CONCRETE WORKS

CW.1 Concretor CW.1.1 The constituent material, manufacture and transport of all for the Works shall comply with the requirements of BS EN 206, Concrete. The exposure class for all substructure work shall be XS2, and for all concrete on the exterior of the building it shall be XS1. The exposure class for protected concrete internal to the building shall be XC1. The relevant exposure class for each concrete element has to be identified depending on its location. The intended working life of the proposed structure is at least 50 years. Nominal covers to reinforcement shall be selected accordingly. In addition, it shall be ensured that the cover is adequate for fire resistance purposes.

CW.1.2 All concrete works shall be carried out in strict accordance with the approved design drawings. Concrete work shall be in accordance with DD ENV 13670-1 Execution of Concrete Structures. Part 1.

CW.2 Materials, Batching and Mixing CW.2.1 Ready-mixed concrete shall be used for all in-situ concrete and shall be obtained from an approved plant. Each mix shall be obtained from only one source unless otherwise approved. The name and address of the supply depot(s) shall be confirmed to the Employer’s Representative in writing before any concrete is delivered. All delivery notes, test certificates, and other similar documentation shall be retained for inspection. Ready- mixed concrete shall be carried in purpose-made agitators, operating continuously, or truck mixers. The concrete shall be compacted and in its final position within 2 hours of the introduction of cement to the aggregate, unless appropriate retardants are used.

CW.2.2 Cement shall be Type CEM I – 42.5 N (or R, where appropriate), conforming to BS EN 197-1, or SRPC.

CW.2.3 Any cement delivered to Site shall be properly stored, in such a way so that separate consignments can be identified, and shall be consumed in order of delivery.

CW.2.4 Any cement below the standard required shall be removed from the Site, or from the approved Ready-Mix supplier, and replaced by the Contractor at his expense. Partially set or damaged cement shall not be used in concrete works. Different brands of cement shall not be mixed in the same batch. The Engineer reserves the right to withdraw his approval of the Ready-Mix supplier, if any cement results below the standard required.

CW.2.5 The Engineer has the right to request from the Contractor, for any consignment of cement used on the Works the cement manufacturer’s certificates in accordance with the relevant standard, which certificates shall be maintained by the Contractor and shall be attached to the Building File.

CW.2.6 Notwithstanding any certificates submitted, the Contractor shall remain responsible for the quality of the cement, and should subsequent test results indicate that any part of the Works was not in accordance with the relevant specifications, or of approved quality, because of the quality of the cement, the Engineer may direct that the Contractor remove and replace at his own expense any concrete made with that consignment of cement.

CW.2.7 Where the concrete is destined for special self-finished in-situ or pre-cast elements, no change in the type, and in the source, of cement shall be allowed during the course of production or construction, to ensure that, as far as possible, the colour of the concrete for the relative elements is constant.

CW.3 Aggregates CW.3.1 Natural aggregates for designed mixes shall be suitable for producing a concrete with a drying shrinkage of concrete not exceeding 0.075%. Aggregates shall be of consistent colour, free from absorbent particles that may cause 'pop-outs', and other particles such as coal and iron sulphide that may be unsightly or cause unacceptable staining.

Aggregates for concrete destined for special self-finished in-situ or pre-cast elements shall be obtained from one source, and it shall be ensured that adequate supplies, of a constant grading, can be maintained throughout the contract. Samples of the proposed aggregates shall be provided to the Engineer on request, where exposed aggregate finishes are envisaged. The Engineer may require that the Contractor arrange a visit to the quarry or other source of aggregate materials to inspect and approve the sources of such materials. The Contractor shall obtain approval from the Engineer before altering any constituent materials or proportions, for concrete that will be exposed in the finished work.

CW.3.2 The Contractor shall obtain approval for the proposed aggregate sources, and shall select suitable aggregate and samples of sand and aggregate for specified testing before procuring the required materials. A similar standard shall be applied to aggregates and sand delivered to the approved Ready Mix Concrete Supplier, for use in this site. Laboratory tests shall be made at regular intervals by the aggregate supplier, to confirm the suitability of the aggregate.

CW.3.3 The following criteria may be requested by the Engineer and shall be ascertained by testing to assess the suitability of aggregate: 1. Grading: Grading tests shall be carried out daily or per 100m3, whichever is the more frequent when concrete is being produced on a regular basis, or beforehand when production is irregular. The combined grading of aggregate shall be constant. The percentage passing any sieve size as determined by approved trial mixes shall be the target grading for all concrete of that type. The combined grading of the Works concrete shall not vary by more than 4% on any one sieve from that target. If the estimated or measured combined grading of the permanent Works concrete does not meet this requirement, then a new trial mix shall be prepared for approval. 2. Magnesium sulphate soundness; 3. Specific gravity and water absorption; 4. Clay, silt and dust content; 5. Organic impurities; 6. Sulphate ad chloride content; 7. Crushing value: alternatively 10% fines value or impact value as approved; 8. Elongation and flakiness; 9. Potential alkali reactivity; 10. Drying shrinkage in accordance with BRS Digest 35; Testing shall be carried out in accordance with the relevant EN, or if not available, the relevant EN standards, as appropriate, and the results shall comply with the limits given therein, or as otherwise stated herein.

CW.3.4 Except where otherwise indicated for concrete destined for special self-finished in-situ or pre-cast elements, coarse aggregate shall consist of first quality crushed hard durable coralline limestone, of the quality known as “tal-prima”, free from earth, loam, clay, organic material, chlorides or other impurities, free from an excessive quantity of quarry dust, passing an 18mm test sieve and retained on a 6mm BS test sieve; the grading shall be within the prescribed limits, so that when mixed with the approved fine aggregate and cement, a workable concrete of maximum density is produced. The amount of material passing a 75 micron fine test sieve, when tested by a wet sieving method, shall not exceed 1% by weight. The flakiness and elongation indices of the predominant size fractions in each single-sized coarse aggregate shall not exceed 20% and 35% by weight respectively.

CW.3.5 Unless otherwise indicated for concrete destined for special self-finished in-situ or pre-cast elements, the fine aggregate or sand used in all concrete work shall be obtained from approved coralline limestone quarries. It shall be clean, sharp, coarse and free from loamy matter or any other deleterious substances. The grains shall be varying uniformly in size to pass a 5mm mesh screen and retaining not less than 25% on a 3mm mesh screen, graded in between these limits. The sand shall be washed and screened.

CW.3.6 The acid-soluble sulphate in aggregate (SO32-) level shall not exceed 0.4% by weight.

The acid-soluble chloride level chloride ion (Cl-) in aggregate as a percentage by weight shall not exceed the limits given in the following table. Concrete Type Coarse Aggregate Fine Aggregate (Sand) CEM I - Reinforced 0.02% 0.04% These limits shall be subject to the overall limits given elsewhere for the concrete as mixed.

CW.3.7 The Engineer may order that any aggregates that do not meet with his approval not be used in the Works. Aggregates rejected by the Engineer shall be removed from the site by the Contractor at the Contractor’s own expense. The Contractor shall remain responsible for the quality of the aggregates. Should subsequent test results indicate that aggregates used in any part of the Works were not in accordance with the relevant Specifications, nor of approved quality, the Engineer may direct that the Contractor shall remove and replace at his own expense any concrete made with that consignment of aggregates.

