ACI Concrete Field Testing Technician - Grade I — Questions and Answers

Question 1: For a 4×8-inch concrete test cylinder made from concrete with a slump between 1 and 3 inches, how many layers and rods per layer are required per ASTM C31?

Three layers, 25 rods per layer
One layer, 50 rods
Two layers, 25 rods per layer (Correct answer)
Two layers, 10 rods per layer

Correct answer: Two layers, 25 rods per layer

ASTM C31 requires 4×8-inch cylinders to be filled in two approximately equal layers with 25 rods per layer for concrete with a slump greater than 1 inch.

Question 2: What is the purpose of air entrainment in concrete exposed to freezing and thawing cycles?

Air reduces concrete density, making the mix easier to pump
Air increases the water-cement ratio, improving workability
Air voids provide pressure relief for freezing pore water, preventing internal cracking and surface scaling (Correct answer)
Air replaces fine aggregate in low-strength mixes

Correct answer: Air voids provide pressure relief for freezing pore water, preventing internal cracking and surface scaling

Entrained air bubbles act as expansion chambers for freezing water in the paste; without them, hydraulic pressure from freezing builds until the concrete cracks or scales.

Question 3: What is the standard curing condition and test age for compressive strength cylinders used to verify mix design acceptance?

Standard moist curing at 73°F ± 3°F, tested at 28 days (Correct answer)
Accelerated curing at 140°F, tested at 24 hours
Ambient field curing, tested at 7 days
Water curing at 50°F, tested at 56 days

Correct answer: Standard moist curing at 73°F ± 3°F, tested at 28 days

ACI 318 specifies acceptance testing at 28 days under standard moist curing (ASTM C31) as the standard reference for evaluating whether a concrete mix meets the specified f'c.

Question 4: Which of the following situations would require the use of the volumetric method (ASTM C173) instead of the pressure method (ASTM C231) for determining the air content of fresh concrete?

The concrete contains a high-range water-reducing admixture.
The concrete has a very high slump (e.g., 8 inches).
The concrete is being placed in a high-temperature environment.
The concrete is made with lightweight aggregate. (Correct answer)

Correct answer: The concrete is made with lightweight aggregate.

The pressure method (ASTM C231) is not applicable for concrete made with lightweight or other highly porous aggregates. The pressure applied during the test would compress the air within the pores of the aggregate, leading to an inaccurate, artificially high air content reading. The volumetric method (ASTM C173) must be used in these cases.

Question 5: What does petrographic examination (ASTM C295) reveal about an aggregate?

The mineralogical composition, physical characteristics, and potential durability issues of the aggregate through microscopic examination (Correct answer)
Only whether the aggregate contains clay
Only the aggregate's color
The aggregate's weight per cubic foot

Correct answer: The mineralogical composition, physical characteristics, and potential durability issues of the aggregate through microscopic examination

Petrographic analysis uses microscopy to identify minerals, assess physical properties, and detect potentially reactive or harmful constituents that could affect concrete performance.

Question 6: A technician fails the practical portion of the ACI Field Testing Technician – Grade I exam on the first attempt. What is the typical ACI policy for retaking the practical examination?

Candidates may retake the practical exam at the next available exam opportunity offered by a Sponsoring Group; there is typically no mandatory waiting period between attempts (Correct answer)
Candidates who fail the practical must retake both the written and practical exams simultaneously
A second failure results in permanent disqualification from ACI certification
Candidates must wait 1 year before retaking any ACI examination

Correct answer: Candidates may retake the practical exam at the next available exam opportunity offered by a Sponsoring Group; there is typically no mandatory waiting period between attempts

ACI allows candidates who fail the practical to retake it at the next available opportunity; re-studying the failed procedure(s) with additional hands-on practice before the retake is strongly recommended.

Question 7: How does the addition of a polycarboxylate-based superplasticizer affect the air content of a mix that already contains an air-entraining admixture?

