PREPARATION
1.1 Description
Site preparation work consists of site clearance, survey, cutting, imported fill, embankment and construction of ditches for drainage. Work of this section includes all measurement and materials required to complete the supply, execution and construction of site preparation.
1.2 Site Clearance
The contractor shall clear, from all areas planned for the work, all buildings, materials, debris, etc, prior to the cutting and filling work taking all necessary precautions to prevent damage to the existing road structures and buildings or other facilities, in the area, which shall not be demolished.
1.3 Survey
Prior to commencement of the work, the contractor shall check the existing bench marks and reference points located on or out of the site as indicated. The contractor shall establish newly standard bench marks and points for the works within the site with the agreement of the Engineer.
a. Traversing
Prior to execution of the works the contractor shall check the existing reference points, and the results shall be submitted to the Engineer for approval.
b. Principal points
Principal points shall be established taking advantage of the existing reference points.
Individual principal point posts shall be of wood, 15cm x 15 cm size, with an indicating nail on the top, the surface of the post above the ground shall be painted white.
c. Bench marks
When establishing bench marks within the site, a minimum of one (1). back and forth leveling operation shall be carried out. Establishment of temporary bench marks shall be determined and performed by the contractor. Temporary bench mark posts shall be of wood, 12cm x 12cm x 100cm in size, with an indicating nail on the top, the surface of the post above ground shall be painted.
d. Other survey
Setting out for survey shall be done with the agreement of the Engineer.
The Engineer may issue instructions or orders for surveys to supplement those listed above or for different surveys with which the contractor shall promptly comply and carry at this own expense.
1.4 Protection from Water
In case of rain, the day’s works shall be stopped so as to confine damage due to rainfall to a minimum. According to the site conditions, temporary drainage ditches shall be provided. In cases where ditches, damage ditches etc. become blocked with sand, earth, etc, such shall be immediately removed. Broken slopes shall be immediately repaired. In case where swamps, pools etc. which are not shown on the Drawings are found, such shall be drained.
1.5 Cutting
Cutting refers to excavation of the natural ground of cut sections. preparatory drainage and disposition of ditches at the cutting sections f temporary disposition, loading, hauling , unloading and spreading of the cut soil at embankment sections , and other temporary works necessary. such excavation shall be carried out in accordance With the Drawings and specifications and as directed by the Engineer.
1.6 Surface Finish
The finished cutting and embankment shall be roughly leveled, a deviation, of approx. 5cm from the proposed height shall be allowed. Slopes shall be protected from damage due to weather during the execution. Final surface finish shall be executed after completion of building work it shall cover the depth after settling to that the levels indicated in the Drawings and specifications are met.
2. EARTH WORK
2.1 Scope of Work
Earth work consists of excavation, back filling and disposal of surplus Material. Work of this section includes all measures and materials required to
complete the design supply, support, use, construction, removal of earth work.
2.2 Excavation
The ground shall be excavated to the lengths, widths and exact depths required for the construction of the works. The contractor shall examine any unsuitable or weak ground material, standards of which are given below and shall report the situation in writing to the Engineer before executing concrete or any other Works.
if the surface of a subgrade is found to be unstable or to include any type of refuse subject to removal in the opinion of the Engineer, the contractor shall excavate and remove such unsuitable Material to the width and depth required by the Engineer. Any excavation to a level lower than that indicated on the drawings shall be compensated for filling with concrete mix (1:4:8) or with other material as directed by the Engineer at the contractor's expense.
Due weather to negligence or error on the part of the contractor or at the request of the Engineer owing to an unstable sub grade, the contract price shall be deemed to cover the whole cost of all excavation, inclusive of replacement with suitable Material, necessary in what so ever typo of earth or ground conditions encountered, e.g. earth With boulders, hard pan , rock, old concrete foundation, roadways, paved areas, etc.
All excavation works shall be kept dry and clean in order that work may not be affected or interfered with by water entering the excavation. The contractor shall pump out all water which may occur or be brought into the excavation employing such equipment as engines, pumps pipe work, chutes and other necessary devices to keep the water level below the bottom of the permanent works during the period required by the Engineer, Raised water shall be conveyed away in such manner as not to cause any nuisance or injury to the occupants of adjacent properties or sites. If pumping is required f it shall be carried out continuously and my not be stopped without the permission of the Engineer .
