Why should aggregate be clean and free of contaminants?

Aggregate should be clean and free of contaminants primarily because contaminants can weaken the bond between the aggregate and the cement paste. A strong bond is essential for the structural integrity and durability of the concrete. When aggregates contain dirt, oils, or other foreign materials, these substances can form a barrier that interferes with the adhesive properties of the cement paste. Consequently, a poor bond can lead to issues such as reduced strength and increased susceptibility to cracking or other forms of failure.

Ensuring that the aggregate is clean allows for optimal adhesion, enhancing the overall performance of the concrete. This helps maintain the strength, durability, and longevity of finished concrete flatwork, which is crucial for its intended application and usability in construction.