CW.3.8 Coarse aggregate for concrete destined for special self-finished in-situ or pre-cast elements shall be obtained in at least two gradings, and such gradings shall be maintained constant over the period of the manufacture or construction of the relative elements. The aggregate shall be stored on a clean hard base in separate compartments or in approved hoppers in the place where the mixing of the concrete is envisaged. Suitable precautions shall be taken to prevent mixing of the sizes or types before they are batched. The storage area shall be clear of trees and care shall be taken to avoid contamination by organic or other material from whatever source. The aggregates shall always be free of pyrites or coal that may stain the surface of the concrete. The Contractor may be required to make test samples of concrete to demonstrate the uniformity and consistency of the colour of the concrete to be produced for these elements.

CW.3.9 Fine aggregate (sand) for concrete destined for special self-finished in-situ or pre-cast elements shall be natural sand within grading Zones 2 or 3. Zone 1 and 4 sands shall not be used.

CW.4 Water CW.4.1 Water shall be clean and fresh, entirely free from oil, acid, alkali, vegetable or organic matter, or any other deleterious substance in suspension or in solution or as sediment. The necessary quantity of water shall be provided by the Contractor at his own expense. Seawater shall not be used.

CW.4.2 The Engineer may require the Contractor to take water samples at intervals throughout the duration of the contract. If the samples are unacceptable, the Contractor shall either change to a new supply, or take steps to improve the existing source, as approved.

CW.4.3 The acid-soluble (SO32-) content shall not exceed 500mg/ l and the acid-soluble chloride ion (Cl-) content shall not exceed 500mg/ l. Tests to establish the contents shall be carried out at monthly intervals. These limits shall be subject to the overall limit given for the concrete as mixed.

CW.4.4 The Contractor may be required to install standby fresh water tanks of sufficient capacity to ensure continuation of concreting for sections of work being cast should water supplies be disrupted.

CW.5 Admixtures CW.5.1 Admixtures shall conform to BS EN 934-2, and shall be used strictly in accordance with their manufacturer's recommendations. In general, no admixtures containing calcium chloride shall be used. The Contractor shall ensure that admixtures are compatible with all other materials, including other admixtures. In the event of admixtures being used, the concrete tests described in these specifications shall be incorporated to ensure that the specified strengths are achieved, and comparison shall be made with concrete manufactured without the admixture to prove that the density has not been reduced. If air-entraining agents are used, the density shall not be reduced by more than 5%.

CW.5.2 When admixtures are used in the Works, very strict control shall be maintained to ensure that the correct quantity of admixture is used at all times.

CW.5.3 The Contractor shall provide, FOR THE Engineer’s approval, all technical information, including: 1. source of manufacture of the admixture; 2. the detrimental effects of adding too much or too little of the admixture; 3. whether or not the admixture leads to the entrainment of air; 4. quantity to be used; 5. the chemical name(s) of the main active ingredient(s). The admixture shall be stored, handled and used strictly in accordance with the manufacturer’s instructions. Such technical information and manufacturer’s instructions shall be submitted with the submittal for approval of the Employer’s Representative of the proposed admixture, and once approved shall be attached to the Building File. Health and safety instructions associated with the admixture shall also be submitted and so attached.

CW.5.4 In all in-situ , but particularly in reinforced concrete water-retaining structures, wall structures of small dimension and the like, as well as where indicated in the drawings, the Bill of Quantities, or instructed by the Engineer, a plasticizing/water-reducing admixture may be required to achieve workability with the lowest appropriate water/cement ratio, so as to obtain concrete with a high degree of durability, and no bleeding and associated plastic settlement and cracking. The price quoted for all concrete shall include for any plasticizer required to obtain the required workability and quality of concrete.

CW.5.5 The plasticising/water-reducing admixture shall be a liquid added directly to the freshly mixed concrete, preferably immediately prior to the discharge of the concrete from the ready-mix truck. Not more than two-thirds of the maximum recommended dosage of the plasticising/water-reducing admixture shall be dispensed at the batching plant, so that at least a third of the maximum recommended dosage is retained for dispensing on site. After dispensing of the admixture, further mixing of the fresh concrete mass for at least three minutes shall take place before discharging the concrete. The addition of the plasticizer shall modify the slump of the concrete mix without addition of water. The action of the plasticizer is likely to promote high early strength, and possibly also high ultimate strength; it shall not however act as a retarder or an accelerator of the setting of the fresh concrete unless this is specifically requested by the Engineer. In the case of the use of 7- day strength to monitor the expected 28-day strength of concrete, account shall be taken of the potential higher early strength that the addition of the admixture may produce, and the relationship this has to the ultimate strength.

CW.5.6 In all reinforced concrete directly in contact with the ground, that is in the foundations, culverts and in reinforced concrete water-retaining structures, and where specifically indicated in the drawings, the Bill of Quantities or instructed by the Engineer, a water- proofing admixture shall be used. The same admixture shall be used for water-proofing pre-cast concrete blocks for use as bond stones or elements bridging the cavity in hollow block masonry construction.

CW.5.7 The water-proofing admixture shall be a liquid added to the constituents of concrete and capable of reacting with such ingredients in order to block the movement of water in the capillaries and pores in the solid concrete, whilst still allowing the solid concrete to remain vapour permeable. It shall be free from chlorides, and shall not affect the setting time of the fresh concrete. The admixture shall be dispensed directly into the mixing water, prior to the addition of aggregates, strictly in accordance with the manufacturer’s instructions.

CW.5.8 Where the delivery of ready-mix concrete is likely to be affected by long haulage distances or high ambient temperatures, such that the concrete arriving on site has already started to set, and hence to lose slump and workability, a set retarding admixture shall be used. It shall be absolutely forbidden to add additional water after departure from the ready-mix depot, and to re-temper. The price quoted for all concrete shall include for any set retarder required to obtain the required workability and quality of concrete. The set-retarding admixture shall be a liquid dispensed directly into the mixing water prior to its

addition to the aggregates. All details of set retarder used shall be submitted to the Engineer and recorded in the Building File.

CW.5.9 In concrete destined for the in-situ reinforced concrete foundations the reinforcement shall be protected by the use of an organic-based corrosion inhibitor admixture. The corrosion inhibitor shall be added to the mixing water of the fresh concrete in accordance with manufacturer’s instructions. It shall not be mixed with any other admixture before being introduced into the mixer. The corrosion inhibitor shall be capable of adsorption to the reinforcement to produce a protective film on the steel surface, and to delay the onset of corrosion even in the presence of marine chlorides. The corrosion inhibitor shall have no effect on the temperature development profile of the concrete, and shall not significantly affect the time available for placing of the concrete and for finishing. It shall also not affect the bond strength between the concrete and the steel. The price quoted for any concrete where a corrosion inhibitor is indicated shall include for such admixture. All details of corrosion inhibitors used shall be submitted to the Employer’s Representative and recorded in the Building File.

CW.6 CW.6.1 The formwork shall be designed and constructed to withstand the worst combination of: - Total weight of formwork, reinforcement and concrete. - Construction loads including dynamic effects of placing, compacting and construction traffic. - Wind loads. CW.6.2 The design of the formwork shall be the responsibility of the Contractor. Formwork shall be designed by competent personnel experienced in the design, construction and use of formwork for the production of high quality concrete surface finishes. The design shall be such that the formwork may be erected, supported, braced and maintained so that it will safely support all loads that may be applied until the concrete has hardened sufficiently to support such loads itself. The formwork shall be capable of being struck and removed safely and without causing shock or excessive stress to be applied to the concrete structure.