Excavated material, approved by the Engineer for re-use for filling shall be selected, loaded and hauled to the specified location for temporary stockpiling. Excavation materials containing brushy roots or other vegetable materials shall be classified as unsuitable for fill.
The sides of excavation shall be supported as necessary to Maintain a vertical face and to prevent fall or slip of any nature at any - time during the duration of excavation and back filling works. The contractor shall be responsible for the design, supply, fixing and removal of the shoring, sheet piling or any works required to support the side of the excavation.
It is also the contractors responsibility to protect existing structures and utilities from damage or interruption of services due to excavation work .
2.3 Disposal of Surplus
The contractor shall be responsible for all surplus soil of excavated material not suitable for re-use . The Engineer my require the contractor to transport such surplus to a disposal area and /or my instruct the contractor to dispose of the surplus to a disposal area to be procured by the contractor himself - This shall all be carried out by the contractor at no extra expense to the employer.
2. 4 Filling
2. 4. 1 Backfilling
Excavation shall not be backfilled until such structures and properties as drainage, insulation pipes, construction details, and water tightness have been inspected, tested and approved by the Engineer .
All available precaution shall be taken during back filling to ensure that the pipes, insulation and construction details are not damaged. All backfill material shall be approved and free from vegetable or organic material, mud, refuse, boulders, rock , stones of over 15 cm and other materials which, in the opinion of the Engineer, are unsuitable.
Filling shall be carried out in such away and to such a generous depth as to ensure that the final surfaces after settlement and compaction conform to the levels indicated in the Drawings and specifications .
2. 4. 2 Compaction
Compaction of fill (under ground pipes and those buildings or structures where concrete fill is not c quir required).
All soil fill material used shall be thoroughly compacted by mechanical means until the specified degree of compaction is obtained. The filling Material shall be approved by the Engineer and placed in even layers of a depth not greater than 30cm . A power driven roller of least 10 tons shall make at least 10 trips for each layer unless otherwise specified.
Every effort shall be made to compact the fill material at its optimum moisture content for compaction. In any case, the dry density of compacted soil shall not be less than 95% of the value obtained in a standard laboratory test. When spade will not permit the use of rollers, other types of approved equipment shall be used to achieve the same degree of degree of compaction specified. Filling and compacting around pipes, cables and conduits shall be done by hand using selected Materials to depth of the least 50cm above such pipes, cables and conduit .
2. 5 Hard Core
Where indicated on the drawings or directed by the Engineer, broken brick, hard stone or gravel free from vegetable matter and lump of clay shall be laid on the compacted subgrade to a thickness of 80mm.
2.6 Protection Against Termites
Selected appropriate anti-termite method approved by the Engineer shall be executed in accordance with the local procedures and Manufacturers instruction on the excavation bottom surface and the materials used for filling or backfilling and to the sores.
3. PILE WORK 3. 1 Preamble 3.1.1 Scope of work
The work comprises supplying of labor, materials, plants, equipment, temporary huts and all other items necessary for the design and installation of the piles as shown on the drawings and described in these specification.
The work is to be executed in accordance with specification and contract documents and to the satisfaction of the Engineer. All tenders shall therefore furnish information about the type of piles they specialize in and other relevant details of design, execution, equipment, testing, etc, complete, in support of their capabilities.
The whole of the work and materials shall conform to the current edition of relevant British standards and codes of practice.
3. 1. 2 Responsibility for design and workmanship
The piling contractor will be responsible for designing and installing the piles to satisfy the performance requirements and minimum design criteria laid down in these specification lie shall provide all necessary details and information to satisfy the Engineer who designed the foundations that his proposals will meet the specification. It will also be his responsibility to produce standard workmanships in the best possible manner, to effect the design in the actual conditions encountered on the ground or below . In particular he shall make whatever day to day minor modifications to the agreed proposals that may be found to be necessary to cater for minor variations in ground conditions. Any variations from the agreed principle shall be in accordance with the Engineer's approval.
