ACI Fresh Concrete Air Content Questions and Answers

Question 1

A technician performing an air content test using the pressure method (ASTM C231) has pressurized the meter, opened the main air valve, tapped the sides of the bowl, and stabilized the gauge.
The gauge reading is 5.8%.
What is the next critical step to determine the final air content percentage?

Accepted Answer

Subtract the aggregate correction factor from the 5.8% reading.

Answer

Record 5.8% as the final air content.

Answer

Release the pressure and read the new value on the gauge.

Answer

Add the manufacturer's calibration factor to the 5.8% reading.

Question 2

When using the volumetric method (ASTM C173) for determining air content, what is the primary purpose of adding a measured amount of isopropyl alcohol?

Accepted Answer

To break down the foam and ensure a stable, accurate reading of the liquid level.

Answer

To accelerate the chemical reaction and speed up the test.

Answer

To act as a calibration agent for the measurement marks on the meter.

Answer

To increase the density of the water, making the air bubbles rise faster.

Question 3

A project's concrete specification requires an air content of 6.0% ± 1.5%. A technician performs a test according to ASTM C231 and gets a final, stable gauge reading of 5.2%. The aggregate correction factor for the mix has been previously determined to be 0.8%. What is the reported air content and does it meet the specification?

Accepted Answer

4.4%; It does not meet the specification.

Answer

5.2%; It meets the specification.

Answer

6.0%; It meets the specification.

Answer

4.4%; It meets the specification.

Question 4

Which of the following situations would require the use of the volumetric method (ASTM C173) instead of the pressure method (ASTM C231) for determining the air content of fresh concrete?

Accepted Answer

The concrete is made with lightweight aggregate.

Answer

The concrete has a very high slump (e.g., 8 inches).

Answer

The concrete is being placed in a high-temperature environment.

Answer

The concrete contains a high-range water-reducing admixture.

Question 5

According to ASTM C231, after placing and rodding each of the three layers of concrete in the measuring bowl, what is the next immediate step before adding the subsequent layer?

Accepted Answer

Tap the sides of the bowl smartly 10 to 15 times with a mallet.

Answer

Weigh the bowl and concrete to check the density.

Answer

Use a trowel to level the surface of the layer.

Answer

Insert a thermometer to measure the concrete temperature.

Question 6

While performing a test with a Type B pressure meter (ASTM C231), the technician pumps air into the chamber until the gauge hand is exactly on the initial pressure line. What is the purpose of then lightly tapping the gauge?

Accepted Answer

To stabilize the gauge hand and ensure an accurate starting pressure.

Answer

To ensure the main air valve is properly seated.

Answer

To check if the concrete sample is fully consolidated.

Answer

To verify that the petcocks are fully closed.

A technician performing an air content test using the pressure method (ASTM C231) has pressurized the meter, opened the main air valve, tapped the sides of the bowl, and stabilized the gauge.The gauge reading is 5.8%.What is the next critical step to determine the final air content percentage?

A technician performing an air content test using the pressure method (ASTM C231) has pressurized the meter, opened the main air valve, tapped the sides of the bowl, and stabilized the gauge.
The gauge reading is 5.8%.
What is the next critical step to determine the final air content percentage?