ACI Concrete Strength Testing Technician Practice Test

What types of materials should be removed from the ends of hardened concrete cylinders?

1. Water and dirt

2. Oily and waxy materials

3. Loose concrete and debris

4. Sand and gravel

The correct answer is: Oily and waxy materials

The correct choice pertains to the removal of oily and waxy materials from the ends of hardened concrete cylinders. This step is crucial for ensuring accurate testing results when assessing compressive strength or other properties of the concrete. When preparing concrete samples for testing, it is essential that the ends of the cylinders are clean and free from contaminants that may interfere with the bond between the cylinder and the compression testing machine’s platens. Oily and waxy substances can create a slip plane or prevent the cylinder from being firmly engaged with the testing machine, leading to erroneous readings. Cleaning these surfaces is part of good practice and compliance with standard testing procedures. Other materials, while potentially problematic, do not pose the same level of interference in a compressive strength test. For instance, water and dirt can be easily wiped away but may not fundamentally affect the test results as significantly as oils. Loose concrete and debris might slightly influence the measurement but generally won't have as much of an impact compared to oily or waxy residues. Similarly, sand and gravel do not typically remain on cylinder ends after proper molding and curing, so they are less relevant to the context of this question. Overall, removing oily and waxy materials is a critical step to ensure that the compressive strength testing