SECTION 2

SECTION 2CONCRETE WORK

1.GENERALLYMaterial used in the works shall be of the qualities and kinds specified herein and equal to approved sample. Delivery shall be made sufficiently in advance to enable further samples to be taken and tested if required. No material shall be used until approved and material not approved shall be immediately removed from the works at the Contractors cost.

In so far as materials practicable, or unless otherwise specified, shall comply with the appropriate British Standard where these exist, with preference for material of local manufacture. They shall be obtained from suppliers or manufacturers. Who shall be approved by the Architect. The Contractor may ascertain from the Architect, the names of such approved suppliers or manufacturers. Where a British Standard quoted in this Specification has been amended or superceded, the current standard will apply. If required the Contractor shall supply to the Architect the appropriate certificate with the standard.

Material shall be transported, handed and stored on site, or elsewhere in such a manner as to prevent damage, deterioration or contamination.

All concrete works shall be carried out in accordance with the British Standard Code of Practice C.P. 114 for The Structural Use of Reinforced Concrete in Building and British Standard Code of Practice C.P 110 for The Structural Use of Concrete.

2.CEMENT

All cement used in the works shall be Ordinary Portland Cement complying with B.S 12 for ordinary and rapid hardening Portland Cement.

The age of the cement at time of delivery to the site shall not be more than two months and the cement shall be used within two months of delivery. With each delivery, the Contractor shall send to the Architect a memo of the quantity delivered and the manufacturers test certificate. The Architect shall have access to the cement store all reasonable consignments and draw samples for testing if he so requires.

All cement shall be stored in a dry shed with a raised floor must be completely weatherproof but ventilated. Different types of cement shall be stored in independent sections of the store. No other material shall be stored with it.

3.TESTING OF CEMENT

`The manufacturers test certificate will normally be accepted as proof of compliance with the specification but the Architect reserves the right to carry out further test is an approved laboratoryThe Architect may, without test being made, order that any bags of cement a portion of the contents of which has hardened, or which appeared to be defective in any way be removed from the site.

The compressive test and not the tensile shall be used to determine the strength of cement.

4.ADDITIVES

No additives admixtures, plasticizers or admixtures for extra workability shall be used without the Architects written instructions. Their use must also be in accordance with the manufacturers instructions and the approval of the Architect. The effect of additives on concrete strength must be predetermined and if ordered, tests are to be carried out to determine strength.

5.WATER

Only clean water from P.U.Bs mains shall be used for concreting and all other purpose.

6.AGGREGATE GENERALLY

All aggregate shall comply with B.S. 882. The use of all-in aggregate will not be permitted. Aggregates shall be obtained from one or more sources known to produce aggregates satisfactory for concrete. Aggregates shall be chemically inert, strong, hard, durable, and free from adhering coats, clay lumps, organic or other impurities that may cause corrosion of the reinforcement or may impair the strength or durability of the concrete. They shall not contain water soluble sulphur trioxide in excess of 0.1%.Aggregates which do not conform to the prescribed standard shall be sieved, washed, graded or rejected and replaced to the satisfaction of the Architect.

7.FINE AGGREGATES

Fine aggregate shall be fresh water river or pit sand, free from coagulated lumps, complying with B.S>882 Table 2. It shall not contain silt or other fine material exceeding 6% by volume when taken in the Standard Method given in B.S 812. Nor shall it contain organic material in sufficient quantity to show a Colour No.3 as described in the B.S. The satisfying of this requirement shall not be conclusive evidence that the aggregate is unacceptable or otherwise further tests may be necessary as determined by the Architect especially when new sources of supply are used.

8. COURSE AGGREGATE

Coarse aggregate shall comply with table of B.S.882

Coarse aggregate shall be crushed granite free from decomposed stone, clay, earth or other deleterious substances. Any Friable, flaky and laminated pieces, mica and shale shall only be present in such quantities as not to affect the strength and durability of concrete.

9.DELIVERY AND STORAGE OF AGGREGATE

Fine and course aggregate shall be delivered and stored separately on site. The storage areas shall be as clear as possible of trees and other sources of contamination by organic material. Aggregates shall be stored on a clean hard base, in separate compartment. Stockpiles of sand shall be allowed to the drain for several hours before use. Sample of the aggregate to be used in the works shall be supplied to the Architect prior to commencement of the works. On approval of the site sample the Contractor shall arrange for and make available ample supplies of both coarse and fine aggregate of the quality and colour selected as specified in the Contract.

10.TESTING OF AGGREGATE

Samples of the site and coarse aggregate shall be sent to an approved laboratory for testing prior to the commencement of the works. Further tests are to be carried out from time to time and when required by the Architect. Test are to be an accordance with B.S.812 and any aggregate which fails to comply with or has become adulterated with foreign matter shall be removed from the site.

