PLAIN AND REINFORCED CONCRETE

8.1       Scope of Work

The Work under this Section of the Specifications consists of furnishing all plant, labour, equipment, appliances and materials and in performing all operations in connection with the supply, manufacturers, transporting, placing, consolidating and curing of plain & reinforced concrete and its constituents. Reinforcing steel does not form part of this Section and is described in Chapter-7.

8.2       General

(i)                 Trades like electrical, mechanical, plumbing etc. shall be well coordinated. Contractor shall take approval of coordinated shop drawings prior to concrete pouring.

(ii)               Suitable templates or instructions or both shall be provided for setting out of items not placed in the forms. Embedded items and other materials for mechanical and electrical operations shall have been completed, inspected, tested and approved before concrete is placed.

(iii)              For special concrete finish and for special methods of construction, formWork Shop Drawings shall be designed and prepared by the Contractor, at his own cost. Approval of shop drawings as well as that of actual samples of concrete finish shall be obtained before Work is commenced.

8.3       Applicable Standards

Latest editions of the following Pakistan, British, ASTM, and ACl Standards are relevant to these Specifications wherever applicable.

8.3.1    Pakistan Standards

(a)               PS 232 Portland cement (ordinary & rapid hardening)

(b)               PS 243 Natural aggregates for concrete

(c)               PS 279 Abrasion of coarse aggregates by the use of Los Angeles machine.

(d)               PS 280 Determination of aggregates crushing value.

(e)               PS 281 Organic impurities in sand for concrete aggregate

(f)                 PS 282 Material finer than No. 200 PS test sieve in aggregates.

(g)               PS 283 Soundness test, for aggregates by the use of sodium sulphate or magnesium sulphate.

(h)               PS 284 Sampling aggregates for concrete

(i)                  PS 285 Sieve or screen analysis of fine and coarse

(j)                  PS 286 Description and classification of mineral aggregates

(k)                PS 421 Sampling fresh concrete

(l)                  PS 422 Slump test for concrete

(m)             PS 560 Making and curing concrete compression test specimen in the field.

(n)               PS 612 Sulphate-resistant Portland cement type ‘A’ and sampling fresh concrete in the laboratory.

(o)               PS 716 Mixing

(p)               PS 717 Compacting factor test for concrete

(q)               PS 746 Definitions and terminology of cements

(r)                 PS 849 Making and curing concrete compression test cubes.

8.3.2    ASTM (American Society for Testing and Materials)

(a)               C 33 Concrete Aggregates.

(b)               C 40 Organic impurities in sand for concrete.

(c)               C 87 Effect of organic impurities in fine aggregates on strength of

mortar.

(d)               C 88 Soundness of aggregates.

(e)               C 94 Ready mixed Concrete.

(f)                 C 109 Compressive strength of hydraulic cement mortars

(g)               C 117 Material finer than No. 200 (0.075mm) sieve

(h)               C 123 Light weight pieces in aggregates.

(i)                  C125 Concrete and concrete aggregates.

(j)                  C 127 Specific gravity and absorption of coarse aggregate.

(k)                C 128 Specific gravity and absorption of fine aggregate.

(l)                  C 131 Resistance to abrasion of small size coarse aggregate.

(m)             C 136 Sieve or screen analysis of fine and coarse aggregate.

(n)               C 142 Clay lumps and friable particles in aggregates.

(o)               C 143 Slump of Portland Cement Concrete

(p)               C 150 Portland cement

(q)               C 156 Water retention by concrete curing material

(r)                 C 171 Sheet material for curing concrete.

(s)               C 185 Air content or hydraulic cement mortar.

(t)                 C 188 Density of hydraulic cement.

(u)               C 191 Time of setting of hydraulic cement by vicat needle

(v)                C 260 Air entraining admixture for concrete.

(w)              C 289 Potential reactivity of aggregate.

(x)                C 309 Liquid membrane forming compounds for curing concrete.

(y)                C 494 Chemical admixtures for concrete.

(z)               C 535 Resistance to abrasion of large size coarse aggregates.

(aa)           C75 Aggregate sampling.

(bb)           C 994 Preformed expansion joint filler for concrete.

(cc)           C 1190            Concrete joint sealer (hot poured elastic type).

(dd)           C 1715            Preformed expansion joint filler for concrete paving and structural concrete.

(ee)           D 1850 Concrete joint sealer (cold application type).

(ff)               E11 Wire cloth sleeves for testing purposes.

(gg)           E 96 Water vapour transmission of materials in sheet form.

(hh)           E 154 Materials for use as vapour barrier under concrete slabs.

(ii)                E 337 Relative humidity by wet and dry bulk psychrometer

8.3.3    ACl (American Concrete Institute)

(a)               Recommended practice for selecting proportions for normal and heavy weight concrete.

(b)               Quality control charts

(c)               Specifications for structural concrete for building.

(d)               Recommended practice for measuring, mixing, transporting and placing concrete.

(e)               Hot weather concreting.

(f)                 Recommended practice for curing concrete.

(g)               Recommended practice for consolidation of concrete

(h)               Manual of standard practice of detailing reinforcement concrete structure.

(i)                  Building code requirement of reinforced concrete.

(j)                  Recommended practice for concrete formWork,

8.3.4    British Standards

(a)               BS 12 Portland cement, ordinary and rapid hardening.

(b)               BS 410 Test Sieves

(c)               BS 812 Methods for the sampling and testing of mineral aggregates, sand fillers.

(d)               BS 822 Concrete aggregates from natural sources 1201

(e)               BS 1881 Methods of testing concrete

(f)                 BS 3148 Tests for water for making concrete

(g)               BS 3837 Expanded polystyrene boards

(h)               BS 3869 Rigid expanded polyvinyl chloride for thermal insulation.

(i)                  Bs 4027 Sulphate – resisting Portland cement

(j)                  CP 8110 Structural use of concrete

(k)                OP 114 Structural use of reinforced concrete in buildings

In addition, the latest editions of other Pakistan and British Standards, American Concrete Institute Standards, American Society for Testing and Materials Standards and other Standards as may be specified by the Engineer for special Materials and Construction are also relevant.

8.4       Materials

8.4.1    Aggregates

Contractor shall run requisite physical and chemical tests of coarse and fine aggregates and submit to the Engineer for approval

(a)               The sources of supply of all fine and coarse aggregates shall be as specified or approved by the Engineer.

(b)               All fine and coarse aggregates shall be clean and free from clay, loam, silt and other deleterious matter. If required, the Engineer reserves the right to have them washed by the Contractor at no additional expense. Coarse and fine aggregates shall be delivered and stored separately at Site. Aggregates shall not be stored on muddy ground or where they are likely be become dirty or contaminated. They shall be placed on sloped hard strata to ensure well drained at all times.

(c)               Fine aggregate shall be hard coarse sand, crushed stone or gravel screenings and shall conform to requirements of PS 243 and/or BS 882 and or ASTM C-33. Only fine aggregate of grading zones 1 to 3 (BS882) shall be used.

(d)               Coarse aggregate shall be crush stone of hard, durable material free from laminated structure and conforming to PS 243 and/or PS 882 and/or ASTM C-33, graded as follows for use in mass concrete as in foundations.

Total Passing BS Sieve	Percent by Weight
76.20mm         (3 inch)	100
38.10mm         (1-1/2 inch)	95 – 100
19.05mm         (3/4 inch)	30 –   70
9.52mm         (3/8 inch)	10 –   35
4.76mm         (3/16 inch)	0 –     5

Coarse aggregate for all cast-in-place concrete other than mass concrete as for foundations shall be graded with the following limits;

Total Passing BS Sieve	Percent by Weight
38.10 mm (1½ inch)	100
19.05 mm (3/4 inch)	95 – 100
9.52 mm (3/8 inch)	25 –   55
4.76 mm (3/16 inch)	0 –   10

           

(i)                 Wherever feasible, the nominal maximum size of aggregate for cast-in place reinforced concrete slabs and other members shall be 3/4 inch. If there are difficulties in placing such a concrete the maximum size may be restricted to ½ inch. Provided the requirements for strength are satisfied, as approved by the Engineer.

