20 Temperature (ASTM C1064) Practice Questions & Answers

Every Temperature (ASTM C1064) practice question from the ACI Concrete Field Testing Technician Grade I Practice Test, with the correct answer and a short explanation.

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1. A project specification sets maximum and minimum temperatures for concrete as delivered. Why does the inspector measure fresh-concrete temperature under ASTM C1064/C1064M when the truck arrives?
- A.To estimate the water-cement ratio, since a warm batch shows that extra water was added at the batch plant
- B.To set the curing period, since the delivered temperature fixes how many days the specimens must cure
- C.To confirm the batch is within the specified limits, since temperature affects setting and strength gain✓ Answer
- D.To correct the measured air content, since every air meter reading must be adjusted for temperature
ASTM C1064/C1064M exists to verify conformance with specified temperature requirements, such as hot- and cold-weather limits, because concrete temperature governs how fast it sets and gains strength. Temperature does not reveal the water-cement ratio, is not used to correct an air content reading, and does not by itself set the curing duration.
Ref QB-CQ5PX4Source: ASTM C1064/C1064M, Standard Test Method for Temperature of Freshly Mixed Hydraulic-Cement Concrete (significance and use)Report a problem with this question
2. ASTM C1064/C1064M notes that concrete whose nominal maximum aggregate size exceeds 3 in. (75 mm) may need up to 20 min after batching before its temperature is uniform. A technician is testing mass concrete with 6-in. (150-mm) aggregate. What is the reason for this allowance?
- A.Large particles must be screened out first, so the extra time covers wet-sieving the concrete sample
- B.Large particles trap entrapped air around the sensor, so the reading stays low until that air escapes
- C.Large particles make the sensor hard to insert, so the extra time is for working it in to full depth
- D.Large particles trade heat with the mortar slowly, so the mix takes longer to reach one temperature✓ Answer
When the coarse aggregate is very large, heat moves slowly between the big particles and the surrounding mortar, so the concrete needs more time before the sensor sees a single, stable temperature; that is why ASTM C1064/C1064M notes that such concrete may need up to 20 min after batching before it is measured. The method does not call for wet-sieving out the large particles, and the extra time is not for releasing air or for inserting the sensor.
Ref QB-U7YGC4Source: ASTM C1064/C1064M, Standard Test Method for Temperature of Freshly Mixed Hydraulic-Cement Concrete (scope; time allowance for oversize aggregate)Report a problem with this question
3. At a slab pour, a new technician asks where ASTM C1064/C1064M permits the temperature of freshly mixed concrete to be measured. Which answer is correct?
- A.In the chute stream as it discharges, with the sensor held in the moving concrete
- B.In the forms, after the concrete has been fully placed and consolidated in them
- C.In a separate sample container, after a composite sample has been remixed in it
- D.In the transporting equipment, in the forms, or in a separate sample container✓ Answer
ASTM C1064/C1064M lets the technician take the reading wherever the device can be fully surrounded by concrete: in the transporting equipment such as a wheelbarrow or buggy, directly in the forms, or in a separate sample container. It does not restrict the reading to a remixed composite sample or to fully consolidated concrete in the forms, and a sensor held in a moving chute stream does not have the stable cover the method requires.
Ref QB-BQSBS3Source: ASTM C1064/C1064M, Standard Test Method for Temperature of Freshly Mixed Hydraulic-Cement Concrete (measuring in transporting equipment, forms or a sample container)Report a problem with this question
4. A technician measures temperature in a separate container. Assume the method requires at least 3 in. (75 mm) of concrete in every direction around the sensor. What is the purpose of this cover requirement?
- A.So the sensor reads the concrete itself, not the container wall or the surrounding air✓ Answer
- B.So the same container holds enough concrete to run the density test right afterward
- C.So the sensor is not damaged by coarse aggregate while concrete is rodded around it
- D.So the sample holds enough mass to stay warm while the slump test is being performed
The cover requirement keeps a thick layer of concrete between the sensor and anything at a different temperature, such as the container wall or the air, so the device reads the concrete's own temperature. It is not about protecting the sensor, preserving heat for other tests or sizing the container for a density (unit weight) test.
Ref QB-T7M673Source: ASTM C1064/C1064M, Standard Test Method for Temperature of Freshly Mixed Hydraulic-Cement Concrete (container and sensor cover requirements)Report a problem with this question
5. Assume the method requires the sensor to have concrete cover of at least 3 in. (75 mm) or three times the nominal maximum size of the coarse aggregate, whichever is greater. The mixture has a 1½-in. (37.5-mm) nominal maximum aggregate size. What minimum cover is required in every direction?
- A.6 in. (150.0 mm)
- B.4½ in. (112.5 mm)✓ Answer
- C.3 in. (75 mm)
- D.1½ in. (37.5 mm)
