Free ACI Strength Testing Technician Questions and Answers 1 — Questions and Answers

Question 1: Following the thermometer's insertion into the concrete:

Cool the surface of concrete with water
Gently press concrete around the thermometer
Tap the side of the container 10-15 times
All of the above (Correct answer)

Correct answer: All of the above

After inserting the thermometer into the concrete, it is important to gently press the concrete around it to ensure good thermal contact for an accurate reading. Tapping the side of the container 10-15 times helps settle the concrete and remove any air pockets around the probe, further improving contact. While cooling the surface with water is not explicitly stated in all standards for temperature measurement, it can be a practice in some field conditions to minimize rapid surface temperature fluctuations or evaporation, contributing to a more stable and representative reading of the bulk concrete temperature.

Question 2: What is one reason, under ASTM C1064, to take a concrete's temperature?

Very slump
Verify conformance
Verify ambient air temperature (Correct answer)
None of the above

Correct answer: Verify ambient air temperature

Under ASTM C1064, one reason to take a concrete's temperature is to verify the ambient air temperature. While the primary purpose is to measure concrete temperature, recording ambient conditions is crucial for understanding the curing environment and potential influences on concrete properties. This data helps in assessing compliance with project specifications related to placement temperatures and environmental factors.

Question 3: Begin testing for slump and air content within after sampling is finished.

15 minutes
10 minutes
2 ½ minutes (Correct answer)
None of the above

Correct answer: 2 ½ minutes

To ensure that slump and air content tests are performed on concrete that is still representative of its fresh state, testing must begin within 2 ½ minutes after the sampling is finished. This strict time limit minimizes the effects of hydration and stiffening, which can rapidly alter the concrete's workability and air content. Adhering to this timeframe is critical for obtaining accurate and reliable test results.

Question 4: In any event, wait to get samples until:

½ of the water has been added
All the water and admixtures have been added to the concrete (Correct answer)
200 revolutions of the drum have been obtained
None of the above

Correct answer: All the water and admixtures have been added to the concrete

To obtain a truly representative sample of concrete, it is crucial to wait until all the water and admixtures have been fully added and thoroughly mixed into the concrete. Sampling before all ingredients are incorporated would result in a non-uniform mixture. This ensures that the sample accurately reflects the final properties of the concrete being delivered or placed.

Question 5: Samples cannot be taken before the batch has been released (_) or after (_).

20% or after 80% (Correct answer)
10% or after 90%
20% or after 90%
None of the above

Correct answer: 20% or after 80%

According to ASTM C172, samples of concrete should be taken from the middle portion of the batch discharge. This means samples cannot be taken before 20% of the batch has been released or after 80% of the batch has been discharged. This practice ensures that the collected sample is representative of the overall concrete mixture, avoiding potential variations found at the very beginning or end of the discharge.

Question 6: To sample concrete from a truck mixer's chute, do the following:

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

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 7: Samples of recent concrete that will be evaluated on the job site should come from:

Two or more regularly spaced intervals during discharge of the middle portion of the batch (Correct answer)
The beginning of mixer discharge
The last concrete discharged
All of the above

Correct answer: Two or more regularly spaced intervals during discharge of the middle portion of the batch

To ensure a representative sample of concrete for evaluation on the job site, samples should be collected from two or more regularly spaced intervals during the discharge of the middle portion of the batch. This method, as specified by ASTM C172, helps to account for any minor variations within the batch and provides a more accurate overall assessment of the concrete's properties. Sampling from the beginning or end of the discharge is not recommended as these portions may not be representative.

Question 8: As to ASTM C172, the duration between acquiring the initial and final parts of the composite sample cannot be greater than:

20 minutes
10 minutes
30 minutes (Correct answer)
None of the above

Correct answer: 30 minutes

As per ASTM C172, the duration between acquiring the initial and final parts of a composite concrete sample cannot be greater than 30 minutes. This time limit is crucial to ensure that the concrete in the sample remains fresh and workable, preventing significant changes in its properties due to hydration or stiffening before testing can commence. Adhering to this timeframe helps maintain the representativeness of the sample.

Question 9: It is important to elevate the droop cone cautiously, steadily, and vertically in ________ seconds.

4 to 8
2 to 6
5 to 9
3 to 7 (Correct answer)

Correct answer: 3 to 7

According to ASTM C143, the slump cone must be elevated cautiously, steadily, and vertically in a period of 3 to 7 seconds. This controlled and consistent rate of removal is critical to prevent lateral or torsional movement that could cause the concrete to collapse prematurely or unevenly. Adhering to this timeframe ensures an accurate and consistent slump measurement, reflecting the true workability of the concrete.

Question 10: The amount of time that has passed between when the slump cone is first filled and when it is removed shall not exceed:

2 1/2 minutes (Correct answer)
1 minute
5 minutes
15 minutes

Correct answer: 2 1/2 minutes

The total amount of time that has passed between when the slump cone is first filled and when it is removed shall not exceed 2 ½ minutes. This strict time limit, specified by ASTM C143, is essential to minimize the effects of concrete stiffening and hydration during the test procedure. Ensuring a rapid execution of the test guarantees that the slump measurement accurately reflects the fresh properties of the concrete.

Question 11: The slump needs to be calculated to the closest

Half of an inch
Tenth of an inch
1 inch
Quarter of an inch (Correct answer)

Correct answer: Quarter of an inch

According to ASTM C143, the slump measurement needs to be calculated and reported to the closest quarter of an inch (6 mm). This level of precision is considered appropriate for field measurements of concrete consistency. It provides sufficient accuracy for practical applications without overstating the inherent variability of the test method.

Free ACI Strength Testing Technician Questions and Answers 1

Following the thermometer's insertion into the concrete: