ACI Aggregate Testing Technician (ATT) Certification Exam — Questions and Answers

Question 1: If a fine aggregate fails the ASTM C40 organic impurities test, what is the most appropriate next step?

Run ASTM C87 mortar strength test (Correct answer)
Reject the aggregate immediately
Reduce the aggregate gradation size
Increase the water-cement ratio

Correct answer: Run ASTM C87 mortar strength test

ASTM C87 (mortar strength test) can determine if the organic impurities actually affect concrete strength, allowing the aggregate to potentially still be used.

Question 2: What is the minimum sample size for a washing test on a fine aggregate (maximum size 3/8 in.) per ASTM C117?

300 g (Correct answer)
500 g
100 g
200 g

Correct answer: 300 g

ASTM C117 requires a minimum sample mass of 300 g for fine aggregate with a maximum size of 3/8 in.

Question 3: When collecting samples from aggregate bins or hoppers, where within the bin should sampling be avoided?

The center discharge zone during active flow
Immediately after fresh material is added to the bin
The top surface of material in the bin
The sides and corners where material stagnates and may not be representative (Correct answer)

Correct answer: The sides and corners where material stagnates and may not be representative

Material at the sides and corners of bins can be stagnant, degraded, or segregated, making it unrepresentative of the material being discharged for use.

Question 4: Why is determining void content in aggregates important?

To measure particle shape
To estimate cement requirements (Correct answer)
To calculate absorption rate
To determine moisture content

Correct answer: To estimate cement requirements

Void content helps assess the space between aggregate particles, influencing concrete workability and mix proportions.

Question 5: How does risk management apply to daily practice in Unit Weight & Voids Testing for ACI Aggregate Testing Technician professionals?

Through annual safety audits exclusively
By avoiding high-risk situations entirely
Through proactive identification of potential hazards and implementation of preventive measures (Correct answer)
Only through responding to incidents after they occur

Correct answer: Through proactive identification of potential hazards and implementation of preventive measures

Effective risk management in Unit Weight & Voids Testing requires proactive hazard identification and preventive measures, not just reactive responses. This approach reduces incidents, improves outcomes, and protects both professionals and clients.

Question 6: For aggregate sampled from flowing streams (chutes or discharge points), the preferred device to collect the full width of material flow is:

A full-width sampling frame or pan that intercepts the entire stream (Correct answer)
A flat-bladed shovel
A core barrel driven vertically into the stream
A hand scoop inserted at the edge of the stream

Correct answer: A full-width sampling frame or pan that intercepts the entire stream

A sampling device that spans the full width of the flowing stream ensures all particle sizes are captured without size-biased collection.

Question 7: What documentation practice is considered essential in Los Angeles Abrasion Testing within the ACI Aggregate Testing Technician field?

Only documenting unusual events or complications
Completing all documentation at the end of the workday
Recording actions, observations, and outcomes in real-time or as close to the event as possible (Correct answer)
Using shorthand notes that can be expanded later if needed

Correct answer: Recording actions, observations, and outcomes in real-time or as close to the event as possible

Real-time or near-real-time documentation in Los Angeles Abrasion Testing ensures accuracy, provides a contemporaneous record, and is considered the gold standard for professional accountability and legal defensibility.

Question 8: Which of the following is the most reliable method for obtaining a representative sample of fine aggregate from a stockpile?

Taking a single large sample from the pile base
Scooping from multiple surface locations on the pile
Sampling from the flowing stream as material is loaded from the pile (Correct answer)
Sampling only from the pile center

Correct answer: Sampling from the flowing stream as material is loaded from the pile

Sampling from the moving stream during loading captures material from throughout the stockpile and avoids surface segregation bias.

Question 9: In AASHTO T 85, what is the required soaking period for coarse aggregate before testing specific gravity?

48 ± 4 hours
12 ± 1 hours
24 ± 4 hours (Correct answer)
72 ± 4 hours

Correct answer: 24 ± 4 hours

AASHTO T 85 requires coarse aggregate to soak in water for 24 ± 4 hours before testing.

Question 10: What does a color darker than the reference standard in the ASTM C40 test indicate?

The NaOH solution is too dilute
The aggregate is suitable for all concrete applications
The aggregate may contain injurious organic impurities (Correct answer)
The aggregate is free of organic impurities

Correct answer: The aggregate may contain injurious organic impurities

A color darker than Organic Plate No. 3 indicates the fine aggregate may contain harmful organic impurities that could adversely affect concrete.

Question 11: When a conflict arises between standard procedures and a unique situation in Aggregate Sampling & Reduction, what should a ATT professional prioritize?

Safety and ethical obligations while seeking expert consultation (Correct answer)
Strict adherence to written procedures without exception
The preference of the client or stakeholder
The most cost-effective solution available

Correct answer: Safety and ethical obligations while seeking expert consultation

Safety and ethics always take priority in Aggregate Sampling & Reduction. When standard procedures don't adequately address a unique situation, consulting with experienced colleagues or supervisors ensures both safety and professional standards are maintained.

Question 12: Which scenario would cause the LA abrasion loss to be artificially LOWER than the true value?

Running the drum at a slightly higher speed than specified
Using more steel balls than specified for the grading
Drying the sample to a higher temperature than specified
Failing to wash fines off the sample before testing (Correct answer)

Correct answer: Failing to wash fines off the sample before testing

If pre-existing fines are not washed off, they remain in the sample mass (denominator) without being lost, mathematically reducing the calculated percent loss.

