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Unformatted text preview: ging from about 150 to 235 kg per iu m ( or 250
to 400 lb per cu yd) to heavily reinforced concrete having a maximum
size of aggregate of 2 cm ( or $ in ) and a cement ‘content of approximately
355 kg per cu m ( or 600 lb per cu yd ). To effect the greatest economy,
the concrete should preferably contain the maximum size aggregate S?litdh?
for the place of use and giving the specified strengths.
4.2 Quality 4.2.1 The proportions of the ingredients in con&ete shaft be detcrmined through preliminary laboratory tests on concrete made from representative samples of ingredients proposed. to be wed in the work. The
tests shall be carried out in accordance iith the procedure described in
Appendix B of *IS: 456-1957.
After the water content has been determined to suit the required consistency, the cement content sl~nll be deteimined in the following manner:
A curve representing the relation between water-cement ratio anti
the average compressive strength of concrete at 28 days or earth_,
at which tt)e concrete is to receive its full working load, shall be established for a range of values at least 15 percent below and 15 percent above 11 times the required strength.
The curve shall bc fiscd
by at least four pointy, each point rctprescnting the avcragc values of
at least three test specimens.
ratio to ho adoptctl
on the work shall correspond to that strength on the curve which
is 1) times the strength actually rccpiircd.
*Second rrvisior~ in 1964. 9 IS : 457 - 1957
tests shall be completed well before the beginning
and a complete
report on the concrete
qualities and Gtability
of available aggregates as also recommendations
for their use at the work shah be made and approved by the engineer-incharge before actual concreting is started.
4.2.2 No substitutions
in the materials used on the work or alterations
in the established
shall be made unless additional
been .:onducted to show that the quality and strengths
of the resulting
concrete are satisfactory.
4.2.3 The engineer-in-charge
may carry out check tests and order
changes in the mix as may be necessary from time to time to maintain
No radical changes, substitutions
the specified quality of the work.
additions in the mix, shall be made without such check tests and subsequent
4.3 Mix Proportions -The
and other ingredients,
if any, necessary to produce concrete of the desired
quality shall be determined
as described under 4.2.1.
The specified watercement ratio shall be strictly adhered to for each class of concrete.
of the proportions
of all ingredients
may be made by the
in accordance with field tests, specified under 7. Both
the rate and the sequence of pouring shall be strictly regulated as laid down
bv the engineer-in-charge.
4.3.1 Determination of Surface Moisture - In the case of fint? aggregates, the surface moist...
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- Fall '13