3. 1. 3 Site conditions
The piling contractor will be deemed to have visited and inspected the site and surroundings before preparing his tender and to have made himself thoroughly acquainted with all details of the site, including those not specifically mentioned herein or on the drawings,
3. 1. 4 Existing services and Adjacent Buildings
The piling contractor will be responsible for any claims arising from damage to services or to adjacent structures or property, at the time of executing the work.
3. 1. 5 Pile length for purpose of payment
The length of each pile for purposes of payment shall be measured in accordance with the standard method of measurement for building and civil engineering work.
3. 1. 6 Records
The piling contractor shall keep on site a complete record of the changes in the nature of the strata through which each passes. Such records shall be made available for inspection by the Engineer during the progress of the piling contract and copy shall be supplied to the Engineer at the completion of piling work .
3. 2 Design
The pile is designed to carry as its part of the total support of the foundation loading. Specified in the drawings.
3. 2. 1 Responsibility
As stated in 3 .1.2, the piling contractor will be responsible for designing the piles and producing a piling that can carry safely the loads indicated on the foundation plans.
3. 2. 2 Approval of Design
Before accepting the piling contractor's tender, the Engineer will be required to satisfy himself that design proposals are sound and reasonable* To this end the piling contractor shall submit any calculations or supporting evidence which the Engineer may call for after receipt of tender .
3. 3 Concreting Materials and Workmanship
3. 3. 1 Materials
cement, aggregate and water to be used shall be in accordance with the requirement of section ( 4-2 ) "concrete work". The piling contractor shall submit details of reinforcements included in his design and tender. All reinforcements used in the piles shall be as per the approval of the Engineer and in accordance with section ( 4- 2) .
3. 3. 2 Concrete
The concrete mix shall be designed by the piling contractor to suit the piling system adopted and shall be dry as possible consistent with that system , and the method of compaction. However, the minimum cylinder strength at 28 days shall be 211 kg/cm2.
3.3.3 Placing and compacting
The concrete shall be placed in its final position as soon as possible and in any case not later than half an hour after mixing. Ready mix concrete must be placed immediately it leaves the mixing truck. The method of placing shall be such as to ensure that the concrete in its final position shall be dense and homogeneous. Concrete shall not be ordinarily placed under water. If water is present within the pile-shell a sealing group of approved quality shall be placed in the bottom of the shell for 1 to 1-2 m depth, the water shall then be pumped from the pile and concrete placed in the dry. Adequate precautions shall be taken to ensure that water leaking out of concrete shall not build up on top of it during the pouring of Concrete in pile shaft, and any such water shall be removed before more concrete is placed in the shaft, The pile shall be concreted in one continuous operation. If the continuity of placing the concrete is interrupted no further concrete shall be placed without the prior approval of the Engineer. The method of compaction shall be proposed by the contractor and approved by the Engineer before placing concrete .
3.3.4 Transporting concrete
Concrete shall be transported from the mixer to the position of the pile in such a manner that segregation of the mix shall not occur
3. 4 Piling Workmanship
3.4.1 Setting out
The main contractor will provide the piling contractor with all necessary layouts and take responsibility for their accuracy and check that the piling contractor executes the work in accordance with these layouts. The piling contractor shall set out the position of each pile.
3.4.2 Tolerances
The maximum permissible positional deviation of the center of each finished pile from the correct center point shown on the setting out drawing is 75 mm in any direction. The maximum permissible deviation from the specified inclination of any finished pile is 2-2.5 % .
The piling contractor shall bear the cost of any additional work which, in the opinion of the Engineer, may be necessary due to any pile being installed in apposition not within these tolerances.
3.4.3 Temporary lining
Adequate precaution shall be taken including the use of a temporary lining tube, water bearing or unstable strata, to prevent the ingress of water, to maintain any pile excavation to its full dimensions and to ensure that the pile shaft shall be formed to its full cross-sectional area, where there is a temporary lining it must be removed in the line of the pile in such a manner that no defect or damage will be sustained by the pile.
The depth to the average levels of the concrete surface of the pile shall be checked before and after any temporary linings are with draw. These measurements shall be recorded.
