The document discusses different types of aggregates used in construction. It defines aggregates as materials like sand, gravel, and crushed stone. It then discusses the purposes of aggregates, which include providing strength, weight, and being economically viable. It also discusses how aggregates are used in concrete, roads, and railways. The document further classifies aggregates according to their formation as natural or artificial, and according to their size as fine or coarse aggregates. It provides details on the types and properties of different aggregates.