Three times 1½ in. is 4½ in., which is greater than 3 in., so under the stated rule the larger value of 4½ in. governs. Using only 3 in. ignores the aggregate-based requirement, 1½ in. is just one aggregate size, and 6 in. applies a multiplier the rule does not state.
Ref QB-AQEZK2Source: ASTM C1064/C1064M, Standard Test Method for Temperature of Freshly Mixed Hydraulic-Cement Concrete (minimum concrete cover around the sensor)Report a problem with this question
6. Before collecting concrete in a container for a temperature reading, a technician picks up a dry, unsealed wooden box from the truck. What does ASTM C1064/C1064M require of the container?
- A.It must be insulated and kept covered, so the sample keeps its heat while being carried
- B.It must be nonabsorptive or dampened before use, and large enough for the required cover✓ Answer
- C.It must be oiled and left dry, so the concrete releases cleanly once the reading is taken
- D.It must be metal and preheated to air temperature, so it cannot shift the concrete reading
A dry, absorbent container draws water out of the concrete it touches, so ASTM C1064/C1064M calls for a nonabsorptive container or one dampened just before sampling, and the container must be big enough to give the sensor the required cover on all sides. Insulating, preheating or oiling the container is not what the method requires.
Ref QB-S79UZZSource: ASTM C1064/C1064M, Standard Test Method for Temperature of Freshly Mixed Hydraulic-Cement Concrete (sample container requirements)Report a problem with this question
7. Which temperature-measuring device is suitable for ASTM C1064/C1064M, provided it meets the method's accuracy and immersion requirements?
- A.A direct-reading resistance device, such as a thermistor probe, pushed into the concrete✓ Answer
- B.An air thermometer hung beside the truck and read as the concrete is being discharged
- C.A noncontact infrared device aimed at the exposed surface of the concrete in the chute
- D.A surface strip thermometer taped to the inside face of the form before concrete is placed
ASTM C1064/C1064M measures the temperature inside the concrete with an immersed device; liquid-in-glass thermometers and direct-reading resistance devices such as thermistors or RTDs are recognized types, provided they meet the accuracy and immersion requirements. Infrared guns, surface strips on the form and air thermometers do not measure the interior concrete temperature and do not satisfy the immersion requirement.
Ref QB-9Q3PEZSource: ASTM C1064/C1064M, Standard Test Method for Temperature of Freshly Mixed Hydraulic-Cement Concrete (apparatus: temperature measuring device)Report a problem with this question
8. Why must a field temperature-measuring device be verified against a reference temperature-measuring device?
- A.To calibrate the reference device, using the field device that sees daily use
- B.To find an offset that is then added to every concrete reading the device takes
- C.To show it reads within its allowed tolerance, traceable back to a known standard✓ Answer
- D.To check the battery and display, since its accuracy is fixed at the factory
Verification compares the field device with a reference device whose accuracy is documented and traceable, which shows that the field device still reads within its allowed tolerance. The reference checks the field device, not the reverse, and the method does not have the technician apply a running offset to concrete readings or rely on factory accuracy.
Ref QB-Z7R68ASource: ASTM C1064/C1064M, Standard Test Method for Temperature of Freshly Mixed Hydraulic-Cement Concrete (verification of the temperature measuring device)Report a problem with this question
9. A technician's field thermometer was verified four months ago, but today it was dropped on the pavement and now reads differently from a coworker's device. What should be done?
- A.Apply the difference from the coworker's device as a correction to every reading today
- B.Compare it with the coworker's device and use whichever reading seems closer to the expected value
- C.Keep using it until the annual verification date, since only the yearly check is required
- D.Verify it against a reference device before using it again, since its accuracy is in doubt✓ Answer
ASTM C1064/C1064M requires verification on a regular schedule and also whenever there is a question about the device's accuracy, so a dropped device that disagrees with another must be checked against a reference before further use. Another field device is not a reference, and guessing or applying an informal correction does not establish accuracy.
Ref QB-GQJZM9Source: ASTM C1064/C1064M, Standard Test Method for Temperature of Freshly Mixed Hydraulic-Cement Concrete (verification whenever accuracy is in question)Report a problem with this question
10. Assume the method requires the field device to be compared with a reference device at two temperatures at least 30 °F (15 °C) apart. A technician compares them at 70 °F and 85 °F in a stirred water bath. What is the correct conclusion?
- A.The check is acceptable, because both points fall within the device's working range
- B.The check is incomplete; a third point at freezing must be added to the two taken
- C.The check is acceptable, because a stirred water bath was used for both points
- D.The check is incomplete; it must be redone at two points at least 30 °F apart✓ Answer
The two stated points are only 15 °F apart, which does not meet the stated spacing, so the comparison does not prove the device across the range and must be repeated at two points far enough apart. A proper bath and in-range points are necessary but do not cure the spacing problem, and the method does not call for an extra freezing point.
