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ACI Special Inspector practice questions

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Question 1Concrete Construction Inspection

According to ACI 318, what is the minimum specified compressive strength f'c for structural concrete unless otherwise permitted by the code?

  1. 3,500 psi
  2. 2,500 psi Correct answer.
  3. 4,000 psi
  4. 3,000 psi

Explanation

ACI 318 requires a minimum specified compressive strength of 2,500 psi for structural concrete unless a higher value is required by design or specific provisions. Higher values are common in practice but are not the code minimum.

Question 2Concrete Construction Inspection

A concrete mix design calls for a slump of 4 in. During field testing, the inspector measures a slump of 6 in. What is the most appropriate first action?

  1. Accept the load because slump tolerance is unlimited
  2. Reject the load and require removal from site
  3. Add water to bring the slump to the target value
  4. Verify the measurement and check whether the load can be adjusted per approved procedures Correct answer.

Explanation

The inspector should first confirm the test was performed correctly and then follow the project's approved procedures for handling nonconforming slump, which may allow adjustment without adding water. Immediate rejection or unauthorized water addition is not the first appropriate step.

Question 3Concrete Construction Inspection

When concrete test cylinders are made for acceptance testing, standard curing before 28-day testing requires the specimens to be:

  1. Cured in a saturated salt solution
  2. Stored in a moist condition at 60 to 80 degrees F Correct answer.
  3. Stored dry at ambient temperature
  4. Cured in the field under the same conditions as the structure

Explanation

Standard-cured specimens must be stored in a moist environment at a controlled temperature of 60 to 80 degrees F until the time of test. This standard curing isolates the concrete quality from field curing effects.

Question 4Concrete Construction Inspection

A set of three 6 by 12 in. cylinders breaks at 3,180 psi, 3,050 psi, and 2,900 psi. What is the reported compressive strength of the test?

  1. 2,900 psi
  2. 3,180 psi
  3. 3,043 psi Correct answer.
  4. 3,050 psi

Explanation

The reported strength is the arithmetic average of the test results, which is (3,180 + 3,050 + 2,900) / 3 = 3,043 psi. The average is used for acceptance evaluation unless a single specimen deviates excessively.

Question 5Concrete Construction Inspection

During a slump test, the inspector should measure the vertical distance from the top of the mold to the displaced original center of the concrete to the nearest:

  1. 1/2 in.
  2. 1/8 in.
  3. 1 in.
  4. 1/4 in. Correct answer.

Explanation

ASTM C143 requires the slump to be measured and recorded to the nearest 1/4 in. This precision is standard for field slump measurement.

Question 6Concrete Construction Inspection

A load of concrete arrives at the jobsite and the delivery ticket shows a batch time of 90 minutes earlier with no retarding admixture. The ambient conditions are hot. What should the inspector do?

  1. Reject the load because it exceeds typical time limits unless approved Correct answer.
  2. Accept the load if slump is within tolerance
  3. Allow placement if the drum is still turning
  4. Add water to restore workability

Explanation

Concrete generally must be placed within a limited time after batching (commonly 90 minutes or before the drum has revolved 300 times) unless a retarding admixture or approved procedure extends the limit. Exceeding the limit without approval is grounds for rejection.

Question 7Concrete Construction Inspection

The standard method for determining the air content of freshly mixed concrete by the pressure method is described in which ASTM standard?

  1. ASTM C231 Correct answer.
  2. ASTM C31
  3. ASTM C173
  4. ASTM C143

Explanation

ASTM C231 covers the pressure method for air content of freshly mixed concrete. This method is suitable for concrete made with normal-weight aggregate.

Question 8Concrete Construction Inspection

When preparing a strength test specimen from a sample, the concrete should be sampled and the cylinders fabricated within what time interval after sampling?

  1. Within 1 hour regardless of conditions
  2. Within 15 minutes after sampling Correct answer.
  3. Immediately, with no remixing allowed at any time
  4. After remixing and waiting 30 minutes

Explanation

ASTM C172 requires that specimens be molded within 15 minutes after sampling, with the concrete remixed to ensure uniformity before molding. Delay beyond this can allow segregation and set.

Question 9Concrete Construction Inspection

Which of the following best describes the purpose of a slump test in the field?