Question 13: Why is it important to sample aggregate from a moving conveyor belt rather than from a stationary pile whenever possible?

Stationary piles are restricted areas under OSHA regulations
Belt sampling is faster and requires less equipment
Moving belt samples capture the full cross-section of material flow, reducing segregation bias (Correct answer)
Belt samples have higher moisture content, making them easier to handle

Correct answer: Moving belt samples capture the full cross-section of material flow, reducing segregation bias

Sampling from a moving belt captures the complete cross-section of aggregate being conveyed, avoiding the segregation bias inherent in stockpile sampling.

Question 14: Chert with a bulk specific gravity less than 2.40 is considered a deleterious substance in coarse aggregate because:

It reduces water demand
It increases workability too much
It has poor freeze-thaw durability and causes pop-outs (Correct answer)
It accelerates cement hydration

Correct answer: It has poor freeze-thaw durability and causes pop-outs

Low-density chert absorbs water and deteriorates rapidly during freeze-thaw cycles, causing surface pop-outs in concrete.

Question 15: In the ASTM C40 test, to what level is the fine aggregate sample placed in the 12-oz prescription bottle?

The 2-oz level
The 7-oz level
The 10-oz level
The 4-1/2-oz level (Correct answer)

Correct answer: The 4-1/2-oz level

ASTM C40 requires fine aggregate to be added to the 4-1/2-oz (approximately 130 mL) level in the 12-oz glass prescription bottle.

Question 16: Which condition makes it necessary to increase the number of increments when sampling from a conveyor belt?

When the belt is moving slowly
When ambient temperature is above 90°F
When the material shows high variability or segregation (Correct answer)
When the aggregate is fine-grained only

Correct answer: When the material shows high variability or segregation

Higher material variability requires more increments to achieve a composite sample that adequately represents the aggregate being sampled.

Question 17: The 'percent passing' and 'percent retained' for any given sieve should always:

Both equal 50% for a well-graded aggregate
Sum to 100% for that sieve (Correct answer)
Equal the cumulative retained on that sieve
Sum to the fineness modulus value

Correct answer: Sum to 100% for that sieve

For any sieve, percent passing + percent retained = 100%, since all material either passes or is retained on each sieve.

Question 18: According to ASTM C33, the maximum allowable clay lumps and friable particles in fine aggregate for concrete is:

2.0%
5.0%
1.0%
3.0% (Correct answer)

Correct answer: 3.0%

ASTM C33 limits clay lumps and friable particles in fine aggregate to a maximum of 3.0% by mass.

Question 19: An aggregate source produces two gradations: one tested per Grading C and one per Grading D of ASTM C131. Which statement about comparing the results is correct?

Grading D always gives a lower loss value than Grading C for the same source
Results are directly comparable because the test machine is the same
Results may not be directly comparable because gradation and charge differ between gradings (Correct answer)
Results must be averaged to obtain the representative value for the source

Correct answer: Results may not be directly comparable because gradation and charge differ between gradings

Different gradings use different steel ball charges and particle sizes, so LA loss values between gradings are not directly comparable.

Question 20: What is the minimum number of increments required when sampling from a flowing stream?

Three
Ten
Five (Correct answer)
Four

Correct answer: Five

A minimum of five equal increments must be taken to ensure a proper composite sample per ASTM D75.

Question 21: A technician towel-dries coarse aggregate and notices that particles clump together with a damp feel. What does this indicate?

The aggregate is still in a wet condition with surface moisture present (Correct answer)
The aggregate has reached SSD condition
The aggregate has zero absorption capacity
The aggregate is over-dried beyond SSD

Correct answer: The aggregate is still in a wet condition with surface moisture present

Clumping and damp feel indicate free surface moisture is still present, meaning the aggregate has not yet reached SSD.

Question 22: When performing the ASTM C117 wash test, how is the mass loss reported?

As a ratio of wet to dry mass
As the percentage of material passing the No. 200 sieve by washing (Correct answer)
As volume of wash water used
As the dry mass of particles collected on the No. 200 sieve

Correct answer: As the percentage of material passing the No. 200 sieve by washing

ASTM C117 results are reported as the percentage of material passing the No. 200 sieve by mass of the original dry sample.

Question 23: Which of the following aggregate sampling locations is generally considered the MOST representative of the material going into a pavement?

From the discharge end of the cold feed conveyor belt (Correct answer)
From one corner of a fully loaded rail car
From the top center of a truck body at the job site
From the outer slope of the stockpile at the plant

Correct answer: From the discharge end of the cold feed conveyor belt

The cold feed conveyor belt captures aggregate in motion before it enters the dryer, giving a representative cross-section of the material actually being fed into production.

Question 24: Which condition would cause a FALSE positive (darker color than actual organic content) in the ASTM C40 test?

Testing aggregate that has been properly washed
Using clean Ottawa sand as the aggregate
Using distilled water to prepare NaOH solution
Presence of iron-bearing minerals that darken with NaOH (Correct answer)

Correct answer: Presence of iron-bearing minerals that darken with NaOH

Certain iron-bearing minerals can react with NaOH to produce a dark color, creating a false positive that does not reflect harmful organic content.

Question 25: What minimum sand equivalent value does ASTM C33 typically require for fine aggregate used in concrete?

