Building Materials, Third Edition

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They are well-burnt furnace residue obtained from furnaces using coal as fuel and are used for
making lime concrete. They should be clean and free from clay, dirt, wood ash or other
deleterious matter. They are classed as A, B and C. Class A is recommended for general
purposes, class B for interior work not exposed to damp conditions, and class C for precast blocks.
Sulphate content should not exceed 1 per cent when expressed as sulphur trioxide and loss
on ignition 10 per cent for class A, 20 per cent for class B, 25 per cent for class C.

Average grading is as under:

Sieve No. Percentage passing

10 mm 10

4.75 mm 80

2.36 mm 60

1.18 mm 40

600 micron 30

300 micron 25

150 micron 16

TII f‚yuix2f‚sgu2gye‚ƒi2eqq‚iqe„i

They are prepared from well-burnt or over-burnt broken bricks free from under-burnt particles,
soil and salt and are used in lime concrete.
Water absorption after 24 hours on immersion in water should not exceed 25 per cent and
water soluble matter should not exceed 1 per cent. Aggregate impact value should not exceed
50 per cent.

Grading is as under:

Sieve No. (mm) Percentage passing (by weight)

80 100

40 95-100

20 45-75

4.75

TIP „iƒ„sxq2yp2eqq‚iqe„iƒ

The size, shape, grading of aggregate and their surface moisture affect directly the workability
and strength of concrete whereas soundness, alkali-aggregate reaction and presence of
deleterious substances adversely affect the soundness and durability of concrete. The following
tests are conducted to ensure satisfactory performance of aggregate.

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Sample of fine aggregate, coarse aggregate or all-in-aggregate, as required to be tested, are
taken in sufficient quantities. The minimum weight of sample for the test should be as follows.