11.PROPORTION OF MATERIAL IN CONCRETE

The measurement of all cement used in the works shall be solely by weight.

The unit of measurement for cement shall be one bag containing 50kg of cement, and in deciding the size of a batch of concrete, the contractor shall not allow for part bags to be used. If the contractor wishes to used in bulk, his method of obtaining the correct proportions of cement with the aggregate must be approved by the Architect before being put into effect.

The coarse and fine aggregate shall be proportioned by weight-batching machines. The accuracy of the weighing equipment shall be 2% of the required weight of cement or of the total weight of aggregate.

Before the commencement of work and subsequently as often as the Architect may direct, measuring equipment shall be calibrated with known weights.

The quantity of water used in each batch shall be accurately measured by means of a calibrated and readily adjustable device which will permit the discharge of water to the mixer only while the latter is being charged. After the devices has been set to discharge the given quantity of water, it shall not be altered or interfered with and any way without the knowledge and consent of the Architect.

PROPORTIONS OF MATERIAL IN CONCRETE (contd)

The accuracy of the measuring device shall be proved to the satisfaction of the Architect before any concrete is mixed and at such other times as the Architect may direct.

The whole of the concrete shall be dense, compact and thoroughly homogenous. It shall be placed in foundations, beams, columns, walls, floors, slabs, moulds or shuttering mixing as practicable and no concrete shall be placed without being thoroughly tamped, pricked with bars, well worked with spades and mechanically vibrated. Tamping and vibrating must be completed before the initial setting of the cement commences.

The concrete shall generally consist of material in the proportions given in the table below. These are nominal mixes specified in C.P 114.

The proportions for other grades of concrete shall be determined by the Contractor by approved methods for each grade specified.

GradeConcrete mixWeight of cementFine aggregate Dry Weight20 mm to 9 mm Aggregate Dry WeightMinimum Crushing Strength (7 days)Minimum Crushing Strength (28 days)

kgkgkgN/mm

35(1:1:1 concrete)5055752435

30(1:1:2 concrete)50651002130

25(1:1 1/2:3 concrete)50801451725

20(1:1 1/2:4 concrete)50901901421

15(1:3:6 concrete)501602908.714

The Architect shall, if he so desires, be present at all preliminary tests. As soon as possible after the acceptance of his tender, the Contractor shall make trial, mixes using samples of aggregates and cement typical of those to be used. If possible, the concreting plant and the means of transport to be employed in the work shall be used to make the trial mixes and to transport them a representative distance.

A clean dry mixer shall be used, and the first batch discarded. Preliminary test cubes shall be taken from the proposed mixes as follows:

a) For each grade other than (1:3:6) concrete, a set of nine cubes shall be made from each three consecutive batches. Three from each set of nine shall be tested at three days, at seven days and at fourteen days respectively. The tests on three days cubes are for early indications of the quality of mix.

b) The cubes shall be made, cured, stored, transported and tested in compression in accordance with B.S.1881. The test shall be carried out in a laboratory approved by the Architect.

c) At seven and fourteen days the following requirement shall be met. The average cube strength shall exceed the specified minimum by not less than twice the standard deviation; and

d) Concreting in the works shall not commence until the specified minimum cube strength at fourteen days has been attained. Before commencing the works, the Contractor shall submit to the Architect for this approval full details of the mixes he proposed to use; with their anticipated average strength, which shall be based on the satisfactory results of this preliminary tests.

e) Workability test shall be carried out in the preliminary trial mixes as specified under Works Testing of Concrete.

f) Once a concrete mix has been approved, no changes in the mix proportions shall be made without the prior approval of the Architect.

g) The water cement ratio shall be the minimum necessary to provide a sufficiently workable mix. The water cement ratio used in the approved trial mix shall not be exceeded except as specified. Whenever the source or quality of cement and/or aggregates is changed or whenever it is proposed to change the mix, the trial mix procedure shall be repeated.

h) The exact quantity of water to be added to each of mix shall be fixed by the Architect after trial mixes have been carried out.

The Architect reserves the right to modify, alter, improve and change the concrete mix from time to time.

No concrete shall be re-mixed after it has once become partially set or hard but shall be rejected and removed from the works.

12CONCRETE TESTS

The samples and testing of concrete in the works shall be undertaken in the following manner:a) Cube Tests

On each day when concreting is in progress, samples of each grade of the concrete as placed, other than (1:3:6) concrete, shall be taken and works test cubes made from each 50 mm of concrete or part thereof, while at the same time consistency test shall be made from the samples and the compacting factors or slumps recorded. A record of these tests shall be kept on the work, identifying them with the part of the work executed.

The placing of the concrete in the cube moulds and the compaction and curing of the cubes shall stimulate as loosely as practicable to the placing compaction and curing of the concrete in the works represented by the cubes. Samples shall be taken and the cubes made, In addition, whenever any of the material or proportion of the mix is changed or whenever so directed by the Architect. Six test cubes shall be made from each sample taken.