80
50 (Correct answer)
25
75

Correct answer: 50

ASTM C33 does not specify a sand equivalent limit directly, but common specifications require a minimum SE of 75–80; however, a value of 75 is the widely accepted minimum for concrete sand.

Question 26: Crushed aggregate typically has a higher particle index than natural gravel because:

It is denser and heavier
It contains more moisture
It has finer gradation
Its angular shape and rough texture create more voids in a loose state (Correct answer)

Correct answer: Its angular shape and rough texture create more voids in a loose state

The angular, fractured faces and rough surface texture of crushed aggregate result in higher void contents and thus a higher particle index compared to rounded natural gravel.

Question 27: When testing for lightweight pieces per ASTM C123, the test result is expressed as:

Percentage by volume
Number of particles per kilogram
Percentage by mass of lightweight pieces (Correct answer)
Parts per million

Correct answer: Percentage by mass of lightweight pieces

ASTM C123 results are reported as the percentage by mass of lightweight pieces in the aggregate sample.

Question 28: Which ASTM standard is used to determine lightweight pieces in aggregate (such as coal and lignite)?

ASTM C40
ASTM C142
ASTM C127
ASTM C123 (Correct answer)

Correct answer: ASTM C123

ASTM C123 is the standard test method for lightweight pieces in aggregate, used to identify coal, lignite, and other low-density particles.

Question 29: What is the purpose of washing aggregate over a No. 200 (75 µm) sieve per ASTM C117?

To determine organic content
To remove material finer than 75 µm including clay and silt coatings (Correct answer)
To separate fine and coarse aggregate
To measure moisture content

Correct answer: To remove material finer than 75 µm including clay and silt coatings

ASTM C117 washing removes clay, silt, and fine dust coatings finer than 75 µm that could weaken the paste-aggregate bond.

Question 30: Which deleterious substance in aggregate is most likely to cause unsightly staining and pop-outs in hardened concrete?

Coal and lignite particles (Correct answer)
Crushed glass
Rounded quartz particles
Well-graded limestone fines

Correct answer: Coal and lignite particles

Coal and lignite particles can expand, cause pop-outs, and produce dark staining on the surface of hardened concrete.

Question 31: What effect does increasing the nominal maximum aggregate size have on the required measure volume for ASTM C29 testing?

Larger NMAS requires a larger measure (Correct answer)
Larger NMAS requires a smaller measure
NMAS has no effect on measure selection
Larger NMAS only affects the number of rod strokes, not the measure size

Correct answer: Larger NMAS requires a larger measure

ASTM C29 requires increasingly larger measures as aggregate nominal maximum size increases to ensure a statistically representative sample.

Question 32: On a gradation chart, a well-graded aggregate will appear as:

A curve with one or more flat sections
A relatively smooth S-shaped curve spanning a wide range of sizes (Correct answer)
A nearly vertical line
A nearly horizontal line

Correct answer: A relatively smooth S-shaped curve spanning a wide range of sizes

A well-graded aggregate has particles distributed across a wide range of sizes, producing a smooth S-shaped curve on a percent-passing gradation chart.

Question 33: How does risk management apply to daily practice in Moisture Content Testing for ACI Aggregate Testing Technician professionals?

Through proactive identification of potential hazards and implementation of preventive measures (Correct answer)
By avoiding high-risk situations entirely
Only through responding to incidents after they occur
Through annual safety audits exclusively

Correct answer: Through proactive identification of potential hazards and implementation of preventive measures

Effective risk management in Moisture Content Testing requires proactive hazard identification and preventive measures, not just reactive responses. This approach reduces incidents, improves outcomes, and protects both professionals and clients.

Question 34: Which of the following is NOT classified as a deleterious substance in aggregates per ASTM C33?

Clay lumps
Chert of low specific gravity
Well-graded crushed granite (Correct answer)
Coal and lignite

Correct answer: Well-graded crushed granite

Well-graded crushed granite is a sound, durable aggregate material and is not classified as a deleterious substance.

Question 35: How many times should washing and decanting be repeated per ASTM C117 until the process is considered complete?

Until the wash water is clear (Correct answer)
Exactly once
Exactly three times
Until the No. 200 sieve shows no visible fines

Correct answer: Until the wash water is clear

ASTM C117 requires repeated washing and decanting until the wash water is clear, indicating all fines have been removed.

Question 36: During an LA abrasion test, the drum is accidentally stopped at 450 revolutions due to a power outage. The technician should:

Report the result as-is, noting the deviation in the test report
Complete the remaining 50 revolutions after power is restored
Discard the sample and start the test over with a fresh specimen (Correct answer)
Extrapolate the result to 500 revolutions mathematically

Correct answer: Discard the sample and start the test over with a fresh specimen

ASTM C131 requires exactly 500 revolutions; an incomplete run compromises the result and the test must be restarted with a fresh sample.

Question 37: ASTM C142 measures which deleterious substance in fine aggregate?

Clay lumps and friable particles (Correct answer)
Lightweight pieces in aggregate
Material finer than No. 200 sieve
Organic impurities

Correct answer: Clay lumps and friable particles

ASTM C142 determines clay lumps and friable particles by hand-crushing moist particles and sieving out the degraded material.

Question 38: Which characteristic of the steel balls (charge) must be verified before each LA abrasion test?

