ACI Concrete Strength Testing Technician Practice Test

What is the minimum requirement for the density of concrete specimens for complete compliance with ASTM C39?

1. Less than 50 lb/ft

2. Exactly 50 lb/ft

3. More than 50 lb/ft

4. No specific requirement

The correct answer is: More than 50 lb/ft

For complete compliance with ASTM C39, which specifies the procedure for testing the compressive strength of cylindrical concrete specimens, the minimum density requirement is indeed more than 50 lb/ft³. This standard reflects the expectation for concrete to be of sufficient density to ensure its structural integrity and performance characteristics. The rationale behind this minimum density is that concrete with a density below this threshold may not possess the necessary strength properties and could lead to unreliable test results. This requirement helps to ensure that the concrete is adequately mixed and cured, leading to a robust product capable of withstanding the mechanical loads it’s designed for. In the context of construction and engineering, adhering to this criterion is critical for guaranteeing the reliability and safety of concrete structures.