ACI Concrete Field Testing Technician - Grade I Practice Exam

How long should the temperature measuring device remain in the freshly mixed concrete?

1. At least 1 minute

2. At least 2 minutes but not more than 5 minutes

3. At least 5 minutes but not more than 10 minutes

4. Indefinitely until the sample is taken

The correct answer is: At least 2 minutes but not more than 5 minutes

The requirement for how long the temperature measuring device should remain in the freshly mixed concrete is established to ensure an accurate reading of the concrete's temperature. For the device to register a stable and representative temperature, it is essential to allow it enough time to equilibrate with the concrete. The correct duration of at least 2 minutes but not more than 5 minutes provides an optimal balance between obtaining an accurate and reliable temperature measurement without unnecessary delays during the testing process. Within this timeframe, the measurement device can effectively reflect the concrete's true temperature, accounting for any thermal gradients in the mix. This range also aligns with standard practices in concrete testing, which aim for efficiency while maintaining precision. Allowing the device to remain for shorter than 2 minutes could lead to readings that do not adequately represent the overall temperature of the mix, while it would be unnecessary to wait longer than 5 minutes, as the measurement will not significantly change after proper equilibration has occurred. Thus, the recommended timeframe is crucial for achieving accurate and consistent results during the concrete testing process.