What is the role of fly ash in concrete?

Fly ash plays a significant role in improving the characteristics of concrete, particularly in enhancing workability and reducing permeability. As a byproduct of coal combustion in power plants, fly ash contains fine particles that can fill voids in the concrete mixture, which helps to produce a denser and more workable mix. This increased workability makes it easier to handle and place the concrete without requiring excessive amounts of water.

Moreover, fly ash has pozzolanic properties, which means it reacts with calcium hydroxide in the presence of water to form additional cementitious compounds. This reaction not only contributes to the strength of the concrete but also reduces the overall permeability of the concrete. A lower permeability means that the concrete is less susceptible to ingress from water and harmful chemicals, which can lead to deterioration over time. This quality is particularly beneficial in structures that are exposed to moisture or aggressive environments.

Other options do not accurately capture the primary benefits of fly ash in concrete. The reduction of weight is not a primary characteristic of fly ash in typical concrete applications. Increasing drying time is generally not associated with fly ash and may actually be reduced due to improved workability. Additionally, fly ash is not typically used as a color additive for concrete. Instead, its main functional benefits involve enhancing