CCIL Aggregate Gradation and Properties 3 — Questions and Answers
Question 1: What does 'bulk specific gravity (SSD)' mean in the context of aggregate testing?
- The ratio of the oven-dry mass to the volume of water displaced
- The ratio of the SSD mass to the mass of an equal volume of water including permeable pores (Correct answer)
- The ratio of apparent volume to oven-dry mass
- The mass per unit volume of freshly quarried rock
Correct answer: The ratio of the SSD mass to the mass of an equal volume of water including permeable pores
Bulk specific gravity (SSD) is the ratio of the saturated surface-dry mass of aggregate to the mass of an equal volume of water, including the volume of permeable pores.
Question 2: What is the flat and elongated particle ratio used to assess?
- Aggregate surface texture
- Aggregate particle shape and potential for crushing under load (Correct answer)
- The proportion of crushed faces in aggregate
- Aggregate moisture absorption rate
Correct answer: Aggregate particle shape and potential for crushing under load
Flat and elongated particles are more susceptible to breaking under compaction loads, and their ratio is measured to assess aggregate durability and compactability in pavement construction.
Question 3: Which ASTM test method is used to determine the unit weight and voids in aggregate?
- ASTM C127
- ASTM C29 (Correct answer)
- ASTM C131
- ASTM C88
Correct answer: ASTM C29
ASTM C29 covers the standard test method for bulk density (unit weight) and voids in aggregate using rodding, jigging, or shoveling procedures.
Question 4: What is the purpose of the aggregate soundness test (ASTM C88)?
- To measure aggregate hardness under impact
- To evaluate the resistance of aggregate to weathering by freeze-thaw or wetting-drying cycles (Correct answer)
- To determine the specific gravity of aggregate particles
- To classify aggregate by particle shape
Correct answer: To evaluate the resistance of aggregate to weathering by freeze-thaw or wetting-drying cycles
The soundness test uses sodium or magnesium sulfate solution to simulate weathering and assess whether aggregate will deteriorate when exposed to freeze-thaw cycling in service.
Question 5: Which aggregate property most directly affects the workability and water demand of a concrete mix?
- Los Angeles abrasion value
- Aggregate gradation and particle shape (Correct answer)
- Soundness loss percentage
- Bulk specific gravity
Correct answer: Aggregate gradation and particle shape
Aggregate gradation and particle shape directly influence void content in the mix; gap-graded or angular aggregates increase void content and water demand, reducing workability.
Question 6: What does the 'percent crushed faces' or 'crushed content' test measure?
- The percentage of aggregate passing the No. 200 sieve after crushing
- The proportion of aggregate particles with one or more mechanically fractured faces (Correct answer)
- The amount of aggregate broken by the Los Angeles machine
- The fraction of angular particles in natural gravel
Correct answer: The proportion of aggregate particles with one or more mechanically fractured faces
Crushed face content measures the percentage of aggregate particles that have at least one fractured face created by mechanical crushing, which improves interlock and stability in pavement layers.
Question 7: When conducting sieve analysis, what is the maximum allowable mass retained on any single sieve to avoid overloading?
- It depends on the sieve diameter and opening size as specified by ASTM C136 (Correct answer)
- 200 grams per sieve regardless of size
- 500 grams per sieve regardless of size
- 10% of the original sample mass per sieve
Correct answer: It depends on the sieve diameter and opening size as specified by ASTM C136
ASTM C136 specifies maximum mass retained per sieve based on sieve diameter and opening size; overloading a sieve can cause particles to be retained that should pass, skewing results.
CCIL Aggregate Gradation and Properties 3
What does 'bulk specific gravity (SSD)' mean in the context of aggregate testing?