Superplasticizers seal entrained air voids permanently, improving freeze-thaw resistance
Some superplasticizers can significantly reduce entrained air content; the effect depends on the superplasticizer chemistry and requires air content to be checked after both admixtures are added (Correct answer)
Superplasticizers have no interaction with air-entraining admixtures
Superplasticizers always increase air content uniformly

Correct answer: Some superplasticizers can significantly reduce entrained air content; the effect depends on the superplasticizer chemistry and requires air content to be checked after both admixtures are added

Certain polycarboxylate-based superplasticizers can destabilize the air void system, reducing measured air content or changing void size distribution, so air must be tested after adding all admixtures.

Question 8: When rodding a 4x8 inch cylinder per ASTM C31, how many strokes are applied per layer?

25 strokes (Correct answer)
50 strokes
10 strokes
15 strokes

Correct answer: 25 strokes

ASTM C31 specifies 25 uniformly distributed rodding strokes per layer for 4x8 inch cylinders.

Question 9: Air content by the gravimetric method (ASTM C138) is calculated as:

Pressure meter reading minus aggregate correction factor
(Actual unit weight minus Theoretical unit weight) divided by Actual unit weight times 100
Slump in inches divided by unit weight times 100
(Theoretical unit weight minus Actual unit weight) divided by Theoretical unit weight times 100 (Correct answer)

Correct answer: (Theoretical unit weight minus Actual unit weight) divided by Theoretical unit weight times 100

Gravimetric air content = (D minus M) divided by D times 100, where D is the theoretical air-free unit weight and M is the measured unit weight.

Question 10: According to ACI 347R, Guide to Formwork for Concrete, which of the following is the most critical factor in determining the safe stripping time for vertical formwork on walls and columns?

The specified 28-day compressive strength of the concrete.
The ambient air temperature at the time of stripping.
The type of cement used in the concrete mix.
The ability of the concrete to support its own weight and resist surface damage. (Correct answer)

Correct answer: The ability of the concrete to support its own weight and resist surface damage.

While factors like temperature and mix design influence strength gain, the primary criterion for safely removing vertical (non-load-bearing) forms is whether the concrete has achieved sufficient strength to be self-supporting without being damaged during form removal operations. Removing forms too early can lead to sloughing, damaged corners, and other surface defects.

Question 11: A concrete finisher is preparing to perform the initial floating of a freshly placed slab. Which of the following is the primary purpose of bull floating?

To embed large aggregate, level the surface, and remove screed marks. (Correct answer)
To cut control joints to a depth of one-quarter the slab thickness.
To create a smooth, dense, hard-troweled surface.
To open the surface to allow bleed water to evaporate quickly.

Correct answer: To embed large aggregate, level the surface, and remove screed marks.

The primary purpose of bull floating is to level ridges and fill voids left by screeding, while also embedding coarse aggregate particles just below the surface. This process prepares the slab for subsequent finishing operations like edging, jointing, and troweling.

Question 12: What should candidates focus on when studying the ACI certification workbook?

Only the theoretical explanations
Both practical procedures and theoretical concepts (Correct answer)
Skipping the workbook entirely for other sources
Only the questions at the end of each chapter

Correct answer: Both practical procedures and theoretical concepts

The ACI certification exams, especially for field testing, assess both theoretical knowledge of concrete properties and the practical ability to perform tests correctly. Therefore, candidates must thoroughly study both the conceptual explanations and the step-by-step procedures detailed in the workbook to succeed.

Question 13: What is the primary purpose of a pre-concrete placement inspection checklist for a reinforced concrete slab?

To verify that all reinforcement, embedments, and form conditions are correct before concrete is ordered (Correct answer)
To document the concrete mix design approval after placement
To record the number of concrete trucks used during the pour
To certify that curing compound was applied correctly

Correct answer: To verify that all reinforcement, embedments, and form conditions are correct before concrete is ordered

A pre-placement inspection ensures all conditions — rebar size, spacing, lap splices, cover, dowels, blockouts, and form integrity — are correct before concrete is irreversibly placed.

Question 14: What is the primary benefit of air entrainment in concrete exposed to freezing and thawing cycles?

