Aggregates

• Aggregates are the materials basically used as filler with binding material in the production of mortar and concrete 
• They give body to the concrete and occupy 70 to 80 percent of volume of concrete . Therefore , they exert considerable impact on the characteristics and properties of concrete 
• They are derived form igneous, sedimentary and metamorphic rocks or manufactured form blest furnace slag , etc. 
• They should be clean , hard, strong durable and graded in size to achieve utmost economy from the paste 
• Earlier aggregate wear considered to be chemically inert but the latest research has revealed that some of them are chemically active and also that certain types exhibit chemical bond at the interface of aggregates and cement paste 
• To increase the bulk density of concrete aggregates are used in two different sizes - the bigger ones known to be coarse aggregate ( grit ) and the smaller ones fine aggregate ( sand ) 
• Coarse aggregate form the main matrix of concrete and fine aggregate from the filler matrix between the coarse aggregate .