Which type of aggregate is NOT suitable for use unless proven by tests for strength and durability?

The choice of non-designated aggregate highlights the importance of thorough evaluation before use in concrete applications. Non-designated aggregates are those that do not have a specified grading or quality standard for specific uses in construction. This means their properties, including strength and durability, are not predetermined or verified through standard testing methods.

Using non-designated aggregates can lead to unpredictable performance in concrete mixes. Because they lack established criteria, their characteristics may vary significantly, potentially affecting the overall strength and durability of the finished product. Therefore, it is paramount to conduct tests to ensure that these aggregates meet the necessary requirements for the intended construction purposes.

In contrast, aggregates that are classified as normalweight or even some exotic aggregates often come with well-documented properties, which means their suitability is more easily assessed. Aggressive aggregate refers to aggregates that may be chemically reactive and could compromise concrete's durability, but these can often be identified through existing guidelines or empirical tests.