What type of aggregate is typically preferred for durability in concrete?

The preferred type of aggregate for durability in concrete is hard, well-graded aggregates. These aggregates contribute to the overall strength and longevity of concrete by providing a strong framework that can withstand various environmental stresses, including freeze-thaw cycles, abrasion, and chemical attacks.

Hard aggregates, such as granite or basalt, possess high durability characteristics because they are less susceptible to weathering and wear. Well-graded aggregates ensure a compact mixture with minimal voids, leading to improved workability and reduced permeability. The combination of hardness and effective gradation enhances the concrete's resistance to cracking and degradation over time, which is essential for structures exposed to harsh conditions.

In contrast, coarse, poorly-graded aggregates may create a concrete mix that is less dense and more prone to cracking due to higher void content and lower overall strength. Pulverized aggregates do not provide the necessary structural integrity needed for concrete durability and often represent lower performance characteristics. Lastly, soft, absorbent aggregates can negatively impact the performance of concrete by introducing excessive porosity and susceptibility to damage from moisture infiltration, reducing durability over time.