How do pozzolans contribute to concrete mixtures?

Pozzolans significantly enhance concrete mixtures by contributing to their strength and reducing heat generation during the curing process. When pozzolans, which are siliceous or siliceous and aluminous materials, are added to concrete, they react with the calcium hydroxide produced from the hydration of cement. This chemical reaction, known as pozzolanic activity, results in additional calcium silicate hydrate, the primary binding agent responsible for the concrete's strength.

Additionally, using pozzolans can lower the heat of hydration, especially in larger concrete pours. This reduction in heat generation is crucial in preventing thermal cracking, which can occur when parts of the concrete cool and shrink at different rates. By improving the durability and long-term performance of concrete, pozzolans play a vital role in creating more sustainable and robust structures.

In contrast, other options do not accurately reflect the role of pozzolans. While changing the aggregate size does affect concrete’s properties, pozzolans do not directly impact the size of aggregates. Improving color is not a primary function of pozzolans; their main benefits lie in strength and performance rather than aesthetic properties. As for being a lightweight substitute for aggregates, pozzolans do not serve this purpose