concrete works specification

Concrete Works Specification

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Concrete for Structure

General

Note: This section is applicable to all kinds of concrete works in the Contract. Specifications for

particular aspects of concrete work are found in other Sections where applicable.

Cement

Cement shall be either Portland cement or Portland blast furnace cement of the best Malaysia

manufacture approved by the JKR.

Portland cement shall comply with the requirements of BS 12 and Portland and blast-furnace

cement shall comply with the requirements of BS 146.

Manufacturer’s certificates of test will in general be accepted as proof of soundness, but the

S.O. may require additional tests to be carried out on any cement which appears to him to have

deteriorated thorough age, damage to containers, improper storage or for any other reason.

The S.O. may, without tests being made, order that any bag of cement, a portion of the contents

of which has hardened, or which appears to be defective in any other way, to be removed from

the Site forthwith.

The Contractor may elect to use either ordinary of rapid hardening Portland cement of Portland

blast-furnace cement, but no extra will be paid on account of using a cement priced higher than

the price entered for ordinary Portland Cement in the Contract, unless work using such cement

is ordered by the S.O.

The cement shall be transported to the site in covered vehicles adequately protected against the

entrance of water. It shall be stored in a weather-proof cement store to the approval of the S.O.

and shall be taken for use in the works in the order of its delivery into the store.

Where cement is delivered in bulk containers, additional arrangements are to be made for bulk

storage to the approval of the S.O., or at his own expense the Contractor may use his bulk

container lorries for storage.

Aggregates

Coarse aggregates shall be ‘granite’ or other hard stone from a source approved by the S.O.

Limestone aggregates shall NOT be used unless otherwise specified.


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a) Quality

Aggregate is to consist of naturally occurring sand, gravel of rock, whole or crushed or a

combination thereof, and is to be hard, durable, clean and free from adherent coatings,

such as clay.

Aggregates are not to contain harmful impurities such as iron pyrites, coal, mica, shale

or similar laminated materials.

Aggregates are not to contain flaky or elongated particles.

Qualitative tests are to be carried out on all aggregates in accordance with BS 812. The

Contractor is to execute all sampling and testing at his own expense. If so directed he is

to deliver duplicate samples to the S.O., properly packed and clearly labeled so as to be

identifiable with the samples used in the tests. The results of the tests are to be submitted

to the S.O. for this approval prior to the delivery or use of the aggregates.

When tested in accordance with the methods described in BS 812 aggregates are to

have the following properties:

I. Aggregate crushing value : not more than 45 %

II. Flakiness Index : not more than 30 %

Unless evidence of general performance is offered which is satisfactory to the S.O., the

maximum quantities of clay, silt and fine dust, and of organic impurities, are not to exceed

the limits given in clause 5d of BS 882.

b) Definitions

The terms ‘fine aggregate’ ‘coarse aggregate’ and ‘all-in aggregate’, are as defined in

clause 2 of BS 882.

c) Grading of Aggregates

The grading of course, fine and all-in aggregates when tested in accordance with BS 812

are to be within the limits defined in the relevant table in BS 882 as specified and

reproduced hereunder:


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B.S. 410 1976 Coarse Aggregate -

Fine Aggregate Fine Aggregate All-In-Aggregate

Test PERCENTAGES BY WEIGHT PASSING B.S. SIEVE

Sieve

Size

Nominal

40 mm

Nominal

20 mm

Grading

Zone 2

Grading

Zone 3

40 mm

Nominal

Size

20 mm

Nominal

Size

75 mm

40 mm

20 mm

10 mm

5 mm

No.7

No. 14

No. 25

No. 52

No. 100

100

95 - 100

30 -70

10-35

0 - 5

-

-

-

-

-

-

-

-

100

90 - 100

75 - 100

55 - 90

35 - 59

8 - 30

0 -10

-

-

-

100

90 - 100

85 - 100

75 - 100

60 - 79

12 - 40

0 -10

-

-

-

100

90 - 100

85 - 100

75 - 100

60 - 79

12 - 40

0 -10

100

95 - 100

45 - 75

-

24 - 45

-

-

8 - 30

-

0 - 6

-

100

95 - 100

-

3- 5

-

-

-

10 - 35

Sampling and Testing of Aggregates

Samples of the fine and coarse aggregates approved by the Superintending Officer shall be kept

on site, and shall give a fair indication of the general quality of the aggregates for comparison

with the aggregates delivered during the course of work. Tests shall be carried out on samples of

the latter taken at intervals as required by the Superintending Officer. The method of sampling

and the amount of aggregates to be provided for the tests shall be in accordance with BS

