CLASSIFY AGGREGATES ACCORDING TO SIZE

HOW TO CLASSIFY AGGREGATES ACCORDING TO SIZE?

According to size the aggregates are classified as:

• Fine Aggregate
• Coarse Aggregate
• All in Aggregate

FINE AGGREGATE

It is the aggregate most of which passes 4.75 mm IS sieve and contains only so much coarser as is permitted by specification. According to source fine aggregate may be described as:

• Natural Sand– it is the aggregate resulting from the natural disintegration of rock and which has been deposited by streams or glacial agencies
• Crushed Stone Sand– it is the fine aggregate produced by crushing hard stone.
• Crushed Gravel Sand– it is the fine aggregate produced by crushing natural gravel.

According to size the fine aggregate may be described as coarse sand, medium sand and fine sand. IS specifications classify the fine aggregate into four types according to its grading as fine aggregate of grading Zone-1 to grading Zone-4. The four grading zones become progressively finer from grading Zone-1 to grading Zone-4. 90% to 100% of the fine aggregate passes 4.75 mm IS sieve and 0 to 15% passes 150 micron IS sieve depending upon its grading zone.

COARSE AGGREGATE

It is the aggregate most of which is retained on 4.75 mm IS sieve and contains only so much finer material as is permitted by specification. According to source, coarse aggregate may be described as:

• Uncrushed Gravel or Stone– it results from natural disintegration of rock
• Crushed Gravel or Stone– it results from crushing of gravel or hard stone.
• Partially Crushed Gravel or Stone– it is a product of the blending of the above two aggregate.

According to size coarse aggregate is described as graded aggregate of its nominal size i.e. 40 mm, 20 mm, 16 mm and 12.5 mm etc. for example a graded aggregate of nominal size 20 mm means an aggregate most of which passes 20 mm IS sieve.

A coarse aggregate which has the sizes of particles mainly belonging to a single sieve size is known as single size aggregate. For example 20 mm single size aggregate mean an aggregate most of which passes 20 mm IS sieve and its major portion is retained on 10 mm IS sieve.

ALL IN AGGREGATE

It is the aggregate composed of both fine aggregate and coarse aggregate. According to size All-in-aggregate is described as all-in-aggregates of its nominal size, i.e. 40mm, 20mm etc. For example, all in aggregate of nominal size of 20mm means an aggregate most of which passes through 20 mm IS sieve and contains fine aggregates also.