CW.6.3 The Contractor shall submit detailed shop drawings for the formwork to be utilised for special self-finished in-situ and pre-cast concrete. The formwork shall be manufactured in steel, and in sections that will then be assembled on site. If the Contractor wishes to manufacture formwork with other materials he shall demonstrate that the formwork can still have the required rigidity to be capable of producing concrete within the specified tolerances, and to maintain the specified standards to the end of the proposed number of re-uses.

CW.6.4 At time of placing it shall be ensured that all surfaces on which concrete is to be placed are clean, with no debris, tying wire clippings, fastenings or free water. Where it is intended to re-use formwork, it shall be thoroughly cleaned and made good to the satisfaction of the Engineer.

CW.6.5 Adequate propping shall be provided to prevent deflection and damage to the structure. Such props shall be carried down to bearings strong enough to provide adequate support. The additional props shall be carried through the floors until an appropriate bearing is found.

CW.6.6 Positions and details of inserts, holes and chases shall ensure that inserts or box outs are fixed as required in correct positions prior to the placing of concrete. All holes and chases shall be formed, and no hardened concrete shall be cut.

CW.6.7 Adequate allowance for deflection of formwork under weight of fresh concrete shall be made. Unless otherwise indicated, all beams of more than 5m span shall be laid to a camber the height of which shall equal in millimetres 140 times the square of the span in metres divided by the depth of the beam in millimetres. The top surfaces of concrete must also be cambered to maintain the required structural depths and profiles. After striking of formwork and removal of props the levels shall be checked to determine extent of any residual camber.

CW.6.8 All formwork shall be constructed so that the true dimensions, shown in the approved drawings are maintained without deflecting more than 1/600 of the unsupported span. Formed surfaces must be free from twist and bow (other than any required cambers), all intersections, lines and angles being square, plumb and true or to the required shapes (such as splayed jambs etc). The Contractor shall make allowance for any settlement or deflection of formwork that will occur during construction so that the hardened concrete shall be within the specified tolerances. The standard of dimensional accuracy of the finished concrete in special self-finished in-situ concrete shall comply with the highest grade in the most recent edition of the document Accuracy in Building.

CW.6.9 Vertical faces of strip footings, bases and slabs may be cast against faces of excavation provided the faces are sufficiently accurate and stable, and adequate measures are taken to prevent contamination of concrete. Faces of walls must be cast against formwork.

CW.6.10 The formwork shall be sufficiently tight to prevent loss of grout, using seals when necessary, especially during vibration, and shall comply with the standards of finish required by this specification. Formwork shall be secured tight against adjacent concrete to prevent formation of steps. All formwork shall be cleaned of all rubbish and deleterious material by means of compressed air before placing the reinforcement and casting.

CW.6.11 All surfaces to come in contact with the concrete shall be treated with a non-staining mould releasing oil or other approved material to prevent adhesion. The release agent shall be one of the following types: (a) cream emulsion, (b) neat oil with surfactant added, (c) chemical release agent. Care shall be taken that the coating material is kept out of contact with reinforcement or embedded steelwork. The same type and make shall be used throughout the entire area of any one finish. The release agent shall be applied evenly, and in a very thin film, to formwork faces, from top downwards, and to horizontal surfaces last, and the minimum amount necessary to obtain a clean release shall be used, so as to prevent excessive local collection. The release agent shall, wherever possible, be applied the day before concreting. Temporary openings shall be provided in stop-ends for the removal of water and debris. All details of release agents used shall be submitted to the Engineer and recorded in the Building File.

CW.6.12 All shuttering and formwork shall be inspected by the Engineer before concrete is placed within it.

CW.6.13 The material and positioning of any ties passing through the concrete shall be approved by the Engineer. The whole or part of any tie passing through the concrete shall be capable of being removed so that no part remaining embedded in the concrete shall be nearer the surface than the specified cover to reinforcement. No metal part of any device for securing forms shall remain within the specified . Any holes left after the removal of ties shall be plugged immediately with a cement mortar of the same richness using non-shrink materials. Particularly in water-retaining structures, through bolts, which are entirely withdrawn on stripping the formwork, shall be used and holes shall be sealed with corks coated with adhesive or other approved material well rammed in from the concealed face. The other side shall be plugged with semi-dry 1:3 cement-sand mortar, well rammed in. Alternatively, the Contractor may propose the use of lost anchors.

CW.6.14 The positions and details of holes and chases shall be confirmed to ensure that alterations to and decisions about their size and location are not made without the knowledge and approval of the Engineer. Inserts or box outs shall be fixed as required in correct positions before placing concrete. All holes and chases shall be formed, and hardened concrete shall not be cut without approval of the Engineer.

CW.6.15 Stop ends for movement joints or construction joints shall be made by splitting them along the lines of reinforcement passing through them, so that each portion can be positioned and removed separately without disturbance or shock to the reinforcement or the concrete. Stop ends made of expanded metal or similar material may only be left permanently in the special self-finished in-situ concrete if any metal ends up permanently in the concrete closer to the surface of the concrete than the specified cover to the

reinforcement. Wood strips inserted for Engineerural treatment shall be kerfed to permit swelling without pressure on the concrete.

CW.6.16 The formwork shall be struck without disturbing, damaging or overloading structure, and without disturbing props. Notwithstanding any other clauses in this specification and any checking or approvals by the Engineer, the responsibility for safe removal of any part of the formwork and any supports without damaging the structure shall rest solely with the Contractor. Formwork shall be removed at times to suit the requirements for its curing and to prevent restraint that may arise from elastic shortening, shrinkage or creep.

CW.6.17 The use of concrete or plastic cover blocks or spacers on face work (exposed self-finished in-situ or pre-cast concrete faces) shall not normally be permitted. The reinforcement shall be held in place by timber battens of a thickness to give the cover required, and which shall be withdrawn progressively as the concrete proceeds. Care shall be taken to avoid scratching or otherwise damaging the form face during this process. Alternatively, the reinforcement cages shall be formed into cages that are rigid enough so as to be self- supporting.

CW.6.18 The following minimum periods (in days) for retaining formwork in position before striking shall apply to class CEM I- 42.5, or SRPC concrete with no admixtures: Average mean of daily minimum and maximum air temperatures during the Type of formwork period 16degC 7degC 3degC

Vertical formwork to 0.5 0.75 1 columns, walls & beams

Soffit forms to slabs 4 6 8 Props to slabs & soffit 10 15 20 forms to beams Props to beams 14 21 28

CW.6.19 The use of retarders on formwork shall not be permitted. A surface retarder may, however, be used for preparing a concrete surface for adhesion to, and for creating a mechanical key with, subsequent concrete casting operations. For concrete destined for an exposed aggregate finish, an approved surface retarder shall be applied to the formwork prior to casting of concrete. The surface retarder appropriate to the absorbance of the formwork shall be used. The surface retarder shall be applied by brush, roller, spray (after dilution with the appropriate thinners), and shall be allowed to dry in accordance with manufacturer’s instructions before concreting takes place. The formwork shall be struck within the maximum time allowed for by the manufacturer’s instructions, and the retarder shall be thoroughly washed with a strong water jet to remove the paste as soon as possible. Any surface retarder remaining on the dried formwork shall be removed with a spatula or wire brush, or shall be neutralised with cement slurry or soda solution before removal. The price quoted for any such special concrete shall include for any surface retarder required to obtain the required surface finish. All details of surface retarder used shall be submitted to the Engineer and recorded in the Building File.