812:1975 Section One “Sampling and Submission of Samples”. The tests shall be those laid down

in BS 812:1975 Section Two to Six inclusive. The tests shall be carried out by the Superintending

Office who may, at his discretion either reject the batch from which the sample was taken, order

it to be washed and/or screened, or permit it to be used with variations in the proportions of

the concrete mixes specified. Any batch aggregate rejected by the Superintending Officer shall

be removed from the works site forthwith.

Handling Aggregates

The sitting and preparation of sites for stock piles of aggregates, the numbers of stock piles, the

sizes of the piles and the method adopted to prevent ‘coning’ or other segregation of

component sizes are to be arranged with the S.O.

Stock piles are to be on concrete or other approved hard surface laid to falls to that water is not

retained in the bas of the stock piles.

Stock piles are to be at least 6 ft. (1.8) in height and built up in layers of not more than 3 ft.

(0.9m) in thickness. Each layer is to be completely in place before beginning the next, which is

not to be allowed to ‘cone’ down over the under layer.

If aggregates of different grading are stockpiled in close proximity, the stock piles are to be

separated by bulkheads.


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All aggregates are to be handled from the stock pile or other source to the batching plant in

such a manner as to secure a typical grading of the material, care being taken to avoid crushing

the aggregates and that they remain free from extraneous matter.

All aggregates produce or handled by hydraulic methods and all washed aggregates are to be

stockpiled for draining least 24 hours before being batched.

Water

Only clean fresh water free from impurities is to be used. Where the water is not obtained from

a public supply the Contractor is to submit a report of its composition to the S.O. The water

must comply with BS 3148.

Batching Concrete

When cement is stored in bulk it is to be measured by weight, when it is supplied in bags each

batch of concrete is to contain a whole numbers of bags of cement.

a) Batching by Weight

The cement and each size of aggregates are to be measured by weight the water may be

measured by weight or volume. The weight batching machines used are to be kept in

good condition while in use under the Contract.

b) Batching by Volume

Where batching by volume is allowed the aggregates are to be measured by volume, the

cement by weight and the water by volume or weight.

The containers in which the aggregates are measured are to be of such shape that their

volume can easily be checked by measurement. Their depths are to be at least equal to

their greatest width and their cross section at the top level of the aggregate is not to

exceed 600 mm x 600 mm.

Mixing Concrete

Concrete required to be mixed mechanically is to be mixed in a batch mixer of approved type

which is to be in good condition and is to have a drum rotating about a horizontal or inclined

axis. Each mixer is to be fitted with a water measuring device capable of accurate measurement

to 1/2 gallon of a 2 cubic yard mixer and pro-rata for smaller sizes and so arrange that the

accuracy is not affected by variations in the pressure in the water supply line.

The siting of the batching and mixing plant is to be arranged with the S.O.


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The fine and coarse aggregates and the cement are to be mixed for at least 4 turns of the drum,

after which the required amount of water is to be added gradually whilst the drum is in motion

and the concrete is then to be mixed for at least 2 minutes and until of a uniform colour and

consistency. (The time may be reduced to 70 seconds where Koehring or other similar and

approved double drum mixer are used).

The amount of concrete mixed in any one batch is not to exceed the rated capacity of the mixer.

The whole of the mixed batch is to be removed before materials for a fresh batch enter the

drum.

On cessation of work, including all stoppages exceeding 20 minutes, the mixer and all handling

plant are to be washed out with clean water.

Concrete mixed as above is not be modified by the addition of water or otherwise in order to

facilitate handling or for any other purpose.

Water / Cement ratio

The term water/cement ratio means the ratio by weight of water to cement in the mix,

expressed as a decimal. The water is that which is free to combine with the cement in the mix,

including free water in the aggregate, but not water absorbed by the aggregate.

