Which factor can lead to increased permeability in concrete?

Increased permeability in concrete primarily occurs when contaminated aggregates are used, as this can introduce various impurities and harmful materials into the mix. Contaminated aggregates might include dirt, organic matter, or chemicals that compromise the integrity and structure of the concrete. Such impurities can create voids and pathways within the concrete matrix, allowing water and other fluids to pass through more easily, thereby increasing permeability.

Using high-quality, uncontaminated aggregates is crucial for ensuring a dense and durable concrete mix, while minimizing the risk of increased permeability that could lead to issues like water infiltration and reduced long-term durability. The other factors, while relevant to concrete quality, do not directly lead to increased permeability in the same manner as contaminated aggregates do.