What role do pozzolans play in concrete mixtures?

Pozzolans play a significant role in concrete mixtures by enhancing their overall performance through various mechanisms. The correct answer highlights that pozzolans can reduce the heat of hydration and increase workability.

When pozzolans are added to concrete, they react with calcium hydroxide released during the hydration of cement, forming additional compounds that contribute to the strength of the concrete. This pozzolanic reaction allows for a more gradual release of heat during the curing process, which is particularly beneficial in large-scale concrete placements, as excessive heat can lead to thermal cracking.

Furthermore, incorporating pozzolans can improve the workability of the concrete mix. This is important for achieving better flow and easier placement of the concrete, especially in intricate forms or densely reinforced areas. The finer particles of pozzolans help fill voids in the mix, leading to a denser, more homogeneous material while allowing for a more manageable consistency during mixing and pouring.

In contrast, the other options describe functions that pozzolans do not typically serve. While pozzolans do not act as a primary binding agent like cement does, they enhance binding properties. They are not primarily used for decorative purposes nor do they directly enhance shrinkage resistance, although they can influence