ACI Concrete Field Testing Technician - Grade I Practice Exam

What conditions must be met for an initial reading of the meter to be valid?

1. The meter is leaking, liquid stabilizes in 4 minutes

2. Meter must not leak, liquid stabilizes within 6 minutes, foam less than 2%

3. The air content must be less than 5%

4. There are no restrictions for a valid initial reading

The correct answer is: Meter must not leak, liquid stabilizes within 6 minutes, foam less than 2%

The validity of an initial reading from the meter is contingent upon specific operational conditions, which ensure accurate measurement of air content in concrete. The correct choice highlights that the meter must not leak, the liquid must stabilize within a specific timeframe of 6 minutes, and the foam percentage should be less than 2%. When the meter is not leaking, it ensures that the measurement reflects only the air content in the concrete without the influence of other external factors, such as loss of air due to a leak. A stabilization time of 6 minutes is crucial; this period allows the sample to settle, ensuring that the measurement is accurate by reducing the effects of any immediate fluctuations in air content. Additionally, maintaining foam at less than 2% is necessary to ensure that the air content reading is free from interference caused by excessive foam, which can distort the actual measurement of voids present in the concrete. These conditions are important because they establish a standardized approach to measuring air content, ensuring both reliability and consistency across tests. Without adhering to these criteria, the readings could be misleading, resulting in incorrect assessments of the concrete mix’s performance characteristics.