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

Question 1: For ASTM C40 (organic impurities), the sodium hydroxide solution used has a concentration of:

10% NaOH by mass
1% NaOH by mass
3% NaOH by mass (Correct answer)
5% NaOH by mass

Correct answer: 3% NaOH by mass

ASTM C40 specifies a 3% sodium hydroxide (NaOH) solution by mass to extract organic compounds from the aggregate for color comparison.

Question 2: Which ASTM standard governs the sand equivalent value test for coarse-grained soils and fine aggregates?

ASTM C136
ASTM D2419 (Correct answer)
ASTM D4791
ASTM C40

Correct answer: ASTM D2419

ASTM D2419 is the standard test method for sand equivalent value of soils and fine aggregate.

Question 3: Which specific gravity value is used in the void content calculation for aggregates (ASTM C29)?

Average of apparent and bulk OD
Apparent specific gravity
Bulk SSD specific gravity
Bulk OD specific gravity (Correct answer)

Correct answer: Bulk OD specific gravity

ASTM C29 uses bulk OD specific gravity to calculate the void content of aggregates in the rodded or jigged unit weight test.

Question 4: During pycnometer calibration for fine aggregate testing, the flask is filled with water and weighed. This calibration mass (C) is used to:

Set the balance zero before weighing samples
Establish the volume of the pycnometer at the test temperature (Correct answer)
Measure the water absorption of the fine aggregate
Determine the total pore volume of aggregate

Correct answer: Establish the volume of the pycnometer at the test temperature

The calibration mass C represents the mass of water the pycnometer holds at a given temperature, establishing flask volume for Archimedes-based Gs calculation.

Question 5: ASTM specifications for concrete aggregates typically limit material finer than No. 200 in fine aggregate to a maximum of what percentage (for concrete subject to abrasion)?

3.0% (Correct answer)
1.5%
5.0%
2.0%

Correct answer: 3.0%

ASTM C33 limits material finer than No. 200 in fine aggregate to 3.0% for concrete subject to abrasion, and 5.0% for other concrete.

Question 6: 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
2 increments taken from the head and tail of the belt
3 increments taken at random intervals (Correct answer)
5 increments taken at random intervals

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.

Question 7: Under ASTM C29, how is the unit weight measure recalibrated when the results from two successive calibration trials differ by more than 0.1%?

Discard both results and run at least two additional trials until consistency is achieved (Correct answer)
Use the higher value since it represents a fuller measure
Report a tolerance flag and proceed with the nearest result
Average the two results and use the average volume

Correct answer: Discard both results and run at least two additional trials until consistency is achieved

If successive calibration trials differ by more than 0.1%, additional determinations are made until two consecutive results agree within 0.1%, and those two are averaged.

Question 8: In the clay lumps and friable particles test (ASTM C142), the sample is soaked in water for a period of:

1 to 4 hours
12 ± 1 hours
24 ± 4 hours (Correct answer)
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 9: Which deleterious substance in aggregate is most likely to cause unsightly staining and pop-outs in hardened concrete?

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

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 10: What is the proper procedure if material is retained on the sieve frame edge?

Push material through the mesh.
Report it as passing.
Return it to the sieve for proper separation. (Correct answer)
Discard the retained material.

Correct answer: Return it to the sieve for proper separation.

Aggregates caught on the sieve frame edge should be moved back into the sieve to ensure accurate mass distribution results.

Question 11: How does aggregate moisture content influence the water-to-cement (w/c) ratio of a concrete mix?

Aggregate moisture always decreases the effective w/c ratio
Moisture only affects workability, not the w/c ratio
Excess moisture in aggregate increases the effective w/c ratio (Correct answer)
It has no effect if aggregate is pre-wetted

Correct answer: Excess moisture in aggregate increases the effective w/c ratio

Free moisture on aggregate surfaces adds to the total water in the mix, raising the effective w/c ratio and reducing concrete strength.

Question 12: What is the PRIMARY purpose of continuing education requirements in Moisture Content Testing for ATT professionals?

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

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

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

Question 13: When using the quartering method per ASTM C702, after forming the flat circular pile and dividing into four quarters, which portions are kept?

Two diagonally opposite quarters are discarded and the other two are combined (Correct answer)
All four quarters are combined into one container
Two adjacent quarters are kept and two are discarded
One random quarter is selected and the rest are discarded

Correct answer: Two diagonally opposite quarters are discarded and the other two are combined

In quartering, two diagonally opposite quarters are kept and recombined; the other two opposite quarters are discarded, ensuring a representative half-sample.

Question 14: When is aggregate considered 'oven-dry' during a moisture content test?

After exactly 24 hours in the oven at 110°C
When successive weighings at 1-hour intervals show less than 0.1% change in mass (Correct answer)
After the aggregate reaches ambient temperature
When the surface of the aggregate appears dry to the touch

Correct answer: When successive weighings at 1-hour intervals show less than 0.1% change in mass

ASTM C566 requires drying until successive weighings (after additional drying intervals) differ by less than 0.1% of the specimen mass, confirming constant mass.