It slows the rate of cement hydration
It reduces the amount of cement needed
It increases unit weight and compressive strength
It creates small voids that relieve hydraulic pressure from freezing pore water (Correct answer)

Correct answer: It creates small voids that relieve hydraulic pressure from freezing pore water

Entrained air bubbles act as pressure-relief chambers, allowing expanding ice to move into voids rather than fracturing the cement paste.

Question 15: To calculate theoretical (air-free) unit weight for the gravimetric air content method, a technician needs:

Water-cement ratio and design compressive strength only
Slump and temperature of the fresh concrete only
Aggregate nominal maximum size and cement content only
Specific gravities and batch masses of all materials in the mix (Correct answer)

Correct answer: Specific gravities and batch masses of all materials in the mix

Theoretical unit weight requires the specific gravity and batch mass of every ingredient (cement, aggregates, water, admixtures) to calculate.

Question 16: Per ASTM C31, concrete with a slump of 1 inch (25 mm) or less must be consolidated in cylinder molds by:

The hand rodding method only
Internal vibration (Correct answer)
External form vibration only
No consolidation is required for stiff mixes

Correct answer: Internal vibration

ASTM C31 requires internal vibration for concrete with slump at or below 1 inch because hand rodding cannot adequately consolidate stiff mixes.

Question 17: How does ACI 318 address the design of concrete structures for seismic regions?

ACI 318 Appendix D covers all seismic provisions as optional guidelines
Seismic design is excluded from ACI 318 and covered only by ASCE 7
Seismic provisions are in ACI 318 Chapter 2 as part of the general load definitions
ACI 318 Chapter 18 provides special provisions for seismic design, including detailing requirements for special moment frames, structural walls, and diaphragms in high seismic design categories (Correct answer)

Correct answer: ACI 318 Chapter 18 provides special provisions for seismic design, including detailing requirements for special moment frames, structural walls, and diaphragms in high seismic design categories

ACI 318 Chapter 18 (Earthquake-Resistant Structures) provides mandatory seismic detailing requirements for concrete structures in moderate and high seismic design categories.

Question 18: What is the minimum number of test cylinders that ACI 318 recommends making per strength test (using 4×8-inch cylinders) for acceptance testing purposes?

At least four, to provide three for testing (one 7-day and two 28-day) plus one spare (Correct answer)
Two cylinders are sufficient for all acceptance testing
Six cylinders per strength test regardless of cylinder size
One cylinder per 50 cubic yards of concrete is the only requirement

Correct answer: At least four, to provide three for testing (one 7-day and two 28-day) plus one spare

ACI 318 requires a strength test to be the average of at least three 4×8-inch cylinders; most QC plans make four per test to provide a 7-day break, two 28-day breaks (the acceptance average), and one spare held for retesting if needed.

Question 19: What is an 'accelerated curing' method for concrete cylinders, and when would it typically be used on a construction project?

Exposing cylinders to UV light to accelerate cement hydration
Curing at elevated temperature (e.g., boiling water or warm water at 35°C per ASTM C684) to estimate 28-day strength within 24–48 hours, used when early strength information is needed for critical decisions (Correct answer)
Curing under high pressure in an autoclave to achieve 56-day strength in 7 days for mass concrete
Using chemical accelerators added to the mix to reduce 28-day curing to 14 days

Correct answer: Curing at elevated temperature (e.g., boiling water or warm water at 35°C per ASTM C684) to estimate 28-day strength within 24–48 hours, used when early strength information is needed for critical decisions

Accelerated curing per ASTM C684 uses elevated temperature to speed hydration; 24-hour or 28-hour accelerated break results provide early indication of mix quality for form stripping decisions or identifying suspect batches.

Question 20: What effect does increasing the temperature of fresh concrete have on its measured air content?