3.4.5 Drilling Mud
Drilling Mud may be allowed only with prior permission of the Engineer and subject to the piling contractor providing satisfactory evidence that its disposal will not foul or contaminate any part of the site or surrounding areas or services.
3.4.6 Cleaning the Excavation
Upon completion of any boring, the excavation shall be cleaned of all losses, disturbed and remolded soil to expose a dry base of undisturbed Material.
3.4.7 Inspection
After the tube has been installed in its final position, the Engineer will inspect the tube for proper plumb, location and other conditions. Only after his approval can the contractor proceed further in placing reinforcement and concreting the pile.
3.4.8 Jetting and pre-boring
Jetting and pre-boring may be used only with the prior permission of the Engineer.
3.4.9 Backfilling empty boring
Where trimmed level of any pile is more than 600nm below the starting level of the piles, empty boring shall be backfilled as soon as possible with sand of colour which contrasts with the surrounding natural soil .
3.4.10 Cleaning the site
The piling contractor shall remove from the site at intervals during the operation of the work, and on completion, all unnecessary plant, rubbish, water and debris resulting from his activities.
3.5 Pile Testing
Tests of completed piles shall conform to British standards CP 2004
3.5.1 Notice of commencement
The Engineer shall be given at least 40 hours notice before the commencement of each test .
3.5.2 Supervision of pile tests
The piling contractor shall Keep the tests under continuous and competent supervision to the satisfaction of the Engineer, All necessary facilities shall be provided to enable the Engineer to check reading during the progress of the tests.
3.5.3 Testing assembly
The piling contractor shall submit complete details of the testing assembly and all details of the proposed arrangement and procedure for test loading for approval of the Engineer before the installation of tension piles. The details shall include a complete list of all equipment being used in the test, including manufacturer's name and the reference number of the equipment.
3.5.4 Test report
At the conclusion of work each day the piling contractor shall send to the Engineer a copy of his daily record sheet . The piling contractor shall also send to the Engineer within one week of the completion of each test, two copies of all record graphs and results of laboratory and in-situ tests conducted on the installation and testing of all trial piles. This information shall include a load Settlement, diagram plotted to scales .
3.5.5 Failure of contract test piles
In the event of a contract the failing to satisfy the test requirements the piling contractor will be instructed to test additional piles.
The piling contractor shall bear the cost of all additional and consequential work as the Engineer may consider necessary due to the failure on one or more piles, to satisfy the requirements of the loading test .
3.5.6 Rejection of piles
The Engineer reserves the right to reject any pile which in his opinion is not structurally sound, or is not in a proper position and alignment. The contractor shall be bound to pull out same and re-drive a new pile in its place , or leave the defective piles install at the contractor's cost one or more additional pile as per the directions of the Engineer in writing.
3.6 Other Pile Types
3.6.1 Steel piles
The work covered by this clause consists of furnishing all materials, labor and equipment and performing all operations for driving and completing steel piles as indicated on the drawings, in addition to driving and testing the test piles, all in accordance with the specification and as directed by the Engineer.
3.6.2 Materials
Steel piles shall be of the type and weights shown on the drawings and shall be manufactured from steel conforming v to ASTM-A36. All piles shall be straight and true to section and any pile which in the opinion of the Engineer, is defective in any way, shall be rejected and shall be replaced by the contractor.
3.6.3 Driving steel piles
Steel piles shall be driven vertically or inclined to true position and secured against lateral movement by leads or other suitable means approved by the Engineer, All piles driven out of line, but of plumb, with incorrect inclination, or twisted, broken or bent, otherwise damaged in driving shall be withdrawal and replaced with other piles, properly driven to the true position and alignment required and to the satisfaction of the Engineer. All piles shall be cut off at the levels indicated on the drawings . A steam hammer shall be used to drive the piles unless other equipment is permitted by the Engineer. Piles may be driven by a hammer and water jets or by water jets alone. An ample supply of water at adequate pressure shall provided. Piles shall be driven by hammer alone for the last 1.5 m of penetration, piles shall be driven to depths or to penetration per blow as directed by the Engineer. Accurate records of the penetration per blow for the last 30 cm shall be kept for the guidance of the Engineer in determining allowable loads on the pile.