(ii)               Except where it can be shown to the satisfaction of the Engineer that a supply of properly graded aggregate of uniform quality can be maintained over the period of the Work, the grading of the aggregates shall be controlled by obtaining the 3/4 inch maximum nominal size, the different sizes being stocked in separate stock piles and recombined in the correct proportion for each batch at the batching plant. The materials shall be stockpiled for a period before use so as to drain nearly to constant moisture content (as long as Site and other conditions permit, preferably for at least a day). The grading of the coarse and fine aggregates shall be tested at least once for every 100 tons supplied, to ensure that the grading is uniform and same as that of the samples used in the preliminary tests.

8.4.2    Cement

(a)               The cement shall be fresh and of approved origin and manufacture. It shall be one of the following as may be specified by the Engineer.

(i)                 Ordinary or Rapid Hardening Portland cement complying with the requirements of P.S.232 or BS 12 or ASTM C-150

(ii)               Sulphate Resisting Portland/Cement complying with the requirements of P.S.612 or BS 4027 or ASTM C-150.

(b)               Unless otherwise specified. Ordinary Portland cement complying with the requirements of BS: 12 shall be used.

(c)               For all fair faced concrete it will be necessary to use approved cement with a view to obtain a light shade concrete as approved by the Engineer.

(d)               The Contractor shall supply to the Engineer at fortnightly intervals, test certificates with the appropriate standard in respect of the samples of cement from the Work Site. These tests shall be carried out in a laboratory approved by the Engineer.

(e)               Only one brand of each type of cement shall be used for concrete in any individual member of the structure. Cement shall be used in the sequence of receipt of shipment, unless otherwise directed.

(f)                 There shall be sufficient cement at Site to ensure that each Section of Work is completed without interruption. If the cement is supplied by the Employer, the Contractor should inform the Employer, of his requirements sufficiently in advance of its use in construction.

(g)               Cement reclaimed from cleaning of bags or from leaky containers shall not be used.

(h)               The Contractor shall provide and erect (at his cost) a suitable plain, dry, well ventilated, weather proof and water proof shed of sufficient capacity to store the cement.

(i)                  The cement shall be used as soon as possible after delivery and cement which the Engineer considers has become stale or unsuitable through absorption of moisture from the atmosphere or otherwise “shall be rejected and removed immediately from the Site at the Contractor’s expense. Any cement in containers damaged so as to allow the contents to spill or permitting access of the atmosphere prior to opening of the container at the time of concrete mixing shall be rejected and removed immediately from the Site at the Contractor’s expense.

(j)                  The mixing together of different types  of cement will  not be permitted

8.4.3    Water

Water shall be tested in accordance with PS 3148 and shall be used only from an approved source.

The Contractor shall supply sufficient water for all purposes, including mixing the concrete, curing and cleaning plant and tools. Where water can be shown to contain any sugar or an excess of acid, alkali or salt, the Engineer may refuse to permit its use.

8.4.4    Additive

All additives such as foaming and water proofing agents shall be from a manufacturer approved by the Engineer.

Air Entraining Admixtures conforming to ASTM C-260, and other Admixtures conforming to ASTM C-494 shall be used subject to approval of the Engineer.

8.5       Nominal Concrete Mixes

8.5.1    Proportions of Mix

(a)               Cement and Aggregates

The cement, fine aggregate and the coarse aggregate shall be weighed separately. The proportions of cement to fine aggregate and coarse aggregate shall be adjusted so as to provide the concrete of the required crushing strength.

(b)               The Contractor shall prepare Concrete Mix Design of various grades and strength of concrete for the approval of Engineer prior to starting concrete Works. He shall regulate and arrange mixing of the ingredients of the concrete by weigh batching. The cost of designing and testing the Concrete Mix shall be borne by the Contractor.

(c)               Water Cement Ratio

The quantity of water used shall be just sufficient to produce a dense concrete of adequate strength and Workability for its purpose. For all external Work and foundations the water/cement ratio should not exceed 0.55.        

(d)               Workability

The Workability shall be controlled by direct measurement of the water content, allowance being made for any water in the fine and coarse aggregates. The concrete shall be sufficiently Workable to be placed and compacted, without difficulty, by the available means.

Workability shall be determined by either the slump or compaction factor tests as directed by the Engineer and these shall be performed in accordance with the methods given in PS 422 and P.S. 177 or ASTM C-143. The slump or compaction factor for each class of concrete shall be determined during the preliminary test mixes and the value obtained shall not be modified without the written consent of the Engineer. Unless otherwise permitted or specified, the concrete shall be proportioned and produced to have a slump of 3 inch or less if consolidation is to be by vibration. A tolerance of up to 1 inch above the indicated maximum shall be allowed for individual batches provided the average for all batches or the most recent 10 batches tested, which ever is fewer, does not exceed the maximum limit. Concrete of lower than usual slump may be used provided it is properly placed and consolidated.

8.5.2    Concrete Requirements

(a)               Concrete made with Portland cement shall comply with the strength requirements of Table-8.1 (Works Test).

Table-8.1:       Strength Requirements for Portland Cement Concrete with Aggregate Complying with BS 882.

Class of concrete (psi)	Cube strength at 28 days (psi)
A	4,500
B	3,750
C	3,000
D	1,500
E	1,000

(b)               All structural concrete shall conform to BS 5328-81.

(c)               Unless otherwise stated, the types of concrete shall be classified on the basis of compressive strength requirements.

(d)               The Contractor shall provide Mix Design by weight for each class of concrete. Contractor shall manufacture 12 Nos. test cubes 6” x 6” x 6” in accordance with the Mix design batching by weight and test 3 cubes each at 3,7,14 & 28 days intervals in the presence of Engineer’s Representative and submit all relevant data and results of tests for approval of the Engineer. The Contractor shall obtain approval from the Engineer in writing for each Mix Design before producing the actual concrete for the Works.

No payments for producing the Mix Design, manufacture of test cubes and testing shall be made. The Contractor shall include this cost in the relevant item of concrete.

8.5.3    Batching

(a)               All cement, including cement supplied in bulk, shall be batched by weight. A bag of cement may be taken as 110 lbs (50 kg). with the prior approval of the Engineer.

(b)               Aggregates shall be batched by weight, due allowance being made for moisture content. The apparatus for weigh-batching may be an integral part of the mixer or a separate unit of a type approved by the Engineer. lt shall be accurate within 2% and shall be checked for accuracy at least once a month.

(c)               The quantity of additives i.e. foaming and water proofing agents etc. shall be as prescribed by the manufacturer or as directed by the Engineer.

(d)               Where the batching plant is of the type in which cement and aggregates are weighed in the same compartment, the cement shall be introduced into the compartment between two sizes of aggregates.

(e)               Each batch shall be so charged into the mixer that some water will enter in advance of the cement and aggregates. Water shall continue to flow for a period which may extend to the end of the first 25 percent of the specified mixing time. Controls shah, be provided to prevent batched ingredients from entering the mixer before the previous batch has been completely discharged.

(f)                 During the production of the Concrete, a representative of the Engineer will be present and issue a Certificate as soon as the Transit mixer will leave the plant in the presence of Contractor.

8.5.4    Mixing

           

The concrete shall be mixed in an approved bath mixer conforming to the requirements of BS 305. It shall be fitted with the manufacturer’s plate stating the rates, capacity and the recommended number of revolutions per minute and shall be operated in accordance therewith. It shall be equipped with a suitable charging mechanism and an accurate water measuring device.