  1. To provide an indication of concrete consistency and workability Correct answer.
  2. To verify the cement content of the batch
  3. To determine the air content of the mix
  4. To measure the compressive strength of the concrete

Explanation

The slump test is a measure of consistency, providing an indication of workability, not strength or composition. It is a quality-control check, not a direct strength test.

Question 10Concrete Construction Inspection

An inspector observes concrete being placed in a deep wall form and dropped from a considerable height, causing visible segregation. What is the recommended corrective action?

  1. Add water to improve flow
  2. Use a tremie or drop pipe to place concrete without segregation Correct answer.
  3. Continue placing and vibrate heavily afterward
  4. Reduce vibration to avoid further segregation

Explanation

Concrete placed from excessive heights can segregate; a tremie or drop pipe should be used to direct the concrete and prevent separation of materials. Vibrating heavily afterward cannot fully correct segregation.

Question 11Concrete Construction Inspection

The standard practice for making and curing concrete test specimens in the field is described in which ASTM standard?

  1. ASTM C192
  2. ASTM C39
  3. ASTM C617
  4. ASTM C31 Correct answer.

Explanation

ASTM C31 covers making and curing concrete test specimens in the field. ASTM C192 covers the same for laboratory conditions.

Question 12Concrete Construction Inspection

A vibrator is being used to consolidate concrete in a column. Which practice is correct?

  1. Leave the vibrator running against the formwork to improve finish
  2. Drag the vibrator horizontally through the concrete to spread it
  3. Vibrate briefly at each lift, inserting the vibrator rapidly and withdrawing slowly Correct answer.
  4. Vibrate only the top surface of the final lift

Explanation

Proper vibration requires inserting the vibrator rapidly and withdrawing it slowly so the concrete flows into the space left, consolidating each lift. Vibration should penetrate into the previous lift to integrate the layers.

Question 13Concrete Construction Inspection

According to ACI 318, the specified compressive strength f'c is based on tests of cylinders at what age, unless otherwise specified?

  1. 7 days
  2. 28 days Correct answer.
  3. 14 days
  4. 56 days

Explanation

Compressive strength f'c is defined at 28 days unless another age is specified for the project. This is the standard reference age for acceptance testing.

Question 14Concrete Construction Inspection

An inspector is evaluating acceptance of a concrete strength test where one cylinder in a set of three deviates significantly from the others. What should be done before computing the average?

  1. Investigate the cause and consider whether the low specimen is valid Correct answer.
  2. Discard the outlier without documentation
  3. Average all three regardless of deviation
  4. Use only the two highest values

Explanation

Before using the average, the inspector should investigate the cause of an outlying specimen (e.g., improper molding, damage, capping) to determine whether the test is valid. Documenting the investigation is essential.

Question 15Concrete Construction Inspection

During cylinder fabrication, the number of rodding strokes per layer for a 6 by 12 in. cylinder using the standard rod is:

  1. 25 per layer Correct answer.
  2. 10 per layer
  3. 15 per layer
  4. 35 per layer

Explanation

ASTM C31 requires 25 rodding strokes per layer for a 6 by 12 in. cylinder, distributed uniformly over the cross section. This ensures proper consolidation without overworking.

Question 16Concrete Construction Inspection

Which of the following is the correct procedure for capping a concrete cylinder before compression testing?

  1. Cap with a sulfur mortar or neoprene pad to provide a smooth, plane surface Correct answer.
  2. Test without capping in all cases
  3. Cap only if the cylinder end is visibly cracked
  4. Grind the ends only when the break is below 3,000 psi

Explanation

Cylinder ends must be capped or ground to provide a smooth, plane surface perpendicular to the axis so the load is applied uniformly. Sulfur mortar, neoprene pads, or grinding are acceptable methods.

Question 17Concrete Construction Inspection

An inspector notices that a concrete truck has been adding water to the mix on site without authorization. What is the primary concern?

  1. It increases the air content of the mix
  2. It increases the water-cementitious ratio and reduces strength Correct answer.
  3. It improves the strength of the concrete
  4. It has no effect on the concrete properties

Explanation

Adding water increases the water-cementitious ratio, which reduces compressive strength and durability. Water additions must be controlled and authorized per the mix design.