Three shall be tested after seven days and the remaining three after fourteen days, in an approved laboratory.

The number of cubes may be reduced by the Architect if consistently satisfactory results are obtained, or increase up to the maximum of twelve per sample when in the opinion of the Architect additional tests are required as for example in the early stages of the work.

The strength requirement for each grade of the concrete specified on the drawings shall be considered to be obtained if the strength of every cube individually satisfies the specified minimum given in the previous table or proportional minimum strength for grades not specified in the table and collective average cube strength of all the cubes exceed the specified minimum by not less than the standard deviation. If the tests result at any stage indicate that the specified requirement have not been complied with the Contractor shall advise the Architect accordingly and shall submit his proposals for adjusting the mix control before proceeding with the concreting. In addition when the cubes tested at seven days shown minimum cube strength less than stipulated above, the concreting works shall stop until the results at fourteen days are known.

If the minimum cube strength at fourteen days is less than that stipulated above, the Contractor shall, if ordered by the Architect:

Hack out remove and replace at the Contractors expense all concrete, mixed and placed on the day when the sample was taken, or Carry out such additional tests and other remedial works as the Architect may consider necessary at the Contractors expense.

The remedial measures to be undertaken shall be at the sole discretion of the Architect.

The sampling, making, curing and testing of the cubes shall be carried out by the Contractor who shall afford all facilities. The cubes shall be made and tested in the presence of the Architect or his representative.

Reports of all tests made shall be supplied to the Architect within twenty-four hours of the cubes being tested.

The remedial measures to be undertaken shall be at sole discretion of the Architect.

The sampling, making, curing and testing of the cubes shall be carried out by the Contractor who shall afford all facilities. The cubes shall be made and tested in the presence of the Architect or his representative.

Reports of all tests made shall be supplied to the Architect within twenty-four hours of the cubes being tested.

b)Workability

While work on concreting is in progress, the Contractor shall carry out in presence of the Architect or his representative tests on the workability of the mix three times daily and in addition whenever any materials or the proportions of the mix are changed, or whenever directed by the Architect. The tests shall, at the discretion of the Architect consist of either the Slump Test or the Compacting Factor Test, as described in B.S.1881. All necessary apparatus shall be supplied by the Contractor.

The slump or the compacting factory shall of least be consistent with the efficient working and full compaction of the concrete mix in the formwork using the specified methods of compaction so that the concrete cal be readily worked into the corners and angles of the formwork and around reinforcement without segregation of the material or bleeding of free water at the surface On striking the formwork the concrete shall present a face which is uniform, free of honeycombing, surface crazing, or excessive dusting.

The preparation and curing of concrete test cubes be carried out in accordance with the procedure laid in British Standard 1881.

The cost of making, curing and forwarding the concrete cubes for testing as well as the testing fees shall be borne entirely by the Contractor.

13.Mixing Concrete

All the plants and equipment used n mixing the concrete shall be maintained in good working condition. The Contractor's attention is especially drawn to the necessity of keeping these clean and free of hard or partially set cement. All concrete mixers shall comply with the requirements of B.S.1305 'Batch Type' Concrete Mixers.

Each batch of concrete shall be mixed for the at least two minutes or such other period as the Architect shall direct to ensure the thorough mixing of the ingredients but on no account shall mixing be carried out until segregation of the ingredients occurs. The period of mixing shall be measured from the time when all material and water are in the mixer.

Mixing Concrete (cont'd)

The entire contents of the mixer shall be discharge before materials of the succeeding batch are fed into the mixer. Materials spilled from a skip or other container shall not be used.

The weight of materials used for each batch shall not exceed the manufacturers rated capacities of the machines.

The Contractor shall not mix any concrete by hand unless permission has been obtained from the Architect in writing, and in the event of this being given, an addition of 10% of cement shall be made at the Contractor's expense.

14.Transporting Concrete

Concrete shall be transported from the place of mixing to the place of final deposit as rapidly as practicable by approved methods which shall prevent segregation, loss or contamination of any of the ingredients.

When barrows are used for transporting concrete, access to the forms shall be provided on a sufficient number of suspended runways placed clear of the reinforcement to ensure a smooth continuous flow of concrete and to avoid displacement or damage to the reinforcement.

All containers used for transporting concrete shall be thoroughly clean.

The written approval of the Architect must be obtained before any method involving the use of spouts, chutes or pumps as a means of transporting concrete is adopted.

15.PLACING OF CONCRETE

No concrete shall be placed until the disposition of the steel reinforcement has been checked and approved by the Architect.