(a)               Mixing shall continue for the period recommended by the mixer manufacturer or until there is apparently a uniform distribution of the materials and the mass is uniform in colour, whichever period is longer. If it is desired to use a mixing period of less than 1½ minute, the Engineer’s approval shall be obtained in writing.

(b)               Controls shall be provided to ensure that the batch cannot be discharged until the required mixing time has elapsed. At least three quarters of the required mixing time shall take place after the last of the mixing water has been added.

(c)               The interior of the mixer shall be free of accumulations that will interfere with mixing action. Mixing blades shall be replaced when they have lost 10 percent of their original height.

(d)               Concrete shall be mixed only in quantities for immediate use. Concrete which has set shall not be re-tempered, but shall be discarded.

8.5.5    Transporting

(i)                 The concrete shall be transported from the place of mixing to the place of final deposit as rapidly as practicable by means which will prevent segregation or loss of or addition to ingredients it shall be depoSited as nearly as practicable in its final position so as to avoid re-handling or flowing. All skips vehicles, or containers used for transporting the concrete shall be thoroughly clean.

(ii)               During hot or cold weather, concrete shall he transported in deep containers, on account of their lower ratios of surface area to mass, which reduces the rate of loss of water by evaporation during hot weather and loss of heat during cold weather.

8.5.6    Placing

(a)               Before placing of concrete, formWork shall have been completed, water shall have been removed reinforcement shall have been secured in place; expansion joint material, and other embedded items shall have been kept in position; and the entire preparation shall have been approved.

No concrete is to be placed into the foundation trenches until the ground to receive the same has been examined and approved by the Engineer for this purpose.

(b)               Concrete shall be depoSited continuously, or in layer of such thickness that no concrete will be depoSited on concrete which has hardened sufficiently to cause the formation of seams or planes of weakness within the Section. If a Section cannot be placed continuously, construction joints shall be located as shown in the Contract Documents or as approved by the Engineer. Placing shall be carried out at such a rate that the concrete which is being integrated with fresh concrete is still plastic. Concrete which has partially hardened shall not be depoSited Temporary spreaders in forms shall be removed when the concrete placing has reached an elevation rendering their services unnecessary They may remain embedded in the concrete only if made of metal or concrete and if prior approval has been obtained.

(c)               The actual sequence of construction proposed by the Contractor shall he subject to the Engineer’s approval before construction starts on any part of the structure, and this sequence shall not be varied without the Engineer’s approval.

(d)               The concrete shall be placed as soon after it has been mixed as is practicable. Once the concrete has left the mixer, no more water shall be added, although the concrete may be mixed or agitated to help maintain Workability. The concrete shall not be used if, through any cause, the Workability of the mix at the time of placing too low for it to be compacted fully and to an acceptable finish by whatever means available.

(e)               The time between mixing and placing should be reduced if the mix is richer or the initial Workability of the mix is lower than normal; if a rapid hardening cement or an accelerator is used, or if the Work is carried out at a high temperature or exposed to a crying atmosphere.

(f)                 The Contractor shall ensure that the delay between mixing and placing does not exceed 45 minutes under any circumstances. Any concrete which does not satisfy this requirement shall not be used.

(g)               The concrete shall be deposited as nearly as possible in its final position to avoid re-handling. In no circumstances may concrete be railed or made to flow along the forms by the use of vibrators. Concreting shall be carried on as a continuous operation using methods which shall prevent segregation or loss of ingredients.

(h)               The free fall of concrete shall not be allowed to exceed 5 ft. (1.5 m) and where it is necessary for the concrete to be lowered more than this depth, it is not to be dropped into its final position, but shall be placed through pipes fed by a hopper. When a pipe is used for placing concrete the lower end shall be kept inside, or close to the freshly depoSited concrete. The size of the pipe shall be not less than 9 inches (225mm) diameter.

(i)                  The Workmen carrying concrete to the Site, and all other Workmen moving about on the reinforcement before the concrete is placed, shall move only along runways or planks placed for the purpose and no person shall be allowed to walk on the reinforcement itself.

(j)                  Prior to the laying of concrete on load bearing masonry walls, bearing plates and at other points, as may be directed by the Engineer, the surface will be brought to a true, hard, smooth, level surface using cement sand mortar in the ratio of 1 part of cement to 3 parts of sand. Two layers of building paper will then be laid flat to separate the concrete from the surface on which it is to be laid.

(k)                All the workmen working on concreting shall be equipped with long boots, gloves, hats and other necessary protecting clothing and gear. The Engineer shall stop the works if this Clause is not followed in litter and spirit on Site.

8.5.7    Construction Joints

(a)               Concreting shall be carried out continuously up to construction joints, the arrangement of which shall be predetermined by the Engineer.

(b)               Joints not shown on the drawings shall be so made and located as to least impair the strength of the structure and shall need prior approval of the Engineer. In general, they shall be located near the middle of the spans of slabs and beams unless a secondary beam intersects a main beam at this point, in which case the joint in the main beam shall be offset a distance equal to twice the width of the secondary beam. Joints in walls and columns shall not be at the underside of floor slabs or beams, and at the top of footings or floor slabs. Beams, brackets, columns, capital haunches and drop panels shall be placed at the same time as slabs. Joints shall be perpendicular to the main reinforcement.

(c)               All reinforcing steel shall be continued across joints. Key and inclined dowels shall be provided as directed by the Engineer. Longitudinal keys at least 1½ inch. (40 mm) deep shall be provided in all joints in walls and between walls and slabs or footings.

(d)               When the Work has to be resumed on a surface which has hardened, such surface shall be roughened in an approved manner which will expose the aggregate uniformly and will not leave laitance, loosened particles of aggregate or damaged concrete at the surface. Feather edges will be avoided.

(e)               The hardened concrete of construction joints and of joints between footings and walls or columns, between walls or columns and beams or floors they support, joints in unexposed walls and all others not mentioned herein shall be dampened (but not saturated) immediately prior to placing of fresh concrete.

(f)                 The hardened concrete of joints in exposed Work, joints in the middle of beams and slabs; and joints in Work designed to contain liquids shall be dampened (but not saturated) and then thoroughly covered with a coat of cement grout similar in proportions to the mortar in the concrete. The grout shall be as thick as possible on vertical surfaces and at least 150 mm thick on horizontal surfaces. The fresh concrete shall be placed before the grout has attained initial set.

(g)               Where the concrete has not fully hardened, all laitance shall be removed by scrubbing the wet surface with wire or bristles and brushed, care being taken to avoid dislodgment of particles of aggregate. The surface shall then be coated with neat cement grout. The first layer of concrete to be placed on this surface shall not exceed 6 inches (150 mm) in thickness, and shall be well rammed against old Work, particular attention being paid to corners and closed spots.

8.5.8    Expansion Joints

Expansion joints shall be provided wherever indicated on the Drawings. In no case shall the reinforcement, corner protection angles, or other embedded items be run continuous or through an expansion joint. All expansion joints shall be carefully placed so as not to be displaced during concreting. The method of placing the expansion joints shall be strictly in accordance with the Drawings and as approved by the Engineer. All materials for use in the expansion joints shall have, prior approval of the Engineer before placing order for supply.

