Asphalt Flashcards
Asphalt
Petroleum Based cementitious material that is mixed with aggregate to form the pavement
Common names for Asphalt
Asphalt, asphalt pavement, asphalt concrete, bituminous Concrete
Is Asphalt Flexible or Rigid?
Flexible
ASTM
American Society for Testing and Materials
AASHTO
American Association of State Highway and Transportation Officials
Thermoplasticity
Deforms under loads
Liquefies with heat
Asphalt is a flexible type of pavement
Viscosity
a measure of a fluid’s resistance to flow
directly influenced by the temperature
Temperature increase means a decrease in viscosity
Asphalt Grades
Degrees of Hardiness Grading for use-type
Asphalt Weathering
Oxidation and evaporation of hydrocarbons causes: Loss of plasticity
Become Brittle with Age
How to avoid weathering in Asphalt?
Slope subbases and subgrades
Proper compaction of layers
Timely sealing
Asphalt Insolvency
Resistant: Water, Salts, Acids, Alkalis
Susceptible: Petroleum
Remedy: Tar Sealer
Asphalt Color
Black
Selection Criteria for Asphalt Cements or Binder
Local Standards and practices
Fine Aggregate (Flows through No. 8 Sieve)
Mineral Dust
Mineral Filler
Coarse Aggregate (Retained by #8 Sieve)
Major Stabilizer
Macadam Aggregate
Coarse Aggregates of uniform size of 1.5-2.5”
Coarse wearing surface
Mixed with asphalt cement
Fine-graded Aggregate
Finer texture
Less road noise
Coarse-Graded Aggregate
Stable pavement
Coarser surface texture
More road noise
Dense-Graded Aggregate
Durable
Watertight surface
Highly stable
Open-Graded Aggregate
Little or no mineral filler Larger aggregates Good strength Rough texture High permeability Used in regions free of frost/thaw conditions
Recycled Glass as Aggregate
Works well in asphalt pavements of heavy use
Aggregate Hardiness (Toughness)
Ability to withstand loads and wear
Resistance to Stripping
Hydrophilic aggregates tend to strip away from the asphalt bond, reducing stability and skid resistance
Compounds (admixture?) added to asphalt mixtures
Surface Texture
Rough surface aids in bonding, stability, resistance to skidding and abrasion
Crushed Shape Aggregate
Interlock and give the pavement more strength
Asphalt Paving Mixtures: Asphalt Concrete
Most Common asphalt paving mixture
Asphalt Paving Mixtures: Surface Treatments
Color coating, sealing, improving skid resistance, or prolonging the service life of a fair to good pavement surface
Asphalt Paving Mixtures: Paving Blocks
Pre-molded
Used for Pedestrian Paving
Asphalt Paving Mixtures: Asphalt-treated Granular Base Courses
Less cost
Can be treated with asphalt cement to produce a stabilized base course
Typical Pavement Sections
(1) Layered Asphalt-Aggregate mixtures over a subgrade/improved subgrade
(2) Layered Asphalt-Aggregate mixtures over an aggregate base over a subgrade
(3) Layered Asphalt-Aggregate mixtures over existing pavement
Pavement Functions
Support loads
Smooth
Resistant to weathering
Minimum total Thickness of the Combined Asphalt Concrete Layers
The minimum total thickness of the combined asphalt concrete layers is 3” - 4”
Full-Depth Design
Asphalt aggregate mixture placed directly on a subgrade
Aggregate Base Design
Asphalt concrete placed on an untreated aggregate base over the prepared subgrade
Used in locations with frost action
Traffic Class I
Parking Lots, Driveways, Light Traffic, Residential Streets, Farm Roads
Traffic Class II
Residential Streets, Rural Farm and Residential Roads
Traffic Class III
Urban Minor Collector Streets
Traffic Class IV
Urban Minor Arterial and Light industrial Streets, Rural Major Collector, Minor arterial Highway
Traffic Class V
Urban Freeways, Expressways, Principal Arterial Highways, Urban interstate Highways, Some Industrial Roads
Road Thickness Design Procedure
Classify the traffic
Classify the subgrade
Determine Optimum asphalt concrete specs
Determine the thickness
Bike Paths and Walkway Width
3”-4” Wide
Use local codes and requirements
Golf Cart Paths
Surface a sand-asphalt mixture
Tennis Courts
Asphalt-concrete base of 0.75” of nominal maximum size designation covered either with sand-asphalt for the surface course or with a proprietary surfacing
Base course 3”
Surface course 1”
Asphalt Curbs
Back-filled with a solid granular material or well-compacted soil
Install on top of a solid, impervious pavement
Asphalt Gutters
Can be formed in a variety of cross-sections
Asphalt Underlayments
Asphalt Concrete is often used as an underlayment for surface courses