Question 18Concrete Construction Inspection

The standard test method for compressive strength of cylindrical concrete specimens is:

  1. ASTM C31
  2. ASTM C39 Correct answer.
  3. ASTM C143
  4. ASTM C231

Explanation

ASTM C39 is the standard test method for compressive strength of cylindrical concrete specimens. It specifies loading rate, specimen preparation, and reporting.

Question 19Concrete Construction Inspection

When sampling concrete from a stationary mixer or truck, the sample should be taken:

  1. From the first portion discharged
  2. From the top of the drum before discharge
  3. From the middle portion of the discharge Correct answer.
  4. After the entire load has been discharged

Explanation

ASTM C172 requires sampling from the middle portion of the discharge, not the beginning or end, to obtain a representative sample. Sampling the first or last portion may not represent the whole batch.

Question 20Concrete Construction Inspection

A project specifies a maximum slump of 4 in. for a normal mix. The inspector measures 4-3/4 in. What does this result indicate?

  1. The concrete is within tolerance and acceptable
  2. The slump is too low for placement
  3. The test is invalid and must be repeated regardless
  4. The slump exceeds the specified value and must be evaluated Correct answer.

Explanation

A measured slump of 4-3/4 in. exceeds the specified 4 in. maximum, so the load must be evaluated per project procedures. It is not automatically acceptable, nor is the test inherently invalid.

Question 21Concrete Construction Inspection

Which of the following best describes the purpose of a field-cured cylinder?

  1. To verify the slump of the concrete
  2. To determine the specified compressive strength for acceptance
  3. To measure the air content of the mix
  4. To evaluate the adequacy of curing and protection of the structure Correct answer.

Explanation

Field-cured cylinders are cured under the same conditions as the structure and are used to evaluate whether curing and protection in the field are adequate. Standard-cured cylinders are used for acceptance.

Question 22Concrete Construction Inspection

Concrete is being placed in cold weather. Which precaution helps prevent freezing damage to fresh concrete?

  1. Maintaining concrete temperature above freezing during and after placement Correct answer.
  2. Placing concrete on frozen ground
  3. Allowing the surface to freeze to seal it
  4. Using cold mixing water

Explanation

Fresh concrete must be protected from freezing until it develops sufficient strength; maintaining adequate temperature during and after placement prevents damage. Frozen subgrade and cold water would worsen conditions.

Question 23Concrete Construction Inspection

An inspector must verify that the concrete delivered matches the approved mix design. Which document provides the primary basis for this verification?

  1. The slump test result
  2. The delivery ticket showing batch weights, mix ID, and admixtures Correct answer.
  3. The cylinder break report
  4. The air content test result

Explanation

The delivery ticket documents batch weights, mix identification, admixtures, and time, and is the primary basis for verifying the load against the approved mix design. Test results reflect properties but do not confirm the mix composition.

Question 24Concrete Construction Inspection

A cylinder tests at 2,400 psi against a specified f'c of 3,000 psi. Under ACI 318 acceptance criteria, what generally governs whether the strength is acceptable?

  1. Strength acceptance is based solely on slump
  2. A single low test always fails regardless of the average
  3. Only the highest test in the set matters
  4. The average of three consecutive tests and the individual test must meet code criteria Correct answer.

Explanation

ACI 318 acceptance criteria require that the average of three consecutive strength test results meet or exceed f'c and that no individual test fall below f'c by more than a specified margin. Both conditions must be satisfied.

Question 25Concrete Construction Inspection

An inspector observes honeycombing and voids on a formed concrete surface after form removal. What is the most likely cause?

  1. Inadequate consolidation or improper vibration Correct answer.
  2. Excessive consolidation
  3. Too much cement in the mix
  4. Curing compound applied too early

Explanation

Honeycombing and voids typically result from inadequate consolidation, such as missed vibration zones, insufficient vibration, or segregation during placement. Proper vibration and placement practices prevent these defects.

Question 26Concrete Construction Inspection

Which document must the inspector check to confirm the maximum size of coarse aggregate permitted for a given reinforced concrete member?