8.5.9    Embedded Items

(a)               The material, design and location of water stops in joints shall be as indicated in the Contract Documents. Each piece of remolded water stop shall be of maximum practicable length in order that the number of end joints will be held to a minimum

(b)               Joints at interSections and at ends of pieces shall be made in the manner most appropriate to the material being used. Joints shall develop effective water-tightness fully equal to that of the continuous water stop material, shall permanently develop not less than 50 percent of the mechanical strength of the parent Section, and shall permanently retain their flexibility

(c)               Electric conduits and other pipes which are planned to be embedded shall not, with their fittings, displace more than four percent of the area of the cross Section of a column on which stress is calculated or which is required for fire protection. Sleeves, conduits, or other pipes passing through floors, walls, or beams shall be of such size or in such location as not to impair unduly the strength of the construction; such sleeves, conduits, or pipes may be considered as replacing structurally in compression the displaced concrete, provided that they are not exposed to rusting or other deterioration, are of uncoated or galvanized iron or steel not thinner than standard steel pipe, have a nominal inside diameter not over 50 mm and are spaced not less than three diameters on centre except  when plans of conduits and pipes are approved by the Engineer embedded pipes and conduits other than those merely passing through, shall not be larger in  out side diameter than one third the thickness of the slab, wall, or beams in which they are embedded nor so located as to ‘ impair unduly the strength of the construction. Sleeve pipes, or conduits of any material not harmful to concrete and within the limitations of this Section may be embedded in concrete with the approval of the Engineer provided they are not considered to replace the displaced concrete.

(d)               All sleeves, inserts, anchors, and embedded items required for adjoining Work or for its support shall be placed prior to concreting.

(e)               All Contractors whose Work is related to the concrete or must be supported by it shall be given ample notice and opportunity to introduce and/or furnish embedded items before the concrete is placed.

(f)                 Expansion joint material, water stops and other embedded items shall be positioned accurately and supported against displacement. Voids in sleeves, inserts, and anchor slots shall be filled temporarily with readily removable material to prevent the entry of concrete into the voids.

8.5.10  Pre-Cast Concrete

Pre-cast concrete units shall be fair faced, cast to the sizes and dimensions as indicated on the Drawings. The concrete used for pre-cast units shall conform to the specifications laid down for cast in situ reinforced cement concrete unless otherwise required and directed by the Engineer.

The Contractor shall be required to submit a sample of pre-cast unit for the approval of the Engineer all pre cast units shall strictly conform to the approved sample.

Pre-casting platform of the size and at the location approved by the Engineer shall be constructed. The concrete in one pre-cast unit shall be placed in one operation, in accordance with the details shown on the Drawings.

The material and design of formWork and the method of pre- casting the units shall be approved by the Engineer.

The erection/installation and removal of the pre-cast units from the pre-casting platform shall not be permitted until and unless they are properly cured to the satisfaction of the Engineer.

All pre-cast units shall be smoothly finished to the required lines, grades, angles etc. Holes, grooves, pockets, hooks shall be provided as shown and/or as directed by the Engineer. The units shall be properly stacked on a platform without causing any cracks and damages. Curing of all the pre-cast units shall be done in accordance with the relevant BSS/approval of the Engineer.

(a)               Erecting Pre-cast Units

All the pre-cast units shall be transported and erected into position in a manner as approved by the Engineer.

The Contractor shall submit his proposal in this regard and obtain approval from the Engineer in advance.

The units shall be embedded or otherwise installed in their permanent positions as shown on the Drawings or as directed by the Engineer.

(b)               Lifting Beams

The Contractor shall use lifting beams at his own cost, for erecting pre-cast members where the Engineer so directs. Lifting beams shall be supplied and erected by the Contractor, at his own cost, at all points where lifting is necessary for maintaining the plant but is inaccessible to mobile cranes or alternatively, covered by overhead traveling cranes. The Contractor, however, is to supply the trolleys and erect them on the lifting beams, and to test operation of installed equipment.

8.5.11  Cement Concrete Pavements

For all concrete Work relevant Specifications of this Section shall apply

(A)       Side Forms and Construction

(i)                 Side forms shall be of steel or any other suitable material and of a design as approved by the Engineer.

(ii)               In general, only materials and methods that have proved their acceptability by past performance will be considered. All form shall be constructed so that they can be removed without hammering or prying against the concrete.

(iii)              Horizontal joints in the forms will not be permitted. Forms shall be thoroughly cleaned and oiled with linseed/mineral oil or shall be given two coats of nitro- cellulose lacquer each time they are used.

(iv)             The forms shall be set on a thoroughly compacted base true to line and level and firmly secured in position by appropriate methods. Conformity with the alignment and levels shown on the Drawings shall be checked as and when required by the Engineer. Where necessary corrections shall be made immediately before placing the concrete; where any form has been disturbed it shall be reset and rechecked.

(v)               Pavements shall be constructed in panels of sizes as shown on the Drawings. The panels shall be laid alternately, the adjoining panels being concreted when the side forms are struck and the jointing materials placed, inspected and approved by the Engineer. Each panel is to be concreted in one operation and no interruptions shall be permitted during the operation. The concrete shall be tipped from the trolley slightly in advance of the Working place and then shoveled into position. The spreading shall be carried out very carefully. Compaction shall be done by means of vibro­ compactors or approved surface vibrators. If a vibro compactor is used. it shall be operated on the concrete and will not be allowed to strike or displace the forms. The spreading and compacting of the successive layers shall proceed without interruptions and as quickly as practicable so as to ensure that the slab is monolithic throughout its depth.

(vi)             The wearing surface shall be laid while the base concrete is still wet and screeded to line and level. When the initial set takes place the surface shall be troweld smooth with a steel trowel to provide a dense closed surface.

(vii)            All the joints shall be carefully formed as shown on the Drawings or as directed by the Engineer. The joint filler together with preformed groove shall provide complete separation of adjacent slabs. The joints shall all be sealed with bitumen as shown on the Drawings or/and as directed by the Engineer.

(B)       Protection and Curing – General Requirements

(i)                 Concrete shall be protected adequately from injurious action sun, rain, flowing water and mechanical injury, and shall not be allowed to dry from the time it is placed until the expiry of the minimum curing periods specified hereinafter. Water curing shall be accomplished by keeping the surface of the concrete continuously wet by covering with water or with approved water saturated covering, where wood forms are left in place for curing.

(ii)               They shall be kept sufficiently damp at all times to prevent openings at the joints and drying out of the concrete. All portions of the structure shall be kept moist for the full curing periods, specified hereinafter.

(iii)              When liquid membrane curing compound is used the surface of the concrete shall be protected from traffic or other abrasive action that may break the membrane, for the full period of curing. The membrane curing compound shall be white colored and shall be approved by the Engineer and shall comply with ASTM Designation C 309, type 2.

(a)        Curing Periods

The curing period shall be at least 10 days, or as directed by the Engineer

(b)       Removal of Forms

The Contractor shall exercise great care in avoiding damage to joints, arises, dowel bars etc. while removing the forms. Under no circumstances will the use of pry bars between the forms and pavement be permitted. Side forms shall not be removed until at least 40 hours have elapsed from the time of completing the concreting of the slab which they contain. In no case shall forms be removed until the concrete has hardened sufficiently to permit removal without damage to the concrete. Concrete Work shall be protected from damage during the removal of formWork and from injury resulting from the storage or movement of material during construction.

(C)       Finishing

All unformed surfaces shall be finished with a wood float except as otherwise specified. Visible vertical surfaces shall have all projections and irregularities removed. The entire surface shall be rubbed if required by the Engineer, with a No. 16 carborundum brick, or other abrasive until even, smooth and of uniform appearance, and shall be washed clean. Plastering of surface, application of cement or other coating will not be permitted.

All exposed corners shall be chamfered, 1 inch x 1 inch  (25x25mm) unless otherwise mentioned or shown in the plans or directed by the Engineer. Concrete surface which will be covered with other materials shall be screeded without floating.

(a)               Spreading. Finishing and floating of concrete in pavements

(i)                 General Requirements

The striking off, compacting and floating of concrete shall be done by mechanical methods, if approved by the Engineer. Where the Engineer determines that it is impracticable to use mechanical methods, manual methods of spreading, finishing and floating may be used on pavement lines as indicated on the Drawings.