If proper resistance to driving is not attained at the predetermined length of pile, or when the length of piling required is in excess of the largest continuous length that can be supplied, an additional length of piling shall be added by butt welding. The joint details shall be as shown or as directed and fulfilling the requirements of AISC standards.
The contractor shall take all the necessary precautions to prevent any damage to the existing properties due to the piling work.
4. CONCRETE WORK
4.1 Description
Concrete work shall consist of mixing, conveying, placing of concrete , for work and reinforcement Work, (it is inclusive of all measures and materials required removal of concrete forms and reinforcement).
4.2 Material
All materials used in the work shall be the best of their kind and shall conform in quality and treatment to the conditions herein specified. The contractor shall submit to the Engineer when required and at his own expense, samples of all materials to be used in the works. The quality of the samples so provided being representative of the Bulk of such materials. The construction of all concrete and reinforced concrete work shall commence at points approved by Engineer and shall be continued and completed in accordance with the programme of work to be submitted to the Engineer for approval before the concrete work is commenced.
Any work considered by the Engineer to be of inferior workman ship and therefore , to present a potential point of weakness in any part of the work shall be demolished and rebuilt at the expense of the contractor.
4.2.1 Cement
Portland cement for all structural concrete shall conform to ASTM C 150, for all concrete construction below ground level and water-retaining structures, sulphate resisting Portland cement Type II of ASTM C 150 or equivalent shall be used and for above ground level Type I shall be used The contractor shall provide appropriate dry, well ventilated weather and water proof sheds of capacity sufficient to store cement so that the cement can be stored in such a manner as to prevent deterioration or intrusion of foreign matter. Floors of the sheds shall be at least 30 cm above ground. The cement while being conveyed to the site in trucks or other vehicles shall be adequately from the weather. The cement shall be used as soon as possible after delivery. Any cement that has deteriorated or has been contaminated shall not be used for concrete.
4. 2. 2 Aggregates a. General
All aggregates shall conform to the requirements of J3.S 882 or equivalent and be locally available. Aggregates failing to meet above mentioned specifications but which have been shown by special test or to actual service to produce concrete of adequate strength and durability may be used when authorized by the engineer. The aggregates shall be dense, hard durable and free from harmful amount of reactive minerals and other chemical compounds and shall conform to the above mentioned standards. Samples of aggregates used in the work shall so provided from the same aggregate sources stockpile at the site, and be submitted to the laboratory authorized by the employer and the written approval of the authorized laboratory shall be given to the engineer for his approval.
b. Grading of aggregate
The grading of- the fine and coarse aggregate shall be such that whe they are mixed in the proportions decided for each class of concrete, the grading of the combined aggregate shall be suitable for making a dense concrete of appropriate workability with the proportions of cement and water with which the aggregate is to be used. The quantity of flaky aggregate shall be limited as much as possible.
When tested by means of laboratory sieve the fine and coarse aggregate shall conform to the requirements of D.S. 002 for graded aggregate. The contractor shall be responsible for mixing the aggregate in the proportions approved by the Engineer for each class of concrete and each section of the work. It shall submit samples of the re-graded material to the Engineer well in advance before commencing any concrete works, 20 mm size shall apply to all concrete having 200mm or less in thickness, for heavier wall, footing and mass concrete 25 mm size may be used, provided that the space between the reinforcing bars therein is one and half times greater than the maximum aggregate size.
4. 2. 3 Water
Water use in mixing concrete shall be clean and free from injurious amounts of oil, acids, alkalis, salts, organic material or other substance which may be deleterious to concrete or reinforcement. The temperature of water use for making concrete in hot weather shall be low enough to attain the proper mixing temperature of concrete, and in any case shall be Lower than 30 degree centigrade. The contractor shall store on the site an adequate supply of fresh water to meet all needs . The contractor must indicate the origin . of the water he intends to use.