Individual ball diameter measured with calipers
Surface hardness using a Rockwell hardness tester
Ball roundness verified with a sphericity gauge
Total mass of the charge within the specified tolerance (Correct answer)

Correct answer: Total mass of the charge within the specified tolerance

The total charge mass must meet the specification for the grading used (e.g., 5,000 ± 25 g for Grading A), verified by weighing.

Question 39: A coarse aggregate soundness result of 18% loss using sodium sulfate would be classified as:

Acceptable only if magnesium sulfate was used instead
Well within typical acceptance limits for most applications
Within AASHTO limits but failing ASTM limits
Exceeding the typical AASHTO limit of 12% for sodium sulfate (Correct answer)

Correct answer: Exceeding the typical AASHTO limit of 12% for sodium sulfate

AASHTO typically specifies a maximum sodium sulfate soundness loss of 12% for coarse aggregate, so 18% would exceed this limit.

Question 40: Which sieve must be placed beneath the No. 200 sieve to prevent damage during the ASTM C117 wash procedure?

No. 4 sieve
No. 50 sieve
No. 16 sieve
No. 100 sieve (Correct answer)

Correct answer: No. 100 sieve

A No. 100 sieve is placed beneath the No. 200 sieve to protect it from damage caused by the force of the wash water stream.

Question 41: Per ASTM C117, what must be done with any material retained on the No. 200 sieve after washing?

Weighed and recorded as the fine material mass
Discarded as it is considered contamination
Returned to the main sample before oven drying (Correct answer)
Reported separately as a clay fraction

Correct answer: Returned to the main sample before oven drying

Material retained on the No. 200 sieve during washing must be returned to the main sample so that the total post-wash dry mass accurately represents all particles coarser than 75 µm.

Question 42: How does risk management apply to daily practice in Los Angeles Abrasion Testing for ACI Aggregate Testing Technician professionals?

Only through responding to incidents after they occur
By avoiding high-risk situations entirely
Through annual safety audits exclusively
Through proactive identification of potential hazards and implementation of preventive measures (Correct answer)

Correct answer: Through proactive identification of potential hazards and implementation of preventive measures

Effective risk management in Los Angeles Abrasion Testing requires proactive hazard identification and preventive measures, not just reactive responses. This approach reduces incidents, improves outcomes, and protects both professionals and clients.

Question 43: A gradation curve that plots entirely near the upper limit of a specification band indicates the aggregate is:

Too fine for the specification (Correct answer)
Gap-graded
Well-centered in the specification
Too coarse for the specification

Correct answer: Too fine for the specification

Upper gradation limits represent more material passing (finer gradation); an aggregate near the upper limit is finer than ideal and may require mix adjustments.

Question 44: According to ASTM C33, the maximum loss for fine aggregate in the sodium sulfate soundness test is:

20%
5%
10% (Correct answer)
15%

Correct answer: 10%

ASTM C33 limits weighted average loss of fine aggregate after 5 cycles in sodium sulfate to a maximum of 10% by mass.

Question 45: How should a field sample be reduced to testing size?

Using a mechanical splitter or quartering method. (Correct answer)
By mixing with water and decanting.
By taking a single scoop from the center.
By handpicking desired particles.

Correct answer: Using a mechanical splitter or quartering method.

Mechanical splitting or quartering methods must be used to reduce the sample without bias.

Question 46: When preparing a grading B sample for ASTM C131, which sieve sizes define the retained fractions?

3/4 in. to 1/2 in. and 1/2 in. to 3/8 in. (Correct answer)
1/2 in. to 3/8 in. and 3/8 in. to No. 4
3/8 in. to No. 4 and No. 4 to No. 8
1 in. to 3/4 in. and 3/4 in. to 1/2 in.

Correct answer: 3/4 in. to 1/2 in. and 1/2 in. to 3/8 in.

Grading B uses material retained between 3/4–1/2 in. and 1/2–3/8 in. sieves with a total mass of 2,500 g each fraction.

Question 47: What does ASTM D75 recommend doing when a sample must be shipped by mail or freight to a distant laboratory?

Double-bag the sample in moisture-resistant bags and seal securely to prevent loss and moisture change (Correct answer)
Add a chemical preservative to prevent biological degradation of the sample
Oven-dry the sample completely to prevent mold growth during transit
Split the sample in half and ship only one half to reduce freight cost

Correct answer: Double-bag the sample in moisture-resistant bags and seal securely to prevent loss and moisture change

ASTM D75 recommends double-bagging and secure sealing to protect the sample from loss of fines and moisture changes that would affect test results during transit.

Question 48: What is the visual indication of organic impurities in fine aggregates?

Yellowish tint in clear water
Dark-colored solution compared to the standard (Correct answer)
Frothy surface layer
Lighter solution than the standard

Correct answer: Dark-colored solution compared to the standard

A darker color in the solution during the ASTM C40 test indicates the possible presence of organic impurities that can affect concrete strength.

Question 49: What is the purpose of using a large enough container during the washing operation in ASTM C117?

To slow the rate of washing so fines settle before decanting
To prevent aggregate from absorbing too much water
To allow complete immersion and vigorous agitation without losing aggregate over the rim (Correct answer)
To maintain a constant water temperature during washing

Correct answer: To allow complete immersion and vigorous agitation without losing aggregate over the rim

Using a container large enough to submerge the sample fully and agitate vigorously prevents coarse particles from spilling over the rim and being counted as fines.

Question 50: When sampling aggregates from a stockpile, where should samples generally NOT be taken from?

