Introduction to Flexible Pavements · 2016. 4. 12. · • Roads indicate a knowledge of pavement...
Transcript of Introduction to Flexible Pavements · 2016. 4. 12. · • Roads indicate a knowledge of pavement...
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Introduction to Flexible Pavements
Introduction to Flexible Pavements
• Video
• History of Pavements
• Terminology
Flexible Pavements – improving life - one generation to the next
http://www.youtube.com/watch?v=Ga-hOY8T8FA
History of Pavements
Can be categorised into four time periods: • Pre-Roman – pre 350BC
• Roman – 350BC to 500AD
• Post-Roman – 500AD – 1750AD
• Urbanisation – 1750AD - present
Sweet Track Somerset UK – 3800 BC
Roman Period
Characteristics • Major expansion and development of road network
essentially for military purposes by AD 200 network of 80,000 km of road
• Roads indicate a knowledge of pavement engineering
– Pavements built up above surrounding ground – Longitudinal edge drainage – Cementitious materials used in base course
Roman Period
Features of a high quality Roman road
Urbanised Period AD 1750 to Present Day
• Revival of pavement engineering – Tresaguet – Telford – McAdam
• Bituminous materials – Tar – Rock Asphalt – Lake Asphalt
• Bituminous surfaces – Penetration – Coated macadam – Mastic
TRESAGUET PAVEMENT
Telford Pavement
McADAM PAVEMENT
Historical Development • NSW
Ø 1789 – 1794 Parramatta, Windsor Ø 1814 Liverpool, Bathurst Ø 1836 Goulburn, Newcastle
• Tasmania Ø 1815 Hobart to Launceston
• Victoria Ø 1836 – 1851 Private roads
Australian Road Network
Urbanised Period
• Problems with macadam pavements – dusty/muddy – unsanitary
• Invention of the bicycle and pneumatic tyre • Increased demand for smoother surfaces in urban areas • Manufactured asphalt
– US development – hot rolled asphalt - UK
• Surface dressing/sprayed seal
Flexible Pavements
n Maximum deflec,on -‐ deflec,on under the tyre n Curvature -‐ difference in deflec,on under tyre and at an
offset of 200mm
Rigid Pavements
n Concrete structure, various types n Requires uniform support, lean mix concrete or bound
subbases
Australian Road Network
Country Persons per km of road
n Small popula,on n Large network n Dispersed popula,on
centers
Australian Road Network Domestic Freight Transport
64.7% road
25.8% rail
3% coastal shipping
2.6% pipeline
3% conveyor
<0.1% air
64.74% 25.8%
Australian Asphalt Pavement Association
National highway 18,620 14.2
Rural arterial 94,854 21.6
Urban arterial 12,398 39.6
Rural local 600,725 6.3
Urban local 84,845 18.3
All road types 811,443 100
Road Type Australia (km) Travel (%)
Road Length and Travel Road Length and Travel
Australian Road Network
Queensland ROAD STATS
177 000 km Total 143 000 km LG 33 347 km QTMR 4 150 km state strategic 24 147 km regional 5 050 km na<onal 25% of Australian State controlled roads, 80% QLD traffic $55b (2014)
Terminology
• Binders
• Aggregates
• Asphalts
• Surfacings
• Pavements
Binders • Bitumen
– Viscous semi-solid at room temperature refined from crude oil • Binder
– any bituminous material used for the purpose of adhesion in the production of surfacings or asphalt
• Tar – destructive distillation of wood/coal
• Cutter oil – light grade distillate (e.g. Kerosene) added to bitumen to reduce
viscosity (e.g. cutback bitumen) – High flash point cutter, flash point > 60°C
• Flux oil – heavy fuel oil added to bitumen for longer term reduction in viscosity
Binders (cont.)
• Emulsion – Fine dispersion of bitumen in water with bitumen droplets either
positively (cationic) or negatively (anionic) charged • PMB
– Polymer modified bitumen • Polymer
– long chain chemical based on one (e.g. PBD) or two (e.g. SBS, EVA) molecules
• Foamed Bitumen
Aggregates
• Asphalt – Coarse > 4.75mm – Fine < 4.75mm – Filler < 0.075mm
• Sealing
– ALD, Average Least Dimension – Particles falling on a surface will preferentially lie on their largest face
i.e. with their shortest dimension pointing upwards. The ALD is the average of the shortest dimensions of a group of stone particles
Asphalts
• Hot mix - dense graded - gap graded; fine (FGG) coarse
(SMA) - open graded - recycled asphalt pavement (RAP)
• Warm mix - may use emulsion - proprietary systems
• Cold mix - uses flux oil to keep workable in stock pile
Surfacings • Spray seal - application of binder followed by layer / layer of
aggregate • SAM - strain alleviating membrane
- seal with modified binder or geotextile
• SAMI - strain alleviating membrane interlayer - as for SAM but overlaid with asphalt
• Slurry - emulsion and small aggregate and fillers mixed in a purpose-built truck and applied to the pavement surface
Surfacings (cont)
• Microsurfacing - slurry using polymer modified emulsion and larger aggregate
• Ultra-thin - thin asphalt surfacing using open-graded or coarse gap graded asphalt
Pavements
• CBR - Californian Bearing Ratio - measure of the strength
of pavement materials and subgrade
• AADT - Annual Average Daily Traffic
- measure of the traffic flow, all types of vehicles
• CV - Commercial vehicles > 3t Gross Weight
Pavements (cont)
• ESA - Equivalent Standard Axle - a standard axle load is 8.2t on a dual-
tyred single axle; other loads and other axle types (e.g. triaxle) can
be expressed as a number of ESAs on the basis of causing equivalent pavement damage
• Flexible pavements - conventional - deep strength - full depth
Critical Properties of Flexible Pavement Materials
• Binders - ADHESION Vs COHESION
• Adhesion is the force that holds two materials together. In asphalt pavements, bitumen serves as the adhesive binder that holds particles of aggregate together.
• Cohesion is the force by which the molecules of a binder are held together
• Asphalt – FATIGUE (Cracking) Vs WHEEL TRACKING (Rutting)
Critical Properties of Flexible Pavement Materials
• Pavement Layers
FATIGUE Vs WHEEL TRACKING (Cracking) (Rutting)
Performance must be in balance to optimise pavement life
Review: Introduction to Flexible Pavements
• Video
• History of Pavements
• Terminology
http://www.youtube.com/watch?v=Ga-hOY8T8FA