  1. The approved project specifications and mix design submittal Correct answer.
  2. The concrete delivery ticket only
  3. The batch plant's aggregate gradation file
  4. The contractor's daily quality control log

Explanation

Acceptance of aggregate size is governed by the project specifications and the approved mix design, which establish limits based on member dimensions and reinforcement spacing. The inspector verifies the delivered material against those approved documents.

Question 27Concrete Construction Inspection

What is the primary purpose of consolidating freshly placed concrete with a mechanical vibrator?

  1. To increase the cement content near the form face
  2. To reduce the total volume of concrete required
  3. To remove entrapped air and ensure the concrete fully surrounds reinforcement Correct answer.
  4. To accelerate the initial set of the mixture

Explanation

Consolidation removes large voids of entrapped air and works the concrete against forms and around embedded items. Proper consolidation improves density, bond, and durability.

Question 28Concrete Construction Inspection

An inspector observes that concrete in a slab is being placed and finished while ambient temperatures are dropping and a freeze is forecast overnight. Which action is most appropriate?

  1. Apply additional water to the surface to slow cooling
  2. Allow the surface to remain exposed so moisture can evaporate
  3. Delay finishing until the following morning
  4. Require protective insulation or covering to maintain the concrete above freezing Correct answer.

Explanation

Fresh concrete must be protected from freezing until it has attained sufficient strength; insulation or covering retains heat of hydration. Surface water loss and rapid cooling both increase the risk of damage.

Question 29Concrete Construction Inspection

Which test measures the consistency of fresh concrete and is commonly used as a field workability indicator?

  1. The pulse velocity test
  2. The unit weight test
  3. The air content pressure test
  4. The slump test Correct answer.

Explanation

The slump test measures consistency, an indicator of workability, by determining how far a molded cone of concrete settles. It is a standard field acceptance check tied to specified limits.

Question 30Concrete Construction Inspection

An inspector is reviewing a batch ticket and notices the ticket lists the time of batching but not the time of discharge at the site. Why is discharge time important?

  1. It sets the required curing duration
  2. It fixes the cylinder break schedule
  3. It determines the required slump at the point of placement
  4. It establishes the elapsed time limit for placing the concrete Correct answer.

Explanation

Elapsed time between batching and discharge governs whether concrete may be placed under the project's time limits. The inspector uses both times to verify compliance.

Question 31Concrete Construction Inspection

What does the term 'honeycombing' describe on a formed concrete surface?

  1. A glossy, overworked surface finish
  2. A pattern of fine shrinkage cracks on the surface
  3. Voids and exposed coarse aggregate where mortar failed to fill the space Correct answer.
  4. A chalky white deposit leached from the concrete

Explanation

Honeycombing appears as voids between coarse aggregate particles where mortar did not fill the form. It usually indicates inadequate consolidation, segregation, or grout loss.

Question 32Concrete Construction Inspection

An inspector is asked to verify the air content of a normal-weight concrete mixture in the field. Which method is the standard field procedure for this measurement?

  1. Sieving method for mortar fraction
  2. Pressure method using a calibrated air meter Correct answer.
  3. Washout method for cement content
  4. Volumetric method using a calibrated meter

Explanation

The pressure method is the standard field procedure for determining air content of normal-weight concrete. It relies on Boyle's law to relate applied pressure to the volume of air in the sample.

Question 33Concrete Construction Inspection

Which of the following best describes the role of the special inspector during concrete placement?

  1. To observe and document compliance with the approved plans and specifications Correct answer.
  2. To direct the contractor's crew and adjust the mix design
  3. To perform the structural design of the member being placed
  4. To approve payment applications for the concrete supplier

Explanation

The special inspector observes, tests, and documents construction to verify compliance with approved documents. The inspector does not direct the contractor's means and methods.

Question 34Concrete Construction Inspection

An inspector observes that concrete is being placed in a wall form in lifts that are too deep for the vibrator to fully penetrate the lower portion. What is the most likely consequence?

  1. Increased air content at the top of the lift
  2. Excessive bleeding at the form face
  3. Voids and inadequate consolidation in the lower portion of the lift Correct answer.
  4. Premature setting of the surface layer

Explanation

Lift depth must allow the vibrator to penetrate into the layer below so voids are removed throughout the placement. When lifts are too deep, the lower portion may not be consolidated and defects such as honeycombing can result.

