I85PREP
⌘ K
ACI Field Testing I study materials
ACI Field Testing I study resources

ACI Field Testing I practice questions

One question at a time. Build your ACI Field Testing I understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Sampling Freshly Mixed Concrete

What is the minimum volume of a fresh concrete sample required for strength test specimens under ASTM C172?

  1. 1.00 ft³ (0.028 m³) Correct answer.
  2. 2.00 ft³ (0.057 m³)
  3. 0.50 ft³ (0.014 m³)
  4. 0.25 ft³ (0.007 m³)

Explanation

ASTM C172 requires a sample of at least 1 ft³ (0.03 m³) when strength specimens are to be made, so enough concrete is available for all tests. Smaller samples may not provide sufficient material for the required specimens.

Question 2Sampling Freshly Mixed Concrete

When sampling from a truck mixer, at what point in the discharge should the sample be obtained?

  1. From the top of the drum before discharge
  2. At the very end of the discharge
  3. From the first concrete out of the drum
  4. After 10% to 15% is discharged Correct answer.

Explanation

C172 specifies sampling after about 10% to 15% of the batch has been discharged so the sample is representative. The first and last portions may be segregated or contain excess water.

Question 3Sampling Freshly Mixed Concrete

For a stationary mixer, when should the sample be taken?

  1. From the first 5% of the discharge
  2. Before any concrete is discharged
  3. After about 10% is discharged Correct answer.
  4. After the entire batch has been discharged

Explanation

The sample should be obtained after approximately 10% of the batch has been discharged, from the middle portion of the discharge stream. This avoids the non-representative first and last portions.

Question 4Sampling Freshly Mixed Concrete

What tool should be used to remix a composite concrete sample before testing?

  1. A steel trowel
  2. A hand scoop
  3. A shovel Correct answer.
  4. A vibrating table

Explanation

C172 requires the composite sample to be remixed with a shovel before tests are performed to ensure uniformity. Trowels and scoops are too small for proper remixing of the full sample.

Question 5Sampling Freshly Mixed Concrete

What is the maximum time allowed between obtaining a sample and starting the tests?

  1. 30 minutes
  2. 15 minutes Correct answer.
  3. 5 minutes
  4. 10 minutes

Explanation

Tests should begin within 15 minutes after the sample is obtained to minimize changes in workability and air content. The sample must be protected during this interval.

Question 6Sampling Freshly Mixed Concrete

Adding water to a fresh concrete sample to adjust slump is:

  1. Permitted if done within 5 minutes
  2. Permitted if the sample is remixed for 2 minutes
  3. Not permitted at any time Correct answer.
  4. Permitted if cement is also added

Explanation

C172 prohibits adding water to the sample because it changes the water-cement ratio and makes the sample unrepresentative. The sample must be tested as obtained.

Question 7Sampling Freshly Mixed Concrete

How should a sample be obtained from a paving mixer?

  1. From the first material discharged from the mixer
  2. Three locations across the width, away from edges Correct answer.
  3. From the edges of the mat where segregation occurs
  4. From one location at the center of the mat

Explanation

C172 requires sampling from at least three locations across the width of the paving machine, avoiding the edges where segregation may occur. This produces a representative composite sample.

Question 8Sampling Freshly Mixed Concrete

When concrete is delivered by pump, where should the sample be taken?

  1. From the pump hopper
  2. From the top of the pump line
  3. From the first concrete out of the hose
  4. At the discharge end of the hose Correct answer.

Explanation

The sample should be obtained at the discharge end of the hose so it reflects the concrete as placed. The hopper and the first portion out of the hose may not be representative.

Question 9Sampling Freshly Mixed Concrete

A container used to hold a fresh concrete sample should be:

  1. Clean, damp, non-absorbent Correct answer.
  2. Coated with a release agent
  3. Made of untreated wood
  4. Dry and highly absorbent

Explanation

The container must be clean, damp, and non-absorbent to prevent loss of water or contamination. This helps preserve the sample's original characteristics.