CW.7 Fresh Concrete CW.7.1 The concrete shall be produced in accordance with the relevant clauses of BS EN 206-1, generally of compressive strength class C25/30, (C8/10 for un-reinforced infill, and in-filling of hollow block work, and C20/25 for kerbs, edgings, pre-cast concrete bond stones, blinding layers), or as otherwise specified in approved drawings. The maximum aggregate size shall be 20mm. Chloride content shall be Class 0,40, for all reinforced concrete. Consistence class shall be appropriate to the element being constructed, and to the intended method of placement, namely S3 for foundations, and S2 for slabs, beams and lintels.

CW.7.2 Specific minimum cement content, cover and workability requirements may be required for special self-finished in-situ and pre-cast concrete. Concrete that is destined for bush-

hammering or point-tooled finish shall have a minimum cement content of 360kg/m3, whilst concrete destined for finishes obtained by abrasive blasting shall have a minimum cement content of 330kg/m3. For these special finishes the Contractor shall provide, as early as possible in the contract period, a sample panel, for every different type of texture or finish, of at least 2m square in accordance with the specification to confirm the suitability of the chosen mix and the formwork to give the desired finish. The sample shall include one horizontal construction joint to the details shown on the drawings and shall be finished exactly in accordance with the specified finish.

CW.8 Transporting, Placing and Compacting CW.8.1 During transport of fresh concrete, steps shall be taken to avoid contamination, segregation, loss of ingredients, excessive evaporation and loss of workability. Concrete shall be covered during heavy rain. Equipment shall be cleaned immediately after use and whenever cement or aggregate is changed. Suitable walkways and barrow runs shall be used for traffic over reinforcement and freshly placed concrete. In the case of transport of fresh concrete for special self-finished in-situ or pre-cast elements, all containers into which materials are placed shall be clean and free of dirt, hardened concrete and materials not intended for inclusions in the concrete.

CW.8.2 For water-tight concrete, the build-up of high temperatures and steep temperature gradients during the first 24 hours after casting, particularly in hot weather, shall be avoided, and rapid changes in temperature during the first 7 days after casting, shall be prevented.

CW.8.3 The time, date and location of all pours shall be recorded by the Contractor. The concrete shall be placed as soon as practicable after mixing and while sufficiently plastic for full compaction. It shall not be allowed to add water or to re-temper mixes after discharge from the mixer. The concrete shall be placed without disturbance to the formwork of the reinforcement, or without contamination by soil or earth in the case of foundations. It shall be ensured that any pipes, ducts, fixings, and hole-formers to be cast in are properly secured, and that no concrete can enter the open ends of pipes and conduits. The Contractor shall ensure that temperature of concrete is not more than 30 deg C in hot weather and not less than 5 deg C in cold weather. The concrete shall be placed in its final position in one continuous operation up to construction joints; the formation of cold joints shall not be allowed. It shall not be allowed to discharge from an excessive height or through reinforcement or other obstructions in a way which may cause uneven dispersal, segregation or loss of ingredients or adversely affect the formwork or formed finishes. Suitable chutes or trunking shall be used where necessary. The concrete shall be placed in layers no thicker than can be effectively compacted with the equipment being used, without delay between layers. The layers shall be merged together by compaction. It shall not be allowed to use immersion vibrators to make concrete flow horizontally into position, except where necessary to achieve full compaction under void formers and cast in accessories and at vertical joints.

CW.8.4 At time of placing it shall be ensured that all surfaces on which concrete is to be placed are clean, with no debris, tying wire clippings, fastenings or free water.

CW.8.5 Before placing structural concrete (not blinding concrete) on hard stone and chippings or other absorbent substrates, polyethylene sheet, 250 microns thick, shall be laid, with lap edges of 150 mm.

CW.8.6 Details of proposed locations of construction joints shall be subject to the approval of the Engineer.

CW.8.7 The Engineer shall be informed before each pour of concrete to allow, if so desired by the Engineer, the opportunity of inspection of reinforcement and surfaces against which concrete is to be placed. The period of notice to be given shall be agreed with the Engineer.

CW.8.8 Concrete shall be fully compacted to full depth (until air bubbles cease to appear on the top surface), especially around reinforcement, cast-in accessories, into corners of formwork and at joints, by immersion vibrators with a frequency of at least 8000 cycles per

minute. Compaction shall start immediately before the concrete is placed, and shall continue during the placing operation so that at no time shall there be a large volume of un-compacted concrete in the formwork. Sufficient immersion vibrators shall be available to ensure that delays, or incomplete compaction, are not caused by mechanical breakdowns. Amalgamation with previous batches shall be ensured, but not to the extent that adjacent partly hardened concrete is damaged. Tamping, ramming or vibrating shall be completed within thirty minutes of mixing. Immersion (poker) vibrators shall not be applied to the reinforcement or to the formwork, unless it is ensured that the latter is rigid enough. The immersion (poker) vibrator shall not remain in contact with the concrete after ten minutes from pouring. Each immersion shall not be for a period longer than 30 seconds, and the vibrator must be withdrawn slowly to ensure no air pockets are left. Points of vibration shall not be further apart than 750mm.

Where, one hour after completing a lift, bleeding of the mixing water is apparent, external vibrations shall be applied to the top 300mm of the concrete and if, because of this additional vibration, the concrete settles in the formwork, it shall be topped with fresh concrete of the same mix and tamped level with the top of the formwork. Concrete shall not be subjected to disturbance between 4 hours and 24 hours after compaction except with the agreement of the Engineer. Whenever vibration has to be applied externally, the design of formwork and disposition of vibrators shall ensure efficient compaction and the avoidance of surface blemishes.

CW.8.9 At the top of deep sections and at significant changes in the depth of concrete sections, the fresh concrete shall be closely and continuously inspected for signs of settlement during the first few hours after placing. While the concrete is still capable of being fluidised by the vibrator, re-vibration shall be applied as necessary to remove settlement cracking that may be forming either on the top surface or against the upper part of the vertical formwork.

CW.8.10 Surface evaporation from concrete throughout the period(s) specified below shall be prevented by: - Retaining formwork in position and, if necessary, covering surfaces immediately after striking, and - Covering top surfaces immediately after placing and compacting each bay, removing covering only to permit any finishing operations and replacing immediately thereafter. Coverings shall be suitable impervious sheet materials or a suitable curing compound containing a fugitive dye and with an efficiency of at least 75% (90% for surfaces exposed to abrasion). This could be achieved by using a minimum of two layers of wet Hessian, or by covering with polythene sheeting, or by applying a patent curing membrane. Coverings shall be effective in preventing evaporation, particular attention being paid to sealing at edges and junctions, and shall not disfigure permanently exposed surfaces, or affect the satisfactory bond of subsequent construction and finishes. Curing compounds applied to surfaces which will be exposed in the finished work or which are to receive bonded finishes shall be removed by light, even grit blasting. Until the exposed top faces of fresh concrete are in a state suitable to receive sheets in direct contact or a sprayed curing compound as applicable, the surfaces shall be covered with waterproof sheeting held clear of the surface and well sealed against draughts at edges and junctions.

CW.8.11 Curing periods, in days, (t = the average number of degrees centigrade air temperature during the curing period) shall generally be as follows: For concrete surfaces that will be exposed, concrete wearing surface floors and pavements, and watertight concrete: Concrete made using CEM I- 42.5, SRPC Drying winds or dry sunny weather, 140/(t+10) Intermediate conditions 100/(t+10) Damp weather, protected from sun & wind 100/(t+10)

For other structural concrete surfaces: Concrete made using CEM I- 42.5, SRPC Drying winds or dry sunny weather, 80/(t+10) Intermediate conditions 60/(t+10) Damp weather, protected from sun & wind no special requirements

CW8.12 The Contractor shall take steps to prevent damage to concrete, including: - protecting surfaces generally, from rain, indentation and other physical damage. - protecting surfaces to be exposed in the finished work, from dirt, staining, rust marks and other disfiguration. - protecting immature concrete, from thermal shock, physical shock, overloading, movement and vibration.

