Unformatted text preview: s except finishing, as are
necessary to consolidate and mould the concrete properly. The rate of
placing mass concrete or reinforced concrete in thin sections. whether
mechanically or by manual labour, shall bc cle,uly defined.
18.104.22.168 Accumulation of water on the surface due to bleeding,
or other causes taking place during compacting shall be stopped as much
as possible by adjustments in the mix. All free water on the surface shall
be removed by sponging or mopping. Under no circumstances shall such
accumulation of water be covered up with concrete, or dry concrete used
to soak up escess water.
rJnless otherwise permitted, all concrete shall be compacted by mechanical vibration.
The number and type of vibrators shall
be subject to the approval of the engineer-in-charge.
In general, only
vibrators of the internal type shall be used. However, in inaccessible
places in the forms where spading, rodding, or forking is impracticabie,
the concrete may be gently Lvorked into place and compacted by light
vibrating or hammering the forms.
4.11.2 Vibrating 22.214.171.124 Wherever practicable, concrete shall be internally vibrated
within the forms, or in the mass, in order to increase the plasticity as to
compact effectively to improve the surface texture and appearance, and to
facilitate placing of the concrete.
126.96.36.199 The intensity and duration of vibration shall be sufficient
to ‘cause complete settlement and compaction without anv stratification
Prehminary experiof the successive layers or separation of ingredients.
ments in vibrating shall be ‘conducted under actual conditions of mix and
placement in order to determine the optimum duration and method of
vibration, as \vc!l as to deveiop the necessary skill.
188.8.131.52 Vibration shall be continued until the entire batch melts
to a uniform appearance and the surface just starts to glisten. -1 minute
film of cement paste shall be discernible between the concrete and the
Over vibration causing segregation,
forms and around the reinforcement.
unnecessary bleeding or formation of laitance shall be avoided.
4.11.3 Internal Type Vibrators 184.108.40.206
M,ass concrete sl:a!l be thoroughly compacted with the
aid of high frequency, mechanical vibrators of the internal type, having
21 IS : 457 - 1957
not less than 3 600 and preferably more than 5 000 impulses per minute.
after depositing the concrete, the vibrators shall be inserted
into each pile, operated from 10 to 20 seconds in one spot and then moved
to another not over 90 cm ( or 3 ft ) away.
The operation shall be repeated over until the entire mass is thoroughly
compacted and the pile
shall be paid to the edge of the pile and
to the centre.
A sufficient number of two-man vibrators shall be used to
compact each batch properly before placing the next one. A sufficient
number of reserve vibrators in good condition shall be kept on hand at
all times so as to assure that there is no slackening or interruption
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- Fall '13
- Bombay, Concrete Association, Concrete Section31 Committee, Concrete Subcommittee