Question 10Sampling Freshly Mixed Concrete

Why is the first portion of discharge avoided when sampling concrete?

  1. It is always colder than the rest of the batch
  2. It is needed only for slump testing
  3. It may be segregated or carry excess water Correct answer.
  4. It contains more cement than the rest

Explanation

The first concrete out of a mixer or truck may be segregated or carry excess water, so it is not representative of the batch. Sampling after 10% to 15% has been discharged avoids this problem.

Question 11Sampling Freshly Mixed Concrete

A composite concrete sample is best described as:

  1. A sample taken after all tests are complete
  2. A sample taken from a single point in the discharge
  3. A sample taken only from the top of the drum
  4. Portions taken from different locations and combined Correct answer.

Explanation

A composite sample combines portions from several locations or times in the discharge to represent the whole batch. The portions are then remixed before testing.

Question 12Sampling Freshly Mixed Concrete

When sampling from a conveyor belt, how should the sample be obtained?

  1. Take material only from the belt edges
  2. Full cross-section at three or more locations Correct answer.
  3. Take one large sample from the end of the belt
  4. Take a small scoop from the center of the belt

Explanation

C172 requires taking the full cross-section of the belt at three or more locations so coarse and fine particles are proportionally represented. Partial samples may miss segregated material.

Question 13Sampling Freshly Mixed Concrete

A fresh concrete sample should be protected from:

  1. Mixing with a shovel
  2. Evaporation and rapid drying Correct answer.
  3. Being placed in a damp container
  4. Testing within 15 minutes

Explanation

The sample must be protected from evaporation, wind, and direct sunlight because water loss changes slump and air content. Covering the sample is a common protective measure.

Question 14Sampling Freshly Mixed Concrete

Which source is acceptable for obtaining a fresh concrete sample?

  1. The top of a settled wheelbarrow
  2. The mixer or truck discharge stream Correct answer.
  3. A concrete stockpile left on the ground
  4. A pile of hardened concrete

Explanation

Samples must be taken from the discharge stream at the point of placement, not from stockpiles or settled containers. Stockpiles may be segregated or contaminated.

Question 15Sampling Freshly Mixed Concrete

The sample should be obtained at the:

  1. Point of discharge Correct answer.
  2. Bottom of the hauling unit
  3. Top of the mixer drum
  4. Point of mixing water addition

Explanation

C172 requires sampling at the point of discharge so the concrete tested matches the concrete delivered. Sampling elsewhere may not represent the batch.

Question 16Sampling Freshly Mixed Concrete

A properly obtained fresh concrete sample should represent:

  1. The top layer of the batch
  2. Only the first batch of the day
  3. The entire batch from which it is taken Correct answer.
  4. Only the concrete used for strength tests

Explanation

The purpose of sampling is to obtain a representative portion of the entire batch. All portions of the batch should have an equal chance of being included.

Question 17Sampling Freshly Mixed Concrete

When sampling from a stationary mixer, the container should be passed through the discharge stream at least how many times?

  1. Four times
  2. Two times
  3. One time
  4. Three times Correct answer.

Explanation

C172 requires passing the container through the discharge stream at least three times to build a representative composite sample. This helps include material from different parts of the stream.

Question 18Sampling Freshly Mixed Concrete

For a given set of tests, the sample should be taken from:

  1. The first batch of the day
  2. Several different batches combined
  3. A single batch Correct answer.
  4. The last batch of the day

Explanation

Each set of tests should represent one batch, so the sample should come from a single batch. Combining batches makes the results difficult to interpret.

Question 19Sampling Freshly Mixed Concrete

After obtaining a sample, it should be transported to the test area:

  1. Only after it has set slightly in the container
  2. In an open, sunny location near the site
  3. Promptly and protected from evaporation Correct answer.
  4. After adding a small amount of water to it

Explanation

The sample should be moved promptly and protected from evaporation to preserve its properties. Delays and water loss can change test results.

