Asphalt and bitumen Flashcards
Asphalt is made up of what?
Aggregate,binder and filler
Disadvantages of unsurfaced road?
It is too dusty and noisy
Deteriorates easily
Low skid
Advantages of surfacing pavement with asphalt?
Better skiding
Provides comforty and safety
Reduced noise and dust
AN engineer is tasked with the design of an asphalt Road which factors must be considered in the design of suitable material for the hot mix us asphalt and Surface seals?
Hot mix asphalt: site-preparation
Pavers and paving
Compaction
Testing
Surface seals: preparation
Pre-coating
Tack coat
Aggregate
Fog spray
Penetration coat
Laboratory Mix design phases
Phase 1: evaluate the design situation
-what traffic volume and speed will pavement experience?
-what construction issues can be encountered?
- which are materials available?
-what climate conditions it will be built on?
Phase 2:Identify design objectives
-prevent rutting
-constructionability
-durability and fatigue
-noise reduction
-dust reduction
-skid resistance
Phase 3:evaluate the materials
-binder
-filler
-aggregate
Phase 4: volumetric design processes
-spatial consideration and selection of gradation
- selection of target binder content
- sample conditioning and compaction
-evaluation volume
- finalise binder content
Phase 5 : performance test
Required test is determined by design objectives in phase 2, if the criteria is met thus the design can be implemented, otherwise phase 4 must be repeated
Marshall stability and flow test procedure
-100mm diameter marshall briquettes are used
-briquettes are immersed in hot water bath
- briquettes are placed in breaking head apparatus
- load is applied at the constant rate until briquettes collapses
- max load is measured in KN(stability value)
-deformation is measured in mm(flow value)
Indirect tensile strength (ITS)
100mm diameter Marshall briquettes are used
Briquettes are placed in breaking head apparatus
Load is applied at the constant rate until briquettes fails
Max load is measured in KN(tensile strength)
Hamburg wheel tracking
150 mm diameter gyratory briquettes are used
Briquettes are trimmed and placed in moulds
Moulds are fastened into empty water bath
Water bath is filled and heated
Testing machine rolls a wheel for the set number of cycles
Rut depth is determined at failure
Binder and its grade systems
Define softning point
Performance grade system:PG 50-20 binder is used in pavement where temperatures vary between 20•C to 50•C
Penetrating grade system: 50/70 binder ..but normally they use 100g needle which goes to the depth at 25•C
50/70binder is used to areas where needle goes through between depth of 50Dmm and 70Dmm
Softening point : The point at which bitumen can no longer maintain 3.5g ball
What is purpose of Bitumen and list all the characteristics/properties of bitumen
The purpose of bitumen is to act as organic glue and water proofing when is combined with inorganic stone and sand
Characteristics:
Cohesion: improved with modification,tensile stress, typical ductile force curves
Elasticity: recovery, improved with modification, fatigue resistance
Adhesion: reduce time lag
Pre coat stone
Use emulsion spray fog
How is adhesion influenced?
Ambient temperature
Moisture and dust
Level of modification
Rheology
Ageing and durability:
Causes; time,temperature, traffic
Prestress on pavement
Cracking: it happens when asphalt is too rigid
Rutting: when asphalt is too flexible
Ravelling: it happens due to stone loss
Bleeding: when there is excessive binder content
Why modify ?
Improved flexibility
Improved stiffness
Improved cohesion
Improved durability,adhesion and toughness
Improved resistance to ageing
Improved consistency
Which areas do we need to apply modifiers?
Cracked areas
Areas of high flexibility
Heavy traffic volume and steep incline
Fluctuating temperatures
Give us the types of modifiers
SBS pellets
EVA pellets
Binder crumbs
Extender oils
Natural hydrocarbons modifiers
