Classification of Aggregates:

Based on the size, weight, source, and shape the aggregates are further classified as given in the subsequent paragraphs.

Source of Aggregate

Based on the source of material of natural aggregates they are classified as:

(a)        Igneous rocks,

(b)       Sedimentary rocks, and

(c)        Metamorphic rocks.

The chemical and other properties of like aggregates are mainly governed through the properties of their parent rocks.

Comments

Generally, people prefer the locally available aggregates for normal concrete works because transportation cost of the aggregate matters a lot. Igneous rocks are hugely available on the face of the earth and are hard, tough and dense. They could be acidic or basic in nature depending upon the percentage of silica content. Highly laminated sedimentary rocks may lead to flaky or elongated aggregates.

Size of Aggregate

Based on the size, the aggregates can be classified as coarse aggregates and fine aggregates (i.e. sand). The aggregates of size > 4.75 mm are called as coarse aggregates and are available in 80, 40, 20, 10, 4.75 mm sizes.

The fine aggregates are those which are having particles of sizes < 4.75 mm. depending upon the fineness modulus (discussed further in this unit) the fine aggregates are categorized as coarse, medium and fine sand.