ACI Certification Practice Exam

What temperature range should be maintained for test cylinders of normal strength concrete during initial curing?

1. 40 to 60 degrees F

2. 60 to 80 degrees F

3. 30 to 50 degrees F

4. 70 to 90 degrees F

The correct answer is: 60 to 80 degrees F

For normal strength concrete, it is essential to maintain an adequate temperature range during the initial curing of test cylinders to ensure the proper hydration of the cement. Keeping the temperature within 60 to 80 degrees Fahrenheit promotes optimal curing conditions. This range helps facilitate effective chemical reactions and ensures that the concrete gains strength as expected. When temperatures are too low, such as in options suggesting lower ranges, the hydration process can slow down significantly, resulting in weaker concrete. Conversely, temperatures above the specified range can lead to rapid evaporation of moisture, creating conditions that can cause incomplete curing and surface cracking, which can also negatively impact the strength and durability of the concrete. Thus, the choice of 60 to 80 degrees Fahrenheit is the most appropriate for achieving reliable and consistent results in the strength development of normal strength concrete.