Suspended runways for the workmen placing and vibrating the concrete are to be provided wherever possible and so constructed to avoid damaging and displacing the reinforcement, Steel fixers shall be constantly in attendance while concreting is in progress to maintain the reinforcement h correct positions. Concrete shall be placed in its final position as soon as possible after mixing and in such a manner as to avoid segregation of tie concrete and displacement of the reinforcement of formworks. The Contractor shall so organize his work as to ensure that placing of the concrete shall be continuous between specified and approved construction joints.

Concrete shall be placed by shovels or other approved implements and shall not be dropped from a height so as to cause segregation. Any concrete unused for more than fifteen minutes after mixing or any concrete dropped during transportation shall be rejected.

16. COMPACTION OF CONCRETE

Concrete shall be thoroughly compacted by means of mechanical vibration during the operation of placing and carefully work around the reinforcement and embedded fixtures (if any) and into corners of the formwork without disturbing them.

The Contractor shall supply sufficient vibrators of each type to ensure that vibration is carried out efficiently without delay and without breaks continuity throughout the operation of concrete placing. Hand compaction shall not be allowed without the prior approval of the Architect.

In general, vibration shall be continued until the concrete mass becomes plastic, mortar begins to come to the surface and air bubbles cease to appear. Over-vibration causing segregation, surface laitance or leakage through formwork shall be avoided.

Concrete shall be placed in layers not exceeding 45Omm thick until vibration of each layer is completed. Care must be taken to ensure that successive layers are well worked together.

Immersion vibrators shall be fully inserted into the concrete at points of application not exceeding 450mm apart and shall be withdrawn slowly to prevent the formation of voids. Immersion vibrators shall not be permitted to come into contract with the formwork, the reinforcement or other embedded fixtures.

Vibrators shall not be used as a means of distributing heaped concrete into position.

All horizontal surfaces of foundation and solid slabs shall be finally compacted by the use of surface vibrators.

Concrete after being placed and compacted must be left absolutely undisturbed while setting.

17.HOT-W EATH ER-CONCRETING

The following measures should be taken to reduce concrete temperature once it reaches 32 Degree Celsius or above:

a) Aggregate stockpiles shall be sprinkled regularly (especially in layers as placed) and shaded. Aggregate may be sprayed also with cold water immediately before use.

b) Water lines may be treated to ensure that no rise in the temperature of water occurs prior to its being used. Lines may be buried, painted white, insulated or shaded.

c) Cement in bags shall be stored in bins painted white or shaded.

d) Mixers, chutes, forms, etc. shall be shaded where practicable or painted white. The sub grade, forms and reinforcement shall be watered immediately before placing of concrete, but care shall be taken not to allow this water to become incorporated in the concrete. Excessive mixing time shall be avoided.

e) Water curing should be started quickly within the first few hours after casting and continued for at least twenty-four hours)

18.CONSTRUCTTON JOINTS

Concreting shall be carried out continuously up to construction joints, the position and arrangement of which shall be as indicated on the drawings or approved by the Architect.

Wherever practicable, construction joints shal1 be either vertical or horizontal joints shall be either vertical or horizontal; vertical joints shall be formed against a rigid stop board and rebated; horizontal joints shall be leveled and formed with a suitable key, if required. Wherever possible, the position of construction joints shall be settled before concreting begins. As a general rule, joints in columns are to be made as near as possible to the underside of the deepest beam. Vertical joints in walls shall be kept to a minimum.

Before placing new concrete, the surface of the old concrete shall be thoroughly roughened and cleaned; in the case of horizontal surface, any laitance or scum on the surface shall be removed by spraying the surface with water and brushing to expose the coarse aggregate.

Immediately before concreting, the roughened joints surface shall be thoroughly cleaned and loose matter removed, preferably without re-wetting, and then treated with a thin layer of cement grout worked well into the surface and followed by a 6mm thick layer of freshly mixed cement and sand mortar of similar richness and consistency to that in the concrete mixture.

19.CURING AND PROTECTION OF CONCRETE

Concrete shall be protected during the first stage of hardening from the harmful effects of sunshine, drying winds, rain or running water and from mechanical injury or premature drying out.

All exposed concrete surface shall be kept constantly wet for seven days by spraying watering or by other approved means as soon as practicable after placing.

No load of any kind, however tight shall be allow on concrete which has not properly set.

20.FIXING AND OPENINGS IN CONCRETE

The Contractor shall ascertain from the drawings or from sub-contractors or from other sources particulars of all bolts and other fixings and of all openings, holes pockets, chases, recesses and other cavities so that before placing of concrete all bolts, boxes and fixings shall be in place. No holes shall be cut after concrete has been placed without the expressed authorization of the Architect.

The Contractor may be required to cut out and re-execute work at his own expense where such openings holes, etc. which he may reasonably be expected to anticipate from the drawings have not been formed and the Architect considers cutting may impair the strength of the work.

