What characterizes a pozzolan in terms of cementitious activity?

A pozzolan is characterized by possessing little or no cementitious activity on its own. Essentially, pozzolans are materials that, when mixed with lime and water, react chemically to form compounds that have cement-like properties. This definition highlights the fact that pozzolans are not inherently cementitious but become so through a reaction with other materials, specifically the calcium hydroxide produced during the hydration of cement.

Understanding this distinction is crucial in recognizing the role pozzolans play in concrete mixtures. They are often used to enhance the properties of concrete when combined with Portland cement, improving durability, reducing permeability, and providing resistance to chemical attacks. These benefits result from the pozzolanic reaction that occurs when pozzolans interact with lime, which is why they are valuable additives in concrete performance.

In contrast, the other choices suggest properties that do not accurately reflect the nature of pozzolans. High cementitious properties would misrepresent them, as pozzolans require a reaction with lime to provide any cement-like characteristics. Claiming that pozzolans are completely inert ignores their potential to react with other materials within the concrete mix. Finally, suggesting that pozzolans are stronger than regular cement overlooks their function as supplementary