ACI Concrete Field Testing Technician - Grade I Practice Exam

Cylinders made for the purpose of determining when a structure may be put into service shall be removed from the mold __________.

1. At the time of the removal of formwork

2. 24 hours after pouring

3. As soon as the concrete reaches initial set

4. After 7 days of curing

The correct answer is: At the time of the removal of formwork

The correct answer reflects the important practice in concrete construction regarding the timing of cylinder removal from the mold in relation to when the structure may be put into service. Removing cylinders at the time of the removal of formwork ensures that the concrete has had the necessary time to cure and gain adequate strength to represent the in-situ conditions of the concrete in the structure. This approach is critical because the strength of concrete continues to develop after it has been placed, and the timing of removing cylinders correlates with the age of the concrete in the structure. This synchronization helps in accurately assessing the strength of the concrete at the time the structure is deemed ready for use, ensuring safety and structural integrity. Other options do not align with best practices or standards. For example, waiting 24 hours after pouring may not account for specific project requirements or environmental conditions affecting cure time. Similarly, removing cylinders as soon as the concrete reaches initial set may not provide sufficient time for concrete to achieve the desired compressive strength. Waiting until after 7 days of curing would be beyond the necessary timeframe for determining when the structure can be put into service, which is usually linked more closely to the timing of formwork removal.