Ref QB-DX4BXJSource: ASTM C1064/C1064M, Standard Test Method for Temperature of Freshly Mixed Hydraulic-Cement Concrete (verification at two temperatures)Report a problem with this question
11. During verification, a field device disagrees with the reference device by more than the allowed tolerance at one of the two test temperatures. What should happen to the field device?
- A.Keep it in service, with the measured difference applied as a correction to readings
- B.Use it for readings near the temperature that passed, and avoid the other range
- C.Take it out of service until it is repaired or replaced and passes a new verification✓ Answer
- D.Accept it if the average of its two differences falls within the allowed tolerance
A device that fails to agree with the reference within tolerance at either verification point has not been shown to be accurate, so it cannot be used for acceptance readings until it is repaired or replaced and passes verification. Correcting readings by an offset, limiting it to part of the range or averaging the errors are not permitted substitutes.
Ref QB-WEAGHKSource: ASTM C1064/C1064M, Standard Test Method for Temperature of Freshly Mixed Hydraulic-Cement Concrete (verification acceptance criteria)Report a problem with this question
12. At a truck discharge, a technician measures temperature directly in a wheelbarrow of concrete. After inserting the sensor to full cover, why does the technician gently press the concrete around the device at the surface?
- A.To mark the insertion spot so the slump sample can later be taken from the same place
- B.To hold the device upright so the sensor stays at mid-depth while it is being read
- C.To close the opening so ambient air cannot reach the sensor and affect the reading✓ Answer
- D.To consolidate the concrete so entrapped air near the sensor is removed as in rodding
Pushing the sensor in leaves a hole that lets air at a different temperature travel down to the sensor, so ASTM C1064/C1064M has the technician gently close the concrete around the device at the surface to keep ambient air from influencing the reading. The step is not consolidation like rodding, not a way to hold the device, and not a sampling marker.
Ref QB-CXRYRHSource: ASTM C1064/C1064M, Standard Test Method for Temperature of Freshly Mixed Hydraulic-Cement Concrete (procedure: closing the concrete around the device)Report a problem with this question
13. A technician measures temperature directly in the forms of a heavily reinforced wall on a cold morning. Where should the sensor be placed?
- A.Within the concrete mass, clear of the form faces and the steel, with full cover✓ Answer
- B.Against a reinforcing bar, so the sensor is held steady at one depth while it reads
- C.Against the inside face of the form, where the concrete is most at risk of freezing
- D.Just under the top surface, so the reading shows the concrete exposed to cold air
Forms and reinforcing steel can be at a very different temperature from the fresh concrete, so a sensor touching or near them reads the boundary instead of the concrete. ASTM C1064/C1064M has the technician keep the sensor within the concrete with the required cover on all sides, away from forms and reinforcement, including the top surface exposed to air.
Ref QB-VEX5CJSource: ASTM C1064/C1064M, Standard Test Method for Temperature of Freshly Mixed Hydraulic-Cement Concrete (measuring in the forms)Report a problem with this question
14. At a pump line, a technician collects concrete from the hose discharge into a dampened container for a temperature reading. Assume the method sets a 5-min limit, counted from obtaining the sample. The technician is delayed and is ready to start the reading 9 min after sampling. What should be done?
- A.Measure the old sample anyway and note the delay, as temperature changes little in 4 min
- B.Measure the old sample anyway, adding extra immersion time to make up for the delay
- C.Remix the old sample in its container, which brings it back to its discharge temperature
- D.Discard that sample, obtain a new one, and complete the reading within the time limit✓ Answer
A sample in a container starts gaining or losing heat to its surroundings as soon as it is taken, which is why the method limits the time between sampling and measurement; once that limit is exceeded the sample no longer represents the concrete being placed, so a fresh sample is needed. Noting the delay, lengthening immersion or remixing does not restore the original temperature.
Ref QB-FXTY9NSource: ASTM C1064/C1064M, Standard Test Method for Temperature of Freshly Mixed Hydraulic-Cement Concrete (time between obtaining the sample and measuring)Report a problem with this question
15. At a truck discharge, an inspector needs only the concrete temperature for a hot-weather check; no slump, air content or cylinder specimens are being taken from this load. The reading will be made in a container. What sampling applies?
- A.A composite sample is not required, because the sample is taken only to determine temperature✓ Answer
- B.A composite sample is required, with portions from the middle part of the discharge combined
- C.A composite sample is required, because every test on fresh concrete needs one under C172/C172M
- D.No container sample is allowed, so the reading must be taken in the truck chute instead