Higher temperature increases air content by accelerating cement hydration gas production
Higher concrete temperature generally reduces air content because warmer concrete has lower surface tension and air bubbles coalesce and escape more easily (Correct answer)
Higher temperature always increases air content by reducing concrete viscosity
Temperature has no effect on air content in properly air-entrained mixes

Correct answer: Higher concrete temperature generally reduces air content because warmer concrete has lower surface tension and air bubbles coalesce and escape more easily

As concrete temperature rises, the viscosity of the paste decreases and surface tension of pore water drops, making it easier for air bubbles to merge and escape, reducing measured air content.

Question 21: Moisture corrections to batch weights are required whenever aggregate moisture content is:

At the saturated surface-dry (SSD) condition
Only when surface moisture is visibly present
Only when aggregate is oven-dry
Above or below the SSD condition (Correct answer)

Correct answer: Above or below the SSD condition

Aggregate above SSD contributes free water to the mix while aggregate below SSD absorbs water from it—both conditions require correcting the batch water quantity.

Question 22: According to ACI 305R, what is the maximum concrete temperature at point of discharge permitted without special hot-weather precautions?

95°F (35°C) (Correct answer)
75°F (24°C) ambient air temperature
85°F (29°C) ambient air temperature
100°F (38°C)

Correct answer: 95°F (35°C)

ACI 305R recommends that concrete temperature at point of discharge not exceed 95°F (35°C); higher temperatures accelerate hydration, reduce workability, and can lead to strength loss.

Question 23: Which ACI certification pathway is most appropriate for a technician who wants to specialize in shotcrete application and inspection?

ACI Flatwork Finisher Technician
ACI Concrete Strength Testing Technician – Grade I
ACI Shotcrete Nozzleman certification (Correct answer)
ACI Aggregate Testing Technician – Grade I

Correct answer: ACI Shotcrete Nozzleman certification

ACI Shotcrete Nozzleman certification is specifically designed for technicians involved in shotcrete application, covering both wet-mix and dry-mix processes and inspection criteria.

Question 24: What form does the rod's tamping end need to take?

A flat plane
A pointed tip
Rounded to a hemispherical tip (Correct answer)
The frustum of a cone

Correct answer: Rounded to a hemispherical tip

The tamping end of the rod used for consolidating concrete specimens must be rounded to a hemispherical tip. This specific shape ensures uniform consolidation without puncturing or excessively disturbing the concrete. A hemispherical tip helps to evenly distribute the tamping force, effectively removing entrapped air and preventing localized stress concentrations that could affect the specimen's integrity.

Question 25: To sample concrete from a truck mixer's chute, do the following:

Passing a receptacle completely through the discharge steam or by completely diverting the discharge into the sample container (Correct answer)
Holding a shovel in the flow and direct half into a bucket
None of the above
Raising chute to stop the flow and scoop concrete from there into the slump cone and cylinder molds

Correct answer: Passing a receptacle completely through the discharge steam or by completely diverting the discharge into the sample container

When sampling concrete from a truck mixer's chute, the correct procedure is to obtain a full cross-section of the discharge stream. This can be achieved by either passing a receptacle completely through the entire discharge stream or by completely diverting the entire discharge into the sample container. This method ensures a representative sample that accounts for any segregation that might occur during discharge.

Question 26: How does ACI certification support compliance with international construction codes?

By offering courses in foreign laws
By exempting certified professionals from inspections
By standardizing procedures across countries (Correct answer)
By replacing the need for local certifications

Correct answer: By standardizing procedures across countries

ACI certification supports compliance with international construction codes by establishing standardized procedures for concrete work. When professionals worldwide are trained and certified to the same ACI standards, it ensures uniformity in concrete quality, testing, and inspection practices. This standardization facilitates adherence to global building regulations and specifications, promoting consistent quality and safety across international projects.

Question 27: Why must concrete test cylinders be stored in a standardized moist curing environment (73 ± 3°F / 23 ± 2°C) after the initial 24-hour field period?

To prevent carbonation of the surface mortar
To simulate ideal hydration conditions and produce strength results that reflect the concrete's potential strength, not the field curing quality (Correct answer)
To allow cylinder molds to be reused immediately after stripping
To accelerate the hydration reaction and obtain results faster

Correct answer: To simulate ideal hydration conditions and produce strength results that reflect the concrete's potential strength, not the field curing quality

Standard laboratory curing conditions eliminate variability from field temperature and moisture, so all cylinders are tested under the same reference conditions, making results comparable and representative of the mix's potential.