Freshly placed material near the delivery point
The base of the stockpile using a trenching method
The center of the stockpile at mid-height
The outer surface or slope of the stockpile (Correct answer)

Correct answer: The outer surface or slope of the stockpile

Segregation occurs along the outer slopes of stockpiles, making surface samples unrepresentative of the bulk material.

Question 51: In the ASTM C29 jigging method, how many times is each side of the measure raised and dropped per layer?

100 times
75 times
50 times (Correct answer)
25 times

Correct answer: 50 times

The jigging method requires each side of the measure to be raised approximately 50 mm (2 in) and dropped 50 times per layer.

Question 52: How does risk management apply to daily practice in Organic Impurities Assessment for ACI Aggregate Testing Technician professionals?

Only through responding to incidents after they occur
Through proactive identification of potential hazards and implementation of preventive measures (Correct answer)
By avoiding high-risk situations entirely
Through annual safety audits exclusively

Correct answer: Through proactive identification of potential hazards and implementation of preventive measures

Effective risk management in Organic Impurities Assessment requires proactive hazard identification and preventive measures, not just reactive responses. This approach reduces incidents, improves outcomes, and protects both professionals and clients.

Question 53: When sampling coarse aggregate from a stationary truck, what depth below the surface should increments be obtained?

From the top 50 mm only
From the exact center of the load by depth
At least 300 mm (12 in.) below the surface (Correct answer)
Any depth is acceptable if spread evenly

Correct answer: At least 300 mm (12 in.) below the surface

ASTM D75 requires digging at least 300 mm below the surface to avoid the biased, segregated layer at the top of the load.

Question 54: What is the purpose of performing a sieve analysis on aggregates?

To determine particle size distribution. (Correct answer)
To check aggregate temperature.
To identify moisture content.
To remove fine particles.

Correct answer: To determine particle size distribution.

Sieve analysis helps determine the particle size distribution, which affects the workability and strength of concrete.

Question 55: How many steel balls (charge) are used for ASTM C131 Grading A?

10 balls
6 balls
12 balls (Correct answer)
8 balls

Correct answer: 12 balls

Grading A in ASTM C131 requires a charge of 12 steel balls weighing 5,000 ± 25 g.

Question 56: Soft particles in coarse aggregate are a concern primarily because they:

Improve freeze-thaw resistance
Reduce bleeding in fresh concrete
Can crush under load and create voids that weaken concrete (Correct answer)
Increase the air content

Correct answer: Can crush under load and create voids that weaken concrete

Soft particles crush under compressive loads, creating voids and weak zones that significantly reduce concrete strength and durability.

Question 57: What is the fineness modulus (FM) of a fine aggregate if the cumulative percentages retained on the standard sieves are: No.100=95, No.50=80, No.30=55, No.16=30, No.8=10, No.4=2?

3.10
1.95
2.50
2.72 (Correct answer)

Correct answer: 2.72

FM = (95+80+55+30+10+2) / 100 = 272/100 = 2.72; fineness modulus sums cumulative percent retained on the six standard sieves divided by 100.

Question 58: What is the PRIMARY purpose of continuing education requirements in Los Angeles Abrasion Testing for ATT professionals?

Maintaining current knowledge and competency as the field evolves (Correct answer)
Networking with other professionals in the field
Earning additional credentials for career advancement
Fulfilling mandatory regulatory requirements only

Correct answer: Maintaining current knowledge and competency as the field evolves

Continuing education in Los Angeles Abrasion Testing ensures professionals maintain current knowledge and skills as standards, technologies, and best practices evolve in the ACI Aggregate Testing Technician field.

Question 59: What is the effect on calculated bulk specific gravity if entrapped air bubbles are not removed from the pycnometer during fine aggregate testing?

Calculated specific gravity will be higher than actual (Correct answer)
No effect, as air bubbles cancel out in the formula
Calculated specific gravity will be lower than actual
The absorption value increases but specific gravity is unaffected

Correct answer: Calculated specific gravity will be higher than actual

Entrapped air reduces the measured mass of water displaced, making the aggregate appear to displace less water and yielding an artificially high specific gravity.

Question 60: Total moisture content of aggregate is defined as:

Only the surface moisture on aggregate particles
Only the moisture inside the aggregate pores
The sum of absorbed moisture and surface moisture (Correct answer)
The moisture in excess of the saturated surface-dry condition

Correct answer: The sum of absorbed moisture and surface moisture

Total moisture content includes both the absorbed moisture within pores and the free (surface) moisture on the outside of particles.

Question 61: In the ASTM C40 test, what solution is added to the sand sample before comparing to the color standard?

Sulfuric acid solution
3% sodium hydroxide (NaOH) solution (Correct answer)
Distilled water
Hydrochloric acid solution

Correct answer: 3% sodium hydroxide (NaOH) solution

A 3% sodium hydroxide (NaOH) solution is added to the sand and shaken, then allowed to stand before color comparison.

Question 62: ASTM C33 limits the amount of material passing the No. 200 sieve in fine aggregate used in concrete subject to abrasion to a maximum of:

5.0%
3.0% (Correct answer)
2.0%
1.0%

Correct answer: 3.0%

ASTM C33 limits material finer than 75 μm (No. 200) to 3.0% for fine aggregate in concrete subject to abrasion, to protect surface durability.

