Which characteristic of fly ash contributes to the durability of concrete?

The characteristic of fly ash that contributes to the durability of concrete is its microfilling properties. Fly ash consists of fine particles that can fill the voids in the concrete mix. This microfilling effect helps to reduce the overall porosity of the concrete, leading to a denser material. As a result, this reduced porosity enhances the durability of concrete by limiting the permeability and making it more resistant to chemical attack and other potential deterioration mechanisms.

Furthermore, the pozzolanic reactions that occur when fly ash is combined with lime in the presence of water can lead to the formation of additional compounds that contribute to the long-term strength and durability of the concrete matrix. This additional binding material can further enhance the cohesive nature of the concrete, resulting in improved performance over time.

In contrast, other choices, such as high pore volume, would detract from concrete durability by allowing moisture and harmful agents to penetrate the material more easily. Organic content could also adversely affect the bonding and overall effectiveness of the concrete, while coloring agents typically have no significant impact on the structural or durability characteristics of concrete.