Question 20Sampling Freshly Mixed Concrete

When sampling from a chute, from which part of the discharge should the sample be taken?

  1. The last concrete out of the chute
  2. The first concrete out of the chute
  3. Concrete clinging to the chute sides
  4. Middle of the discharge stream Correct answer.

Explanation

The middle portion of the discharge is most representative because the first and last portions may segregate. The container should be passed through the stream several times.

Question 21Sampling Freshly Mixed Concrete

Why is sampling from a pump hopper not acceptable?

  1. The hopper concrete has already hardened
  2. The hopper is always dry inside
  3. The hopper is too small to hold a sample
  4. Hopper concrete may not be representative Correct answer.

Explanation

Concrete in the pump hopper may have segregated or changed due to pumping, so it may not represent the concrete delivered at the hose. The sample must be taken at the discharge end.

Question 22Sampling Freshly Mixed Concrete

Why should the edges of a paving mixer be avoided when sampling?

  1. Edges may be segregated and not representative Correct answer.
  2. The edges contain too much cement paste
  3. The edges are always too wet compared with the center
  4. The edges are too cold for sampling

Explanation

Edges of a paving mat can segregate, with coarse aggregate or fines concentrating there. Sampling across the width but away from edges gives a more representative composite.

Question 23Sampling Freshly Mixed Concrete

When concrete is delivered in a non-agitating truck, where should the sample be obtained?

  1. From the discharge stream Correct answer.
  2. From the top of the load
  3. From the first material dumped
  4. From the bottom of the truck bed

Explanation

Non-agitating trucks can segregate, so the sample must be taken from the discharge stream as the concrete is placed. Sampling from the top, bottom, or first material may not represent the load.

Question 24Sampling Freshly Mixed Concrete

Which portion of a mixer discharge should be avoided when sampling?

  1. The portion after 15% has been discharged
  2. The middle 50% of the batch
  3. The portion between 20% and 80% of discharge
  4. The first and last portions Correct answer.

Explanation

The first and last portions of a discharge can be segregated or contain excess water, so they are avoided. Sampling from the middle portion gives a more representative sample.

Question 25Sampling Freshly Mixed Concrete

If a sample must wait before testing, how should it be stored?

  1. In a dry, absorbent container
  2. With added water to keep it workable
  3. Covered and protected from drying Correct answer.
  4. In an open container in the sun

Explanation

The sample should be covered and protected from evaporation, wind, and sunlight during any wait. Adding water or using absorbent containers changes the sample.

Question 26Sampling Freshly Mixed Concrete

What is the minimum volume of a fresh concrete sample that should be obtained for routine field tests?

  1. About 1 ft³ (28 L) Correct answer.
  2. About 0.25 ft³ (7 L)
  3. About 2 ft³ (57 L)
  4. About 0.5 ft³ (14 L)

Explanation

Standard sampling practice requires a fresh concrete sample of at least 1 ft³ (28 L) for routine field tests. The sample must be large enough to complete all required tests and still have material left over, so the tests are not compromised by a shortage. A larger sample is needed when the nominal maximum aggregate size is large or when extra tests are specified.

Question 27Temperature of Freshly Mixed Concrete

According to the standard test method for temperature of freshly mixed concrete, a field thermometer must be accurate to within:

  1. ±0.5 °C (±1 °F) Correct answer.
  2. ±5 °C (±10 °F)
  3. ±2 °C (±4 °F)
  4. ±1 °C (±2 °F)

Explanation

The test method requires the thermometer to measure the temperature of fresh concrete to an accuracy of ±0.5 °C (±1 °F) across its working range. This tight tolerance is needed because the result is compared directly with specification limits such as 95 °F, where a coarse instrument could hide an excursion.

Question 28Temperature of Freshly Mixed Concrete

What is the minimum depth to which the sensing portion of the thermometer must be immersed in the concrete?

  1. 75 mm (3 in.) Correct answer.
  2. 25 mm (1 in.)
  3. 250 mm (10 in.)
  4. 150 mm (6 in.)