Question 63: The proportional caliper device used in ASTM D4791 testing measures:

The surface area of particles
The volume of particles
The mass of individual particles
The ratio between two dimensions of a particle (Correct answer)

Correct answer: The ratio between two dimensions of a particle

The proportional caliper used in ASTM D4791 is set to a specific ratio (e.g., 1:3 or 1:5) and directly indicates whether a particle's dimensional ratio exceeds the threshold.

Question 64: How should the glass bottle be handled during the ASTM C40 test after adding the NaOH solution?

Left undisturbed for 24 hours immediately
Heated to 60°C for 1 hour
Stirred with a glass rod every hour for 8 hours
Vigorously shaken for several minutes, then allowed to stand for 24 hours (Correct answer)

Correct answer: Vigorously shaken for several minutes, then allowed to stand for 24 hours

The bottle is vigorously shaken for several minutes to ensure thorough contact between the NaOH solution and aggregate before being left to stand for 24 hours.

Question 65: In ASTM C117 (material finer than No. 200), after washing the aggregate is dried to constant mass at what temperature?

110 ± 5°C (Correct answer)
200 ± 5°C
150 ± 5°C
60 ± 5°C

Correct answer: 110 ± 5°C

After washing, the aggregate is dried to constant mass at 110 ± 5°C in accordance with ASTM C117.

Question 66: In the clay lumps and friable particles test (ASTM C142), the sample is soaked in water for a period of:

24 ± 4 hours (Correct answer)
1 to 4 hours
12 ± 1 hours
48 hours minimum

Correct answer: 24 ± 4 hours

ASTM C142 requires soaking the sample in water for 24 ± 4 hours before attempting to break particles with the fingers.

Question 67: Which of the following applications is MOST sensitive to aggregate LA abrasion loss?

Concrete pavement wearing course (Correct answer)
Granular sub-base fill
Bedding sand for utilities
Embankment fill material

Correct answer: Concrete pavement wearing course

Concrete pavement wearing courses experience direct traffic abrasion, making aggregate hardness critical and LA loss limits most restrictive.

Question 68: Which ASTM standard covers the test method for clay lumps and friable particles in aggregates?

ASTM C136
ASTM C142 (Correct answer)
ASTM C117
ASTM C131

Correct answer: ASTM C142

ASTM C142 is the standard test method for clay lumps and friable particles in aggregates.

Question 69: What does 'nominal maximum size' of an aggregate refer to in the context of sampling?

The largest sieve in the gradation set
The smallest sieve that retains more than 10% of the material (Correct answer)
The sieve size used to wash fine material
The sieve size equal to the maximum particle diameter

Correct answer: The smallest sieve that retains more than 10% of the material

Nominal maximum size is the smallest sieve opening through which the entire amount of aggregate is permitted to pass, retaining no more than 10% on that sieve.

Question 70: When a conflict arises between standard procedures and a unique situation in Unit Weight & Voids Testing, what should a ATT professional prioritize?

Strict adherence to written procedures without exception
The preference of the client or stakeholder
The most cost-effective solution available
Safety and ethical obligations while seeking expert consultation (Correct answer)

Correct answer: Safety and ethical obligations while seeking expert consultation

Safety and ethics always take priority in Unit Weight & Voids Testing. When standard procedures don't adequately address a unique situation, consulting with experienced colleagues or supervisors ensures both safety and professional standards are maintained.

Question 71: What is the maximum allowable material loss during sieve analysis per ASTM C136?

0.2%
0.5%
1.0%
0.3% (Correct answer)

Correct answer: 0.3%

Material loss should not exceed 0.3% of the original mass to ensure the accuracy of the test results.

Question 72: When sampling from a flowing aggregate stream at a discharge point, when should increments be collected?

Only at the beginning and end of the flow
At random time intervals throughout the entire flow period (Correct answer)
Only when flow rate is highest
After the stream has been running for at least 10 minutes

Correct answer: At random time intervals throughout the entire flow period

Increments must be collected at random time intervals spanning the full duration of flow to ensure the composite sample represents all material discharged.

Question 73: What is the maximum allowable lightweight pieces (coal and lignite) in fine aggregate per ASTM C33 for concrete subject to surface wear?

2.0%
1.5%
0.5% (Correct answer)
1.0%

Correct answer: 0.5%

For fine aggregate in concrete subject to surface wear, ASTM C33 limits lightweight pieces (coal and lignite) to 0.5% by mass.

Question 74: After the LA abrasion test, the aggregate and charge are separated using a sieve with an opening size of:

No. 8 (2.36 mm)
No. 12 (1.70 mm) (Correct answer)
No. 4 (4.75 mm)
No. 16 (1.18 mm)

Correct answer: No. 12 (1.70 mm)

The material is removed from the machine and sieved over a No. 12 (1.70 mm) sieve to determine loss.

Question 75: Why is the pycnometer method preferred over the wire basket method for fine aggregates?

The pycnometer provides faster results
Wire baskets cannot be submerged fully in water
Fine aggregates have higher specific gravity than coarse aggregates
Fine particles would fall through the openings of a wire basket (Correct answer)

Correct answer: Fine particles would fall through the openings of a wire basket

Fine aggregate particles are too small to be retained in a wire basket, so a volumetric pycnometer is used instead.

