PIC Aggregate & Binder Specifications 3 — Questions and Answers
Question 1: Which test method determines the specific gravity of fine aggregate for use in HMA volumetric calculations?
- AASHTO T 84 (Correct answer)
- AASHTO T 85
- AASHTO T 166
- AASHTO T 209
Correct answer: AASHTO T 84
AASHTO T 84 determines the bulk specific gravity and absorption of fine aggregate (passing the 4.75mm sieve) used in volumetric mix design.
Question 2: The Dynamic Shear Rheometer (DSR) measures asphalt binder properties related to:
- Rutting and fatigue cracking resistance (Correct answer)
- Low-temperature thermal cracking
- Aggregate-binder adhesion
- Binder oxidation rate
Correct answer: Rutting and fatigue cracking resistance
The DSR measures the complex shear modulus (G*) and phase angle (δ) of asphalt binder, which predict rutting resistance at high temperatures and fatigue cracking at intermediate temperatures.
Question 3: When aggregate flakiness or elongation exceeds specification limits, the most likely pavement distress is:
- Particle breakdown and reduced stability (Correct answer)
- Increased skid resistance
- Improved compaction density
- Reduced permeability
Correct answer: Particle breakdown and reduced stability
Flat and elongated aggregate particles are prone to breaking under compaction and traffic loads, reducing mix stability and long-term performance.
Question 4: The 'dust-to-binder ratio' (P0.075/Pbe) in Superpave mix design should typically fall between:
- 0.6 and 1.2 (Correct answer)
- 0.3 and 0.6
- 1.5 and 2.5
- 2.0 and 4.0
Correct answer: 0.6 and 1.2
Superpave specifies a dust-to-binder ratio between 0.6 and 1.2 to ensure proper filler-binder interaction without excess stiffening or weakening of the mixture.
Question 5: Which test evaluates the stripping potential of HMA by measuring retained strength after moisture conditioning?
- AASHTO T 283 (Lottman test) (Correct answer)
- AASHTO T 182
- AASHTO T 176
- AASHTO T 96
Correct answer: AASHTO T 283 (Lottman test)
AASHTO T 283 (commonly called the modified Lottman test) measures tensile strength ratio (TSR) by comparing conditioned to unconditioned specimens to evaluate moisture susceptibility.
Question 6: A coarse aggregate with a crushed face count requirement of '95/90' means:
- 95% of particles have at least one crushed face; 90% have two or more (Correct answer)
- 90% pass a 95mm sieve
- 95% retained on 90mm sieve
- 90% particles with 95% angularity index
Correct answer: 95% of particles have at least one crushed face; 90% have two or more
The notation 95/90 means 95% of aggregate particles must have at least one mechanically fractured face and 90% must have two or more fractured faces, ensuring angularity.
Question 7: What is the primary purpose of anti-stripping additives (hydrated lime or liquid anti-strip) in asphalt mixes?
- Improve adhesion between asphalt binder and aggregate in the presence of moisture (Correct answer)
- Increase binder viscosity at high temperatures
- Reduce aggregate degradation during mixing
- Lower the required mixing temperature
Correct answer: Improve adhesion between asphalt binder and aggregate in the presence of moisture
Anti-stripping additives enhance the chemical bond between asphalt binder and aggregate surfaces to prevent moisture-induced stripping (loss of adhesion).
PIC Aggregate & Binder Specifications 3
Which test method determines the specific gravity of fine aggregate for use in HMA volumetric calculations?