Question 35Concrete Construction Inspection

During cylinder fabrication, the inspector observes the technician striking off the top of the cylinder with a trowel and then leaving the surface open in the sun. What is the correct practice?

  1. Add water to the top of each cylinder
  2. Cover the cylinders to prevent moisture loss and protect them from the elements Correct answer.
  3. Place cylinders directly on the ground in the sun
  4. Leave the surface open to allow rapid drying

Explanation

Freshly molded cylinders must be protected from moisture loss and temperature extremes during initial curing. Covering the specimens preserves the water needed for hydration.

Question 36Concrete Construction Inspection

An inspector is checking formwork before a wall pour. Which condition most directly threatens the specified concrete cover over reinforcement?

  1. Form ties that are slightly overtightened
  2. Missing or displaced chairs and spacers Correct answer.
  3. Formwork that is slightly damp
  4. Form release agent applied too thinly

Explanation

Cover is maintained by properly positioned chairs, spacers, and supports. Missing or displaced devices allow reinforcement to shift against the form, reducing cover and durability.

Question 37Concrete Construction Inspection

Concrete is being placed in a slab and the inspector observes the finisher adding water to the surface to make troweling easier. What is the appropriate response?

  1. Require the addition of cement to compensate
  2. Permit it if the slump is within limits
  3. Allow it only on the top half of the slab
  4. Stop the practice and require the contractor to finish without adding water Correct answer.

Explanation

Adding water at the surface raises the local water-cement ratio and weakens the surface, promoting dusting and scaling. The practice is not permitted and must be stopped.

Question 38Concrete Construction Inspection

An inspector must confirm that a truckload of concrete is within the specified slump range. Which procedure is correct?

  1. Measure slump from the last portion of the discharge
  2. Measure slump from the first portion of the discharge
  3. Measure slump from a sample obtained after at least a portion of the load has been discharged Correct answer.
  4. Measure slump from any portion of the load

Explanation

Samples for slump and other tests should be representative of the middle portion of the discharge, not the first or last portions. This ensures the test reflects the whole load.

Question 39Concrete Construction Inspection

A concrete mix is specified with a maximum water-cementitious materials ratio of 0.45. The batch ticket shows a water-cementitious ratio of 0.50. What should the inspector do?

  1. Accept the load and document the ratio for records only
  2. Accept the load because it is within 10 percent
  3. Accept the load if the slump is within limits
  4. Reject the load or refer it to the engineer for disposition Correct answer.

Explanation

The water-cementitious materials ratio is a specified acceptance requirement. A load exceeding the limit does not comply and should be rejected or referred to the engineer for a decision.

Question 40Concrete Construction Inspection

An inspector observes a concrete truck discharging a load that has been in the drum for an extended period and is noticeably stiff. Which action is most consistent with good practice?

  1. Add sand to the drum to loosen the mix
  2. Add water freely to restore workability
  3. Discharge the load and place it in a nonstructural area
  4. Refer the load to the engineer or reject it if it cannot be placed within specified limits Correct answer.

Explanation

Stiff concrete that cannot be placed within the specified time or workability limits should not be accepted. The inspector should refer it for disposition or reject it rather than alter the mix.

Question 41Concrete Construction Inspection

Which of the following conditions most directly indicates that formwork is inadequately braced before a pour?

  1. The forms are clean and free of debris
  2. The forms show visible deflection or movement under load Correct answer.
  3. The form ties are spaced per the shop drawings
  4. The release agent is evenly applied

Explanation

Visible deflection or movement of forms under load indicates inadequate bracing or support and can lead to misalignment or failure. The inspector should require correction before placement.

Question 42Concrete Construction Inspection

An inspector is reviewing the results of a set of field-cured cylinders and notes that the strength is lower than the specified value. What is the most appropriate first step?

  1. Immediately require removal of the concrete
  2. Assume the cylinders were tested incorrectly
  3. Compare the results with the specified acceptance criteria and investigate the cause Correct answer.
  4. Accept the results because field-cured cylinders are always lower

Explanation

Field-cured results must be evaluated against the applicable acceptance criteria, and the cause of low strength should be investigated before any action is taken. Premature conclusions can lead to unnecessary removal.

