In order to keep out moisture, cement or fly ash samples must be placed in a container sealed with?

The correct choice emphasizes the need for a sealing mechanism that effectively prevents moisture from penetrating the container, which is critical for maintaining the integrity of cement or fly ash samples during testing. A friction lid is designed to create a tight seal that is not only secure but also easy to remove when needed, minimizing the risk of moisture exposure.

Friction lids generally provide a snug fit, ensuring that external elements, especially moisture in the air, cannot easily infiltrate the container. This is particularly significant because moisture can lead to chemical reactions that alter the properties of the cement or fly ash, potentially compromising the results of any testing that would be conducted on the samples.

Other sealing methods, while they may provide some level of protection, might not offer the same degree of reliability as a friction lid. Options like a screw top or removable cap may not guarantee a completely airtight seal, particularly under varying environmental conditions. Plastic wrap, although it can provide a temporary barrier, is not designed for long-term storage and may not effectively hold up against moisture ingress over an extended period. Thus, the choice of a friction lid stands out as the most effective solution for maintaining sample integrity by keeping moisture at bay.