21.CONCRETE COVER

Unless otherwise specified or shown on the drawings reinforcement, is to have the following minimum cover of concrete;

a) For main bars in sub-structures including columns and beams below ground - not less than 5Omm.

b) For main bars in columns - not less than 40mm

c) For main bars in beams and walls - not less than 25mm or the diameter of such bars whichever is the greater.

d) For main bars in slabs - not less than 13mm nor less than the diameter of such bars.

22.CONCRETE SEALING COAT

Immediately following the hand excavation to formation level for floor or foundations, where shown on the drawings or as directed by the Architect, a sealing coat of 50mm minimum thickness of (l:3:6) concrete shall be placed on the surface of the formation and carefully spade finished to an even surface. Utmost care shall be taken to preserve the natural water content of the ground below formation level as far as possible should the ground be exposed to the weather and become either drier or wetter than its natural state, due to delay on the part of the Contractor in placing the sealing coat or due to any other cause, the Contractor shall excavate such ground as may be affected and replace it by concrete (l:2:4) at his own expense and as may be directed by the Architect.

Floors or foundations shall be laid on the sealing coat as soon as may be practicable, this being especially important during hot weather. If required by the Architect, the sealing coat shall be kept thoroughly damp by watering.

23.FINISH OF CONCRETE

On removal of the formwork and after the approval of the Architect, honeycombed surfaces shall be made good immediately by a method approved by the Architect and superficial water and air holes shall be fi1led in.

Unless instructed to the contrary, the face of exposed concrete placed against formwork shall be rubbed down with a carborundum stone immediately upon removal of the formwork to remove fins or other irregularities. The face of concrete for which formwork is not provided, other than slabs, shall be smoothed with a wooden float to give a finish equal to that of the rubber down face where formwork is provide. The top face of a slab which it is not intended to cover with other materials shall be leveled and floated while unset to a smooth finish at the levels or falls shown on tire drawings or elsewhere. The floating shall be done so as not the bring an excess of mortar to the surface of the concrete. Indentations in the surface of the concrete shall be formed by approved implements to the depths and patterns described. The top face of slab intended to be surfaced with mortar, granolithic or similar materials shall be left with a spaded finish.

Concealed concrete face shall be left as from the formwork except that honeycomb surface shall be made good. Faces of concrete intended to be rendered shall be roughened by approved means to form a key. Faces of concrete that are to take finish other than those specified shall be prepared in an approved manner as instructed.

24. WATERPROOF CONCRETE

All waterproof concrete are to be watertight and approved additives are to be strictly used in accordance with the manufacture instructions.

25.READY- MIXED CONCRETE

If the Contractor proposes to use ready-mixed concrete, he shall give prior notice to the Architect of his intention to do so Ready-mixed concrete shall be mixed, delivered and supplied in accordance with the requirements of B.S. 1926 and shall comply with all the requirements of this Specification. The Contractor shall submit to the Architect before concreting, previous and current strength test results for concrete of, the strength required, and for his approval, details of mix proportions by weight currently in use.

For each truck delivery, the mix proportion including water content, the slump or compacting factors obtained onsite, and the times of introduction, mixing and delivery shall be recorded on the delivery note, a copy of which is to be submitted to the Site Office for retention.

The Contractor shall make available, if required, facilities for the inspection of materials used and the processes of batching and mixing employed in the manufacture of ready-mixed concrete. The Architect shall have the right to stop further use of ready-mixed concrete during the progress of the works if any requirement specified herein has not been satisfactorily complied with.

26.PUMPING CONCRETE

Where the Contractor proposes to utilise a pumping method to transport concrete on site, he shall give full details of his equipment and operation arrangement to the Architect for his approval, and shall indicate what sections of the structure he will cast with pumped concrete.

The type and capacity of the equipment used, including the pump and pipe line shall be suitable for its purpose on the project and shall be correlated to the mixing and batching plant. The whole of the operation shall be adequately planned and executed. The sequence of placing shall be predetermined.

27.STRUCTURAL TESTS

The Architect shall instruct the Contractor to make a loading test on the works or any part thereof if in the Architect's opinion such a test is necessary.

If the test so instructed to be made solely or in part for the reason that the site-made concrete cubes fail to attain the specified strength the test shall be made because of one or more circumstances attributable to the alleged negligence on the part of the Contractor. The Contractor shall be reimbursed for the cost of the test if the result thereof is satisfactory. Should the test be instructed to be carried out for any reason other than the foregoing, the Contractor shall make the test and shall be reimbursed for all costs relating thereto, irrespective of the result of the test.

For the purpose of testing floors, roofs arid similar structures and their supports, the test load shall be equivalent to one-and-a -quarter (1 2/4) times the live load for which the works or part thereof to be tested has been designed. The test load shall not be applied within 28 days after the placing of the concrete has been completed in the part of the works to be tested. The part of the concrete shall be unsupported during the test by the formwork or other non-permanent support. The test shall be made as instructed.

