ACI Concrete Strength Testing Technician Practice Test

Which of the following is a component of the testing machine required by ASTM C39?

1. Two wooden bearing blocks

2. One spherically seated block and one solid block

3. A single bearing plate

4. Two spherical blocks

The correct answer is: One spherically seated block and one solid block

The correct choice is indeed the option that includes one spherically seated block and one solid block, which are integral to the testing machine used in ASTM C39 for compressive strength testing of cylindrical concrete specimens. The spherically seated block is crucial because it allows for the alignment of the specimen during the testing process, accommodating any slight misalignments that may occur and helping to apply the load evenly. The solid block serves as a stable point of contact to transfer the load from the testing machine to the specimen. This setup ensures accurate measurement of the compressive strength of concrete by minimizing any additional stresses or errors in the load application. The presence of two wooden bearing blocks would not satisfy the requirements set by ASTM C39, as it specifies the need for a properly designed setup that includes materials that can withstand the high forces involved in the test procedure. A single bearing plate does not provide the necessary dual contact needed to ensure uniform load application or proper alignment of the concrete test specimen. Utilizing two spherical blocks is also not compliant, as ASTM C39 specifically designates the combination of a spherically seated block and a solid block to maintain testing integrity and reliability.