(ii)               Mechanical Methods

The concrete shall be spread uniformly between the forms, immediately after it is placed, by means of an approved spreading machine. The spreader shall be followed by an approved finishing machine equipped with two oscillating or reciprocating screeds. The spreading machine or the finishing machine shall be equipped with vibrating equipment that will vibrate the concrete for the full paving width. Internal vibrators shall be used adjacent to the longitudinal edge of the pavement. These vibrators shall be attached to the rear of the spreading machine onto the finishing machine. Vibrators shall not rest on new pavements or side forms or in contact with any dowel bars, and the arrangement of power supply to the vibrators shall be such that when the motion of machine is stopped, vibration shall cease. The rate of vibration shall be not less than 8000 vibrations per minute. The concrete shall be spread to full width before being struck off and compacted so that the surface will conform to the finished grade and cross-Section as shown on the plans and at the same time leave sufficient material for the floating operation. The spreading & finishing machine shall move over the pavement as many times and at such intervals as may be required by the Engineer to ensure thorough compaction.

Except, as otherwise specified, after the pavement has been struck off and compacted, it shall be finished with an approved longitudinal float. The Contractor may use a longitudinal float composed of one or more cutting and smoothing Floats, suspended from and guided by rigid frame. The frame shall be carried by four or more visible wheels riding on and constantly in contact with the forms.

The Contractor may use a longitudinal float which Works with a sawing motion, while held in a floating position parallel to the road centre line and passing gradually from one side of the pavement to the other. Movements ahead, along the centre line of the road, shall be in successive advances of not more than half the length of the float.

Instead of using other type of longitudinal float a single machine which will affect satisfactory compaction, finishing and floating may be used. This machine may be towed by a spreading machine: This combination, finishing floating machine shall be equipped with screeds and vibrators as hereinafter specified for spreading and finishing machine Floating shall be accomplished by means of a non-oscillating float held in a suspended position from the frame.

If any spreading. Finishing and floating equipment is not maintained in full Working order or if the equipment as used by the Contractor proves inadequate to obtain the results prescribed, such equipment shall be improved or satisfactory equipment substituted or added at the direction of the Engineer.

(iii)              General Requirement

The concrete shall be spread uniformly immediately after it is placed and shall be leveled and then struck-off to such an elevation that, when properly compacted, the surface will conform to the required grade and cross-Section. The strike board shall be moved forward with a combined longitudinal and transverse motion, the manipulation being such that neither end is raided from the side forms during the process. While striking off, a sight excess of concrete shall be kept in front of the cutting edge at all times. Prior to tamping, the concrete along the forms shall be thoroughly spaded or vibrated. The entire area of pavement shall be tamped or vibrated in a manner that will ensure maximum compaction. The concrete shall be brought to the required grade and shape by tile use of a tamper consisting of a heavy plank whose length exceeds the width of the pavement by 300 mm or by the use of a mechanical vibrating unit spanning the full width of the spread The tamper shall be constructed with properly trussed rods to stiffen it and prevent sag and shall be shod with a heavy strip of metal for a tamping surface. The tamper shall be moved with a combined tamping and longitudinal motion, raising it from side form and dropping it so that the concrete will be thoroughly compacted and rammed into place. A small surplus material is compacted and rammed into front of the tamper or vibrating unit and tamping or vibrating shall continue until the true cross-Section is obtained and the mortar flushes slightly to the surface.

(b)               Expansion and Construction Joints

All the expansion and construction joints shall be carefully formed as shown on the Drawings or as directed by the Engineer. The joint filler together with the preformed groove shall provide complete separation of adjacent slabs or building. The preformed chase shall be thoroughly cleaned of all dust, debris, stones or other hard material.

All joints are to be filled with flexcell expansion joint filler, or an approved elastic, compressible, durable, and rot-proof equivalent of sufficient rigidity to enable it to be satisfactorily installed in the joint and resist deformation during the passage of the concreting equipment. The filler is to be of the same thickness as the joint width.

Construction joints shall be provided as shown on the Drawings.

The assembly and method of constructing the expansion joints/construction joints shall be subject to the approval of the Engineer

(c)               Consolidation

(i)                 All concrete shall be consolidated by vibration, spading, rodding or forking so that the concrete is thoroughly Worked around the reinforcement, around embedded items, and into corners of forms, eliminating all air or stone pockets which may cause honeycombing, pitting, or planes of weakness. Internal vibrators shall have a minimum frequency of 8000 vibrations per minute and sufficient amplitude to consolidate the concrete effectively. They shall be operated by competent Workmen. Use of vibrators to transport within forms shall not be allowed. Vibrators shall be inserted and withdrawn at points approximately 1-1/2 ft. (1/2 meter) apart. At each insertion, the duration shall be sufficient to consolidate the concrete but not excessive so as to cause segregation, generally from 5 to 15 sec. A spare Vibrator shall be kept on the job Site during all concrete placing operations. Where the concrete is to have an as-cast finish, a full surface of mortar shall be brought against the form by the vibration process, supplemented, if necessary, by spading to Work the coarse aggregate back from the formed surface.

(ii)               If there is any tendency for the mix to segregate during consolidation, particularly if this produces excessive resistance, the mix proportions shall be modified to effect an improvement in the quality of the concrete to the satisfaction of the Engineer and in conformity with the provisions of Clause 5.

(iii)              Vibrators shall not be allowed to touch the formWork or the reinforcing bars during consolidation operation.

(iv)             Mechanical vibrators shall he of a type suited in the opinion of the Engineer  to the particular conditions

(v)               Over vibration or vibration of very wet mixes is harmful and should be avoided.

(d)               Curing and Protection

(i)                 Beginning immediately after placement, concrete shall be protected from premature drying, excessively hot or cold temperatures and mechanical injury, and shall be maintained with minimum moisture loss at a relative constant temperature for the period necessary for hydration of the cement and hardening of the concrete. The materials and methods of curing shall be subject  to approval of the  Engineer

(ii)               For concrete surfaces not in contact with forms, one of the following. procedures shall be applied immediately after completion of placement and finishing.

(A)               Pending or continuous sprinkling.

(B)              Application of absorptive mats or fabric kept continuously wet.

(C)              Application of waterproof sheet materials approved by the Engineer.

(D)              Application of other moisture-retaining covering as approved.

Application of a curing compound conforming to ASTM C 309 type 2. The compound shall be applied in accordance with the recommendations of the manufacturer immediately after any water sheet which may develop after finishing has disappeared from the concrete surface. It shall not be used on any surface against which additional concrete or other material is to be bonded unless it is proved that the curing compound will not prevent bond, or unless positive measures are taken to remove it completely from areas to receive bonded applications.

(iii)              Moisture loss from surface placed against wooden forms or metal forms exposed to heating by the sun shall be minimized by keeping the forms wet until they can be safely removed. After form removal, the vertical faces of concrete shall be cured until the end of the time prescribed in sub-clause 5.13.4 by one of the methods of sub-clause 5.13.2.

(iv)             Curing in accordance with sub-clause 5.13.1 & 5.13.2 above shall be continued for at least 14 days in the case of all concrete except concrete with rapid- hardening Portland Cement for which the period shall be at least 3 days. Alternatively, if tests are made of cubes kept adjacent to the structure and cured by the same methods, moisture retention measures may be terminated when the average compressive strength has reached 70 percent of the minimum specified Works cube strength. If one of the first four curing procedures of sub-clause 5.13.2 is used initially, it may be replaced by one of the other procedures of that sub-clause any time after the concrete is one day old provided the concrete is not permitted to become surface dry during the transition.

(v)               When the mean daily outdoor temperature is less than 410F then temperature of the concrete shall be maintained between 50 0F – 68 0F for the required curing period.

(vi)             When necessary, arrangements for heating, covering insulation or housing the concrete Work shall be made in advance of placement and shall be adequate to maintain the required temperature without injury to concentration of heat. Combustion heaters shall not be used during the first 24 hours unless precautions are taken to prevent exposure of the concrete to exhaust gases which contain carbon dioxide.

