The question asks us to classify cement concrete under one of the types of dampness-checking materials. To answer this, we should understand the properties of these materials:

1. Flexible Materials: These materials can adjust to minor movements and are generally made of materials like bituminous felt or plastic sheeting. They have good elasticity and are used where flexibility is required.
2. Rigid Materials: These are non-flexible and remain stable. Cement concrete falls under this category because it is a solid, non-flexible material that is effective in creating a barrier to moisture.
3. Grout: This is a construction material used to fill gaps and is common in applications such as waterproofing and strengthening structures. It is not primarily used as a damp barrier by itself.
4. Temporary Materials: These materials provide short-term solutions and are often used in construction or repair works for temporary water stoppage.

Conclusion: Cement concrete is classified as a rigid type of dampness-checking material due to its stable and solid nature, making it suitable for creating a permanent moisture-resistant barrier.

This categorization is crucial in construction to ensure the desired performance and durability of structures exposed to moisture.