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The method shall be by means of jets o 4”air
and water applied at high velocity with such additional [email protected] of the
18 IS : 457 - 1957
surfact? means of stiff-wire brushes as may be required. Brushing shall
be done by jabbing and digging into the surface rather than by merely
sweeping. The whole process shall be conducted in such manner as not
to loosen the coarse aggregates but vigorously enough to erp&- a fresh
clean-cut concrete surface.
18.104.22.168 Should the next lift be delayed, the contact surface shall
be kept wet and covered so as tr3 minimize the evalmration of curing water
which may cause an injurious coating on the joint. Where necessary all
defective and undesirable concrete shall be removed by chipping and
picking by hand or, if so required, by wet sand blasting the top to a depth
just sufficient to expose a fresh, clean-cut surface over the entire area,
which shall then be thoroughly flushed with water. Every precaution
shall be taken to afford suitable bond for the succeeding lift.
22.214.171.124 Immediately before depositing fresh concrete, the contact
surface shall again be gone over and thoroughly washed to remove all
debris and loose material.
The final pick-up of loose materials shall be
made near the centre of the joint and away from the outside edges of the
Dry contact surfaces shall be kept saturated with water for not
less than 24 hours, but all standing water shall be removed from deprcssions before-spreading the mortar layer. The joint shall then be coveicd
with about 1.5 cm ( or ) in ) of mortar (in the same proportion as in the
original concrete but not lower than 1: 2 ) and the concrete immediately
-deposited thereon according to the manner speciticd under 4.9.2 for rock
126.96.36.199 Hardened surfac1.s of old ITI:IW~W on which new. concrete
is to be placed shall, unless otherwise or&red, be prepared in the same
manner as provided for rock foundations under 4.9.2.
4.10.6 P94eumatic Plmitg - Tht: pneumatic method of placing concrete or mortar may IN: used to: sucl1 sj)ecial purposes as tulintl linings,
under-pinning foundations, prcssurc grouting, etc, provided special permission has been granted and the method approved.
4.10.7 Rule 0.fPltrcing --- Concr&ng shall be continued without avoidable intcrruptioii until the structure or ycction is complctcd or until satisfactory construction joints can bc made. Concrctc slinll not bc placed
faster than the placing crew ~a.11 compact it properly. In placing concrete in thin mcmbcrs and columns, prccautious shall he taken against too
rapid a placement which may result in movomcnt or fsilurr of the form
due to excessive internal pressure. An interval of at least 4 and prcferably 24 hours should elapse bctwecn the completion of columns alid
walls and the placing of slabs, beams _orgirders supported by them in order
All concrete shall be placed in apto avoid cracking due to settlement.
proximately horizont‘al lifts not exceeding 150 cm ( or 5 ft ) in th...
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This document was uploaded on 10/01/2013.
- Fall '13