What property does fly ash primarily improve in a concrete mix, aside from strength?

Fly ash is a byproduct of burning pulverized coal in electric power generating plants and is commonly used as a supplementary cementitious material in concrete. Aside from enhancing the strength of concrete, one of the key properties that fly ash significantly improves is workability.

When fly ash is added to a concrete mix, it enhances the workability of the mixture. This is due to its fine particle size and spherical shape, which allows for better flow and reduces the friction between the particles in the concrete. Improved workability is particularly beneficial during the mixing, transporting, and placing phases of concrete construction, as it allows for easier handling and finishing of the concrete.

In contrast, while other options like thermal expansion, soundness, and viscosity have their importance in concrete characteristics, fly ash does not primarily target improvements in these specific areas. Instead, its role is predominantly recognized in contributing to workability, along with other benefits such as reducing water demand and enhancing durability.