ASTM C1064/C1064M has the technician obtain the sample per C172/C172M but waives the composite-sample requirement when the only purpose of the sample is to determine temperature, so the reading need not wait for a composite. A container reading is permitted, and the C172/C172M composite rule is not applied to a temperature-only sample.
Ref QB-YEZ5VNSource: ASTM C1064/C1064M, Standard Test Method for Temperature of Freshly Mixed Hydraulic-Cement Concrete (sampling: composite sample not required for temperature only)Report a problem with this question
16. A technician's sensor has been in the concrete long enough and the reading has stabilized. How should the temperature be read?
- A.Withdraw the device, wipe the sensor clean, and read it after the display settles
- B.Read it with the sensor still in the concrete, before the device is withdrawn✓ Answer
- C.Withdraw the device and read it promptly, before the sensor reaches air temperature
- D.Read it at insertion and again at removal, and report the average of the two
Once the sensor leaves the concrete it begins to move toward air temperature, so ASTM C1064/C1064M has the reading taken while the device is still in the concrete. Reading after withdrawal, even quickly, and averaging an unstabilized insertion reading both produce a value that is not the concrete temperature.
Ref QB-EXFN4MSource: ASTM C1064/C1064M, Standard Test Method for Temperature of Freshly Mixed Hydraulic-Cement Concrete (procedure: reading the device in place)Report a problem with this question
17. Which sequence correctly describes a temperature measurement in a sample container under ASTM C1064/C1064M?
- A.Insert the sensor, wait for a stable reading, pull out the device, then press the concrete closed over the hole
- B.Insert the sensor with full cover, rod the concrete in three layers, pull out the device, then read it at once
- C.Insert the sensor with full cover, press the concrete closed around it, wait for a stable reading, read in place✓ Answer
- D.Fill and strike off the container, insert the sensor partway, read at once, then read again a few min later
The method's order is to place the sensor with full cover, close the concrete around it at the surface so air cannot reach it, leave it until the reading stabilizes, and read it while it is still in the concrete. Closing the hole after removal is too late to help, rodding in layers belongs to other tests, and a partway, immediate reading has neither the cover nor the stabilization the method requires.
Ref QB-XENTPMSource: ASTM C1064/C1064M, Standard Test Method for Temperature of Freshly Mixed Hydraulic-Cement Concrete (procedure sequence)Report a problem with this question
18. Assume the method requires the device to stay in the concrete at least 2 min, or until the reading stabilizes, and no longer than 5 min. At a truck discharge, after 2 min the reading is still rising. What should the technician do?
- A.Remove the device, reinsert it at a new spot, and record the first value shown there
- B.Leave the device in place until the reading stops changing, within the time limit✓ Answer
- C.Record the reading at the 2-min mark, because the minimum immersion time is met
- D.Record the highest reading seen over several minutes, even past the 5-min limit
The time rule exists so the device and concrete reach the same temperature; a still-rising reading shows that has not happened, so the technician waits for it to stabilize while staying within the stated maximum. Reading at the minimum time, restarting at a new spot or chasing the peak past the limit all defeat the purpose of the stabilization requirement.
Ref QB-HXHNMQSource: ASTM C1064/C1064M, Standard Test Method for Temperature of Freshly Mixed Hydraulic-Cement Concrete (procedure: immersion time and stabilization)Report a problem with this question
19. On a hot afternoon, a technician measures 97 °F at the forms; the project specification limits concrete temperature to 95 °F at placement. What should the technician do?
- A.Record and report the 97 °F reading, and let the responsible party decide on acceptance✓ Answer
- B.Report 95 °F, because a 2 °F gap is within the accuracy allowed for the field device
- C.Reject the load personally and send the truck away before more concrete is placed
- D.Wait a few minutes and remeasure, then report the lower reading if that one meets the limit
The technician's job under ASTM C1064/C1064M is to measure and report the temperature as found; acceptance or rejection under the project specification is a decision for the responsible party. Shopping for a lower reading or shading the value by the device tolerance falsifies the record, and the method does not give the technician authority to reject the load.
Ref QB-2FQT7RSource: ASTM C1064/C1064M, Standard Test Method for Temperature of Freshly Mixed Hydraulic-Cement Concrete (reporting the measured temperature)Report a problem with this question
20. Assume the method requires the temperature to be recorded to the nearest 1 °F. A technician's device displays 74.6 °F once the reading has stabilized. What value should be reported?
- A.74.6 °F
- B.75 °F✓ Answer
- C.74.5 °F
- D.74 °F
Rounding 74.6 °F to the nearest whole degree gives 75 °F. Reporting 74.6 °F claims more precision than the stated rule, truncating to 74 °F rounds the wrong way, and 74.5 °F uses a half-degree increment the stated rule does not call for.
Ref QB-TVSG63Source: ASTM C1064/C1064M, Standard Test Method for Temperature of Freshly Mixed Hydraulic-Cement Concrete (reporting temperature to the required precision)Report a problem with this question

