CCIL Asphalt and Aggregate 5 — Questions and Answers
Question 1: What is the purpose of the Rolling Thin Film Oven (RTFO) test in asphalt binder evaluation?
- Simulate long-term in-service aging of binder
- Simulate short-term aging during mixing and construction (Correct answer)
- Measure binder viscosity at mixing temperatures
- Determine binder flash point for safety
Correct answer: Simulate short-term aging during mixing and construction
The RTFO test (AASHTO T240 / ASTM D2872) simulates short-term oxidative aging of asphalt binder that occurs during hot-mix production and placement.
Question 2: Which aggregate test method quantifies the percentage of crushed faces on coarse aggregate particles?
- ASTM C131
- ASTM D5821 (Correct answer)
- ASTM D4791
- AASHTO T96
Correct answer: ASTM D5821
ASTM D5821 determines the percentage of fractured particles in coarse aggregate by counting particles with one or more mechanically fractured faces.
Question 3: In field density testing of compacted asphalt, what does the nuclear gauge method measure to determine density?
- Electrical resistance of the compacted layer
- Attenuation of gamma radiation passing through the material (Correct answer)
- Rebound deflection under a falling weight
- Thermal conductivity of the asphalt layer
Correct answer: Attenuation of gamma radiation passing through the material
Nuclear density gauges use a Cesium-137 or Radium-226 source; the attenuation of gamma radiation passing through or backscattered from the material correlates with its density.
Question 4: What is the primary mechanism causing stripping in asphalt pavements?
- Oxidative hardening of the binder at the surface
- Loss of adhesion between asphalt binder and aggregate in the presence of water (Correct answer)
- Freeze-thaw expansion cracking of aggregate
- Thermal contraction of binder below glass transition temperature
Correct answer: Loss of adhesion between asphalt binder and aggregate in the presence of water
Stripping occurs when water penetrates the asphalt-aggregate interface and displaces the binder, breaking the adhesive bond and weakening the pavement structure.
Question 5: Which test is used to evaluate moisture susceptibility of compacted asphalt mixtures according to AASHTO T283?
- Lottman test for tensile strength ratio (TSR) (Correct answer)
- Marshall Stability comparison before and after soaking
- Hamburg Wheel Track test with submerged specimen
- Cantabro abrasion loss test
Correct answer: Lottman test for tensile strength ratio (TSR)
AASHTO T283 determines moisture sensitivity by comparing the indirect tensile strength of conditioned (freeze-thaw saturated) specimens to unconditioned specimens as a Tensile Strength Ratio (TSR).
Question 6: What aggregate property does the 'sand equivalent' test (ASTM D2419) evaluate?
- The proportion of fine plastic fines or clay-like material in fine aggregate (Correct answer)
- The specific gravity of sand particles
- The moisture content of fine aggregate
- The angularity of sand particles
Correct answer: The proportion of fine plastic fines or clay-like material in fine aggregate
The sand equivalent test measures the relative proportions of clay-like or plastic fines versus clean, desirable aggregate fines in fine aggregate materials.
Question 7: In the context of CCIL proficiency testing, what is the primary purpose of participating in an interlaboratory study (ILS) for asphalt testing?
- To obtain certified materials for mix design
- To evaluate laboratory precision and identify systematic errors relative to peer labs (Correct answer)
- To train new technicians on test procedures
- To verify that equipment meets manufacturer specifications
Correct answer: To evaluate laboratory precision and identify systematic errors relative to peer labs
Interlaboratory studies allow labs to compare their test results against peer laboratories, identify bias or poor precision, and demonstrate competence for accreditation purposes.
CCIL Asphalt and Aggregate 5
What is the purpose of the Rolling Thin Film Oven (RTFO) test in asphalt binder evaluation?