ACI Concrete Strength Testing Technician Practice Test

Which of the following is NOT a requirement for the testing machines used in ASTM C39?

1. They must apply loads at variable rates

2. They must verify accuracy upon installation

3. They must continuously apply the load

4. They must be power operated

The correct answer is: They must apply loads at variable rates

In the context of ASTM C39, which outlines the standard test method for compressive strength of cylindrical concrete specimens, the requirements for testing machines are significant for ensuring reliable test results. The testing machines are specifically designed to apply load in a controlled manner, typically at a consistent rate, rather than variable rates. This is crucial because a consistent loading rate helps to accurately assess the specimen's strength. The requirement for the machine to verify accuracy upon installation is essential for ensuring that the machine is functioning correctly and provides reliable measurements. This process involves calibration, which guarantees that the load applied during the test truly reflects the force exerted onto the concrete specimen. Continuous application of load is also a necessity, as it ensures that the specimen is subjected to the pressure until failure occurs without any interruption, thereby reflecting true performance under real-world conditions. Power operation is another requirement because these machines need to exert significant force, which manual methods cannot achieve consistently and safely. Therefore, the notion that machines must apply loads at variable rates is not a requirement set forth in ASTM C39. Instead, the standard emphasizes the need for a consistent application of load to ensure accurate and reproducible results.