How is a concrete specimen typically prepared for compression testing in a laboratory?

The preparation of a concrete specimen for compression testing is crucial to ensure accurate results. Placing the specimen in the testing machine and aligning it properly within the compression plates is essential because proper alignment ensures that the load is applied evenly across the specimen. Any misalignment may lead to inaccurate readings and potentially premature failure of the specimen. This process involves securely positioning the concrete sample between the compression plates, which are designed to apply a uniform compressive force, allowing for a precise measurement of the specimen's strength when the load is applied.

While some other options may touch on elements related to concrete testing, they do not directly relate to the proper preparation process for compression testing. For example, immersing the specimen in water is typically associated with curing but is not part of the preparation for testing itself. Leaving the concrete to cure for an additional week might be related to achieving desired strength, but it does not address the preparation immediately before testing. Additionally, coating with an insulating material is not standard practice for preparing concrete test specimens for compression testing and may interfere with the test results. Thus, ensuring that the specimen is correctly aligned in the testing machine is the critical step in the preparation process.