Question 43Concrete Construction Inspection

Which of the following is the correct order of operations when preparing a standard test cylinder in the field?

  1. Cure, fill, rod, strike off
  2. Fill, strike off, rod, cure
  3. Rod, fill, cure, strike off
  4. Fill, rod, strike off, cure Correct answer.

Explanation

Concrete is placed in layers, each layer is rodded, the top is struck off, and the specimen is then cured. Following this order ensures proper consolidation and a flat, sound specimen.

Question 44Concrete Construction Inspection

An inspector observes that concrete is being placed in a deep form and allowed to fall freely from a considerable height, causing segregation. Which action is correct?

  1. Continue placement and vibrate heavily afterward
  2. Require the use of a drop pipe or chute to limit free fall Correct answer.
  3. Reduce the vibrator frequency
  4. Add water to the mix to improve flow

Explanation

Free fall from excessive height causes segregation of coarse aggregate from mortar. Using a drop pipe or chute limits fall height and preserves homogeneity.

Question 45Concrete Construction Inspection

An inspector observes that a concrete surface has developed a network of fine cracks shortly after finishing on a hot, windy day. Which cause is most likely?

  1. Alkali-silica reaction
  2. Sulfate attack
  3. Plastic shrinkage from rapid surface moisture loss Correct answer.
  4. Freezing and thawing damage

Explanation

Hot, windy conditions accelerate evaporation from the surface, causing plastic shrinkage cracking before the concrete sets. Prompt curing and evaporation control reduce this risk.

Question 46Concrete Construction Inspection

A concrete mixture is specified with a maximum slump of 4 in. The inspector measures 5 in. on a load that otherwise meets all requirements. What is the correct interpretation?

  1. The load exceeds the specified limit and should be referred for disposition Correct answer.
  2. The load complies if the air content is within limits
  3. The load complies because slump is only a guide
  4. The load complies if the strength test later passes

Explanation

The specified slump limit is an acceptance requirement. A measured slump exceeding the limit means the load does not comply and should be referred for disposition.

Question 47Concrete Construction Inspection

An inspector is evaluating a concrete placement where the specified cover is 1.5 in. over reinforcement in a wall. The inspector observes that the reinforcement is positioned 0.75 in. from the form face at several locations. What is the most appropriate action?

  1. Accept the placement and note it for future reference only
  2. Require additional vibration to compensate
  3. Require correction of the reinforcement position before the pour continues Correct answer.
  4. Accept the placement because the wall is not exposed to weather

Explanation

Cover is a specified durability and protection requirement. Reinforcement positioned closer than the specified cover does not comply and must be corrected before concrete is placed.

Question 48Concrete Construction Inspection

An inspector is reviewing a curing operation where the contractor plans to remove curing protection from a slab after 24 hours in cool weather. Which consideration is most relevant to the acceptability of this plan?

  1. The slump measured at placement
  2. Whether the concrete has attained sufficient strength and the specified curing duration has been met Correct answer.
  3. The color of the curing compound
  4. The number of workers assigned to the curing operation

Explanation

Curing must continue until the specified duration is met and the concrete has gained sufficient strength to resist damage. Removing protection prematurely can reduce durability and strength development.

Question 49Concrete Construction Inspection

An inspector observes that a concrete load has been retempered with water at the site beyond the amount shown on the batch ticket, and the slump now falls within the specified range. How should the inspector treat this load?

  1. Treat it as noncompliant because the water-cementitious ratio has been altered without authorization Correct answer.
  2. Accept it if the concrete is placed within 30 minutes
  3. Accept it if the air content is also within limits
  4. Accept it because the slump is now within limits

Explanation

Adding water at the site beyond the approved batch quantity alters the water-cementitious materials ratio and is not permitted without authorization. Compliance with slump does not cure the alteration.

Question 50Concrete Construction Inspection

An inspector must determine whether a concrete placement in a cold-weather condition is acceptable. Which factor is most directly relevant to the decision?

  1. The color of the formwork
  2. The temperature of the concrete as placed and the protection provided Correct answer.
  3. The number of cylinders fabricated
  4. The type of finishing tool used

Explanation

Cold-weather acceptance depends on the concrete temperature at placement and the protection provided to prevent freezing and ensure strength development. These are the controlling factors.