ACI Concrete Strength Testing Technician Practice Test

Is it permissible to reuse compound from old caps when capping cylinders with a compressive strength of 35 MPa (5000 psi) or greater?

1. Yes, always

2. Yes, under certain conditions

3. No, it is not permitted

4. Only with special approval

The correct answer is: No, it is not permitted

When capping cylinders made of concrete with a specified compressive strength of 35 MPa (5000 psi) or greater, it is not permitted to reuse compound from old caps. The primary reason for this restriction is that the integrity and consistency of the compound used in capping directly affect the accuracy of the compressive strength test. Using fresh compound ensures that there are no impurities or inconsistencies that could arise from previously used material. Old capping material may contain hardened particles, air bubbles, or other contaminants that can compromise the bond between the capping material and the cylinder, resulting in an inaccurate strength measurement. Furthermore, fresh compound guarantees uniformity in application and properties, which is crucial for reliable test results. By adhering to this guideline, technicians ensure the validity of the testing process, reduce the likelihood of testing errors, and maintain the quality control standards required in concrete testing.