Question 28: What is the primary document recommended for studying the ACI Concrete Field Testing Technician—Grade I certification?

ACI 318-19
ASTM C94/C94M
OSHA Construction Safety Handbook
ACI CP-1 Workbook (Correct answer)

Correct answer: ACI CP-1 Workbook

The ACI CP-1 Workbook is specifically designed by the American Concrete Institute as the primary study guide for the Concrete Field Testing Technician—Grade I certification. It covers all the required ASTM standards and practical procedures, making it the most comprehensive and recommended resource for preparation.

Question 29: According to ACI standards, what is the proper depth for a saw-cut contraction joint in a 6-inch thick slab-on-ground?

At least 1 inch
At least 1 1/2 inches (Correct answer)
At least 2 inches
At least 1/2 inch

Correct answer: At least 1 1/2 inches

ACI recommends that the depth of a saw-cut or tooled contraction joint should be at least one-quarter (1/4) of the slab thickness. For a 6-inch slab, this calculates to 1.5 inches (6 inches / 4 = 1.5 inches).

Question 30: The concrete sample that will be used for the slump test needs to be obtained in compliance with ASTM Standard _____.

0.75 in. [19 mm], 1.50 in. [38 mm]
Removed by wet sieving the sample over 1.5 in. [37.5 mm] sieve
C172, Standard Practice for Sampling Freshly Mixed Concrete (Correct answer)
2 5/8 in. [70 mm], 6 1/8 in. [160 mm]

Correct answer: C172, Standard Practice for Sampling Freshly Mixed Concrete

The concrete sample for a slump test must be obtained in compliance with ASTM Standard C172, Standard Practice for Sampling Freshly Mixed Concrete. Adhering to this standard ensures that the sample is representative of the concrete batch, which is critical for accurate and reliable test results. Proper sampling prevents misleading data that could lead to incorrect assessments of concrete quality.

Question 31: A technician is preparing to perform a flexural strength test (Modulus of Rupture) on a concrete beam specimen in accordance with ASTM C78. Which of the following loading configurations is specified by this standard?

Cantilever loading
Uniformly distributed loading
Center-point loading
Third-point loading (Correct answer)

Correct answer: Third-point loading

ASTM C78/C78M, "Standard Test Method for Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading)," explicitly requires the use of a third-point loading setup. This method applies the load at two points, each one-third of the span length from a support, which creates a region of maximum bending moment in the middle third of the beam.

Question 32: When testing 4×8-inch cylinders instead of 6×12-inch cylinders, what does ACI 318 Section 26.12.2 require for defining a 'strength test'?

The 4×8-inch cylinder results must be multiplied by a factor of 0.94
No adjustment is needed; one cylinder constitutes a test for both sizes
Four cylinders are required for 4×8-inch cylinders
A strength test must be the average of at least three 4×8-inch cylinders rather than the two required for 6×12-inch cylinders (Correct answer)

Correct answer: A strength test must be the average of at least three 4×8-inch cylinders rather than the two required for 6×12-inch cylinders

ACI 318 requires averaging at least three 4×8-inch cylinders per test to account for their higher inherent variability compared to 6×12-inch cylinders that require only two.

Question 33: Which ISO standard establishes the requirements for the competence and impartiality of testing and calibration laboratories, and how does it relate to ACI certification programs?

ISO 45001; ACI certifications fulfill workplace safety requirements under this standard
ISO 14001; ACI certifications are required for ISO 14001 environmental compliance
ISO 9001; all ACI certifications automatically satisfy ISO 9001 quality management requirements
ISO/IEC 17025; ACI certification programs align with its requirements for personnel competency, which helps accredited labs demonstrate that their technicians meet international quality benchmarks (Correct answer)

Correct answer: ISO/IEC 17025; ACI certification programs align with its requirements for personnel competency, which helps accredited labs demonstrate that their technicians meet international quality benchmarks

ISO/IEC 17025 is the global standard for testing laboratory competence; ACI certification of technicians supports a lab's ISO/IEC 17025 compliance by demonstrating personnel qualification in concrete testing methods.

