Tender Document - irpmu.railnet.gov.in
Tender Document - irpmu.railnet.gov.in
Tender Document - irpmu.railnet.gov.in
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25.1.2 Batch mixers will be tested for their performance <strong>in</strong> accordance with IS: 4634 or<br />
such other testes as the Eng<strong>in</strong>eer-<strong>in</strong>-charge may require.<br />
25.1.3 Mixers, which have been out of use for more than 30 m<strong>in</strong>utes, shall be thoroughly<br />
cleaned before putt<strong>in</strong>g <strong>in</strong> a new batch. Unless otherwise agreed to by the<br />
Eng<strong>in</strong>eer. The first batch of concrete from the mixer shall conta<strong>in</strong> only two thirds<br />
of the normal quantity of coarse aggregate. Mix<strong>in</strong>g plant shall be thoroughly<br />
cleaned before chang<strong>in</strong>g from one type of cement to another.<br />
25.1.4 Concrete shall not be mixed when the air temperature <strong>in</strong> the shade is below 3<br />
degree (Celsius 93.8 degree F) unless special precautions are taken which have<br />
been approved by the Eng<strong>in</strong>eer.<br />
Dur<strong>in</strong>g the hot weather the contractor shall ensure that the constituent materials<br />
are sufficiently cool to prevent the concrete from stiffen<strong>in</strong>g <strong>in</strong> the <strong>in</strong>terval between<br />
its discharge from the mixer and its f<strong>in</strong>al deposition.<br />
25.1.5 Concrete shall be mixed for not less than 120 seconds and nor more than 5<br />
m<strong>in</strong>utes from the time all constituents have been <strong>in</strong>troduced <strong>in</strong>to the mixer and till<br />
all materials are uniformly mixed.<br />
26.0 COMPACTION OF CONCRETE<br />
26.1 All concrete members shall be compacted by vibration. Generally <strong>in</strong>ternal<br />
vibrators shall be used on all sections that are sufficiently large to admit them.<br />
26.1. Vibrator shall have operat<strong>in</strong>g frequency of at least 3600 impulses per m<strong>in</strong>ute.<br />
Higher frequencies up to twice the m<strong>in</strong>imum are preferred.<br />
26.2 The follow<strong>in</strong>g techniques shall be followed for vibration:-<br />
i) Vibrators shall be so distributed so that the concrete becomes uniformly<br />
dense and plastic mass.<br />
ii)<br />
iii)<br />
iv)<br />
Vibrators shall be used for compaction only, not for mov<strong>in</strong>g concrete<br />
horizontally along the form.<br />
For horizontal and vertical operations of form vibrators, the spac<strong>in</strong>g of po<strong>in</strong>ts<br />
of vibration shall be such that the zones of <strong>in</strong>fluence overlap.<br />
For concrete deposited <strong>in</strong> one layer the vibrators shall be <strong>in</strong>serted vertically<br />
and allowed to s<strong>in</strong>k due to its own weight to the bottom of the layer and be<br />
slowly withdrawn. For concrete deposited <strong>in</strong> more than one layers, the<br />
vibrator shall penetrate the surface of the previous layer. Compaction shall<br />
be accord<strong>in</strong>g to clause 13.3 of IS: 456-2000.<br />
27.0 CURING<br />
All concrete work <strong>in</strong> cement mortar/plaster po<strong>in</strong>t<strong>in</strong>g etc. shall be cont<strong>in</strong>uously<br />
cured for the prescribed period as per directions of the Eng<strong>in</strong>eer-<strong>in</strong>-charge ,<br />
cur<strong>in</strong>g shall be done by cover<strong>in</strong>g the newly laid concrete with gunny bags and<br />
keep<strong>in</strong>g them wet cont<strong>in</strong>uously. If it is found that the contractor is not properly<br />
OS/Works 57
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