28. Properties of AC

Question 1

Purity (solubility)

Answer 1

Asphalt should consist of almost pure bitumen. Impurities are not active and can be detrimental to performance

Question 2

Safety

Answer 2

Flash point: temperature where vapour given off will burn
Fire point: temperature where binder will burn

Question 3

Consistency

Answer 3

Degree of fluidity at a particular temperature

Question 4

Penetration test

Answer 4

Oldest asphalt test. Penetration of a standard needle into the asphalt sample

Question 5

Viscosity

Answer 5

Absolute (60C), max HMA temp during summer, and kinematic (135C), mixing and laydown temps

Question 6

Rotational viscometer

Answer 6

Machine to measure viscosity at 135C, controls pumpability, mixability, and workability

Question 7

Time and temperature

Answer 7

Properties are dependent on rate of loading and temperatures. Slow moving causes more damage

Question 8

Specific gravity

Answer 8

Changes with temperature, usually the S.G. at 27C is used for buying/selling asphalt binders

Question 9

Durability

Answer 9

How properties change with age, result of oxidation, volatilization, and polymerization

Question 10

Aging of bitumen

Answer 10

Asphalt binders become harder and stiffer due to aging, penetration decreases and viscosity increases

Question 11

Aging simulations

Answer 11

Short term: thin film oven (TFO) and rolling thin film oven (RTFO)
Long term: 7-10 yrs, pressure aging vessel (PAV)

Question 12

Rutting

Answer 12

Depressions that form in wheel paths

Question 13

Fatigue cracking

Answer 13

Function of repeated traffic loads over time (looks like crocidile skin)

Question 14

Thermal cracking

Answer 14

Transverse cracking from temperature drops