Why should aggregates be free of deleterious substances?

Aggregates should indeed be free of deleterious substances primarily because these materials can negatively affect the strength and durability of concrete. Deleterious substances include contaminants like clay, silt, organic materials, or other impurities that can interfere with the cement paste's ability to adhere properly to the aggregate particles.

When these substances are present, they can create weak points within the concrete mix, lead to poor bonding, and ultimately compromise the structural integrity of the concrete. This can result in various issues such as cracking, increased permeability, and reduced resistance to environmental factors, all of which can significantly shorten the lifespan and performance of concrete structures.

Ensuring that aggregates are clean and free from these harmful materials is essential for achieving high-quality concrete that meets the required standards for strength, durability, and overall performance.