Building Materials, Third Edition

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Aggregates are the materials basically used as filler with binding material in the production of
mortar and concrete. They are derived from igneous, sedimentary and metamorphic rocks or
manufactured from blast furnace slag, etc. Aggregates form the body of the concrete, reduce
the shrinkage and effect economy. They occupy 70-80 per cent of the volume and have
considerable influence on the properties of the concrete. It is therefore significantly important
to obtain right type and quality of aggregates at site. They should be clean, hard, strong,
durable and graded in size to achieve utmost economy from the paste. Earlier aggregates were
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 markedly
different sizes—the bigger ones known to be coarse aggregate (grit) and the smaller ones fine
aggregate (sand). The coarse aggregate form the main matrix of concrete and the fine aggregate
from the filler matrix between the coarse aggregate.

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The aggregates may be classified into natural aggregates and artificial aggregates.

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