For a test on a floor, roof or similar construction, the result shall be deemed to be satisfactory if upon removal of the load the residual deflection does not exceed one-quarter of the maximum deflection after maintaining the load in position for twenty-four hours. If the residual deflection exceeds this amount, the test shall be repeated and tie result shall be deemed to be satisfactory if the residual deflection after removal of the load for the second time does not exceed one-quarter of the maximum deflection occurring during the second test.

lf the result of the test is not satisfactory, the Architect shall instruct that part of the work to be taken down or cut out and reconstructed to comply with this Specification, or that other measures shall be taken to make the works secure. If in accordance with this specification, the Contractor is liable to conduct the test at his own cost, he shall also at his own cost take down or cut out and reconstruct the defective work or shall execute remedial measures as instructed.

28.FA ULTY WORK

Any structural members of the work indicating defective work either before or after the removal of formwork and whether due to improper depositing, compacting or inadequate supporting of formwork or due to omission or incorrect placing or displacing of reinforcement or from any other cause '"whatsoever which might prejudicially affect the strength and durability of the construction, such defective work shall be removed and reconstructed to the satisfaction of the Architect at the Contractor's sole expense.

29.REINFORCEMENT

Steel rod reinforcement shall be obtained from approved manufacturers and shall comply with B.S. 4449 'Hot Rolled Steel Bars for the Reinforcement of Concrete or 'B S. 4461' Cold Rolled Steel Roads for the Reinforcement of Concrete '.

Steel fabric reinforcement shall comply with B.S. 4483

High tensile deemed steel bars shall have a guaranteed yield stress of not less than 420 N/mm Mild steel bars shall have a guaranteed yield stress of not less than 25ON/mm.

All reinforcement shall be hammered free from mill scale, scrapped and wire-brushed free from all loose rust, adhering earth and other materials that may cause corrosion of the reinforcement or disintegration of the concrete.

No reinforcement shall be coated with any grease, oil, lime-wash, cement grout, paint or preservative.

The Contractor shall produce a Certificate of Origin and results of tensile tests on all steel bars delivered or to be delivered to the site for use on the works.

The Architect reserves the right to order independent tests to be performed by an approved laboratory and the Contractor shall provide test specimens of not less than 600mm long for each diameter bar used, selected at random by the Architect. Any test specimens not complying with the requirement s as stipulated above, the Architect shall have the right to order re-tests on further samples or to reject the whole or part of the consignment- Rejected steel shall be removed from the site forthwith.

30.BEND ING REINFORCEMENT

Reinforcement bars shall be bent by machine or other approved means producing a gradual and even motion. Bars shall be bent cold unless the Architect approves bars of over 25mm in size being bent hot. Bar bent hot shall not be heated beyond cherry red colour and after bending shall be allowed to cool slowly without quenching. Bars depending on cold working for their strength shall always be bent cold.

All bending, cutting and fixing of reinforcement bars shall conform to B S 4466 ''Bending Dimensions and Scheduling of Bars for Reinforcement to Concrete".

Bars incorrectly bent shall be used only if the means used for straightening and rebending be such as shall not injure the material. No reinforcement shall be bent when in position in the work without approval, whether or not it is partially embedded in hardened concrete.

31.FIXING REINFORCEMENT

Reinforcement shall be accurately fixed and by approved means maintained in the position described on the drawings or elsewhere. Bars intended to be in contact al passing points shall be securely wired together at all such points with No.l6 gauge soft-iron tying wire. Binders and the like shall tightly embrace the bars with which they are intended to be in contact and shall be securely wired or if approved welded thereto.

Immediately before concreting, the reinforcement shall be examined for cleanliness and accuracy of the placing and cleanliness and corrected if necessary.

No concreting shall commence until the Architect has inspected the reinforcement in position and until his approval has been obtained.

Reinforcement projecting from work being concreted or already concreted shall not bent out of its correct position for any reason unless approved and shall be protected from deformation or other damage.

The cover of concrete to the reinforcement shall be as described in Clause 2l of this Section or on the drawings and shall be provided and maintained within a tolerance of 3mm under and over (except where specified as a minimum) by means of distance pieces of concrete blocks or other approved materials.The vertical distances required between successive layers of bars in beams of similar members shall be maintained by the provision of mild steel spacer bars inserted at such intervals that the main bars do not perceptibly sag between adjacent spacer bars.

Special care shall be taken to ensure the correct level of the top bars in cantilevers and the support of beams.

32.WELDING REINFORCEMENT

Should butt jointing of reinforcement bars by electric arc welding be approved, B.S, 1856, the Architects requirements or the regulations of the local or other authority shall be complied with and all operations connected therewith shall be done only by men skilled thereat. No welding shall be done in connection with twisted bars or other reinforcement, the strength of which depends on cold working.

