CCIL Aggregate Gradation and Properties 2 — Questions and Answers
Question 1: What does the term 'fineness modulus' represent in aggregate testing?
- The percentage of fines passing the No. 200 sieve
- A single number representing the average size of particles in a sand sample (Correct answer)
- The ratio of coarse to fine aggregate by mass
- The degree of angularity of aggregate particles
Correct answer: A single number representing the average size of particles in a sand sample
Fineness modulus is computed by summing cumulative percentages retained on a standard sieve series and dividing by 100, yielding a number that represents the average particle size of a sand sample.
Question 2: According to ASTM C136, sieve analysis of aggregates requires that each sieve be shaken for a minimum of how many minutes?
- 1 minute (Correct answer)
- 5 minutes
- 10 minutes
- 15 minutes
Correct answer: 1 minute
ASTM C136 requires that sieving continue until no more than 1% of the retained material passes the sieve in 1 minute of hand sieving.
Question 3: Which sieve size is used to separate coarse aggregate from fine aggregate in standard practice?
- No. 4 (4.75 mm) (Correct answer)
- No. 8 (2.36 mm)
- 9.5 mm (3/8 in)
- No. 16 (1.18 mm)
Correct answer: No. 4 (4.75 mm)
The No. 4 (4.75 mm) sieve is the standard dividing line between coarse aggregate and fine aggregate per ASTM definitions.
Question 4: What is the primary purpose of performing a wash sieve analysis before dry sieve analysis?
- To remove lightweight particles from the sample
- To separate aggregate by shape
- To remove clay, silt, and dust coatings that could blind sieves (Correct answer)
- To increase the aggregate's absorption capacity
Correct answer: To remove clay, silt, and dust coatings that could blind sieves
Washing the sample before sieve analysis removes clay, silt, and dust that would otherwise clog or blind the sieve openings and give inaccurate gradation results.
Question 5: Gap-graded aggregate is characterized by which of the following gradation patterns?
- A uniform distribution across all sieve sizes
- An absence of intermediate particle sizes, with concentrations at coarse and fine ends (Correct answer)
- All particles retained on a single sieve
- A gradation dominated by the middle fraction sizes
Correct answer: An absence of intermediate particle sizes, with concentrations at coarse and fine ends
Gap-graded aggregate lacks particles in one or more intermediate size ranges, resulting in a gradation curve with a near-horizontal (flat) section.
Question 6: What does a high Los Angeles abrasion loss value indicate about an aggregate?
- The aggregate has high resistance to degradation
- The aggregate is highly porous
- The aggregate is weak and susceptible to breakage (Correct answer)
- The aggregate has excellent soundness
Correct answer: The aggregate is weak and susceptible to breakage
A high Los Angeles abrasion loss percentage indicates that the aggregate breaks down easily under impact and abrasion, meaning it has low durability.
Question 7: In aggregate gradation, what is the significance of a steep gradation curve on a semi-log plot?
- It indicates a well-graded aggregate with particles distributed across all sizes
- It indicates a uniformly graded or single-sized aggregate (Correct answer)
- It indicates a gap-graded aggregate
- It indicates an open-graded mixture
Correct answer: It indicates a uniformly graded or single-sized aggregate
A steep or near-vertical gradation curve indicates that most particles are concentrated within a narrow size range, characteristic of uniformly graded or single-sized aggregate.
CCIL Aggregate Gradation and Properties 2
What does the term 'fineness modulus' represent in aggregate testing?