Explanation

The sensing portion must be submerged at least 75 mm (3 in.) below the concrete surface so that the reading reflects the concrete rather than the surrounding air or the container. Shallow immersion biases the result toward ambient conditions.

Question 29Temperature of Freshly Mixed Concrete

How long must the thermometer remain in the concrete before the temperature is read?

  1. 30 s
  2. 10 min
  3. 15 s
  4. 2 min Correct answer.

Explanation

The thermometer stays in the concrete at least 2 minutes, or until the reading becomes stable, so the sensing element reaches thermal equilibrium with the concrete. Reading earlier can capture a value that still reflects the air or the container.

Question 30Temperature of Freshly Mixed Concrete

To what precision is the concrete temperature read and recorded?

  1. 0.5 °C (1 °F) Correct answer.
  2. 2 °C (5 °F)
  3. 0.1 °C (0.2 °F)
  4. 1 °C (2 °F)

Explanation

The temperature is read and recorded to the nearest 0.5 °C (1 °F), which matches the accuracy the method requires of the instrument. Reporting a coarser value would lose meaningful information near a specification limit.

Question 31Temperature of Freshly Mixed Concrete

Which standard is the test method for temperature of freshly mixed hydraulic-cement concrete?

  1. ASTM C1064 Correct answer.
  2. ASTM C172
  3. ASTM C231
  4. ASTM C143

Explanation

ASTM C1064 is the standard test method for temperature of freshly mixed hydraulic-cement concrete. It covers the thermometer requirements, the measurement procedure, and the reporting of results.

Question 32Temperature of Freshly Mixed Concrete

Where should the sensing portion of the thermometer be positioned in a sample of fresh concrete?

  1. On the bottom of the container, where the concrete is coolest
  2. Just under the surface, no deeper than 25 mm
  3. In the interior, at least 75 mm from the container wall Correct answer.
  4. At the surface, where the reading responds fastest to air temperature

Explanation

The sensor belongs in the interior of the sample, at least 75 mm (3 in.) from the container wall, so neither the container nor the air controls the reading. Concrete is a poor conductor, so edge and surface locations can be noticeably off.

Question 33Temperature of Freshly Mixed Concrete

The thermometer used for this test must have a range that includes at least:

  1. −18 to 0 °C (0 to 32 °F)
  2. 0 to 25 °C (32 to 77 °F)
  3. 0 to 100 °C (32 to 212 °F)
  4. 0 to 50 °C (30 to 120 °F) Correct answer.

Explanation

The instrument must span at least 0 to 50 °C (30 to 120 °F) so it can cover both cold-weather and hot-weather concrete temperatures. A narrower span would not read hot-weather concrete.

Question 34Temperature of Freshly Mixed Concrete

Unless the project specifications state otherwise, the general maximum temperature of concrete at the time of placement is:

  1. 50 °C (120 °F)
  2. 35 °C (95 °F) Correct answer.
  3. 25 °C (77 °F)
  4. 40 °C (104 °F)

Explanation

The general upper limit for concrete at the time of placement is 35 °C (95 °F). Above that, workability, air content, and cracking tendency become harder to control.

Question 35Temperature of Freshly Mixed Concrete

A thermometer is checked in a properly prepared ice-water bath and reads 1.0 °C (34 °F). What is the correct action?

  1. Deduct 1.0 °C from each future reading and continue testing
  2. Use it, because an ice bath is not a valid field check
  3. Remove it from service until it is recalibrated or replaced Correct answer.
  4. Use it, since errors under 2 °C are tolerated

Explanation

The permitted error is ±0.5 °C (±1 °F), so a 1.0 °C deviation in an ice bath shows the thermometer is out of tolerance. It must be taken out of service until it is recalibrated or replaced.