33.FORMWORK

All formwork for concrete shall be rigidly constructed of approved material and shall be true to the shape and dimensions described on the working drawings. Timbers shall be well seasoned, free from loose knots and, except where otherwise approved, wrot on all faces. Faces in contact with concrete shall be free from adhering grout, projecting nails, splits or other defects. Joints shall be sufficiently tight to prevent the leakage of cement grout and to avoid the formation of fins or other blemishes.

Connections shall be constructed to permit easy removal of the formwork and shall be either nailed, screwed, clamped, wired or otherwise secured so as to be strong enough to retain the correct shape during consolidation of the concrete. Connections shall be concealed and measures taken to prevent rust stains on the concrete.

Contractor is to provide two sets of formwork for this project.

Formwork shall be provided for the top faces of sloping work and anchored to prevent flotation where the slope exceeds 1 in 2 1/2.

Formwork shall be true to line and braced and strutted to prevent deformation under the weight pressure of the wet concrete, constructional loads, wind and other forces. The deflection shall not exceed 3mm. Bottom of beam boxes shall be erected with an upward camber of 3mm for each 3,000mm span. If so directed, the calculations and designs for the formwork shall be submitted for approval before construction.The formwork for beams and slabs shall be erected so that the formwork on the sides of the beams and of the soffits of slabs can be removed without disturbing the beam bottom. Repropping of beams shall not be done except when, with the approval of the Architect, props be reinstated in anticipation of loads in excess of the design load. Vertical props shall be supported on wedges, or other measures shall be taken whereby the props can be gently lowered vertically when commencing to remove the formwork. Props for and upper storey shall be placed directly over those in the storey immediately below and the lowest prop shall bear upon work sufficiently strong to carry the load.

If the formwork for a column is erected to the full height of the column, one side shall be left open and shall be built up in sections as the placing of the concrete proceeds.

Before placing the concrete bolts and fixing shall be in position" Cores and other devices used for forming openings, holes, pockets, chases, recesses and other cavities shall be fixed to the formwork. No holes shall be cut in any concrete unless approved.

The Contractor may be required to cut out and re-execute works at his own expense where such openings, holes, etc. which he may reasonably be expected to anticipate from the drawings have not been formed, such cutting through, in the Architects opinion might cause impairment the strength of work.

An approved mould oil or other material shall be applied to faces of formwork in contact with concrete to prevent adherence of the concrete. Such coatings shall be insoluble in water, non-staining and not injurious to the concrete and shall not become flaky or be removed by rain or wash-water. Liquids that retard the setting of concrete shall only be used when approved. Mould oil, retarding liquid and similar coating shall be kept from contact with the reinforcement.

34.REMOVAL OF FORMWORK

Formwork shall be removed by gradual easing without jarring. Before removal of formwork, the concrete shall be examined and removal shall proceed only in the presence of a competent supervisor and when the concrete has attained sufficient strength to support its own weight and any load likely to be imposed upon it. If the imposition of a load exceeding the design load is anticipated, props shall be provided in al approved manner after removal of the formwork and before the imposition of the load. The Contractor shall record on the drawings or elsewhere the date upon which the concrete is placed in each part of the work and the date upon which the formwork is removed there from. The normal minimum period between the placing of the concrete and the removal of the formwork for the various part of the structure shall be as listed below:Beam sides, walls and columns3 daysSoffit of slabs unloaded (with props left under)4 daysSoffit of beam unloaded (with props left under)7 daysRemoval of props under slab14 daysRemoval of props under beam16 days

The formwork for a part of structure suspended from concrete placed subsequently to that in or on the formwork concerned shall not be removed until the supporting concrete has matured and such formwork shall be prominently marked as a warning against premature removal.

Under no circumstances should formwork be struck until concrete reaches cube strength of at least twice the stress to which concrete may be subjected at the time of striking. All formwork should be removed without such shock or vibration as would damage the reinforced concrete.

35.PRECAST CONCRETE IN GENERAL

The concrete shall be Grade 20 (l:2.4) as described in Clause 11 of this Section; unless otherwise stated, all exposed faces shall be smooth and even.

The concrete in one precast piece shall be placed in one operation. No piece shall be removed from the mould or erected until sufficiently matured to ensure that no damage shall be done to the piece A piece shall be suspended or supported only at the points described on the working drawings or elsewhere. A piece that is cracked or otherwise damaged during, before or after erection shall be removed from the works and replaced by the Contractor free of charge. Pieces shall be bedded or otherwise fixed in their permanent positions as instructed.

Where possible lintels shall be precast and shall not be built on for 14 days after casting unless adequately strutted. Whenever reinforced concrete lintels are not detailed in the drawings, they can be constructed in accordance with the table that follows; the length of the reinforcirg bars being equal to the minimum length of the lintels.

