CCIL Aggregate Gradation and Properties 4 — Questions and Answers
Question 1: What is the definition of 'apparent specific gravity' of aggregate?
- The ratio of oven-dry mass to the volume including all permeable pores
- The ratio of oven-dry mass to the volume of the solid material excluding all permeable pores (Correct answer)
- The ratio of SSD mass to total volume including all pores
- The mass of aggregate per unit bulk volume including air voids between particles
Correct answer: The ratio of oven-dry mass to the volume of the solid material excluding all permeable pores
Apparent specific gravity is the ratio of the oven-dry mass to the volume of the impermeable solid material only, excluding permeable pore space.
Question 2: Which gradation type typically produces the highest density and lowest void content in a compacted aggregate layer?
- Uniformly graded
- Open graded
- Well-graded (dense graded) (Correct answer)
- Gap graded
Correct answer: Well-graded (dense graded)
Well-graded (dense-graded) aggregate has particles distributed across a range of sizes so smaller particles fill the voids between larger particles, maximizing density and minimizing void content.
Question 3: What does the organic impurities test (ASTM C40) assess in fine aggregate?
- The clay content by weight percent
- The presence of organic matter that could interfere with concrete strength development (Correct answer)
- The sulfate content of the aggregate
- The chloride ion concentration in the aggregate
Correct answer: The presence of organic matter that could interfere with concrete strength development
ASTM C40 uses a sodium hydroxide solution color comparison to detect organic impurities in fine aggregate that could retard cement hydration and reduce concrete strength.
Question 4: What aggregate characteristic does the 'sand equivalent value' (ASTM D2419) measure?
- The ratio of sand to gravel in a blended aggregate
- The relative proportion of fine dust or clay-like material to sand-size particles (Correct answer)
- The specific gravity of fine aggregate
- The percentage of flat and elongated particles in fine aggregate
Correct answer: The relative proportion of fine dust or clay-like material to sand-size particles
The sand equivalent test measures the relative proportion of clay-like or plastic fines to sand-size material in fine aggregate or soil, with higher values indicating cleaner material.
Question 5: What is the nominal maximum aggregate size (NMAS) as defined in mixture design?
- The largest sieve size on which any aggregate is retained
- One sieve size larger than the first sieve to retain more than 10% of the aggregate (Correct answer)
- The sieve size at which 50% of the aggregate is retained
- The largest aggregate particle size present in the sample
Correct answer: One sieve size larger than the first sieve to retain more than 10% of the aggregate
Nominal maximum aggregate size is defined as one sieve size larger than the first sieve in a standard series that retains more than 10% of the aggregate.
Question 6: Which test method is used to determine the relative density and absorption of coarse aggregate per ASTM standards?
- ASTM C127 (Correct answer)
- ASTM C128
- ASTM C29
- ASTM C566
Correct answer: ASTM C127
ASTM C127 covers the test method for relative density (specific gravity) and absorption of coarse aggregate using submersion in water and SSD condition measurement.
Question 7: How does aggregate absorption affect concrete mix water content?
- High absorption aggregates require less mix water since they absorb excess water
- High absorption aggregates require additional mix water to compensate for water absorbed into the aggregate pores (Correct answer)
- Absorption has no effect on mix water demand
- High absorption aggregates increase slump without additional water
Correct answer: High absorption aggregates require additional mix water to compensate for water absorbed into the aggregate pores
Aggregate with high absorption will absorb mix water during batching, reducing the effective water-cement ratio; additional water must be added to maintain target workability and w/c ratio.
CCIL Aggregate Gradation and Properties 4
What is the definition of 'apparent specific gravity' of aggregate?