Question 36Temperature of Freshly Mixed Concrete

A field thermometer is dropped on the pavement but looks undamaged. Before it is used again it must be:

  1. Verified against an ice bath or a reference thermometer Correct answer.
  2. Shaken down and returned to its protective case
  3. Compared with the reading of a second field thermometer
  4. Replaced, because a dropped thermometer can never be reused

Explanation

Any thermometer that has been dropped, or whose accuracy is in doubt, must be verified against a reference thermometer or an ice bath before further use. Verification, not appearance, decides whether it can stay in service.

Question 37Temperature of Freshly Mixed Concrete

How often does the temperature test method require the temperature of fresh concrete to be measured?

  1. The method sets no frequency; the specifications do Correct answer.
  2. Once for every 50 m³ (50 yd³) of concrete produced
  3. Once per day, at the start of the first truck of the day
  4. Each time the ambient air temperature changes by 5 °C (10 °F)

Explanation

The test method describes how to measure and report the temperature but does not establish how often it is done. Sampling frequency comes from the project specifications or the quality control plan.

Question 38Temperature of Freshly Mixed Concrete

When a sample is taken from a truck mixer for a temperature measurement, the concrete should be obtained:

  1. From the last portion of the discharge, after full mixing
  2. From the first portion of the discharge, which is warmest
  3. From the middle portion of the discharge Correct answer.
  4. From the drum after the truck has been stopped for 10 minutes

Explanation

Standard sampling practice requires the sample to come from the middle portion of the discharge. The first and last portions are not representative of the batch.

Question 39Temperature of Freshly Mixed Concrete

After the thermometer has been in the concrete for the required time, the technician should:

  1. Read it while the sensing portion stays immersed Correct answer.
  2. Withdraw it slowly and read it before the column begins to fall
  3. Lift it out quickly and read it at eye level against the sky
  4. Wipe the stem clean, then read the temperature to the nearest 1 °C

Explanation

The reading is taken with the sensing portion still in the concrete, because removing it exposes the sensor to air and the indicated value changes. The reading is recorded to the nearest 0.5 °C (1 °F).

Question 40Temperature of Freshly Mixed Concrete

Unless the project specifications state otherwise, the minimum temperature of concrete at the time of placement is:

  1. 5 °C (40 °F)
  2. 10 °C (50 °F) Correct answer.
  3. 0 °C (32 °F)
  4. 21 °C (70 °F)

Explanation

The general minimum placement temperature is 10 °C (50 °F) unless the specifications set a different value. Colder concrete gains strength slowly and is vulnerable to early freezing.

Question 41Temperature of Freshly Mixed Concrete

A sample sits in a wheelbarrow in direct sunlight for several minutes before the temperature is taken, and the reading is 3 °F higher than the previous truck. The most likely reason is:

  1. The thermometer was immersed too deeply in the sample
  2. The concrete was over-mixed in the drum before discharge
  3. The small sample absorbed heat from the sun and warm air Correct answer.
  4. The sensing portion was still equilibrating with the concrete

Explanation

A wheelbarrow sample has little thermal mass, so direct sun and hot air can raise its temperature within minutes. Samples should be protected from the sun and tested promptly.

Question 42Temperature of Freshly Mixed Concrete

Which statement about using a digital thermometer for this test is correct?

  1. A digital instrument must be recalibrated after every test
  2. It may be used if its accuracy meets the requirement Correct answer.
  3. Digital instruments are not permitted by the test method
  4. A digital instrument may be used only below 20 °C (68 °F)

Explanation

The test method does not restrict the type of instrument; any thermometer that meets the range, readability, and accuracy requirements and has been verified may be used. Digital thermometers are common in field work.

Question 43Temperature of Freshly Mixed Concrete

A truck arrives and the concrete temperature is 97 °F (36 °C). With respect to the general maximum placement temperature, the technician should:

  1. Record the reading and test the next truck instead
  2. Accept the load, since the limit applies only after placement
  3. Report that the concrete exceeds the 95 °F (35 °C) limit Correct answer.
  4. Wait 30 minutes for the concrete to cool before placing

Explanation

The general maximum is 95 °F (35 °C) at the time of placement, so 97 °F is a nonconformance that must be reported. The technician does not have authority to accept out-of-limit concrete.