M.S Rein. BarsWith 6mm CoverIn BottomClean spanMin. lengthMinOf Lintel Depth 115mm 230mm 345mm 450mm Width Width Width Width

Up toclear span1200mm+300mm150mm 10mm D 10mm D 10mm D 10mm D

1200mm toclear span1900mm +450mm230mm 13mm D 13mm D 13mm D 13mm D Note: D denotes diameter

36.EXPANSION JOINTS

Expansion joints shall be formed as and where shown on the drawings.

37.BONDING TILES

Bond ends of brick wall to reinforce concrete walls or columns are to be provided with 6mm diameter mild steel bonding ties 450mm long at 450mm centre, the end cast into reinforced concrete wall or column and hooked around reinforcement and the other end built into brickwork.

38. WATERPROOF BUILDTNG PAPER

Waterproof building paper shall be as B-S. t521, laid with lS0mm end and side laps and suitably secured before the concrete is placed.

39. ROUNDED EDGES AND CORNERS

For this project all external edges of columns and beams, floor junctions, wall returns, etc are to be rounded smooth.

40.WATERPROOFING TO BASEMENT FLOOR SLAB (for mechanical carpark)

40.1MATERIAL

The waterproofing membrane shall be l.5mm thick uniseal 1000 HC or other equal and approved 1.5mrn thick self adhesive waterproof membrane.

40.2 Workmanship

I. A layer of Uniprimer D4l or other equal and approved primer shall be applied on the lean concrete surfaces to soffit of basement/ground floor slab. The uniseal 1000 HC membrane shall be laid on top of the primer including dressing into 25 x 25 grooves in beams complete with pointing with approved sealant. A 25mm thick cement and sand (l:3) screed shall be laid on the membrane as a protection layer.II. The laying of the waterproofing membrane shall be executed by a specialist firm approved by the Architect.III. All substrates that are to receive waterproofing membrane shall be sound, clean, free from water puddles, grease, dust coating or other foreign material in accordance with the manufacturers instructions.

Adequate protection of the finished waterproofing membrane in the form of dust sheet, plywood or planks shall be used during the progress of works.

IV. The Contractor shall furnish a guarantee of ten (10) years against leaks and defect for the whole waterproofing works. The Contractor shall be responsible for arranging and procuring the said guarantee and this guarantee shall be a joint guarantee of the Contractor and Sub-Contractor in favour of the Employer.

41. TANKING TO BASEMENT (For mechanical car park)

41.1MATERIAL

The waterproofing membrane shall be Uniseal l000HC or other equal and approved 1.5mm thick self adhesive waterproofing membrane.

41.2WORKMANSHIP

I.General

The tanking to the basement shall be executed by a specialist firm in accordance with the detail requirements and strict specification approved by the Architect.

II.Priming of Surfaces

The surface to be laid over the membrane shall first be applied with an Uni-Primer D4l or other equal arid approved primer to ensure a dust free state, using a roller, brush or spray. The primer must be allowed to dry one hour, or until tack -free. Priming should be limited to what can be laid over with membrane in a working day.

III.Jointing Technique

The individual lengths of membrane shall be joined by welding techniques in accordance with manufacturers guidelines. All edge end beams must be overlapped at least 75 mm.

IV.Detailing

a) Corners, penetrations and terminations shall be treated according to manufacturers details. All corners should be covered with an initial strip of 30cm width, centered on the axis of the corner.

b) Termination to concrete wall shall include a similar detail. Installation to be carefully carried out prior to casting of wall slabs.

c) All vertical and horizontal terminations shall be sealed with an approved rubberized asphalt based mastic.

V.Construction and Expansion Joints

Unless otherwise specified, Serviseal waterstop or other equal and approved PVC external waterstop would be in the form of full initial strip of 300mm width across expansion joint and construction joint. Installation should be carefully executed to ensure proper alignment prior to casting of wall/ground slabs, by the waterproofing specialist.

VI.Sub-Strate Requirements

Surfaces supporting the membrane must be flat and smooth, free from sharp edges and protrusions, with loose gravel and foreign matter or debris removed. Concrete need not be fully cured before overlaying with membrane but must have hardened sufficiently to allow laying operations to proceed.

Surface must be inspected and approved by Architect before commencement of waterproofing works.

VII.Protection of Membrane

The membrane should be protected to avoid damage from other trades, construction materials or backfill. On walls, protect the membrane using 12mm expanded polystyrene boards spot bonded to membrane with mastic.

VIII.Guarantee

The Contractor shall furnish a guarantee of ten (10) years against leaks and defects for the whole waterproofing works. The Contractor shall be responsible for arranging and procuring the said guarantee and this guarantee shall be a joint guarantee of the Contractor and Sub-Contractor in favour of the Employer.