Note-1: For crushed stone sands, the
permissible limit on 150 micron IS Sieve is increased
to 20 percent. This does not affect the 5 percent
allowance permitted in 4.3 applying to other sieve
Note-2: Fine aggregate complying with the requirements
of any grading zone in this table is suitable for
concrete but the quality of concrete produced will
depend upon a number of factors including proportions.
Note-3: Where concrete of high strength and good durability
is required, fine aggregate conforming to any one
of the four grading zones may be used, but the concrete
mix should be properly designed. As the fine aggregate
grading becomes progressively finer, that is, from
Grading Zones I to IV, the ratio of fine aggregate
to coarse aggregate should be progressively reduced.
The most suitable fine to coarse ratio to be used
for any particular mix will, however, depend upon
the actual grading, particle shape and surface texture
of both fine and coarse aggregates.
Note-4: It is recommended that fine aggregate conforming
to Grading Zone IV should not be used in reinforced
concrete unless tests have been made to ascertain
the suitability of proposed mix proportion.
Aggregates Impact Value
- The aggregate impact value may be determined in
accordance with the method specified in IS: 2386 (Part
IV) – 1963. The aggregate impact value shall
not exceed 45 percent by weight for aggregates used
for concrete other than for wearing surfaces and 30
percent by weight for concrete for wearing surfaces,
such as runways, roads and pavements.
Aggregate Abrasion Value –
Unless otherwise agreed to between the purchaser and
the supplier, the abrasion value of aggregates, when
tested in accordance with the method specified in
IS: 2386 (Part IV) – 1963 using Los Angeles
machine, shall not exceed the following values:
a)For aggregates to be used in concrete for wearing
surfaces. -30 percent
aggregates to be used in other concrete
- 50 percent
Deleterious Materials – Aggregates
shall not contain any harmful material, such as pyrites,
coal, lignite, mica, shale or similar laminated material,
clay, alkali, soft fragments, sea shells and organic
impurities in such quantity as to affect the strength
or durability of the concrete. Aggregates to be used
for reinforced concrete shall not contain any material
liable to attack the steel reinforcement. Aggregates
which are chemically reactive with alkalis of cement
are harmful as cracking of concrete may take place.
NOTE-1 – The
presence of mica in the fine aggregate has been found
to reduce considerably the durability and compressive
strength of concrete and further investigations are
underway to determine the extent of the deleterious
effect of mica. It is advisable, therefore, to investigate
the mica content of fine aggregate and make suitable
allowances for the possible reduction in the strength
of concrete or mortar.
– The aggregate shall not contain harmful
organic impurities (tested in accordance with IS:
2386 (Part-II) 1963] in sufficient quantities to affect
adversely the strength or durability of concrete.
A fine aggregate which fails in the test for organic
impurities may be used, provided that, when tested
for the effect of organic impurities on the strength
of mortar, the relative strength at 7 and 28 days,
reported in accordance with 7 of IS: 2386 (Part VI)
– 1963 is not less than 95 percent.
Properties of Cement Compounds
The two silicates, namely C3S and C2S which together
constitute about 70 to 80 percent of the cement ,
control the most of the strength giving properties.
Upon hydration both C3S and C2S give the same product
called calcium silicate hydrate (C3S2H3) and calcium
hydroxide. Tricalcium silicate (C3S) having a faster
rate of reaction accompanied by greater heat evolution
develops early strength. On the other hand, dicalcium
silicate (C2S) hydrates and hardens slowly and provides
much of the ultimate strength. It is likely that both
C3S and C2S phases contribute equally to the eventual
strength of the cement. C3S and C2S need approximately
24 and 21 percent water by weight, respectively, for
chemical reaction but C3S liberates nearly three times
as much calcium hydroxide on hydration as C2S. However,
C2S provides more resistance to chemical attack.
Five types of cements are in general use. They are:
1) Ordinary Portland cement (OPC) 33
2) Ordinary Portland cement (OPC) 43
3) Ordinary Portland cement (OPC) 53
4) Portland slag cement (PSC)
5) Portland Pozzolana Cement (PPC)
OPC 33 grade means the minimum 28 days
compressive strength of cement is 33 MPa. Similarly
43 & 53 grades. All the three grades of ordinary
Portland cement are produced from the same materials.
But the higher strengths are achieved by increasing
the tricalcium silicate (C3S) content and also by
fine grinding of the clinker.
The BIS limits for the various types of cements are
mentioned here in below:
Forms shall not be released until the concrete has
achieved a strength of at least twice the stress to
which the concrete may be subjected at the time of
removal of form work. The strength referred to shall
be that of concrete using the same cement and aggregates
and admixture, if any, with the same proportions and
cured under conditions of temperature and moisture
similar to those existing on the work.
While the above criteria of strength shall be the
guiding factor for removal of form work, in normal
circumstances where ambient temperature does not fall
below 15?C and where ordinary Portland cement is used
and adequate curing is done, following striking period
may deem to satisfy the guideline given in 11.3 of
other cements and lower temperature, the stripping
time recommended above may be suitably modified.
The number of props left under, their sizes and disposition
shall be such as to be able to safely carry the full
dead load of the slab, beam or arch as the case may
be together with any live load likely to occur during
curing or further construction.
Where the shape of the element is such that the form
work has re-entrant angles, the form work shall be
removed as soon as possible after the concrete has
set, to avoid shrinkage cracking occurring due to
the restraint imposed.
for concrete sampling
The minimum frequency of sampling of concrete of each
grade shall be in accordance with the following:
OF STANDARD DEVIATION: The standard deviation
refers to minor changes in the mix which might be
made at site either to correct consistently higher
results or vice-versa, where as the materials remain
the same, and particularly the water-cement ratio.
But note that at least 30 samples should be used for
this ‘purpose, according to the test results
on specimens are obtained from the field as the concreting