When determining the moisture content of the aggregate for this purpose, the aggregate is not

being dried in an oven, but is to be surface-dried with absorbent cloth or similar material. The

moisture content of the fine aggregate may be calculated in accordance with Section 4 of BS

812.

Aggregate / Cement ratio

The term aggregate/cement ration means the ratio by weight of aggregate to cement in the mix

expressed in decimal terms.

For this purpose the aggregate is assumed to be surface-dry as specified in the previous clause.

Placing Concrete

Concrete shall be placed as soon as possible after mixing and shall be thoroughly compacted by

both hand tamping and mechanical vibration. It shall be thoroughly worked into the corners of

formwork by hand tamping. After tamping into place the concrete shall not be subjected to

disturbance other than such as is incidental to compaction by vibration.

The concrete shall be placed in the formwork in layers not exceeding 600 mm deep in walls and

deep beams and placed to the full depth in slabs and small beams.


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Vibrators hall be used solely for compacting the concrete and not for distributing it into place.

Concreting shall be carried out continuously and up to predetermined construction joints, in one

sequence of operation. The surface of the concrete shall be maintained reasonably level during

placing.

In the event of unavoidable stoppage in positions not determined the concreting shall be

terminated on horizontal planes, and by the sue of stopping-off boards, against vertical faces.

A record shall be kept on the Site of the time and date of placing the concrete in each portion of

any structure together with the reference numbers of the test cubes pertaining to the batches

of concrete placed in particular of any structure.

Compacting Concrete

Concrete maintained between the two faces of forms shall be compacted by vibrators of the

internal type and concrete in slabs shall be compacted either by vibrators of the pan type or by a

vibrating screed. The vibrators shall be of ample power and of a kind approved by the S.O. and

shall be operated by workmen skilled in their use who shall be additional to the labourers

employed on placing and tamping the concrete.

The internal vibrators shall be inserted and withdrawn slowly and at uniform rate of

approximately 100 mm per second. Compaction shall be deemed to be compete when cement

mortar appears in a circle around the vibrator. Over-vibration, leading to segregation of the mix,

must be avoided. The vibrators shall be inserted at points judged by the area of mortar showing

after compaction with a certain allowance made for overlapping. They shall not be allowed to

come into contact with the formwork or the reinforcement and shall be inserted at a distance of

75 mm from the former.

The pan vibrators shall be placed on the surface of the concrete, which shall have previously

been tamped and levelled and an allowance in height left for compaction, until the cement

mortar appears under the pan. The vibrator shall then be lifted and placed on the adjoining

surface and the operation repeated until the whole surface has been compacted. Alternatively a

vibrating screed spanning the full width of the surface may be used.

Concrete Proportion (Based on C.P 110)

The grade of concrete used in all reinforced concrete members for the works shall be as stated

or indicated in the Drawing. The coarse aggregates shall be as stated or indicated in the

Drawing. The coarse aggregates shall be 20 mm nominal maximum size, unless otherwise stated.

The proportions of materials per 50 kg bag of cement for the various grades of concrete shall be

as stated in the following tables obtained from CP 110. Concrete mixes of grade higher than


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grade 30 (used for e.g. in prestressed concrete) where specified, shall be designed as specified in

Clause 13C of this section.

Prescribed mixes for normal structural concrete per CP 110: proportions per 50 kg bag of cement

Concrete

grade

Nominal maximum size of

Aggregate (mm)

40 20 14 10

Workability Medium High Medium High Medium High Medium High

15

Total aggregate (kg)

Fine aggregate (%)

Vol. of finished concrete (m3

)

370

30 – 45

0.200

330

30 – 45

0.184

320

35 – 50

0.178

280

35 – 50

0.160

- - - -

20


Sand: Zone 1 (%)

Zone 2 (%)

Zone 3 (%)


)

305

35

30

30

0.165

270

40

35

30

0.155

280

40

35

30

0.156

250

45

40

35

0.143

255

45

40

35

0.146

220

50

45

40

0.130

240

50

45

40

0.137

200

55

50

45

0.121

25


Sand: Zone 1 (%)

Zone 2 (%)

Zone 3 (%)


)

