ACI Concrete Strength Testing Technician Practice Test

The density requirement for specimens in the ASTM C39 test is that they must be more than how many pounds per cubic foot?

1. 30 lb/ft

2. 40 lb/ft

3. 50 lb/ft

4. 60 lb/ft

The correct answer is: 50 lb/ft

In the ASTM C39 test, which is the standard test method for compressive strength of cylindrical concrete specimens, the density requirement is that the concrete must have a density greater than 50 pounds per cubic foot (lb/ft³). This specification is crucial because it ensures the quality and performance characteristics of the concrete being tested. A density of less than 50 lb/ft³ could indicate a mixture that may be too lightweight and potentially inadequate for structural purposes, which would not reliably represent standard concrete used in construction. Adhering to this density criterion helps maintain the integrity of the testing process and ensures that the test results reflect a concrete mix that meets common structural requirements.