFONTEIN
CAPE TOWN
MUSSINA
55.0
50.0
40.0
40.0
45.0
CHIPINGE
FRANCISTOWN
KEETMANSHOOP
LESOTHO
EASTERN CAPE
WESTERN CAPE
NORTHERN CAPE
FREE STATE
NORTH WEST
KWAZULUNATAL
NAMIBIA
BOTSWANA
MOCAMBIQUE
DURBAN
GABORONE
WINDHOEK
PORT ELIZABETHMOSSEL BAY
55.0
MAPUTO
WALVIS BAY
BEIRA
EAST LONDON
50.0
50.0
50.0
45.0
45.0
45.0
45.0
45.0
40.0
40.0
45.0
Result of ignoring embedment
Embedment…Values above 3mm – Warning !
Recommended adjustments
• Subdivision of representative areas• Measurements:
– inside and outside wheel track– record penetration for 1 and 2 blows
• Observe and record– Main cause of ball penetration value
• Embedment• Crushing• Displacement
– Existing surface type– Degree of dry/brittleness and fattiness– Measure surface temperature (> 25 oC)
Embedment…
Recommended adjustmentsExisting surface type and degree of fattiness
Recommended K –factor (mm/°C)
Dry/ Brittleness (TMH9)
Fattiness/ Bleeding (TMH9)
(Degree >=3)
(Degree <3)
(Degree 3 - 4)
(Degree 5)
Single and multiple seals
0,0 0,02 0,04 0,08
Slurry seals and sand seals
0,03 0,05 0,06 0,08
Cape Seals 0.03 0,06 0,07 0,08
Asphalt (Sand Mastic)
0,05 0,07 0,08 0,08
Asphalt (Stone mastic)
0,02 0,04 0,05 0,08
Embedment…
Macro texture depth
• Function of vehicle speed to– displace water– improve skid resistance
Speed < 60km/h = min 0.5mmSpeed >60 < 100km/h = min 0.7mmSpeed > 100km/h = min 1.0mm
Texture…
Adjustment for existing surface texture
• How much extra ?30%
Min
Max
Texture…
Concerns raised
• Test method – Different methods
(Hand or box)– Variation up to 30%– Difference in and in-
between wheel tracks
• Could we ignore existing texture depth for specific conditions ?
Texture…
Impact of 30% variation Existing Texture Adjustment
Existing texture depth
0.20
0.30
0.40
0.10
0.00
0.05
0.15
0.25
0.35
0.45
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
<2000 elv
3000 elv
4000 elv
>10000 elv
5000 elv
texturetreatment
recommended
only modified bindersor split applications
Existing Texture Adjustment
Existing texture depth
0.20
0.30
0.40
0.10
0.00
0.05
0.15
0.25
0.35
0.45
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
<2000 elv
3000 elv
4000 elv
>10000 elv
5000 elv
texturetreatment
recommended
only modified bindersor split applications
0.20
0.30
0.40
0.10
0.00
0.05
0.15
0.25
0.35
0.45
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
<2000 elv<2000 elv
3000 elv3000 elv
4000 elv4000 elv
>10000 elv>10000 elv
5000 elv5000 elv
texturetreatment
recommended
only modified bindersor split applications
Ad
dit
ion
al
bin
de
r re
qu
ire
d (
l/m
2)
Texture…
Impact not significant- Very small with high traffic
- Low volume (large envelope)
When to ignore texture depth
Texture…
Best solution
• Designer on site• Understand what is
measured• Evaluate how the
new seal will fit into the existing texture
• Decide if additional binder is required
Texture…
Traffic/gradient
Adjustment for Gradient
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
00 2 4 6 8 10
Gradient (%)
Bin
de
r re
du
cti
on
(%
)
Adjustment for Gradient
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
00 2 4 6 8 10
Gradient (%)
Bin
de
r re
du
cti
on
(%
)
Bleeding generally occurs when heavy vehicle speed below 40km
Vehicle speed vs gradient
Aggregate spread rate
Shoulder to shoulder Open matrix
Impacts on binder application rate
Pushing the operational limits
• Major performance benefits in using seals on high volume roads
• Seals can compete with UTFC on high volume roads • High volume roads = heavy truck traffic• 1 heavy = 40 Equivalent Light Vehicle (ELV)• TRH 3 covers up to 20,000 elv• Good performance report up to 60,000 elv
Design aspects
• Traffic – Concentrated in wheel paths
• Geometry– Heavier trafficked roads generally higher
geometric standards
60% of lane width subject to ELV of 20-30% of design traffic
Design aspects - binder
• Use modified binders TG1:2007 – Bitumen rubber (S-R1) R&B > 55 °C– SBS (S-E2) R&B > 60 °C– SBR (S-E1) R&B > 50 °C
• Performance characteristics required– Good initial adhesion– High binder application rate– High temperature resistance to flow– Low temperature adhesion
• No cutting back
Design aspects - aggregates
• Most control over– Shape, size and hardness
• Aim for single sized with low flakines index– eg <10% on 13.2 mm
• Do seal design in reverse to determine ALD to fit traffic and binder
• Will result in higher aggregate costs
• Consider alternative such as steel slag
Construction aspects
• Accommodation of traffic– Ability to deal with traffic influences seal
selection– Can the lane be closed for 24 hours?
• Opening to traffic– Open seal to traffic for 2 hours before
temperature drops <25°C– Only open seal to traffic when
temperature 15°C below softer point
Joints between sprays
• Position of longitudinal joints
• Binder overlap– String lines– 100% coverage
Contractors equipment
• Adequate capacity and good working order
• Sufficient equipment to cover binder in 5 min– Trucks– Rollers– Self propelled brooms
Project specifications• Restrictions with respect to climatic conditions• Aggregate requirements• Accommodation of Traffic• Opening to Traffic• Isolated application of additional binder• Joint positions• Equipment
– Rollers– Rotary Brooms
Conclusions
• Selection based on performance and not economics
• Best quality materials required• Attention to detail during construction• Design cannot be done from the office• Adjustments on site if/ when required• Recommendations to be considered for
minor adjustments to TRH3 and TMH6
Conclusions
Need to link between the countries to transfer updating in concepts and practice – Texture depth / speed– Texture depth – spreader box vs sand
patch– Aggregate spread rate – visual standard ?– Ball penetration – corrections &
interpretation – Heavy vehicle “high impact areas” – slow
travel zones
Thank you