Sampling - Performance Exam Practice

The following questions are derived from the actual checklist used in the ACI performance examination. Click each question to view the answer.

1. What must occur before a sample of concrete can be taken from a revolving drum mixer?

All water and admixtures must be added to the mixer

2. When sampling from a stationary or revolving drum mixer, what is collected and when is it taken during discharge?

In two or more portions of concrete

At regularly spaced intervals

From the middle of the batch

3. How are the sample portions obtained from the discharge stream of a stationary or revolving drum mixer?

Repeatedly pass a receptacle through the entire discharge stream

Completely divert the discharge stream into a sample container

4. Describe the procedure for collecting a sample from a paving mixer.

Discharge the contents of the paving mixer

Obtain samples from at least five different portions of the pile

5. What is the minimum size for a sample when strength test specimens are to be molded?

1 ft³ (28 L)

6. What is the maximum allowable time between obtaining the first and final portions of the composite sample?

15 min

7. What action is required after the individual concrete samples have been transported to the place where tests are to be preformed?

Combine and remix the samples with a shovel

8. What should be done if the concrete contains aggregate larger than is appropriate for the size of the molds or equipment being used?

Wet sieving (screening)

9. Start the tests for slump, temperature, and air content within how many minutes after obtaining the final portion of the composite sample?

5 min

10. Start molding specimens for strength tests within how many minutes after fabricating the composite sample?

15 min

11. From what must the concrete sample be protected?

Sun, wind, and rapid evaporation

Contamination