What is the difference between "clean" and "dirty" aggregates in testing?

The distinction between clean and dirty aggregates hinges on the presence of dust or fines within the material. Clean aggregates are characterized by having little to no dust, silt, or fine particles, which means they are primarily composed of larger aggregate particles. This lack of fine material is significant because it allows for better grading and ensures that there is a sufficient relationship between the aggregates in terms of void spaces and bonds when mixed with cement or asphalt.

The cleanliness of aggregates is important for producing stable, durable mixes that perform effectively in construction applications. Excessive fines or dust in dirty aggregates can adversely affect the mixing process, the final properties of the concrete or asphalt, and can lead to issues such as reduced workability, increased water demand, and decreased strength. Thus, the defining characteristic of clean aggregates is their minimal content of fine materials, which is critical for ensuring optimal performance in construction materials.