CW.9 Testing/Certification CW.9.1 Sampling and testing of hardened concrete shall comply with BS EN 206.

CW.9.2 Complete correlated records shall be maintained by the Contractor for each mix including: - Information in accordance with BS EN 206 - All sampling, site tests and identification numbers of all specimens tested in the laboratory. - The location of the part(s) of the structure represented by each sample. - The location in the structure of the batch from which each sample is taken.

CW.9.3 Concrete test-cubes shall be made, cured and tested, in accordance with BS EN 206, at the expense of the Contractor. At least four samples from each truckload shall be made, two tested at 7 days and two at 28 days; otherwise, the sampling rates indicated in BS EN 206. Each sample shall be marked on its surface, without etching any of the surfaces, with a distinguishing number and the date, and a record shall be kept of the following data: Delivery note number Date Cube number Work location within Site Design mix Name of sampler Crushing test results Date Strength Density All samples shall be stored on site in their moulds for at least 24 hours, in a place free from vibration, under damp matting and completely covered with polythene. When the concrete has matured sufficiently the samples shall be de-moulded and immediately submerged until they are taken for testing. No sample shall be dispatched for testing before it is three days old.

CW.9.4 All specified testing shall be carried out by an independent and approved laboratory. The Contractor shall submit the name of the selected laboratory to Engineer, for approval, as soon as possible and in any case before making trial mixes or concrete for use in the works. Copies of test reports shall be despatched to the Engineer within one day of the completion of each test. A complete set of reports shall be kept on site. In addition, the test laboratory shall keep separately the pieces of each cube that fails to meet the compliance requirements for individual results.

CW.9.5 A regime of accelerated or normal curing and early testing which is capable of predicting the 28 day strength of concrete mixes may be used for determining compliance, subject to prior approval. If such a regime is adopted, two additional samples must be made from

each sample and cured normally so that, in the event of non-compliance, they can be tested at 28 days to provide information that will help in deciding the action to be taken.

CW.9.6 If a concrete sample fails to achieve specified criteria or to pass specified tests, the Engineer shall be informed without delay and the Contractor shall submit to the Engineer: - Confirmation of the validity of the test results, and/or - Proposals for further tests to assess the strength of the concrete in the structure, and/or - Proposals for rectification. The Engineer may issue instructions for the work to be stopped or delayed until reasons for the failure have been established, possible consequences assessed and appropriate preventative and remedial measures taken.

CW.9.7 Wherever the specified sampling, testing and compliance procedures show that a concrete mix is not in accordance with the specification (even if the work is eventually accepted), and measures are taken to help in establishing whether or not the work is acceptable, such measures: - will be at the expense of the Contractor, and - will not be considered as grounds for extension of time. The criteria of compliance shall be as specified in BS EN206. A qualified acceptance may be made, provided the Engineer is satisfied that the technical consequence of non- compliance is not serious.

CW.9.8 Sudden irregularities in the surface of concrete structural floors shall not be permitted. When measured with a slip gauge, the variation in gap under a straightedge (with feet) placed anywhere on the surface shall not be more than the following:

Floors which are to be self-finished, and floors 5 mm under a 3 m straightedge to receive sheet or tile finishes directly bedded in adhesive 2 mm under a 1 m straightedge Floors to receive /toppings/beds up 10 mm under a 3 m to 50 mm thick straightedge Floors to receive mastic asphalt flooring or 10 mm under a 3 m underlay laid over mastic asphalt levelling straightedge coat(s) as recommended in Concrete Surface regularity of wearing surfaces of Society Technical Report 30 (TR structural concrete ground floors 34) and supplement CS 114.

CW.9.9 Watertight concrete shall be tested in accordance with clause CW.9.10. If the work fails to meet the specified tests, further tests and investigations shall be carried out to identify the cause or causes of leakage. Remedial work by pressure grouting, waterproof rendering or other approved means necessary to make the work watertight, shall be carried out. On completion of the remedial work the specified test for water-tightness shall be repeated. Payment for such investigations, remedial work and additional tests may be withheld if and to the extent that the cause of leakage was the Contractor's failure to comply with the specification, drawings or other instructions.

CW.9.10 Testing of water retaining structures shall be carried out by: - Filling the completed structure to capacity with water, at a uniform rate not exceeding 2 m depth in 24 hours; - Maintaining the level by adding further liquid for an agreed stabilizing period. - Marking and recording the exact filled level, then recording the drop in level at intervals of 24 hours for the next 7 days. The total drop in level over the 7 days should not exceed 10 mm after allowing for evaporation and rainfall. If the drop in level during the first 7 days exceeds the permissible drop, the structure shall be refilled and the test repeated for a second period of 7 days. If the permissible drop in level is still exceeded, but the daily drop in level is decreasing, the structure shall be refilled and the test repeated for a third and final period of 7 days, the results of which will determine compliance.

CW.10 Reinforcement for In-situ and CW.10.1 All steel reinforcement shall comply with BS EN 10080, and shall be cut and bent to relevant EN standards. For each consignment of reinforcing steel, the Contractor shall retain Manufacture’s test sheets, including Ladle analysis, and the Mill Test Certificate indicating the grade of steel being provided, and the Test Certificate reference number; in addition, the Contractor shall supply the importation reference code for traceability purposes. This information shall be included in the Building File on a regular basis.

CW.10.2 Reinforcement shall not be roughly handled, dropped from a height, or subjected to shock loading or mechanical damage. At the time of placing concrete, reinforcement shall be clean and free of corrosive pitting, loose mill scale, loose rust, oil and other substances that may adversely affect the reinforcement, concrete, or bond between the two.

CW.10.3 Laps in nominal bar reinforcement shall conform to the requirements of EC2. Structural welded joints shall not be permitted, except for tack or positional welding between plain mild steel rods crossing approximately at right angles so as to fix them in position. Welding of high tensile or work hardened mild steel rods will not be allowed. Mechanical joints may be substituted for lapped joints subject to full details, including joint type(s) and location(s), being submitted for approval. In order to prevent rust staining, all starter bars for special self-finished in-situ or pre-cast concrete shall be covered with plastic sleeves or, where heavy reinforcement projects through the concrete with a waterproof cover, or alternatively projecting steel shall be thoroughly but thinly covered with a cement- polyvinyl acetate grout.

CW.10.4 The welding of miscellaneous fixings such as holding-down bolts, edging angles etc., to the reinforcement detailed on the Drawings shall not be permitted. However, the Contractor may add lengths of austenitic stainless steel reinforcement which is to be conventionally wire-tied to the detailed reinforcement, and to which he may weld for the purposes of providing adequate support for fixings during the placing of concrete. An electrically insulating material such as plastic may need to be inserted between the additional reinforcement and the detailed reinforcement in order to minimize corrosion due to stray electrical currents.

CW.10.5 Unless otherwise permitted reinforcement shall be fixed in position before placing concrete. In addition to any spacers and chairs shown on drawings or schedules, adequate support and secure ties shall be provided to maintain the specified cover. The Contractor shall comply generally with Concrete Society Report CS 101 'Spacers for reinforced concrete' 1989. Unless otherwise specified 16 swg annealed tying wire shall be used and it shall be ensured that tying wire does not intrude into the concrete cover. No tack weld shall be allowed. Reinforcement shall not be placed or fixed in contact with nonferrous metals.