265

35

30

30

0.147

240

40

35

30

0.137

240

40

35

30

0.137

215

45

40

35

0.127

220

45

40

35

0.130

195

50

45

40

0.118

210

50

45

40

0.124

175

55

50

45

0.110

30


Sand: Zone 1 (%)

Zone 2 (%)

Zone 3 (%)


)

235

35

30

30

0.134

215

40

35

30

0.127

210

40

35

30

0.124

190

45

40

35

0.115

195

45

40

35

0.115

170

50

45

40

0.106

180

50

45

40

0.109

150

55

50

45

0.097

Percentages are by weight of fine aggregate in weight of total dry aggregates. Volumes of fully-

compacted finished concrete are approximate only. Cement must comply with BS 12 of BS 146

aggregates with BS 882

Concrete Proportions (Nominal Mixes)

Where nominal mixes have been specified or so indicated in the drawings, the concrete shall be

proportional in the following manner: cement by weight or bags of 50 kg each, aggregated by

weight, water by volume. The fine and coarse aggregates shall be measured separately. The

proportions of materials for various nominal mixes shall be as follows:

Nominal mix Portland cement (kg) Fine Aggregate (kg) Coarse Aggregate (kg) Water including water

in aggregate (litres)

1 : 3 : 6 0 150 296 As directed by the S.O.

1 : 2 : 4 50 107 199 28.0

1 : 1 1/2 : 3 50 82 150 25.5


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The weights of the fine and coarse aggregates specified in the above table refer to the materials

in the drawing state. Tests shall be carried out twice daily, or more frequently if considered

necessary by the S.O. to ascertain the moisture content of the aggregates. Allowances shall be

made for the water contained in the aggregates when calculating the quantity of water to be

added to the mix.

While the proportions of the mix are to be generally as given in the above table, the

Superintending Officer shall have the right to order variations in these proportions should tests

show such variations to be necessary to produce a dense concrete of the specified strength and

of a consistency that will permit of its being worked into position and compacted satisfactorily in

the different parts of the work. The proportions of the mix as specified in the are expected to

produce works cube strengths in excess of the requirements of the Specification and workability

sufficient to ensure that the concrete can be worked and fully compacted using the methods of

vibration specified in this section. If, however, it is shown during the preliminary trials and the

course of the Works that the concrete mix is stiffer that can be placed satisfactorily, an

adjustment of up to 5 per cent may be made in the water/cement ratio but any further

adjustment of the mix shall be made by increasing the proportion of both the water and the

cement without increasing the water/cement ratio. The cement proportions shall be increased

up to 10 per cent if the cube strengths fall below those specified.

Design Mixes

Concrete mix of grade higher than grade 30 for prestressed concrete and certain portions of the

work as specified as shown in the drawings shall be designed by the Contractor and the mix

approved by the S.O. prior to concreting. The method of carry out designed mixes shall be in

accordance with the recommendation of Section 6.5 “Requirements for Designed Mixes” of CP

110: Part 1 : 1972.

Grout

Where grout is shown on the Drawings this shall consist of a 1 : 3 cement/sand slurry containing

only sufficient water to ensure the desired workability.

Additives

The use of additives in the concrete, for the purpose of promoting rapid hardening, for water-

proofing, for creasing workability of for any other reason, may permitted in special

circumstances.

Such additives shall be a brand and type, approved by the S.O. and shall be used strictly in

accordance with the makers’ instructions. Permission for their use must be obtained from the

S.O. who may require test to be carried out with the additives before granting such permission.


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Steel Works Built Into Concrete

The surface of all structural steel which is to be built or cast in the concrete of any structure

shall be thoroughly cleaned of any protective paint or other adherent coatings and shall be free

from rust, oil or any other deleterious matter immediately before casting the concrete.

Transporting Concrete

Concrete shall be transported from the mixer to the place of deposit in the Works as rapidly as

practicable and by means which will prevent segregation of the materials and/or loss or

contamination of ingredients.

It shall be deposited as near practicable to its final position to avoid re-handling or flowing.

The concrete shall be conveyed by chutes only with the express permission of the S.O. and

arrangements for these shall be to his satisfaction.