4.2.4 Steel reinforcing bars
Reinforcing bar should be deformed bars for all reinforced concrete work, and should have minimum yield strength of 414 N/mm2 ( 60000 psi) in accordance to ( ASTM A 184 and A 185) . Representative samples of all steel reinforcement that the contractor proposes to use in the Works together with manufacture's certificate stating clearly for each sample, the place of manufacture expected date and size of deliveries to site, and all relevant details as regards composition manufacture, strength and other qualities of the steel shall be submitted to the Engineer for written approval.
4.2.5 Formwork
Icuan ply wood, 5-ply, 12 mm thick, or wood boards shall be used . Wood boards or ply wood for shuttering shall be such as not to damage the placed concrete owing to its containing imparities and shall be able to withstand loading occurring during placing of concrete.
4.2.6 Preformed expansion joint sealer and filler
Bitumen Impregnated fiber board to be used for joint filler, shall be robust,durable, waterproof, rat-proof , non- staining, made from selected hard and soft wood fibers impregnated with bitumen emulsion, preformed expansion joint seals shall consist of synthetic resin cover , hard PVC cap, steel anchors and elastic filler as shown on the drawings .
4. 3 Concrete Mixes
Concrete shall be proportioned to have the following specified compressive strengths, as determined by the specified testing and test evaluation procedure, specified compressive strength ( f'c) shall be as indicated on the drawings.
4.4 Water-cement ratio
Water-cement ratio shall be determine so as to achieve the required workability and to obtain the specified concrete strength, which shall be subject to the approval of the Engineer.
4. 5 Test of Concrete
Work cylinder test ( cubes in case B.S. is to be applied) shall be made on concrete sampled during the works. Samples shall be taken for each new grade concrete, from each 100 m3 of concrete when the same grade is being used continuously, except for lean concrete and other non load bearing concrete. The number of specimens taken shall not less than 3 for each compressive strength test, All tests shall be performed in accordance with ASTM C. 39, B.S, 1881. and shall be carried out in an authorized laboratory at the contractor's own expense. If the results of the 28 days test are unsatisfactory, all concrete work shall be stopped at contractor's expense and shall not proceed further without the written permission of the Engineer. Should the test prove that the concrete is not satisfactory or the Engineer Judge any section to be defective , the condemned concrete shall be cut out, removed and replaced by the contractor.
4.6 Mixing and placing concrete 4. 6. 1 Mechanical Mixing, batching .
All concrete shall be Machine Mixed. The location for the batching and minding plant shall be agreed by the Engineer, and the contractor must submit to the Engineer for approval before erection of any mixing plant his proposed arrangements for the storage of aggregate and batching and mixing of concrete. The contractor must also submit details on the type or types of mixers and machines to be used and proposals for the moans of convoying nixed concrete from the miser to the points of deposition.
All concrete shall be batched by weight and the weight-batching machines used shall be of a type approved by the Engineer and shall be kept accurate and in good condition while in use at the works. Checks shall be made as required by the engineer to determine whether the weighting devices are registering correctly. Each mixer shall be fitted with a water measuring device. If aggregate batching by volume is allowed, the cement shall be batched by weight and the water by weight or volume.
Any deposit of old concrete in the mixer drum shall be cleaned out by rotating clean aggregate and water in the drum before any fresh concrete is mixed.
4. 6. 2 Placing and compacting
Immediately after Mixing, the concrete shall be transported to the place of final deposit- by method which prevent separation , loss contamination of any of the ingredients.. Any method involving the use of pipes or chutes for transporting concrete shall not be permitted, except with the written approval of the Engineer.
Transport of concrete from the mixers must be as rapid. as possible and the contractor shall always be responsible to place and compact the concrete.
Before any concrete is poured, the formwork must be thoroughly cleaned of all dirt, shavings, loose stones, etc, and the wood form which will come in contact with the concrete shall be soaked well with an approved mould oil. The concrete shall be placed gently in position and shall normally not have a free fall of more than one meter. To convey, the concrete as near as possible to its final position, rubber or metal drop chutes shall be used for small sections, and bottom opening buckets or other suitable vessels for large sections. The concrete shall be placed in such a manner so as to prevent water from collecting at the ends, corner or along the faces of the forms, and it shall not be placed in large quantities at a given point and allowed to run or b be worked over a long distance in the form . All concrete shall be placed and compacted in even layers with each batch adjoining the previous one. The thickness of the layers shall be between 15-30 cm for reinforced concrete and up to 45 cm for un-reinforced concrete in relation to the width of the forms.