CW.10.6 All reinforcement shall be free from oil, loose rust, loose mill scale, paint, grease, mud or other matter likely to interfere with the adhesion between steel and concrete.

CW.10.7 Reinforcement shall in all cases be covered with the thickness of concrete shown on the approved drawings. Accurate cover shall be secured by the use of plastic distance pieces of the correct size or other approved means. For all exposed external work, the cover required shall be increased by 5mm to allow for material removed by tooling.

CW.10.8 On no account shall any reinforcement be left out for insertion into wet concrete during the progress of concreting, and in no case may any portion of the concrete be put into position and allowed to set in order to act as a base upon which to set up any of the reinforcement for the member.

CW.10.9 The position of the reinforcement in the hardened concrete shall be checked as soon as practicable after casting using a magnetic induction digital display type . Particular attention shall be paid to columns, beams, cantilevers, soffit of slabs and all faces that will be exposed to the weather in the finished building.

CW.10.10 Making good, particularly for special self-finished in-situ or pre-cast concrete shall be kept to an absolute minimum. Where it is essential, such as when it is necessary to fill tie-rod holes, this shall be done using the same mix as the concrete except that the coarse aggregate shall be excluded and that the cement shall consist of a mixture of white and ordinary grey contained in such proportions that the colour of the making good mortar matches exactly that of the surrounding hardened concrete. The area to be made good shall be cleaned thoroughly first by brushing and washing with clean water and then the filling shall be well compacted by trowel or rod and finished with a float faced with a rubber sponge.

CW.11 Finishes CW.11.1 Rough board finish shall consist of rough textured softwood boards with smooth planed joint faces, seasoned to a moisture content of not more than 25% and not less than 18%, arranged to give uniform overall effect, and assembled to prevent penetration of grout between them. The finish shall be left as struck.

CW.11.2 Plain fair-faced smooth finish shall mean a smooth even finish produced with a sheet material (e.g. lined plywood), with panels arranged in a regular pattern as a feature of the surface; - Abrupt irregularities shall not be greater than 5 mm. - Gradual irregularities, expressed as maximum permissible deviation from a 1 m straight edge, shall not be greater than 5 mm. - Variation in colour resulting from the use of an impermeable form lining shall be permitted but the surface shall be free from discolouration caused by contamination or grout leakage. - Blowholes less than 10 mm in diameter shall be permitted but otherwise the surface shall be free from voids, honeycombing, segregation and other large defects. - Projecting fins shall be removed and the concrete surface shall be rubbed down with a wet carborundum stone but otherwise the finish shall be left as struck. Making good of small defects will normally be permitted after inspection. - Formwork tie holes shall be in an approved regular pattern, filled with matching mortar to an approved sample.

CW.11.3 Bush hammered finish shall mean applying to the hardened concrete blows with a bush- hammer with a roller head, in order to remove the initial surface and to obtain a light texture. The bush-hammering shall be applied when the concrete is at least 3 weeks old, or before it has reached a compressive strength of at least 25N/mm2, whichever is the later. The bush-hammering shall not remove more than 3-4mm of surface material. Tooling shall stop short of arrisses,

CW.11.4 Washed exposed aggregate finish shall mean applying a set retarder to the surface of the concrete, and washing and brushing with a soft brush four hours after striking the formwork. The shall be struck not later than 3 days after casting, depending on the ambient temperature. Trials shall be carried out to establish the optimum striking time and optimum time for washing and brushing after striking, so as to achieve a medium deep texture. The concrete shall contain a mixture of white and grey cement, and white marble or quartz aggregate or other special aggregate. The total aggregate content of the concrete for this type of finish shall be around 70%.

CW.11.5 Broom-finish concrete shall be formed by drawing a stiff broom or wire brush across the previously power floated horizontal surface treated with a surface hardener while still green, to produce a lightly textured surface suitable for vehicular traffic.

CW.11.6 Tamped finish shall be formed by tamping the cast horizontal concrete surface with edge of a board or beam to give an even texture of parallel ribs.

CW.11.7 Floated finish shall be formed either by using a wood float to give an even slightly coarse texture to the cast horizontal concrete surface, or by using a hand float or skip float on the cast horizontal concrete surface to give a level and even surface, in both cases without ridges or steps.

CW.11.8 Power floated finish shall be formed by using a power float on the green concrete to give an even level compact surface with no ridges or steps.

CW.11.9 Power ground finish for wearing surfaces shall be formed by floating to an even surface with no ridges or steps, then immediately commencing curing as specified previously. When concrete is sufficiently hard for sand particles not to be torn from the surface, power grinding shall be used to remove 1-2 mm from surface to give an even glass-paper texture, free from blemishes and trowel marks. All dust shall be removed and the surface washed down. Curing shall be resumed without delay.

CW.11.10 Surface hardener shall consist of natural mineral aggregate (quartz) aggregate dry shake surface hardener, applied at the approximate rate of 5 to 7 kg/m2, or as otherwise recommended by the manufacturer, monolithically on the green concrete, during the power ground finishing, so as to produce a surface with increased resistance to penetration of oils and grease, with increased slip resistance, and which can be easily cleaned. A suitable surface hardener shall be Armorex Quartz or approved equivalent.

CW.11.11 Surface sealer, where required, shall consist of an approved clear acrylic resin polymer sealer, with or without an integral colour, applied by a single spray application, to the concrete wearing surface floors in accordance with manufacturer's recommendations, in order to cure, harden, seal and dustproof the concrete. Surface sealer shall be used on all internal vehicular circulation routes.

CW.11.12 All construction/movement joints shall be accurately located, straight and well-aligned, and truly vertical or horizontal or parallel with the setting out lines of the building. Joints shall be formed accurately to detail and in locations shown on the approved drawings. Concrete shall not be allowed to enter any gaps or voids in the formwork or to render the movement joints ineffective, or to impregnate or penetrate any materials used as compressible joint fillers. Concrete shall not be placed simultaneously on both sides of movement joints. Construction joints in watertight concrete, additional to joints required by the designer, will not be permitted. Construction joints in concrete exposed to view, additional to joints required by the designer, will not be permitted. Construction joints in concrete wearing surface floors, additional to joints required by the designer, will not be permitted. Formed joints in concrete wearing surface floors shall be square edged with a steel top surface and in good condition. Construction joint faces shall be brushed and sprayed while concrete is still green to leave a thoroughly roughened exposed aggregate finish. Construction joints, particularly for special self-finished in-situ concrete, shall be prepared in accordance with the approved drawings. Horizontal joint surfaces shall be well brushed with a wet brush and washed off with a spray of water 2 to 4 hours after casting to expose the aggregate and to provide a key for the next lift. Before the formwork for the next lift is placed the exposed aggregate shall be well scrubbed to remove all laitance and loose material.

CW.11.13 Unless otherwise indicated on the approved drawings, all exposed arrises shall be chamfered 25mm x 25mm. Any defective concrete finish shall be rejected and the defect(s) cut out and made good.

CW.12 Performance Specified Proprietary Floors CW.12.1 Composite pre-slab floors shall consist of pre-stressed or reinforced permanent concrete slabs, typically 60mm thick, with a typical width of 2400mm, laid to receive in-situ concrete. Composite pre-slab floors may be allowed as alternatives to in-situ concrete slabs, at the discretion of the Engineer, and are subject to the submittal of detailed design literature.