Question 76: In ASTM C123, lightweight particles are separated from aggregate by:

Heating to 100°C and measuring mass loss
Magnetic separation
Immersion in a heavy liquid of specified density (Correct answer)
Acid dissolution

Correct answer: Immersion in a heavy liquid of specified density

ASTM C123 uses a heavy liquid (such as zinc chloride solution) with a specific gravity between 1.95 and 2.0 to float out lightweight particles.

Question 77: If a sieve analysis shows that 68% passes the No. 4 sieve for a blended aggregate, the percent retained on the No. 4 sieve is:

68%
34%
32% (Correct answer)
Depends on the gradation curve shape

Correct answer: 32%

Percent retained = 100% − percent passing = 100% − 68% = 32%; this relationship is always true for any sieve.

Question 78: When two LA abrasion tests are run on samples from the same lot, the results are 34% and 39%. What action should the technician take?

Report both values and check if the difference exceeds the allowable precision (Correct answer)
Average the two results and report 36.5%
Discard the higher result and report 34%
Run a third test and average all three

Correct answer: Report both values and check if the difference exceeds the allowable precision

ASTM C131 provides precision statements; both results should be reviewed against the multi-laboratory or single-operator precision limits before averaging.

Question 79: Which environmental condition is most likely to affect the moisture content of a field sample between collection and testing?

Storing the sample in a sealed plastic bag
Placing the sample in a cooler without ice
Keeping the sample at room temperature indoors
Prolonged exposure to direct sunlight or wind in an open container (Correct answer)

Correct answer: Prolonged exposure to direct sunlight or wind in an open container

Open exposure to sun and wind causes evaporative drying that alters moisture content, potentially affecting absorption and unit weight tests.

Question 80: After collecting a field sample, what information must be recorded as a minimum on the sample identification tag?

Project number and the testing laboratory name only
Weight of the sample and sieve size only
Only the date and material type
Sample ID, material description, source location, date and time, and sampler's name (Correct answer)

Correct answer: Sample ID, material description, source location, date and time, and sampler's name

Complete identification including source, time, date, and sampler ensures traceability and allows results to be linked back to a specific lot of material.

Question 81: For a combined sieve analysis (ASTM C136 + ASTM C117), where should the material finer than No. 200 obtained by washing be entered in the gradation calculation?

It is divided equally among the three finest sieves
It is added to the No. 200 pan mass from the dry sieve analysis (Correct answer)
It is reported only as a separate supplemental value
It replaces the No. 200 sieve fraction entirely

Correct answer: It is added to the No. 200 pan mass from the dry sieve analysis

The washed fines are added to the pan (material finer than No. 200) from the dry sieve analysis to determine the total amount passing No. 200.

Question 82: What is the significance of the 'increment' in aggregate sampling terminology?

A measured volume of water used in washing tests
The total field sample mass
A single portion of material collected in one operation that is combined with others to form the field sample (Correct answer)
The smallest particle retained on the No. 200 sieve

Correct answer: A single portion of material collected in one operation that is combined with others to form the field sample

An increment is one individual scoop or cut of material; multiple increments are combined to create the composite field sample used for testing.

Question 83: What minimum sample mass of coarse aggregate (3/4-in. maximum size) is typically required for a field sample per ASTM D75?

25 kg (55 lb) (Correct answer)
100 kg (220 lb)
5 kg (11 lb)
50 kg (110 lb)

Correct answer: 25 kg (55 lb)

ASTM D75 specifies approximately 25 kg (55 lb) as the minimum field sample mass for coarse aggregate with a 3/4-in. nominal maximum size.

Question 84: During the ASTM C88 soundness test, how many cycles of immersion and drying are typically performed?

5 cycles (Correct answer)
7 cycles
3 cycles
10 cycles

Correct answer: 5 cycles

The standard soundness test procedure performs 5 cycles of immersion in sulfate solution followed by oven drying.

Question 85: Which type of aggregate coating is most harmful to concrete strength because it prevents proper bonding with cement paste?

Fine silica dust
Thin calcium carbonate dust
Clay and silt coatings (Correct answer)
Iron oxide surface film

Correct answer: Clay and silt coatings

Clay and silt coatings are most harmful because they create a weak interface that prevents cement paste from bonding to aggregate surfaces.

Question 86: Which of the following organic substances is LEAST likely to be detected by the ASTM C40 colorimetric test?

Tannic acids
Lignite compounds
Hydrocarbons such as motor oil (Correct answer)
Humic acids

Correct answer: Hydrocarbons such as motor oil

Hydrocarbons like motor oil do not react with NaOH to produce the characteristic yellow-brown color, making them less detectable by the ASTM C40 method.

Question 87: Rain has just fallen on a coarse aggregate stockpile. How should this affect the timing of moisture content testing for the next concrete batch?

Test immediately; rain water only affects the surface
Skip testing; use the absorption value instead
Delay testing until the stockpile has drained and moisture is more representative
Increase test frequency or test just before batching to capture current conditions (Correct answer)

Correct answer: Increase test frequency or test just before batching to capture current conditions

After rain, moisture content is elevated and may be changing as water drains; testing immediately before batching gives the most accurate current moisture value.

Question 88: Which ASTM standard governs the practice of reducing samples of aggregate to testing size?

ASTM C117
ASTM D75
ASTM C136
ASTM C702 (Correct answer)

Correct answer: ASTM C702

ASTM C702 covers the standard practice for reducing samples of aggregate to testing size using methods such as mechanical splitting or quartering.