Sampling and Testing Concrete for Consistency

While work on concreting is in progress, test on the workability of the mix shall be carried out

twice daily and, in addition whenever any materials or the proportions of the mix are changed,

or when directed by the S.O. The tests shall consist of either the slump test or the Compacting

Factor tests, as described in BS. 1881.

Sampling and Testing Concrete for Strength

While work on concreting is in progress, sample of the concrete as placed shall be taken and

work test cubes made from them. While at the same time consistency tests shall be made from

the samples and the slump and/or compacting factors recorded.

A record of these tests shall be kept on the works, identifying them with the part of the work

executed. The samples shall be taken and the test cubes made and matured, in accordance with

the standard methods laid down in BS 1881.

A set of six 150 mm cubes shall be cast each day when concreting is in progress. Where more

than 130 m3 of concrete are placed in a day, a set of six cubes shall be cast from each 130 m3 of

such concrete placed that day. The Contractor shall provide for all attendance and apparatus

necessary for carrying out all the tests required.

Three of the cubes shall be tested at age 7 days and three at age 28 days. The strength

requirement shall be considered to be satisfied if none of the strength of the three cubes at

each age is below the specified works test cube strength for the respective age, or if the average

strength of the three cubes is not less than the specified cube strength and the difference

between the greatest and the lowest strengths is not more than 20 % of that average.


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If the 7 days strength exceeds that specified, the 28 days test may be dispensed with at the

discretion of the S.O.

When the cubes tested at 7 days show a resistance of crushing less than that specified, the right

is reserved by the S.O. to order work on concreting to stop until results of the tests at 28 days

are known. If the resistance to crushing of the cubes at 28 days is less than that specified, the

S.O. has the power to reject and have any concrete from which the test cubes were taken to be

cut and removed.

When the cube failures occur, cores may, at the discretion of the S.O., be taken from the in-situ

concrete which the cube represents. Such costs and that of subsequent tests carried out on the

cores shall be borne by the Contractor.

The specified minimum works cube strength of various concrete mixes is as follows:

Concrete Grade 7 days cube strength N/mm3

28 days cube strength

N/mm3

Prescribed mixes for normal

structural concrete as per CP

110

20

25

30

14.3

17.9

21.9

20

25

30

Nominal mixes

1 : 3 : 6

1 : 2 : 4

1 : 1 1/2 : 3

8.5

14.0

17.0

12.5

20.5

26

Designed mixes Grades higher As per requirements in “Requirements for Designed Mixes” of

Section 6.5. of CP 110 : Part 1 : 1972.

Construction Joints

Construction joints shall be located in positions directed by the S.O. Such joints shall be in a

horizontal plane when forming the upper surface of lifts in beams. Wooden fillets 50 mm x 50

mm, slightly chamfered shall be fixed to forms at 600 mm centers so as to produces rebates in

the face of the joints.

Joints shall have all excess water and laitance removed from the surface after the concrete has

been compacted and before it has set. Before concreting is resumed, the face of the joint

already formed shall have all further laitance removed and shall be well roughened, scrubbed

clean and thoroughly saturated with water.

The face shall then be rendered with 12 mm thick layer of mortar, composed of equal parts of

Portland Cement and sand, against which the freshly mixed concrete shall be immediately

deposited and thoroughly tamped.


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Curing and Protection Of Concrete

Exposed surfaces, immediately after final set, shall be protected from the sun in a manner

approved by the S.O. All concrete shall be well watered after it has set and shall be kept

continuously damp until deemed by the S.O. to be thoroughly cured.

Provision shall be made for adequate water distribution to all parts of the Site, so that, if

required this treatment can be continued efficiently throughout the whole period of

construction on any part of the Site.

In order to keep the concrete damp as specified all exposed surfaces shall be covered with

continuously damped gunny bags or shall have water impounded on them for the full period of

curing, which shall be not less ten days.

All work shall be protected from damage by shock or overloading or falling earth, etc.

Surface Treatment

As soon as the formwork has been removed and after inspection by the S.O. honeycombing or

small holes in the surfaces of the concrete shall be filled with cement mortar composed of equal

parts of Portland Cement and sand. No further treatment shall be given to concealed surfaces.