CW.12.2 The Contractor shall submit the name of the proposed manufacturer to the Engineer for approval, and, following approval, shall supply detailed design literature to the Engineer. Pre-cast elements shall be supplied accompanied by a certificate attesting the quality control procedures under which they have been manufactured, their geometrical characteristics and the characteristics of the materials used in their manufacture. They shall be installed in strict accordance with the manufacturer’s recommendations. The pre- cast slab manufacturer or specialist subcontractor shall be required to prepare location

and assembly drawings showing every aspect of the construction, incorporated components and features, trimming for voids, holes for services, any additional steel reinforcement forming part of the pre-cast slab system to be incorporated in the cast-in situ part of the slab, any other structural members shown on the approved drawings and related work by others. Basic fire resistance shall be determined without regard to applied finishes and in accordance with BS EN 1992.

CW.12.3 Composite pre-slab floors shall be transported to the site in stacks, on semi-trailers, with stacking bearers at approximately 1.5m centres to minimise stresses during transport. The panel schedule shall include all details on any penetrations or block-outs, which shall be formed into the panels during manufacture. Small penetrations, such as those required for waste pipes and electrical outlets can be formed on site by core-drilling. Where temporary prop supports are specified by the manufacturer, the props shall be rigid and stable, and laid out in accordance with the specified spacing limits. Unless otherwise specified in writing by the manufacturer, the panels shall be lifted from 4 points, for panels of up to 8m length, from 8 points for panels of up to 10m length, and using an appropriate lifting frame for panels greater than 10m. In the case of reinforced pre-cast panels, with projecting reinforcement trusses, the lifting hooks or shackles shall be passed through both top and diagonal reinforcing bars.

CW.12.4 Concrete topping and joint infill shall be laid against thoroughly clean and wet surfaces of pre-cast units, avoiding segregation, and compacting thoroughly to eliminate voids. It shall be ensured that the pre-cast units do not move until concrete has gained sufficient strength. A grouting mixture, consisting of three parts sand to one part cement, shall be used to fill the side and end joints. Where a structural concrete is to be used, the joints between slabs shall be grouted at the same time as the screeding operation.

CW.12.5 All bearing surfaces for pre-cast panels shall be level to ensure alignment between units and to minimise twisting of panels; in the case of bearing on masonry walls, the bearing surfaces may require levelling with concrete mortar. All bearing surfaces for the pre- stressed panels shall be level. Bearing lengths shall not be less than 100mm.

CW.12.6 In situations where the composite pre-slab soffit is to be used as an exposed finish, the longitudinal joint shall be filled to form a smooth surface. Where expanded polystyrene void formers are specified, the formers shall be made of lightweight cellular plastic material, treated with a fire retardant additive. The polystyrene formers shall be attached to the panels at the factory. The thickness of concrete topping above void formers shall not be less than 65mm.

CW.13 Concrete Screeds CW.13.1 Concrete screeds for roofs and floors shall generally be of partially bonded construction and shall normally consist of 75mm thick Grade C15 concrete, in accordance with approved drawing details. The screed shall be power float finished smooth, as described in these specifications.

CW.13.2 Shortly before laying screed, the levelling screed shall be thoroughly washed clean and kept well wetted for several hours. Free water shall be removed and a slurry bonding coat of creamy consistency shall be brushed in. Alternatively, a proprietary screed bonding agent shall be used. Details of such bonding agent shall be attached to the Building File. The concrete screed/topping shall be laid while slurry or bonding agent is still wet to ensure a good bond.

CW.13.3 No admixtures containing calcium chloride shall be used. The water content of mixes shall be the minimum necessary to achieve full compaction, low enough to prevent excessive water being brought to the surface during compaction. Materials shall be mixed thoroughly to a uniform consistence. Mixes other than no-fines shall be mixed in a suitable forced action mechanical mixer. A free fall type (drum) mixer shall not be used. Concrete screeds shall be used whilst the mix is sufficiently plastic for full compaction. Ready-mixed retarded screed mortar shall be used within the working time and site temperatures recommended by the manufacturer. Re-tempering shall not be allowed.

CW.13.4 Screeds/toppings shall not be laid unless their surface temperature can be maintained above 5degC for not less than 4 days thereafter. In hot weather the time between operations shall be reduced or alternatively other measures shall be used to prevent premature setting or drying out.

CW.13.5 Before starting work, it shall be ensured that the levelling screed (“torba”) bases for concrete screeds are such as to permit specified levels and flatness/regularity of finished surfaces, bearing in mind the permissible minimum and maximum thickness. All surfaces shall be sound and free from significant cracks and gaps, and bases shall be clean and free from plaster, dirt, dust and oil. Concrete slabs to receive fully or partially bonded construction shall be allowed to dry out by exposure to the air for not less than 6 weeks.

CW.13.6 Where screeds are to be cast in bays, all joints shall be coordinated with the movement joints required for the floor finish and/or the structural base. Unless otherwise specified, bay sizes shall not be more than 10sq m, and the ratio of length to breadth not more than 3:2, a joint occurring over every construction joint in the base slab. Control joints, 10mm wide, shall be left between the screeding bays. These joints shall subsequently be filled with cement slurry. Where location of bay joints is not shown on drawings the Contractor shall obtain approval before starting work. Forms for joints shall be square edged with steel top surfaces, securely fixed. Concrete screeds shall be compacted thoroughly at edges to give level, closely abutted joints with no lipping. Alternatively, toppings may be cast continuously, bay joints being formed with approved plastics or metal dividing strips.

CW.13.7 Permissible deviations in the level of surface of screeds (allowing for thickness of coverings) and toppings, measured from the datum shall not exceed +/-10 mm.

CW.13.8 Sudden irregularities in the surface of screeds or toppings shall not be permitted. When measured with a slip gauge, the variation in gap under a straightedge (with feet) placed anywhere on the surface shall not be more than the following: - Screeds to receive toppings or beds 15-30 mm thick: 10 mm under a 3 m straightedge - Screeds to receive mastic asphalt flooring/underlays: 5 mm under a 3m straightedge - Screeds to receive sheet or tile finishes bedded in adhesive: 5 mm under a 3m straightedge Falls shall be sufficiently even to prevent ponding.

CW.13.9 Curing and surface finishes shall be as previously specified. Roof screeds shall be covered during wet weather, and the building programme shall be arranged to ensure that they are as dry as practicable when weather-tight coverings are laid.

CW.14 Precast Concrete CW.14.1 All the above specifications shall apply to the pre-cast concrete mix. Pre-cast elements shall be supplied accompanied by a certificate attesting the quality control procedures under which they have been manufactured, their geometrical characteristics and the characteristics of the materials used in their manufacture. They shall be installed in strict accordance with the manufacturer’s recommendations. Manufacture CW.14.2 All pre-cast units shall be manufactured in accordance with the details shown in the approved drawings and in accordance with this Specification. They shall be fabricated straight, smooth, and true to size and shape, with exposed edges and corners precise and square, unless otherwise indicated.

CW.14.3 Manufacturer’s shop location and assembly drawings for the units shall be prepared and submitted for approval. Shop drawings shall show: i. the in-place location, fabrication details, plans, elevations, anchorages, reinforcement, dimensions, connection details and methods, profile dimensions, grade of concrete, holes for services, lifting points, finishes, and relation to adjacent materials; ii. the system of identifying units for placement and erection purposes. The Contractor shall imprint a casting date and piece mark on all units together with his identification mark/ name, to be concealed from view in the finished structure. The piece mark shall be according to shop drawings to distinguish

varying pieces and to facilitate erection of the structure; iii. setting diagrams, templates, instructions and directions as required for installation.