Question 44Temperature of Freshly Mixed Concrete

Of the following, which normally has the greatest influence on the temperature of a freshly mixed batch?

  1. The temperature of the cement
  2. The temperature of the entrained air
  3. The temperature of the admixtures
  4. The temperature of the aggregates Correct answer.

Explanation

Aggregates make up most of the mass of a concrete mixture and their specific heat is comparable to that of the paste, so their temperature dominates the batch temperature. Cement, water, and admixtures are smaller fractions.

Question 45Temperature of Freshly Mixed Concrete

For the temperature reading to be valid, the sample must:

  1. Be held in a metal container fitted with a lid
  2. Be at least 24 hours old before measuring
  3. Fill the container almost to the rim before reading
  4. Be deep enough to surround the sensor on all sides Correct answer.

Explanation

The sample has to be deep enough that concrete surrounds the sensing portion on all sides; otherwise the reading is influenced by the container and the surrounding air. Container material and fill height are not the controlling requirements.

Question 46Temperature of Freshly Mixed Concrete

The temperature of a batch should be measured:

  1. As soon as the coarse aggregate enters the drum
  2. Before any water is added to the drum
  3. After all ingredients have been mixed together Correct answer.
  4. While the cement is being added at the plant

Explanation

The temperature is measured on concrete, meaning after all ingredients are in the drum and mixing is complete. Partial batches or dry materials do not represent the concrete being delivered.

Question 47Temperature of Freshly Mixed Concrete

Ice is more effective than an equal mass of water at the same temperature for cooling concrete because:

  1. Ice dissolves in the mix and lowers the water-cement ratio
  2. Ice floats and spreads more evenly through the drum
  3. Melting ice absorbs latent heat in addition to warming Correct answer.
  4. Ice has a much higher specific heat than liquid water

Explanation

Melting ice absorbs a large amount of latent heat, roughly 144 Btu per pound, on top of the sensible heat gained as it warms to the concrete temperature. That is why a kilogram of ice removes far more heat than a kilogram of cold water.

Question 48Temperature of Freshly Mixed Concrete

A 1.2 m (4 ft) thick foundation mat is placed at 80 °F (27 °C). Why may the highest temperature the concrete reaches occur hours after placement?

  1. Because the ambient air is usually warmer in the afternoon
  2. Because the aggregate continues to absorb water and warm up
  3. Because the thermometer used in the field is not accurate enough
  4. Because hydrating cement releases heat that builds up in the mass Correct answer.

Explanation

Cement hydration is exothermic, and in a thick section the heat cannot escape quickly, so the interior temperature climbs for hours after placement. The peak internal temperature can be well above the temperature measured at discharge.

Question 49Temperature of Freshly Mixed Concrete

A thermometer reads 0.4 °C (33 °F) in a properly prepared ice-water bath. How should the technician proceed?

  1. Accept it only if the same error appears in boiling water
  2. Reject it; any deviation from 0 °C is a failure
  3. Accept it; the reading is within ±0.5 °C of the ice point Correct answer.
  4. Reject it; error must be under 0.1 °C to be acceptable

Explanation

An ice-water bath is at 0 °C (32 °F), and an error of 0.4 °C is inside the ±0.5 °C (±1 °F) tolerance, so the thermometer may be used. It is not necessary for the instrument to read exactly zero.

Question 50Temperature of Freshly Mixed Concrete

A project specification sets a maximum concrete temperature of 90 °F, while the general industry limit is 95 °F. Which limit applies, and why?

  1. 95 °F, because the specification limit is only a suggestion
  2. 95 °F, because the general limit governs all concrete placement
  3. Either limit, since both are recognized industry standards
  4. 90 °F, because the more restrictive project limit governs Correct answer.

Explanation

Both documents apply, and where the specification is stricter, the stricter requirement controls. The project specification may tighten the general limit but may not relax it.