Question 34: The absorption capacity of aggregate is important because it affects what aspect of concrete?

The aggregate's resistance to freezing
Only the aggregate's weight
The color of finished concrete
The effective water available for cement hydration — high-absorption aggregate soaks up batch water, reducing the water available for the cement reaction (Correct answer)

Correct answer: The effective water available for cement hydration — high-absorption aggregate soaks up batch water, reducing the water available for the cement reaction

If aggregate absorbs water from the mix, less water is available for cement hydration. Mix designs must account for aggregate absorption to ensure the correct water-cement ratio.

Question 35: What does the 'aggregate correction factor' account for in the ASTM C231 pressure meter air content test?

The difference in air content between the top and bottom of the bowl due to aggregate settlement
The reduction in air content caused by adding aggregate to the mix
The aggregate's own absorbed air or compressible pores that cause the pressure meter to over-read the true entrained air content in the paste (Correct answer)
The increase in required air content for larger maximum aggregate sizes

Correct answer: The aggregate's own absorbed air or compressible pores that cause the pressure meter to over-read the true entrained air content in the paste

The aggregate correction factor (G) accounts for the slight compressibility of aggregate pores and absorbed moisture that would cause the pressure meter to read a slightly higher air content than actually exists in the paste; it is subtracted from the meter reading.

Question 36: Which of the following is the correct tamping procedure for filling a 0.5 ft³ unit weight measure when performing the test for Density (Unit Weight) of Concrete (ASTM C138)?

Fill in 3 equal layers, rodding each layer 50 times. (Correct answer)
Fill in 2 equal layers, rodding each layer 50 times.
Fill in 2 equal layers, rodding each layer 25 times.
Fill in 3 equal layers, rodding each layer 25 times.

Correct answer: Fill in 3 equal layers, rodding each layer 50 times.

For a measure with a volume of 0.5 ft³, ASTM C138 requires the concrete to be placed in three approximately equal layers. Each layer must be rodded 50 times with the tamping rod, distributing the strokes evenly over the cross-section.

Question 37: When making concrete beam specimens for flexural strength testing per ASTM C31, which consolidation method is permitted when the measured slump is 3 inches (75 mm) or greater?

External vibration only
Either rodding or internal vibration (Correct answer)
Internal vibration only
Rodding only

Correct answer: Either rodding or internal vibration

Per ASTM C31, when slump is 3 inches or more, consolidation may be achieved by either rodding or internal vibration.

Question 38: What is the purpose of 'field-cured' test cylinders made in addition to standard laboratory-cured cylinders at a construction site?

To replace laboratory-cured cylinders when the concrete plant is far from an accredited lab
To measure the 7-day strength only, as field curing is not valid for 28-day acceptance testing
To provide backup cylinders in case laboratory-cured specimens are lost or damaged
To evaluate the actual in-place concrete strength under the temperature and curing conditions that the structure experienced, which may justify earlier form removal or loading (Correct answer)

Correct answer: To evaluate the actual in-place concrete strength under the temperature and curing conditions that the structure experienced, which may justify earlier form removal or loading

Field-cured cylinders represent the actual curing history (temperature, moisture) of the in-place concrete and are used to evaluate structural maturity for decisions like form stripping, post-tensioning, and traffic loading.

Question 39: An inspector is checking the placement of reinforcing steel in a 12-inch thick foundation wall prior to concrete placement. The project specifications reference ACI 318 for concrete cast against and permanently exposed to earth. What is the minimum required concrete cover over the reinforcing steel?

3/4 inch
2 inches
1 1/2 inches
3 inches (Correct answer)

Correct answer: 3 inches

ACI 318 specifies a minimum concrete cover of 3 inches for concrete cast against and permanently exposed to earth. This substantial cover is required to protect the reinforcing steel from moisture and corrosive elements in the soil, ensuring the long-term durability of the structure.

