North Carolina Building Contractor License Practice Exam

How frequently should strength test samples be taken for concrete?

1. Every 100 square feet

2. Every 200 square feet

3. Every 300 square feet

4. Every 400 square feet

The correct answer is: Every 100 square feet

Strength test samples for concrete are typically required to be taken at regular intervals to ensure the concrete has reached the desired strength before being subjected to loads. The standard practice is to take samples based on the volume of concrete being poured and the frequency recommended by codes such as those from the American Concrete Institute (ACI) or the relevant local building codes. Taking samples every 100 square feet serves as a guideline for achieving a reliable representation of the concrete’s strength in a particular area. This frequency allows for more rigorous quality control, ensuring that any potential issues with the concrete mix or placement can be detected early. It helps in assessing the consistency of the concrete mix. If problems are identified with the strength, adjustments can be made to the mix or pouring process before too much of the structure is completed. This practice is important because concrete must meet specific compressive strength requirements to ensure the integrity and safety of a structure. Samples are often tested at various intervals post-pouring, typically at 7 and 28 days, to monitor the curing process and development of strength. The other choices suggest longer intervals between sampling, which may not provide the necessary oversight to catch any inconsistencies or defects in the concrete early in the construction process. Regular testing at the recommended frequency is crucial