Volume-IF - JantERmantER

, ( OCPL-K9A01
established to suit the purpose depending on availability of
aggregates.
d) M"IX design also should be so done that II has a slump of 50
mm at the point where concrete is placed under an ambient
temperatura of around 40 Oeg.C. This wlll also keep vibration
by needle vibrators to required minimum. Slump should 'not
drop down to zero In less than 45 minutes. Suitable ratarding
agent and plasticizer of approved manufaCture may be added
in mix to achieve this purpose. These admlxturas to be
properly Identified by praliminary tests both for pedormance
and for compatibility with particular type Qf cement propoSed 1(,
be used.
Additlonal steps Ike spraying of water over tha shutters and
keeping down the temperatura of coarse aggregates by
continuous spraying of water over those may be rasorted 10 kl
ambient temperatura is more than 40 Oeg.C.
,
3.
t.
2. Cere must be taken to pravent twist. which predominantly occur in the
initial stages because of low ,tipping rate, in the horizontal plane of
Slip-form assembly. A thorough check on this aspect must be kept at
every 15 minutes interval. One person should exclusively be assigned
this work together wfth rectifying any defect.
Every endeavour has to be made so as not to occur any tilt in the
shutter assembly. To achieve thls following steps need be1aken :
a) Performance of jacks has to be closely observed and any
defective one needs Immediate replacement. Difference' In
levels of opposite jaclls at any instant of time should not
exceed 5 mm.
(: b) Loading on Stip-form Inlsslyokes has to be fairly equal.
•
c) Sleeve through whlOn jacking rod passes has to be of
sufficient length so' that· later gets an uniform clearance· and
. does not get any chance to bll SJeeveshouldhavea minimum
wan thickness of 3.25 mm and should' bE! such that jacking
#:.:: rod gats a maximum clearance of 1 mm to 1.5 mm alround.
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4. For taper walled chimneys ovellapping of shutt!)rs which are kept te
efIact the tapering. needs careful attention otherwise these may be
ruled with concrete slurry.
t
5. . In designing the mix fOllowing aspects should be borne in mind :
t
a) Cement used should have an initial selting time of not less
than 50 minutes and preferably should have a specifIC surface
around 3600 Sq.Cm.per gram.
t:. .;, b) Coarse and fine aggregates should be well graded a
42~,~
(PCA,C0-003.S80SCSA24.dOC.dOC) V.U-02lS-XXIV: 19
t;
327
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