(vii)            When necessary, provision for wind-brakes, shading for spraying, sprinkling, ponding or wet covering with a light colored material shall be made in advance of placement, and such protective measures shall be taken as quickly as concrete hardening and finishing operation will allow.

(viii)          Changes in temperature of the air immediately adjacent to the concrete during and immediately following the curing period shall be kept as uniform as possible and shall not exceed 370F in any one hour or 500F in any 24 hour period.

(ix)             During the curing period, the concrete shall be protected from damaging by mechanical disturbances, such as load stresses, heavy shock and excessive vibrations. All finished concrete surfaces shall be protected from damage by construction equipment, materials or methods by application of curing procedures, and by rain or running water. Self-supporting structures shall not be loaded in such a way as to overstress the concrete. No traffic should be allowed on pavement for at least 7 days after casting.

(e)               Works in Extreme Weather

(i)                 Unless adequate protection is provided and approval is obtained, concrete shall not be placed during rain. Rain water shall not be allowed to increase the mixing water nor to damage the surface finish.

(ii)               When the temperature of the surrounding air is expected to be below 41 ⁰F  during placing or within 24 hours thereafter, the temperature of the plastic concrete, as placed, shall be no lower than 55 degree F for Sections less than 300 mm in any dimension nor 50 0F for any other.

(iii)              During hot weather, the temperature of the concrete as placed shall met be so high as to cause difficulty from loss of slump, flash set, or cold joints and should riot exceed 900F. When the temperature of the concrete exceeds 900F precautionary measures approved by the Engineer shall be put into effect. When the temperature of the steel is greater than 1220F steel forms and reinforcement shall be sprayed with water just prior to placing the concrete ingredients shall be cooled before mixing, or flaked ice or well crushed ice of a size that will melt completely during mixing may be substituted for all part of the mixing water if, due to high temperature, low slump, flash set or cold joints are encountered.

     Other precautions recommended by ACl 305 shall also be adopted.

8.6       Test of Concrete Quality

(a)               The Contractor shall provide samples of concrete for testing at the Engineer’s direction. Proper facilities shall be provided for making and curing the test specimens in accordance with PS 560 and PS 849. A competent person shall be employed by the Contractor whose first duty shall be to supervise all stages in the preparation and placing of the concrete. All test specimens shall be made and Site tests carried out under his direct supervision.

(b)               Test sample shall be taken at the mixer or as directed by the Engineer. The test specimens shall be cured in accordance with PS 560, PS 849 and BS 1881. The strength shall comply with the standard of quality specified in table-8.1.

(c)               The five test cubes are to be tested for compressive strength as specified in BS 1881. These tests shall be carried out at Site or in a laboratory approved by the Engineer. Two cubes shall be tested at the age of seven days and three at 28 days and the strengths determined are to comply with the standard of quality specified. The laboratory tests shall be carried out by an independent organization, such as Government Testing Laboratory or such other undertakings approved by the Engineer. The original test reports received from the above authorities should be submitted to the Engineer.

(d)               For all grades of concrete, the appropriate strength requirement shall be considered to be satisfied if none of the strengths of the cubes is below the specified cube strength or if the average strength of the three cubes is not less than the specified cube strength and the difference between the greatest and the least strength is not more than 20% of the average.

(e)               When the results of Works cube tests show that the strength of any concrete is below the minimum specified the Engineer may give instructions for the whole or part of the Work concerned to be removed and replaced at the expense of the Contractor. The Contractor shall bear the cost of any other part of his, or any other Contractor’s Work, which has to be removed and replaced as a result of the defective concrete. If any concrete is held to have failed, the Engineer may order the proportions of that class of concrete to be changed in order to provide the specified strength.

8.7       Finishing of Formed Surfaces

8.7.1    General

(a)               After removal of forms, the surfaces of concrete shall be given one or more of the finishes specified below in locations designated by the Contract Documents.

(b)               When finishing is required to match a small sample furnished to the Contractor, the sample finish shall be reproduced on an area at least 100 sq ft. in an inconspicuous location designated by the Engineer before proceeding with the finish in the specified location.

(c)               Allowable deviations from plumb or level and from the alignment, profile grades, and dimensions are specified in clause 9. Tolerances for concrete construction are defined as tolerances to be distinguished from irregularities in finish as described herein. The finish requirements for concrete surfaces shall be as generally specified in this clause and as indicated on the Drawings. Finishing of concrete surfaces shall be performed only by Workmen who are skilled in concrete finishes. The Contractor shall keep the Engineer advised as to when finishing of concrete will be performed. Unless inspection is waived in each specific case, finishing of concrete shall be performed only in the presence of the Engineer. Concrete surfaces will be tested by the Engineer where necessary to determine whether surface irregularities are within the limits herein after specified, surface irregularities are classified as abrupt or gradual. Offsets caused by displaced or misplaced form sheeting or lining or Section, or otherwise defective form lumber will be considered as abrupt irregularities, and will be tested by direct measurements.  All other irregularities will be considered as gradual irregularities, and will be tested by use of a template, consisting of a straight edge or the equivalent thereof for curved surfaces. The length of the template 2 meters for testing of formed surfaces and 3 meters for testing of unformed surfaces.

8.7.2    As-cast Finishes

Unless otherwise specified or indicated on the Drawings the classes of finish shall apply as follows:

(a)               Rough form Finish

No selected form facing materials shall be specified for rough form finish surfaces. The holes and defects shall be patched. Otherwise, surfaces shall be left with the texture imparted by the forms.

(b)               Fair face Finish

Fair face finish applies to concrete formed surfaces, the appearance of which is considered by the Engineer to be of special importance, such as surfaces of structures prominently exposed to public inspection. Surfaces of concrete structures requiring fair face finish as shown in the Drawings. Surface irregularities, measured as described in sub-clause 7.2.1, ‘Rough form finish’, shall not exceed 4 mm for gradual irregularities and 6mm for abrupt irregularities, except that abrupt irregularities will not be permitted at construction joints. Abrupt irregularities at construction joints and elsewhere in excess of 6 mm and gradual irregularities in excess of 1/8 inch. (3mm) shall be reduced by grinding so as to conform to the specified limits. Abrupt irregularities at construction joints shall be ground on level of 1 to 20 ratio of height to length.

Unless otherwise approved, repair of imperfections in formed concrete shall be completed within 24 hours after removal of forms. The form facing material shall produce a smooth, hard, uniform texture on the concrete. It may be plywood, temperated concrete form grade hardboard metal, plastic paper, or other approved material capable of producing the desired fair face finish. The arrangement of the facing material shall be orderly and symmetrical, with the number of seams kept to the practical minimum. It shall be supported by studs or other backing capable of preventing excessive deflection. Material with raised grain, torn surfaces, worn edge, patches, dents, or other defects which will impair the texture of the concrete surface shall not be used. The holes and defects shall be patched. All fins shall be completely removed. 

(c)               Architectural Finish Concrete

Architectural finish to concrete formed surfaces as shown on the Drawings is required by the Engineer where the architectural appearance of surfaces of structures exposed to public view is of special consideration and importance. The Contractor shall use approved special material for formWork and design the forms in conformity with the specified architectural patterns, textures and finishes in order to obtain first class architectural finish on formed concrete surface without any defect, irregularities, blemishes, imperfections and encrustations.

Sample approvals of pre cast & in-situ concrete:

These samples will be reviewed and approved on the basis of colour, dimensional accuracy, and finish of surfaces and general appearance. The same requirements for sample approval will be required for both pre cast and in-situ concrete exposed surfaces.

(i)                 Forms

The Contractor must maintain the forms unusually tight and braces to prevent movement, mal-alignment and bleeding that will result in sand streaks, honeycomb, fins, stain or unsightly appearance.

