AAPA training

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