Question 15: After mechanical splitting of an aggregate sample, the technician notices one half is significantly heavier than the other. What is the most likely cause?

The aggregate was too dry to split evenly
The splitter chutes were of unequal width or material bridged during splitting (Correct answer)
One half contained more elongated particles
The aggregate has two different specific gravities

Correct answer: The splitter chutes were of unequal width or material bridged during splitting

Unequal chute widths or bridging during mechanical splitting are the most common causes of uneven mass distribution between the two halves.

Question 16: When calculating voids in aggregate using bulk specific gravity (dry basis), which formula is correct?

Voids (%) = [1 − (UW / (SG × 62.4))] × 100 (Correct answer)
Voids (%) = (UW / SG × 62.4) × 100
Voids (%) = (SG − UW) / 62.4 × 100
Voids (%) = (UW × SG / 62.4) × 100

Correct answer: Voids (%) = [1 − (UW / (SG × 62.4))] × 100

ASTM C29 defines percent voids as [1 − (W / (S × D))] × 100, where W = unit weight, S = bulk specific gravity (dry), and D = density of water.

Question 17: In ASTM C123, lightweight particles are separated from aggregate by:

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

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 18: The Speedy Moisture Tester (calcium carbide method) determines moisture content based on which principle?

The electrical resistance of wet aggregate
The weight loss of aggregate after microwave drying
The pressure generated when calcium carbide reacts with free moisture (Correct answer)
The temperature change during aggregate drying

Correct answer: The pressure generated when calcium carbide reacts with free moisture

Calcium carbide reacts with free water in the sample to produce acetylene gas; the resulting pressure on the gauge is correlated to moisture content.

Question 19: What is the standard number of revolutions for the LA abrasion test on aggregates tested per ASTM C131?

100 revolutions
1000 revolutions
500 revolutions (Correct answer)
300 revolutions

Correct answer: 500 revolutions

The standard test per ASTM C131 requires exactly 500 revolutions of the LA machine drum.

Question 20: Which of the following is a significant limitation of the microwave oven method for aggregate moisture content?

It may cause overheating and damage to certain aggregates, giving erratic results (Correct answer)
It requires a minimum sample size of 5 kg
It cannot be used for fine aggregate
It only measures surface moisture, not absorbed moisture

Correct answer: It may cause overheating and damage to certain aggregates, giving erratic results

Some aggregates (especially those with high iron content) can overheat or spark in a microwave, causing inconsistent or unsafe results.

Question 21: Which ASTM standard specifically governs the practice of reducing field samples of aggregate to testing size in the laboratory?

ASTM C127
ASTM C136
ASTM C702 (Correct answer)
ASTM D75

Correct answer: ASTM C702

ASTM C702 is the standard practice covering methods for reducing field samples of aggregate to testing size, including mechanical splitting and quartering.

Question 22: What documentation practice is considered essential in Aggregate Sampling & Reduction within the ACI Aggregate Testing Technician field?

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

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 Aggregate Sampling & Reduction ensures accuracy, provides a contemporaneous record, and is considered the gold standard for professional accountability and legal defensibility.

Question 23: A project specification requires LA abrasion loss ≤ 40%. A test result of 38% means the aggregate:

Requires retesting because results within 5% of the limit are inconclusive
Passes because 38% is less than 40% (Correct answer)
Fails because the value is close to the limit and a safety margin applies
Fails because ASTM rounds results up to the nearest 5%

Correct answer: Passes because 38% is less than 40%

The aggregate passes because 38% is below the 40% maximum limit; no additional safety margin is required by ASTM C131.

Question 24: What is the purpose of washing aggregate over a No. 200 (75 µm) sieve per ASTM C117?

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

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 25: A sieve is considered overloaded during a sieve analysis when:

More than 5% of the sample is retained on one sieve
The mass of material retained exceeds the limits specified in ASTM C136 for that sieve size (Correct answer)
The sieve frame bends under the weight of the material
Any single layer of particles covers more than 50% of the sieve area

Correct answer: The mass of material retained exceeds the limits specified in ASTM C136 for that sieve size

ASTM C136 specifies maximum mass limits per unit area for each sieve size; exceeding these limits causes particles to stack and prevents accurate separation.

Question 26: 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)
Discard the higher result and report 34%
Run a third test and average all three
Average the two results and report 36.5%

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 27: 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 28: The LA abrasion test primarily measures resistance to:

Abrasion and impact degradation (Correct answer)
Chemical weathering and dissolution
Surface coating adhesion
Freeze-thaw cycling

Correct answer: Abrasion and impact degradation

The test measures resistance to abrasion (grinding) and impact (tumbling with steel balls), simulating degradation during handling and service.

Question 29: What is the maximum allowable material loss during sieve analysis per ASTM C136?

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

Correct answer: 0.3%

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

Question 30: What is the purpose of using a large enough container during the washing operation in ASTM C117?

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

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.

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.

Questions

35 min

Time Limit

70%

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