It wood forms are chosen to be used by the Contractor they shall .be constructed of 3/4 inch. (20mm) minimum thickness plywood constructed in a fashion to allow many re-uses with all surfaces sealed with a polyurethane varnish.

Edges, surfaces and corners of forms shall be sealed to prevent loss of any matrix or unequal absorption of water. Corners of wood forms shall be filled with suitable compound and all contact surfaces sealed with a polyurethane varnish.

Re-use of forms shall be subject to approval of the Engineer.

(ii)               Curing

Curing shall be done in shade (out of direct sunlight) and shall be for a minimum period of 4 days.

(d)               Finishing procedures

Finishing procedures for filling air void in smooth finished concrete developed by a formed surface

While the concrete surface is still damp (not more than three days after removal of forms), apply a thin coat of medium consistency neat cement slurry by means of bristle brushes to provide a bonding coat within any pit or blemishes in the parent concrete; avoid coating large areas of the finished surface. Before slurry has dried or changed colour, apply a dry (almost crumbly) grout comprised of one part cement, of the type and brand of cement used in the original concrete, to one and one-half parts clean masonry sand with a fineness modulus of approximately 2.25 and complying with the gradation requirements of the ASTM Specifications C144. Mix proper amounts of white cement and colouring with the parent mortar to produce a satisfactory colour match with the parent concrete after hardening. Use samples previously prepared.

Apply the finishing grout uniformly with damp (neither dripping wet nor dry) pads of coarse burlap approximately 6 inch square used as a float. Scrub the grout well into the pits to provide a dense mortar in all the imperfections to be filled. Allow the mortar to partially harden, from one to two hours, depending upon the weather. Avoid direct hot sunlight. If the air is hot and dry, keep the concrete surface damp during this period using a fine fog spray. When the grout has hardened sufficiently so it can be scraped from the surface with the edge of a steel trowel without damaging the grout from the small pits of holes, cut off all that can be removed with a trowel without delay; next allow the surface to dry thoroughly and rub it vigorously with clean, dry burlap to completely remove any dried grout. No visible film of grout shall remain after this rubbing. Complete the entire cleaning and grouting operation for the grout to dry after it has been cut with the trowel, so it can be wiped off clean with the burlap.

On the day after the repair Work, the concrete surfaces should again be wiped off clean with dry burlap to remove any inadvertent dust leave no built-up surfaces on the parent surfaces. Employ, if possible a used piece of burlap containing old hardened mortar to act as a mild abrasive. Use of find abrasive stone if needed to remove any remaining built-up film without breaking through the surface film of the original concrete. Such scrubbing should be light and sufficient only to remove excess material without Working up a lather of mortar or changing the texture of concrete. Following the final bagging or stoning operation, provide a thorough wash down with stiff bristle brushes to remove all extraneous materials and spray the concrete surface with a fine fog spray periodically to maintain a continually damp condition for at least three days after application of the pit repair grout.

(i)                 Rust Stains

All rust stains are to be removed employing the following procedure:

The rust stain shall be soaked for 10 minutes with a solution of (0.055 lb.) 25gm of sodium citrate in (0.33lb) 150 gms water (brushing the solution at short intervals is satisfactory). Then the surface is sprinkled with crystals of sodium hydrosulfite and covered with a paste of Fuller’s Earth and water. On a vertical surface, the paste is applied with a trowel, with the crystals first sprinkled on the paste so they will be in direct contact with the stain. The paste is allowed to dry for 10 minutes then scraped off and the treatment repeated if necessary.

(ii)               Repairing of Formed Surfaces

It is the intention of Specification to require, forms, mixture of concrete and Workmanship so that concrete surfaces, when exposed, will require no patching. Any concrete which is not formed as required and conforming to approve samples or for any reason is out of alignment or level or shows a defective surface, shall be removed from the job by the Contractor at his expense unless the Engineer grants permission to repair the defective area. Permission to patch any such area shall not be considered as waiver of the Engineer’s right to require a complete removal of defective Work if the repair does not, in his opinion, satisfactorily restore the quality and appearance of the surface. The Engineer shall be the sole judge of acceptability of appearance.

8.8       Repair of Surface Defects

8.8.1    General

(a)               Any concrete failing to meet the specified strength or not formed as shown on drawings, concrete out of alignment, concrete with surfaces beyond required tolerances or with defective surfaces which cannot be properly repaired or patched in the opinion of the Engineer shall be removed at Contractor’s cost. The Engineer may reject any defective concrete and order it to be cut out in part or in whole and replaced at the Contractor’s expense.

(b)               All ties and bolt holes and all repairable defective areas shall be patched immediately after form removal.

8.8.2        Repair of Defective Areas

(a)               All honeycombed and other defective concrete shall be removed down to sound concrete. The area to be patched and an area at least 6 inch. (150 mm) wide surrounding it shall be dampened to prevent absorption of water from the patching mortar. A bonding grout shall be prepared using a mix of approximately 1 part cement to 1 part fine sand passing a No. 25 BS Sieve and shall then be well brushed into the surface.

(b)               The patching mixture shall be made of the same material and of approximately the same proportions as used for the concrete, except that the coarse aggregate shall be omitted and the mortar shall consist of not more than 1 part cement to 2-1/2 parts sand by damp loose volume. White Portland cement shall be substituted for a part of the grey Portland cement on exposed concrete in order to produce a colour matching the colour of the surrounding concrete, as determined by a trial patch.

(c)               The quantity of mixing water shall be no more than necessary for handling and placing. The patching mortar shall be mixed in advance and allowed to stand with frequent manipulation with a trowel, without addition of water, until it has reached the stiffest consistency that will permit placing.

(d)               After surface water has evaporated from the area to be patched, the bond coat shall be well brushed into the surface. When the bond coat begins to loose the water sheen, the premixed patching mortar shall be applied. The mortar shall be thoroughly consolidated into place and struck off so as to leave the patch slightly higher than the surrounding surface to permit initial shrinkage it shall be left undisturbed for at least 1 hour before being finally finished. The patched area shall be kept damp for 7 days. Metal tools shall not be used in finishing a patch in a formed wall which will be exposed

(e)               Where as-cast finishes are specified, the quantity of patched area shall be strictly limited. The combined total of patched areas in as-cast surfaces shall not exceed 6 sq ft. In each 100 sq ft of as-cast surface. This is in addition to form tie patches, if the project design permits ties to fall within as-cast areas.

(f)                 Any patches in as-cast architectural concrete shall be indistinguishable from surrounding surfaces. The mix formula for patching mortar shall be determined by trial to obtain a good colour match with the concrete when both patch and concrete are cured and dry. After initial set, surfaces of patches shall be dressed manually to obtain the same texture as surrounding surfaces.

(g)               Patches in architectural concrete surfaces shall be cured for 7 days. Patches shall be protected from premature drying to the same extent as the body of the concrete.

8.8.3    Tie and Bolt Holes

After being cleaned and thoroughly dampened, the tie and bolt holes shall be filled solid with patching mortar.

8.8.4    Proprietary Materials

If permitted or required by the Engineer, proprietary compounds for adhesion or as patching ingredients may be used in lieu of or in addition to the foregoing patching procedures. Such compounds shall be used in accordance with the manufacturer’s recommendations with prior approval of the Engineer.

8.9       Concrete Construction Tolerance

Where tolerances are not stated in the specifications or drawings for any Individual structure or feature thereof maximum permissible deviations from established lines, grades and dimensions shall conform to the following. The Contractor is expected to set and maintain concrete limits. These allowable tolerances shall not relieve the Contractor of the responsibility for correct fitting of indicated materials. Those tolerances are not cumulative.

(a)               Variation from the plumb (or the specified better for inclined walls)

(i)                 In the lines and surfaces of columns, piers, and walls and in arises.