Question 40: What is 'alkali-silica reactivity' (ASR) and why is it tested in aggregates?

A measure of how quickly aggregate dissolves
A test of aggregate color stability
A harmful chemical reaction between certain silica minerals in aggregate and alkalis in cement that causes cracking and expansion in concrete over years (Correct answer)
A test of aggregate strength

Correct answer: A harmful chemical reaction between certain silica minerals in aggregate and alkalis in cement that causes cracking and expansion in concrete over years

ASR causes internal gel formation that absorbs water and swells, creating internal pressure that cracks the concrete from the inside out. Affected structures may need expensive repair or replacement.

Question 41: Why is networking an advantage of earning ACI certification?

It automatically provides access to international conferences
It is required to pass the certification exam
Certification events connect professionals across the industry (Correct answer)
It eliminates the need for professional references

Correct answer: Certification events connect professionals across the industry

Earning ACI certification often involves attending workshops, seminars, and examination sessions, which are excellent venues for professional networking. These events gather industry peers, experts, and potential employers, allowing certified individuals to forge valuable connections. Such networking opportunities can lead to job prospects, collaborative projects, and knowledge sharing, enhancing career growth within the concrete industry.

Question 42: Per ASTM C143, the height of the standard slump cone is:

10 inches
8 inches
12 inches (Correct answer)
14 inches

Correct answer: 12 inches

The standard slump cone is 12 inches (305 mm) tall per ASTM C143.

Question 43: How does the use of fly ash with high carbon content (high LOI) affect air entrainment in concrete?

SCMs have no effect on air entrainment regardless of composition
Fly ash always reduces the required AEA dosage by improving paste workability
High carbon content in fly ash can absorb air-entraining admixture, requiring higher AEA dosage to achieve specified air content (Correct answer)
Silica fume always increases air content by generating pozzolanic reaction gases

Correct answer: High carbon content in fly ash can absorb air-entraining admixture, requiring higher AEA dosage to achieve specified air content

Carbon (LOI) in fly ash adsorbs the surfactant molecules of the AEA before they can stabilize air bubbles, requiring significantly increased AEA doses; LOI variability makes air content management difficult.

Question 44: Why is the soundness test performed on concrete aggregates?

To test if aggregate is solid enough to walk on
To measure how much noise aggregate makes
To evaluate the aggregate's resistance to disintegration from repeated cycles of wetting and drying or freezing and thawing — simulating weathering (Correct answer)
To determine the speed of sound through aggregate

Correct answer: To evaluate the aggregate's resistance to disintegration from repeated cycles of wetting and drying or freezing and thawing — simulating weathering

The soundness test (ASTM C88) simulates weathering by soaking aggregate in sodium or magnesium sulfate solution that crystallizes in pores, creating expansion pressure similar to ice crystal formation.

Question 45: How does passing an ACI technician certification benefit a testing laboratory seeking AASHTO Materials Reference Laboratory (AMRL) accreditation?

AMRL accreditation requires documented evidence of personnel qualifications; ACI certifications directly satisfy the personnel competency requirements for the specific test methods covered, reducing the documentation burden during AMRL audits (Correct answer)
ACI certifications benefit only field personnel; lab accreditation is unrelated to field certifications
ACI certifications automatically grant AMRL accreditation without a separate application
AMRL only accepts ISO certifications; ACI certifications are not recognized

Correct answer: AMRL accreditation requires documented evidence of personnel qualifications; ACI certifications directly satisfy the personnel competency requirements for the specific test methods covered, reducing the documentation burden during AMRL audits

AMRL auditors evaluate technician qualifications as part of the laboratory accreditation process; ACI certifications in the relevant test methods provide clear third-party documentation of competency that satisfies this personnel requirement.

Question 46: After the last layer has been firmed up, what should be done if there is an excessive amount of concrete in the measurement?