Permanently visible surfaces shall be then treated as follows:-

a) All projecting imperfections shall be rubbed down with carborundum stone or other

materials approved by the S.O. and the grit or dirt there from thoroughly washed off

with clean water.

b) As a separate operation, after completion of (i) above, surfaces shall be brushed over

with a coating of Portland cement wash which shall be rubbed into the pores and

smoothed off with carborundum blocks, The finished surfaces shall be protected against

drying too rapidly by the use of damp sacking or by other approved means.

c) Surfaces for which formwork is not provided shall be floated to a smooth finish with a

wooden float after compaction of the concrete.

Formwork

Formwork shall be constructed of sound, well-seasoned timber of such quality and strength as

will ensure complete rigidity throughout the placing, ramming, vibration and setting of the

concrete: it shall be sufficiently tight to prevent loss of liquid grout or mortar from the concrete.

Where formwork is not provided with special lining the faces in contact with concrete shall be

planed smooth, true to alignment and free from surface imperfections and the joints between

boards shall be tongued and grooved or caulked with tight-fitting fillets recessed into adjacent

boards and covering the joint.


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Internal ties or struts shall be avoided as far as possible, and if used, they shall be of metal and

capable of removal without injury to the concrete. No part of any metal tie or spacer, remaining

permanently embedded in the concrete, shall be nearer than 40 mm to the finished surface of

the concrete.

Construction details shall be arrange to permit each removal of the formwork and wedges and

bolts shall be employed wherever possible in preference to nails.

If he so choose the Contractor may, with the approval of the S.O. use steel formwork. This

should be so constructed as to remain sufficiently rigid during the placing of the concrete and

should be sufficiently tight to prevent loss of liquid grout or mortar from the concrete.

The detailed design of any formwork should be submitted to the S.O. for his approval.

Lining to Formwork

Formwork for all permanently visible concrete surfaces shall be lined with lining material

approved by the S.O. The Contractor may use linings to formwork for other surfaces if he so

desires.

The lining shall be carefully joined and finished so as to present a perfectly smooth and even

surface.

Cleaning and Treatment of Formwork

Before concrete is deposited, the forms shall be thoroughly cleaned and freed from sawdust

shavings, duct, mud or other debris by hosing with clean water and temporary opening shall be

provided in the forms to drain away and water and rubbish.

Unless otherwise directed by the S.O. the inside surface of forms shall be coated with lime wash

or approved mould oil. There shall be no excess coating material in the forms prior to

concreting.

All formwork shall be inspected by the S.O. after preparation and immediately prior to

depositing concrete and no concrete shall be deposited until approval of the formwork has been

obtained from the S.O.

Removal of Formwork

Formwork shall be removed without such shock or over vibration as would damage the

concrete.

Before general removal of the formwork the concrete shall be exposed over a small area in

order to ascertain that the concrete has sufficiently hardened.


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The table below specifies the minimum periods which shall elapse between the placing of the

concrete and the removal of the formwork but compliance with these requirements shall not

relieve the Contractor of the obligation to delay the removal of formwork, until the concrete has

sufficiently hardened.

Position of Formwork Ordinary Portland (Days) Rapid Hardening Portland

Cement (Days)

Slabs (props left under) Beam Soffits (props left under) Beam/Slab Sides, Walls, & Columns (Unloaded) Removal of Props to Slab Removal of Props to Beams

4 8 3

10 21

3 5 2 5 8

The table above is given as a guide for normal and rapid-hardening Portland Cement and gives

the minimum striking times which will normally be approved by the S.O. but who may, at his

discretion, increase the above times if the considers such increase to be necessary.

Any variations proposed by the Contractor by virtue of the use of other types of cement

additives hall be subject to the approval of the S.O.

Reinforcement

Reinforcing bars shall comply with the requirements of BS 785 of BS 1144.

The Contractor shall furnish, for reinforcement supplied by him, manufactures certificates and

these shall be submitted for acceptance by the S.O. before any material is brought onto the Site.

In addition, the Contractor shall, on request, furnish the S.O. with a test sheet for any batch

bars, giving the results of each of the mechanical tests required under BS 785.

