The density of an aggregate is the ratio between its mass and the mass of an equal volume of water. This variability in density can be used to create concrete with different unit weights, as seen in Table. Generally, aggregates are classified into three categories based on their specific gravity: light, normal weight, and heavy weight. The bulk density or unit weight of an aggregate is the mass or weight of the aggregate that is needed to fill a container of a given unit volume.
Aggregates can be divided into several categories based on criteria such as size, font, and unit weight. Examples of lightweight aggregates include ash, blast furnace slag, volcanic pumice, and expanded clay. For normal concrete used for structural elements such as beams and columns, the maximum size of the coarse-grained aggregate is usually around 25 mm. However, it is important to note that aggregates are not completely inert since their physical, thermal, and sometimes chemical properties can affect the performance of concrete.
In addition to reducing cost, aggregate in concrete can reduce shrinkage and creep of cement paste. The behavior of fresh concrete such as flowability, cohesiveness, and rheological behavior is largely influenced by the quantity, type, surface texture, and size gradation of the aggregate.