Add additional concrete to keep an excess of concrete above the top of the mold at all times
Lightweight, air-cooled blast furnace slag, or aggregates of high porosity
C172, Standard Practice for Sampling Freshly Mixed Concrete
Remove a representative quantity of concrete with the scoop or trowel before the strike off (Correct answer)

Correct answer: Remove a representative quantity of concrete with the scoop or trowel before the strike off

If there is an excessive amount of concrete in the mold after the last layer has been consolidated, a representative quantity should be removed with a scoop or trowel before striking off the top surface. This ensures that the mold contains the correct volume of concrete for accurate density measurements and allows for a clean, level strike-off. Adding more concrete would only be necessary if there was insufficient concrete after consolidation.

Question 47: What is the maximum time limit for completing all fresh concrete tests from the time of composite sampling per ASTM C172?

No time limit as long as the concrete remains workable
30 minutes from time of truck arrival at the site
Sampling must take no more than 5 minutes; all individual tests must start within 5 minutes of sampling and be completed within 15 minutes (Correct answer)
60 minutes from time of batching

Correct answer: Sampling must take no more than 5 minutes; all individual tests must start within 5 minutes of sampling and be completed within 15 minutes

ASTM C172 requires composite sampling to take no more than 5 minutes and all tests to be started within 5 minutes of obtaining the composite sample and completed within 15 minutes.

Question 48: According to ACI 318, the maximum w/cm ratio for concrete exposed to freezing and thawing in a moist condition is:

0.40
0.45 (Correct answer)
0.60
0.55

Correct answer: 0.45

ACI 318 limits the w/cm to 0.45 for concrete subjected to freezing and thawing in moist conditions to control permeability.

Question 49: As part of a pre-placement inspection for a concrete slab-on-ground, which of the following items is most critical to verify is correct immediately before concrete discharge begins?

The subgrade is moist but free of standing water, and all formwork is clean. (Correct answer)
The laboratory has submitted the 7-day strength results from a previous pour.
The finishing tools have been cleaned and staged.
The curing compound has been delivered and is stored in a shaded area.

Correct answer: The subgrade is moist but free of standing water, and all formwork is clean.

A proper subgrade condition (moist to prevent rapid water loss from the concrete, but not puddled) and clean forms are essential for the quality and integrity of the concrete at the moment of placement. These must be checked and confirmed immediately prior to placement. The other items are important project tasks but are not immediate pre-discharge requirements that directly affect the concrete quality as it is being placed.

Question 50: Per ASTM C1064, the minimum immersion depth for a concrete temperature-measuring device is:

4 inches (100 mm)
3 inches (75 mm) (Correct answer)
2 inches (50 mm)
1 inch (25 mm)

Correct answer: 3 inches (75 mm)

ASTM C1064 requires the temperature device to be inserted to a minimum depth of 3 inches (75 mm) to ensure an accurate reading.

Question 51: Which of the following is an appropriate action immediately after molding and finishing a concrete test specimen?

Place the specimen in its initial curing location, protected from moisture loss and disturbance. (Correct answer)
Leave the specimen uncovered to allow bleed water to evaporate quickly.
Move the specimen to the final curing location in the laboratory.
Submerge the specimen in ice water to rapidly cool it to the required curing temperature.

Correct answer: Place the specimen in its initial curing location, protected from moisture loss and disturbance.

Immediately after molding, specimens must be moved to an initial curing environment that prevents moisture loss, maintains the specified temperature, and is free from vibrations or other disturbances that could affect the concrete's integrity.

Question 52: Which ASTM standard covers the procedure for sampling freshly mixed hydraulic cement concrete?

ASTM C143
ASTM C138
ASTM C31
ASTM C172 (Correct answer)

Correct answer: ASTM C172

ASTM C172 is the standard practice for sampling freshly mixed concrete and is the first step before any other fresh concrete testing.

ACI Concrete Field Testing Technician - Grade I

This certification demonstrates proficiency in performing and recording the results of seven basic field tests for concrete.

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Unanswered questions count as wrong — answer everything
10 pretest questions are mixed in and don't affect your score
Timer auto-submits when time runs out
Your progress is auto-saved every 30 seconds