In the event of any reinforcement being found to be not in accordance with BS 785 in the course

of being worked, it may be rejected by the S.O. notwithstanding any previous acceptance on the

strength of the test certificates and the S.O. may call for additional tests to be made on samples

taken from the batch of bars form which the faulty reinforcement came. If the samples do not

comply with the BS 785 then the S.O. may reject the whole batch and require its removal from

the Site. High tensile fabric when used shall comply with the requirement of BS 1221.

Cleaning / Bending Reinforcement

The reinforcement shall be cleaned free from loose mill scale and rust before being placed in the

forms and shall be free from these and from oil, grease or other harmful matter at the time

when the concrete is placed.

The reinforcement shall be bent cold in an approved bar-bending machine. The bending

dimensions and tolerances and the dimensions of end anchorages, hooks, binders, stirrups, links

and the like where used shall be in accordance with BS 1478.


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The internal radius at the corner of stirrups and binders shall not be less than the radius of the

longitudinal bars embraced by the stirrups or binders.

Welding Reinforcement

Welding of reinforcement by electric are may be permitted by the S.O. under suitable conditions

and with suitable safeguards.

Welding if permitted shall be carried out in accordance with BS 1856. But welds shall be of the

double wire type and two butt weld bend tests shall be carried out on a specimen prepared to

represent each form of butt welded joint used in welding the reinforcement and for each

position of welding.

The method of making butt-weld test shall be that laid down in BS 709. The specimen shall pass

the tests to the satisfaction of the S.O. before approval is accorded to use the joint which the

specimen represents. Tack Welds between reinforcing bars, used merely to fix them in position

shall not be subjected to these tests.

Placing Reinforcement

The reinforcement shall be placed in the forms and held firm against displacement by approved

types of small precast concrete fixing blocks and wire ties in the position shown in the Drawings.

Fixing blocks may be left embedded in the concrete in cases where the S.O. approves.

Bars intended to be in contact when passing each other shall be securely held together at

intersection points with typing wire. Binders and stirrups shall tightly embrace the longitudinal

reinforcement to which they shall be securely wired or spot welded.

The wire ties shall be No. 16. S.W.G soft annealed iron wire; the ends shall be turned in from the

face of the formwork and shall not be left projecting beyond the reinforcing bars.

The reinforcement shall be inspected and passed by the S.O. or his representative before

concrete is placed in the forms.

The specified cover to the reinforcement shall be given when the reinforcement is placed in the

forms and shall be maintained during concreting. PRECAST CONCRETE

Pre-Cast Units

Where indicated on the Drawings components are to be precast in the mixes specified.

The clauses of the Section shall be generally applicable to this class of work together with the

following more specific clauses.


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Manufacture

Concreting of each component shall be carried out in on continuous operation, and vibration,

either by the methods specified in clause 4.12 by means of vibrators attached to the formwork,

is to be used to ensure adequate compaction

Formwork

Lined formwork as specified in clause 18 is to be used for the precast components which are to

be kept in the forms for a period of eight days.

Provided that the concrete has become sufficiently hard the formwork may then be removed

but the components must be kept adequately supported on level blocks for a further period of

six days before removal for stacking.

Curing

Throughout the above period of hardening the components shall be cured by covering with

sacking which shall kept continuously damp by watering.

Handling

Lifting and handling of precast components shall be carried out in a manner that will avoid

damage or overstressing, and when lifting points are indicated on the Drawings the components

shall be lifted by slinging at these points and at no other.

Should any components in the opinion the S.O. be so damaged by mishandling as to be

inadequate for its purpose the S.O. may order its removal from the site to be replaced at the

Contractor’s expense.

Stacking

Components shall be stacked in such a manner that no damage is caused to them by the weight

of upper layers of the stack, and when necessary they shall be placed in such a manner that

their removal in correct order or age is facilitated.

Fittings

All fittings, splice bars, etc. as shown on the Drawings to be cast into precast components shall

be accurately positioned in the formwork and held to maintain their position during concreting.

The fittings shall be protected after removal of the formwork to ensure that during subsequent

handling and stacking no damage is cause to them.


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Positioning

The components shall be fixed accurately in the positions shown on the Drawings. They shall be

true in alignment and level and where units are reinforced in one face only every care shall be

taken to ensure the placing of the units correctly as shown on the Drawings.

concrete works specification

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