Which waste product is used in concrete to improve strength and reduce permeability?

Fly ash is a byproduct of burning finely ground coal in electric power plants. When it is used in concrete, it significantly improves strength and reduces permeability. The pozzolanic properties of fly ash allow it to react with calcium hydroxide released during the hydration of cement, forming additional cementitious compounds. This leads to increased strength, durability, and resistance to chemical attacks, while also enhancing workability. The use of fly ash in concrete mixes can also reduce the overall cement content required, leading to more sustainable construction practices.

In contrast, while other materials like slag and cement kiln dust also have beneficial effects on concrete, they do not specifically focus on the strength and permeability improvements to the same extent as fly ash. Slag, for instance, primarily enhances durability and resistance to sulfate attack but may not contribute as significantly to permeability reduction. Similarly, pulverized fuel ash may be another term for fly ash, but it is less commonly used and can sometimes refer to different properties based on its source and composition.