1. A project specification sets maximum and minimum temperatures for concrete as delivered. Why does the inspector measure fresh-concrete temperature under ASTM C1064/C1064M when the truck arrives?

2. ASTM C1064/C1064M notes that concrete whose nominal maximum aggregate size exceeds 3 in. (75 mm) may need up to 20 min after batching before its temperature is uniform. A technician is testing mass concrete with 6-in. (150-mm) aggregate. What is the reason for this allowance?

3. At a slab pour, a new technician asks where ASTM C1064/C1064M permits the temperature of freshly mixed concrete to be measured. Which answer is correct?

4. A technician measures temperature in a separate container. Assume the method requires at least 3 in. (75 mm) of concrete in every direction around the sensor. What is the purpose of this cover requirement?

5. Assume the method requires the sensor to have concrete cover of at least 3 in. (75 mm) or three times the nominal maximum size of the coarse aggregate, whichever is greater. The mixture has a 1½-in. (37.5-mm) nominal maximum aggregate size. What minimum cover is required in every direction?

6. Before collecting concrete in a container for a temperature reading, a technician picks up a dry, unsealed wooden box from the truck. What does ASTM C1064/C1064M require of the container?

7. Which temperature-measuring device is suitable for ASTM C1064/C1064M, provided it meets the method's accuracy and immersion requirements?

8. Why must a field temperature-measuring device be verified against a reference temperature-measuring device?

9. A technician's field thermometer was verified four months ago, but today it was dropped on the pavement and now reads differently from a coworker's device. What should be done?

10. Assume the method requires the field device to be compared with a reference device at two temperatures at least 30 °F (15 °C) apart. A technician compares them at 70 °F and 85 °F in a stirred water bath. What is the correct conclusion?

11. During verification, a field device disagrees with the reference device by more than the allowed tolerance at one of the two test temperatures. What should happen to the field device?

12. At a truck discharge, a technician measures temperature directly in a wheelbarrow of concrete. After inserting the sensor to full cover, why does the technician gently press the concrete around the device at the surface?

13. A technician measures temperature directly in the forms of a heavily reinforced wall on a cold morning. Where should the sensor be placed?

15. At a truck discharge, an inspector needs only the concrete temperature for a hot-weather check; no slump, air content or cylinder specimens are being taken from this load. The reading will be made in a container. What sampling applies?

16. A technician's sensor has been in the concrete long enough and the reading has stabilized. How should the temperature be read?

17. Which sequence correctly describes a temperature measurement in a sample container under ASTM C1064/C1064M?

18. Assume the method requires the device to stay in the concrete at least 2 min, or until the reading stabilizes, and no longer than 5 min. At a truck discharge, after 2 min the reading is still rising. What should the technician do?

19. On a hot afternoon, a technician measures 97 °F at the forms; the project specification limits concrete temperature to 95 °F at placement. What should the technician do?

20. Assume the method requires the temperature to be recorded to the nearest 1 °F. A technician's device displays 74.6 °F once the reading has stabilized. What value should be reported?

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