The concrete shall be carefully and continuously compacted and worked around the reinforcement and into the corners of the formwork so that it will be in close contact with the reinforcement and free from honeycombing. Over-vibration causing segregation shall be carefully avoided and the redistribution of concrete in the formwork by means of vibrators shall not be permitted.
The concrete shall be compacted by mechanical or electro-mechanical vibrators of a type approved by the Engineer. The plunger type vibrators shall have a diameter compatible with the spacing of the reinforcement., and sufficiently high frequency.
All vibration, compaction and finishing operations shall be completed immediately after placing of the concrete in its final position, workers shall not be permitted to walk over freshly placed concrete until it has hardened sufficiently to carry their weight without distortion, and great care shall be taken to ensure that reinforcement projecting from recently placed concrete is sot shaken ox1 disturbed so as not to destroy or damage the initial set of the concrete in contact with it.
Concreting in any one part or section of the work shall be carried out in one continuous operation and no interruption of concreting work shall be allowed without the approval of the Engineer .
4. 7 Concreting in Hot weather
The recommendations set out in (( Recommended practice for hot weather concreting) ( ACI- 305-72) . The temperature of the mixed concrete shall not exceed 35 before placing in hot weather. In ambient temperatures coarse aggregates shall be sprayed with clean water for cooling. In order to keep the temperature of mixed concrete below the specified temperature, the contractor may use cooling equipment. Fresh concrete shall be protected from premature drying. Concrete in transit shall be shaded from direct sunlight and special care shall be taken to maintain the correct water/ cement ratio. The formwork and reinforcement in and around which the concrete is to be placed shall be sprayed with water to cool the surfaces and prevent excessive absorption from the concrete when placed. Generally all concrete shall be shaded from direct sunlight and drying winds and from excessive ambient temperature during placement.
4.8 Concreting in cold weather
Ho concrete shall be made with frozen aggregates or placed up on frozen surfaces. In cold weather, the contactor shall take special precautions, such as heating aggregates and mixing water to ensure that the temperature of the concrete when placed is not less than 4C .
4.9 Curing
Curing shall start as soon as practical after placing or finishing . concrete shall be cured with water unless membrane curing is employed.
The surface of placed concrete shall be covered with damped mats or other approved materials for a suffocation period talking into consideration weather conditions during the period. Horizontal surfaces shall be covered by a suitable method so as to avoid the effect of sunshine, drying wind and other harmful effects, vertical surfaces such as walls and column sides shall be wetted for a sufficient period by sprinkling water to forms, or other suitable methods.
4.10 Reinforcement
This article shall apply to the fabrication and erection of reinforcing steel bars. The materials to be used shall be specified in section 4.2.4 of this specification.
4.10.1 Bending and anchorage
Bending specifications shall be drawn up as applicable in accordance with the approved codes, and each reinforcement bar shall be bent to the exact dimensions specified in the relevant specification . All bars shall be bent cold. Bars shall not be welded without the approval of the Engineer. No splices shall be made in the reinforcement except where approved by the Engineer, and all splices or overlaps shall comply entirety with the requirements of proved.
4.10.2 Fixing of reinforcement
The steel reinforcement shall be assembled to the exact shapes and dimensions as approved by the Engineer. The rods shall have the approved cross-sectional area and shall be fixed accurately in the moulds. The ends of all tying wires shall be turned into the main body of the concrete and shall not be allowed to project towards the surface. Spacing blocks shall be used to ensure accurate cover to the reinforcement, where necessary, and these blocks shall be of precast concrete of a strength at least equal to that of the concrete being placed. They shall be as small as possible in view of practicality and shall be securely fixed in position by means of wires to be cast into them.
No temporary supports for the reinforcement shall be allowed to be incorporated into the finished concrete. At the time of concreting all reinforcement shall have been thoroughly cleaned and made free
of all loss rust (crude oil or any other coatings that might destroy or reduce the bond).
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