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Terms in this set (58)
What is asphalt cement? A viscous cementitious material composed primarily of bitumen or high molecular
weight hydrocarbons.
What is bitumen? Natural occurring black or brown sticky substance principally of high molecular
weight hydrocarbons soluble in carbon disulfide (now replaced by
trichloroethylene).
What is asphalt concrete? A complex material consisting of a mixture of asphalt cement and mineral
aggregates.
How is asphalt cement produced? Artificially as a by-product from the treatment of crude oil for the extraction of
gasoline, kerosene, and diesel.
Where is asphalt used? Roads, roofing and weather resistant elements, water proofing elements.
What type of material is asphalt cement? Is it viscous? Thermoplastic. Yes it is viscous.
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Describe the process of age hardening/aging - asphalt is subjected to heating for variable time periods at a wide range of
temperatures during mixing, curing, and service life
- substantial changes occur in the structure and composition of the asphalt
molecules during these processes
- due to volatilization of light hydrocarbon fractions and oxidation by reacting with
the oxygen in the environment
- these changs in turn cause the asphalt cement to harden or become less
ductile.
What is viscosity? The fundamental materials property relating to the rate of shear strain in a fluid to
the applied shear stress (resistance to flow).
What is consistency? An empirical measure of the resistance offered by a fluid to continuous
deformation when subjected to a shearing stress.
How does viscosity vary with time? Viscosity of asphalt cements increases with time, due to aging or age hardening.
Where does the greatest extent of aging in asphalt In the surface of asphalt concrete pavements where the binder is most exposed
occur? to oxygen and UV light.
How is consistency measured? Empirical penetration resistance test. Measured in terms of depth that a standard
needle penetrates a sample under standard conditions of loading, time and
temperature.
It identifies an asphalt as to its hardness or grade. It measures changes in
hardness due to heating or changes in temperature.
What is the flashpoint test? Determines the temperature to which an asphalt can be safely heated in the
presence of an open flame.
What is the ductility test? Measures the distance a standard asphalt cement sample will stretch without
breaking under standard testing conditions.
High ductility -- high temperature susceptibility
Low ductility -- poor adhesive property
Describe the elastic/plastic behaviour of asphalt cement. At low temperatures or short load durations, behaviour is elastic.
At high temperatures, or long load durations, behaviour is plastic.
Typical field behaviour lies somewhere between these two extremes.
Describe temperature susceptibility of asphalt cement. The greater the rate of change of viscosity with temperature, the more
temperature susceptible the asphalt cement becomes - the more liable it is to
fracture or crack at low temperature or to deform excessively at high temperature
Describe the tensile strength of asphalt cement. Tensile strength is dependent upon its viscoelastic and physical characteristics,
rate of loading, and temperature.
Reaches a max of 2-4 MPa at low temps and decreases as load duration and
temp increase.
What are the required properties of asphalt cement? - low temp susceptibility
- good adhesion and cohesion
- good durability - low rate of hardening.
- proper viscosity for high and low service temps (to avoid rutting and shrinkage
cracks).
What are liquid asphalts? When an asphalt cement is combined with a liquid solvent of lower viscosity to
reduce overall viscosity.
After placement the solid evaporates, leaving only the asphalt cement, resulting
in a gradual increase in viscosity.
What are the two basic types of liquid asphalts? - cutback asphalts
- emulsified asphalts
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