The slump test is a commonly used test to determine the workability of fresh concrete. It measures the consistency and flowability of the concrete mixture, providing valuable information about its ease of placement and ability to be compacted. The correct answer to the question is option 'C' - workability.

Explanation:
1. Slump Test: The slump test involves filling a standard conical metal mold with fresh concrete in three layers, each compacted with a rod. The mold is then lifted vertically, and the amount of settlement or "slump" of the concrete is measured. This slump measurement indicates the workability of the concrete.

2. Workability: Workability refers to the ease with which fresh concrete can be mixed, placed, compacted, and finished without segregation or excessive bleeding. It is an important property as it directly affects the construction process. The slump test provides an indication of the workability of the concrete, helping construction workers determine if the concrete can be easily handled and placed.

3. Importance of Workability: The workability of concrete is crucial for achieving proper compaction and consolidation, ensuring that the mixture is free from voids and air pockets. It also affects the finishing operations, such as screeding, troweling, and surface texture. Inadequate workability can lead to difficulties in placing and finishing the concrete, resulting in poor quality and compromised strength.

4. Strength: While the slump test indirectly provides information about the workability of the concrete, it does not directly determine the strength of the hardened concrete. Strength testing is typically carried out on hardened concrete specimens using compression tests, such as the cube or cylinder test.

5. Durability: The slump test is also not specifically designed to determine the durability of concrete. Durability is a measure of the concrete's ability to resist various environmental factors, such as freeze-thaw cycles, chemical attack, and abrasion. Durability testing involves assessing the concrete's resistance to these factors through specialized tests and analysis.

In conclusion, the slump test is primarily used to evaluate the workability of fresh concrete. It provides valuable information about the consistency and flowability of the mixture, helping construction workers ensure that the concrete can be easily placed, compacted, and finished.