5.10 : Shape and Texture of Coarse Aggregate

Aggregate shape is classified based on the relative sharpness or roundness of the edges and corners. This classification includes categories like rounded, angular, elongated, and flaky, each with specific characteristics. Rounded aggregates, fully shaped by attrition, are typical of river or seashore gravel, while angular aggregates, such as crushed rock, have well-defined edges. Aggregates that are elongated and flaky are less desirable, as they can reduce the workability and strength of concrete.

The texture of aggregates refers to their surface characteristics, which can range from smooth to rough. The texture affects the bond between aggregate and cement. Smooth textures, resulting from weathering by water or the breakage of fine-grained rocks, may require less water for concrete mixing, whereas rough textures, like those of crushed basalt or limestone, provide better bonding with cement but may increase water demand. The surface textures in aggregates can also include glassy, granular, honeycombed, and crystalline forms.

The packing of aggregates is also influenced by their shape and texture. Aggregates that are angular and rough offer less efficient packing but potentially stronger mechanical interlock in concrete compared to rounded and smooth aggregates.