CW.14.4 Formwork shall be substantial enough so that it does not deflect beyond the tolerance limits during casting. Chamfers shall be straight and true to shape and line. Formwork shall be kept clean of adhering slurry so that cast surfaces are smooth. Water, dirt, tie wires sawdust and other foreign matter shall be removed from the formwork prior to casting. Seals shall be fitted to prevent loss of cement past through joints in the formwork.

CW.14.5 Lifting and erection holes or inserts shall be planned in a position consistent with the shape and design of the units to avoid stresses which would cause cracking or damage. These holes shall be located in as unobtrusive a position as possible, and shall be limited to the number shown in approved shop drawings. The holes shall then be made good using concrete plugs.

CW.14.6 The Contractor shall submit proposed concrete mix design for approval by the Engineer, where particular integral finishes are envisaged.

CW.14.7 Cross-section dimensions shall be accurate to + 5mm. Length of units, and lengths between centre to centre of the bearings shall not vary by more than 0.06% from the specified length with a maximum of 20mm. Centre-to-centre spacing of holes or inserts shall not vary by more than 10mm from the specified position. Cover to reinforcement, and position of reinforcement shall not vary by more than + 5mm.

CW.14.8 Any pre-cast lintel and coping units shall be produced in a pre-casting yard, or in controlled conditions on Site, to the profiles and dimensions indicated in the detail drawings. The materials for all blocks shall be mechanically batch-mixed and include a proprietary water-proofing additive. The units shall be manufactured to the following grades: Specially profiled lintels: - The concrete used for the pre-cast concrete lintel units shall have a minimum grade of C25/30. Specially profiled copings: - The concrete used for the pre-cast concrete coping units shall have a minimum grade of C18/20. Transport and Handling CW.14.9 Pre-cast concrete elements shall not be transported from the place of manufacture until the greater of 4 days from casting or the time when the concrete has attained 70% of the specified 28 day characteristic strength.

CW.14.10 Units shall be handled, transported and stored in a manner that will avoid damage to them, such as cracking, distortion and staining. They shall only be lifted at designated lifting or supporting points as shown on approved Shop Drawings. The panels, culverts and other longitudinal elements shall be adequately braced to prevent whipping and bending. The Contractor shall submit details of the method of lifting proposed for approval by the Engineer.

CW.14.11 Adequate timber packs shall be provided to support and firmly hold pre-cast concrete elements during transport. Storage CW.14.12 The Contractor shall avoid on-site storage wherever possible. Should this be unavoidable, the panels shall be stored clear from the ground on adequate timber supports placed on a plane surface in a manner that will prevent physical damage such as warping and staining, and so that markings remain visible. The ground shall be stable and not liable to subsidence during dry or wet spells. The Contractor shall not permit the units to rest on corners.

CW.14.13 Beams and panels may be stacked up to 6 layers high provided that timber supports are provided to separate each layer. Timber supports for upper layers shall be placed directly above the supports of the layer below. Erection CW.14.14 Units which are chipped, warped, spalled or otherwise do not conform to requirements as shown or specified, shall be discarded, and replaced unless repairs are approved by the Engineer. Unit having ragged or irregular edges, excessive air voids (blow holes) in the surface, rust stains, non-uniformity of colour/ texture, foreign material embedded in the face and visible cracks shall be discarded.

CW.14.15 Line and grade along which the units shall be erected shall be checked prior to erection, to permit any necessary corrections.

CW.14.16 Units shall be erected level, plumb and true to line in a manner that will prevent damage to units being erected and those already in place. Temporary supports and bracing shall be provided by the Contractor as required to maintain position, stability and alignment until members are permanently connected.

CW.14.17 Horizontal and vertical joint alignment and uniform joint width shall be maintained as erection progresses.

CW.14.18 The Contractor shall take measures to prevent development of cumulative dimensional errors. Adjustments such as shimming which would place additional stress on units shall not be permitted.

CW.14.19 Any units damaged during erection shall be replaced.

CW.14.20 The Contractor shall protect finished surfaces from soiling or damage especially during cleaning works. Following erection, any soiled or stained exposed surfaces of the units shall be cleaned by washing and rinsing. The Contractor shall scrub these faces with a fibre brush using mild detergent, and water, and then rinse thoroughly with clean running water. Any mortar on the face of the pre-cast shall be removed. No acids or prepared cleaners shall be used. Cleaning shall be tested on a small area of a panel to verify adequacy and safety of materials and methods. Formwork CW.14.26 Formwork shall not be removed until curing is sufficient to ensure that stripping does not have an effect on the appearance of the final product.

CW.14.27 Forms shall have acceptable form facing materials such as metal that are non-reactive with concrete or form release agents and will produce required finish surfaces as per approved prototype. Forms shall be constructed and maintained so that pre-cast concrete units are produced of shapes, lines and dimensions indicated, within specified fabrication tolerances.

Tolerances CW.14.28 Completed pre-cast concrete elements shall comply with the tolerances set out below. Tolerance (mm) Pre-cast Concrete Thickness of Length or Internal Element Straightness* Squareness Any Section Width Dimensions

Slabs and Panels  3  3 - 3  3 in 500mm Pits, gullies and +5, -3  5  5 -  5 in 500mm manholes Kerbs, channels +5, -3  5 - 5  3 in 500mm and blocks

Retaining walls  5  10 - 3  5 in 500mm

Culverts +5, -3  10  5 6  4mm across

unit section thickness * Deviation from a 1 metre long straight-edge

CW.14.29 Elements shall be free from fractures and cracks wider than 0.1mm. Dents not exceeding 3mm in depth and bulges not exceeding 3mm in height shall be permitted provided they do not extend over the surface for a distance of more than 180mm or twice the thickness of concrete where they occur, whichever is the smaller.

CW.14.30 Air holes exceeding 12mm in lateral dimension and having a depth greater than 3mm shall be filled in and repaired.

CW.14.31 The horizontal and vertical alignments of kerbs and culverts shall not vary from those specified by more than  10mm. Notwithstanding such tolerances, the alignments of the kerb or channel shall have smooth lines. The overall dimension of the kerb or channel shall nowhere be less than that shown on the Drawings.

CW.14.33 The tolerance for cover to steel reinforcing elements in saltwater conditions and in culverts shall be +10mm, -0mm where a positive value indicates the amount of clearance cover to reinforcement may increase and a negative value indicates the amount that cover may decrease. The tolerance for cover to steel reinforcing in all other elements shall be 5mm. Repairs CW.14.34 The Contractor shall ensure that there is no cutting of concrete members other than that, if any approved by the Employer’s Representative. If approved, cutting operations shall provide neat end surfaces which shall then be given two coats of tar epoxy paint or other approved.

CW.14.35 Any damaged areas shall be marked out by the Contractor, and the Employer’s Representative’s approval shall be sought as to whether the units may be repaired or need to be replaced.

CW.14.36 Patching shall meet the finish requirements of the project as regards texture, quality and colour. The pre-cast shall show no obvious repairs or imperfections other than minimal colour variations, if any, when viewed with the unaided eye at a distance of less than 7m. Acceptance CW.14.37 Pre-cast concrete elements shall remain available for inspection for a minimum of 3 days.

CW.14.38 The acceptability of pre-cast concrete elements shall be determined by inspection on the basis of visual inspection, geometric measurement, measurement of clear cover to reinforcement, reinforcement spacing and location and concrete strength.

CW.14.39 Pre-cast concrete elements may be rejected should they fail to meet any of the requirements of this specification.