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8/12/2019 Modification Specification of Concrete http://slidepdf.com/reader/full/modification-specification-of-concrete 1/3 Specification of concrete  Standard Mixes  Concrete mixes will be standard mixes, The mix proportions for standard mixes are based on the use of cements of standard strength classes Constituent Materials The material used shall be selected to minimise the risk of damage due to alkali- silica reaction associated with the selection of materials or mix proportions. Deliver and Storage of Materials  Cement shall be stored in a dr weatherproof  place on a raised wooden floor or in a silo. Coarse aggregates shall be delivered to Site in separate si!es "# si!es where the maximum si!e is #$mm%. &ll aggregates brought upon the Site shall be kept free from contact with deleterious matter and in the case of aggregates passing a 'mm sieve the should be deposited on Site for not less than ( hours before use. &ggregates of different si!es shall be stored in different stockpiles which shall be kept separate from each other. Mixing Concrete  Concrete shall be mixed in a batch tpe mixer manufactured in accordance with )S.*+$' or similar approved tpe and shall be maintained to the manufacturers specification. Mixers which have been out of use for more than +$ minutes shall be thoroughl cleaned before an fresh concrete is mixed. Mixing plant shall be thoroughl cleaned before changing from one tpe of cement to another.  Concrete shall not be mixed when the air temperature in the shade is below +C "+(% unless special precautions are taken which have been approved b the ngineer. /o fro!en material or materials containing ice shall be used. During hot weather the Developer shall ensure that the constituent materials of the concrete are sufficientl cool to prevent the concrete from stiffening in the interval between its discharge from the mixer and compaction in its final  position. 0ead-Mixed Concrete  0ead-mixed concrete shall onl be secured from a certified supplier, certified b the following bodies1- 0ead-mixed concrete as defined in )S.*2#3, batched off site, shall compl with all re4uirements of the Specification.

Modification Specification of Concrete

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8/12/2019 Modification Specification of Concrete

http://slidepdf.com/reader/full/modification-specification-of-concrete 1/3

Specification of concrete

 Standard Mixes

  Concrete mixes will be standard mixes, The mix proportionsfor standard mixes are based on the use of cements of standard strength classes

Constituent Materials

The material used shall be selected to minimise the risk of damage due to alkali-

silica reaction associated with the selection of materials or mix proportions.

Deliver and Storage of Materials

  Cement shall be stored in a dr weatherproof

 place on a raised wooden floor or in a silo. Coarse aggregates shall be delivered

to Site in separate si!es "# si!es where the maximum si!e is #$mm%.&ll aggregates brought upon the Site shall be kept free from contact with

deleterious matter and in the case of aggregates passing a 'mm sieve theshould be deposited on Site for not less than ( hours before use. &ggregates of

different si!es shall be stored in different stockpiles which shall be kept separate

from each other.

Mixing Concrete

  Concrete shall be mixed in a batch tpe mixer manufactured inaccordance with )S.*+$' or similar approved tpe and shall be maintained to

the manufacturers specification.

Mixers which have been out of use for more than +$ minutes shall bethoroughl cleaned before an fresh concrete is mixed. Mixing plant shall bethoroughl cleaned before changing from one tpe of cement to another.

 Concrete shall not be mixed when the air temperature in the shade is below +C

"+(% unless special precautions are taken which have been approved b thengineer. /o fro!en material or materials containing ice shall be used.

During hot weather the Developer shall ensure that the constituent materials ofthe concrete are sufficientl cool to prevent the concrete from stiffening in the

interval between its discharge from the mixer and compaction in its final

 position.

0ead-Mixed Concrete

  0ead-mixed concrete shall onl be secured from a

certified supplier, certified b the following bodies1-0ead-mixed concrete as defined in )S.*2#3, batched off site, shall compl

with all re4uirements of the Specification.

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The concrete shall be carried in purpose made agitators, operating continuousl

or truck mixers. The concrete shall be compacted and in its final position

within # hours of the introduction of cement to the aggregates. The time of suchintroduction shall be recorded on the Deliver /ote, together with the weight of

the constituents of each mix.

5hen truck mixed concrete is used, water shall be added under supervision at

the central batching plant, under no circumstances shall water be added in

transit.

Truck mixer units and their mixing and discharge performance shall compl

with the re4uirements of )S.6#'*. Mixing shall continue for not less than *$$

revolutions at a rate of not less than 7 revolutions per minute.

1 Transport and 8lacing

  Concrete shall be so transported and placed that

contamination does not occur.&ll formwork and reinforcement contained in it shall be clean and free from

standing water, snow or ice immediatel before the placing of concrete.

resh concrete shall not be placed against in-situ concrete which has been in

 position for more than +$ minutes unless a construction 9oint is formed.

Concrete shall be compacted in its final position within +$ minutes of discharge

from the mixer unless carried in purpose made agitators, operating

continuousl, when the time shall be within # hours of the introduction ofcement to the mix and within +$ minutes of discharge from the agitator.

 

Concrete shall not be dropped into place from a height exceeding #m. 5hentrucking or chutes are used the shall be kept clean and used in such a wa as to

avoid segregation.

 /o concrete shall be placed in flowing water, or below standing water.

Compaction of Concrete

  &ll concrete shall be compacted to produce a densehomogeneous mass and shall be compacted with the assistance of vibrators

unless agreed otherwise b the ngineer.

Concrete shall not be sub9ected to vibration between 6 and #6 hours after

compaction.

Curing of Concrete

  :mmediatel after compaction and for 7 das thereafter,

concrete shall be protected against harmful effects of weather, including rain,

rapid temperature changes, frost and from dring out. The methods of

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 protection shall be approved b the ngineer, but in all cases shall prevent loss

of moisture from the concrete.

Cement Mortar 

  Cement mortar shall have the properties of cement 1 sand of * 1

+. Sand shall be a natural sand or crushed natural stone or a combination of both.

Mortar shall be mixed thoroughl either b hand or mechanicall until its colourand consistenc are uniform. The constituent materials shall be accuratel

gauged, allowance being made for bulking of sand. Mortar shall be made in

small 4uantities onl as and when re4uired. Mortar which has begun to set or

which has been mixed for a period of more than* hour shall be discarded.

&ggregates for Concrete

  &ggregates for concrete shall consist of naturalloccurring material compling with the re4uirements. &lternativel with the

approval of the ngineer, coarse aggregate ma consist of crushed air-cooled blast-furnace slag .

Testing of Concrete  Testing of concrete, other than testing of lean concrete, shall

compl with the following re4uirements1-

; 5here a batch has been sampled for the purpose of making cubetests, * cube shall be made from each of the + samples for test at #( das.

; The cubes shall be made.

 ; The appropriate strength re4uirements for each set of + cubes

shall be satisfied.

;1 &dmixtures

<nless agreed b the ngineer neither admixtures nor cements containing

additives shall be used.