Question 89: For coarse aggregate with a nominal maximum size of 1 in., what minimum sample mass is required for the ASTM C117 washing test?

500 g
5000 g
1000 g
2000 g (Correct answer)

Correct answer: 2000 g

ASTM C117 requires a minimum 2000 g (2 kg) sample for coarse aggregate with a 1-in. nominal maximum size.

Question 90: Which LA abrasion percent loss value represents BETTER aggregate quality?

45%
55%
25% (Correct answer)
35%

Correct answer: 25%

A lower LA abrasion percent loss indicates a harder, more wear-resistant aggregate; 25% represents better quality than higher values.

Question 91: What is the primary reason aggregate samples should be transported to the laboratory in sealed, airtight containers or bags?

To prevent loss of fines and moisture change (Correct answer)
To prevent oxidation of the aggregate surface
To maintain the aggregate's specific gravity
To allow gases to escape from the aggregate pores

Correct answer: To prevent loss of fines and moisture change

Sealing samples prevents loss of fine material and limits evaporation or absorption of moisture, both of which affect test results.

Question 92: When a conflict arises between standard procedures and a unique situation in Los Angeles Abrasion Testing, what should a ATT professional prioritize?

Strict adherence to written procedures without exception
The most cost-effective solution available
Safety and ethical obligations while seeking expert consultation (Correct answer)
The preference of the client or stakeholder

Correct answer: Safety and ethical obligations while seeking expert consultation

Safety and ethics always take priority in Los Angeles Abrasion Testing. When standard procedures don't adequately address a unique situation, consulting with experienced colleagues or supervisors ensures both safety and professional standards are maintained.

Question 93: How does risk management apply to daily practice in Aggregate Sampling & Reduction for ACI Aggregate Testing Technician professionals?

Through proactive identification of potential hazards and implementation of preventive measures (Correct answer)
Through annual safety audits exclusively
Only through responding to incidents after they occur
By avoiding high-risk situations entirely

Correct answer: Through proactive identification of potential hazards and implementation of preventive measures

Effective risk management in Aggregate Sampling & Reduction requires proactive hazard identification and preventive measures, not just reactive responses. This approach reduces incidents, improves outcomes, and protects both professionals and clients.

Question 94: If a technician finds that the LA machine drum rotational speed is 40 rpm instead of the specified range, the test result will likely:

Overestimate abrasion loss due to increased impact energy
Be unaffected because total revolutions still equals 500
Be invalid and must be discarded per ASTM C131 (Correct answer)
Underestimate abrasion loss due to reduced tumbling action

Correct answer: Be invalid and must be discarded per ASTM C131

ASTM C131 specifies a speed of 30–33 rpm; results obtained outside this range are not valid per the standard.

Question 95: The percent retained on a given sieve is calculated by dividing the mass retained on that sieve by:

The total original dry sample mass (Correct answer)
The combined mass of all sieves below it
The mass retained on the next larger sieve
The mass passing that sieve

Correct answer: The total original dry sample mass

Percent retained = (mass retained on sieve / total original dry sample mass) × 100, using the total original sample as the denominator.

Question 96: Many highway specifications require that coarse aggregate for base course have an LA abrasion loss no greater than:

15%
25%
50% (Correct answer)
65%

Correct answer: 50%

A maximum LA abrasion loss of 50% is a common specification limit for coarse aggregate used in base course applications.

Question 97: An aggregate is described as 'oven-dry.' Which statement best describes this condition?

Air-dried at ambient temperature for 24 hours
Pores fully saturated, surface dry
All evaporable moisture removed by heating to 110 ± 5°C (Correct answer)
Surface dry but internal pores partially saturated

Correct answer: All evaporable moisture removed by heating to 110 ± 5°C

Oven-dry (OD) condition means all evaporable water has been removed by drying at 110 ± 5°C to constant mass per ASTM C566.

Question 98: The shelf (lifter) inside the LA abrasion machine drum is positioned:

At a 45-degree angle to redirect aggregate flow
Projecting inward along the full length of the drum (Correct answer)
On the outside of the drum parallel to the axis
Bolted to the drum door as a removable insert

Correct answer: Projecting inward along the full length of the drum

The shelf projects inward along the full interior length of the drum to lift and tumble the charge during rotation.

Question 99: The purpose of a sample splitter (riffle splitter) is to:

Reduce a large sample to a smaller representative portion (Correct answer)
Separate fine aggregate from coarse aggregate by size
Increase the moisture content of the sample before testing
Measure the bulk specific gravity of the sample

Correct answer: Reduce a large sample to a smaller representative portion

A riffle splitter divides a sample into two equal halves, allowing repeated halving to reach a target sample mass while maintaining representativeness.

Question 100: According to ASTM D75, what is the minimum number of increments required to constitute a field sample of aggregate from a conveyor belt?

10 increments taken at regular intervals
5 increments taken at random intervals
2 increments taken from the head and tail of the belt
3 increments taken at random intervals (Correct answer)

Correct answer: 3 increments taken at random intervals

ASTM D75 requires a minimum of 3 increments taken at random intervals to form a representative field sample from a conveyor belt.

ACI Aggregate Testing Technician (ATT) Certification Exam

The ACI Aggregate Testing Technician certification validates competency in performing ASTM and AASHTO aggregate sampling, gradation, and physical property tests on fine and coarse aggregates used in concrete and construction materials.

100

Questions

120 min

Time Limit

70%

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