(A)               In any 10 ft. (3 meter) of length or height:       1/4” (6 mm)

(B)              In any storey or 20 ft. (6 meter) maximum:    3/8” (10 mm)  

(C)              Maximum for the entire length or height:        1” (25 mm)

(i)                 For exposed corner columns, control joint grooves and other conspicuous lines.

(A)               In any bay or 20 ft. (6 meter) maximum         1/4” (6 mm)

(B)              Maximum for the entire length or height         1/2” (13 mm)

(b)               Variation from the level or from the grades indicated on the drawings.

(i)         In floors, ceilings, beams soffits and in arises.

(A)       In any 10 ft. (3 meter) of length                       1/4” (6 mm)

(B)       In any bay or 20 ft. (6 meter) maximum         3/8” (10 mm)

(C)              Maximum for the entire length                        3/4” (20 mm)

(ii)               For exposed Iintels, sills, parapets, horizontal grooves and other conspicuous lines.

(A)       In any bay or 20 ft. (6 meter) maximum         1/4” (6 mm)

(B)       Maximum for the entire length                        3/8” (10 mm)

(c)               Variation of the linear building lines from established position in plan and related position of columns, walls and partitions.

(A)       In any bay or 10 ft. (3 meter) maximum         1/2” (13 mm)

(B)       Maximum for the entire length                        1” (25 mm)

(d)               Variation in the sizes and locations of sleeves,

Floor and wall openings                                                          +1/4” (+6mm)

(e)               Variation in cross-Sectional dimensions of columns and beams and in the thickness of slabs and walls.

(A)       Minus                                                               1/4” (6mm)

(B)       Plus                                                                 1/2” (13mm)

(f)                 Footings

(i)         Variation in dimensions in plan Minus

(A)       Minus                                                               1/2” (13 mm)

Plus (plus variation applied to concrete only, not to reinforcing bars or dowels).

(ii)        Misplacement or eccentricity

2 percent of the footing width in the direction of

misplacement but not more than (applies to

Concrete only, not to reinforcing bars or dowels).     2” (15 mm)

(iii)       Reduction in thickness Minus 5 percent of specified thickness

(g)               (i)         Variation in Steps

(A)       Rise                                                                 1/8” (3 mm)

(B)       Tread                                                               1/4” (6 mm)

(ii)        In consecutive Steps:

(A)       Rise                                                                 1/16” (1.5 mm)

(B)       Tread                                                               1/8” (3 mm)

(h)               Tolerances for Pavements

(A)       Departure from established alignment           ± 1/2” (413mm)

(B)       Departure from established longitudinal

grade on any time                                           ±1/4” (±6mm)

(C)       Departure from transverse template

contour except at transverse joints.               ± 1/8” (3mm)

(D)              Departure from transverse template             

contour at transverse joints,

width of one traffic lane                                   ±1/8”(+3mm)

(i)                  Pavements for parking areas

The tolerances are twice the values listed for pavements.

8.10     Acceptance of Structure

8.10.1  General

(a)               Completed concrete Work which meets all applicable requirements will be accepted subject to the other terms of the Contract Documents.

(b)               Completed concrete Work which fails to meet one or more of the requirements and which has been repaired to bring it into compliance will be accepted subject to the other terms of the Contract Documents.

(c)               Completed concrete Work which fails to meet one or more of the requirements and which cannot be brought into compliance may be accepted or rejected as provided in these Specifications or in the Contract Documents. In this event, modifications may be required to assure that remaining Work complies with the requirements.

8.10.2  Dimensional Tolerances

(a)               Formed surfaces resulting in concrete outlines smaller  than permitted by the  tolerances of clause 9 shall be considered potentially deficient in strength and subject to the provisions of sub clause 9.4

(b)               Formed surfaces resulting in concrete outlines larger than permitted by the tolerance of clause 9 may be rejected and the excess material shall be subject to removal. If removal of the excess material is permitted, it shall be accomplished in such a manner as to maintain the strength of the Section and to meet all other applicable requirements of function and appearance. Permission is required if excess material is to be removed in accordance with this clause.

(c)               Concrete members cast in the wrong location may be rejected if the strength, appearance or function of the structure is adversely affected or if misplaced items interfere with other construction.

(d)               Inaccurately formed concrete surfaces exceeding the limits of Clause 9 or of Clause 5.1 of Section FormWork’ shall be removed and replaced and those that are exposed to view, may be rejected and shall be repaired or removed and replaced if required.

8.10.3  Appearance

(a)               Architectural concrete with surface defects exceeding the limitations of Sub-clause 5.1 of Clause 5 of the Section, ‘FormWork’ shall be removed and replaced.

(b)               Other concrete exposed to view with defects which adversely affect the appearance of the specified finish may be repaired only be approved methods.

(c)               Concrete not exposed to view is not subject to rejection for defective appearance.

8.10.4  Strength of Structure

(a)               The strength of the structure in place will be considered potentially deficient if it fails to comply with any requirements which control the strength of the structure, including but not necessarily limited to the following conditions.

(i)                 Concrete strength requirements not considered to be satisfied in accordance with clause 6 hereof

(ii)               Reinforcing steel size, quantity, strength, position or arrangement at variance with the requirements as listed under specification of ‘Reinforcement’ or in the Contract documents.

(iii)              Concrete which differs, from the required dimensions or location in such a manner as to reduce the strength.

(iv)             Curing less than that specified.

(v)               Inadequate protection of concrete from extremes of temperature during early stages of hardening and strength development.

(vi)             Mechanical injury, construction fires, accidents of premature removal of formWork likely to result in deficient strength.

(vii)            Poor Workmanship likely to result in deficient strength.

(b)               Structural analysis and/or additional testing may be required when the strength of the structure is considered potentially deficient.

(c)               Core tests may be required when the strength of the concrete in place is considered potentially deficient.

(d)               Core tests are inconclusive or impractical to obtain or if structural analysis does not confirm the safety of the structure, load tests may be required and their result evaluated in accordance with British Standard, CP 110 or ACI 318.

(e)               Concrete Work judged inadequate by structural analysis or by results of a load test shall be reinforced with additional construction if so directed by the Engineer or shall be replaced, at the Contractor’s expense.

(f)                 The Contractor shall pay all costs incurred in providing the additional testing and/or analysis required by this Section.

(g)               All costs of additional testing and/or analysis which is made at the Employer request and which is not required by these Specifications, or by the Contract Documents shall be borne by the Contractor

8.11     Vapour Barrier

(a)               Vapour barrier shall be polyethylene building film, the film shall be 200 micron thick.

(b)               The quality of material shall be approved by the Engineer prior to use in the Works.

(c)               Vapour barrier shall be laid in position wherever shown on the Drawings or as directed by the Engineer.

(d)               The material shall be supplied in rolls and laid by rolling over the prepared surface at the levels and position in the areas shown on the Drawings. Where joint is necessary at the side or end of a sheet, this shall be a double weld folded joint made by placing the edges together and folding over twice continuously taking the top edge prior to concreting. The Contractor shall protect the film sheets from damages during laying and subsequent operations and shall replace at his cost all damaged film sheets to the satisfaction of the Engineer.

(e)               Manufacturer’s recommendations and instructions along with the sample of material shall be submitted to the Engineer for his approval.

8.12     PVC Water Stop/Hydrofoil

8.12.1  Material

All PVC water stops/hydrofoil shall be central bulb type from a manufacturer approved by the Engineer. The specific gravity of PVC water stop/hydrofoil shall not be less than 1.37 & full stretch Break cut intensity when tested at normal temperature shall not be less than 1878 Psi.

The material shall have a modulus of rigidity of 853 Psi at 50 0F & 10544 Psi at 680F.

8.12.2  Placing & Connections

In general all PVC water stops/hydrofoil shall be placed in the centre of the structural member. Each piece of the water stop-hydrofoil shall be of maximum practicable length. An ordinary sharp knife saw or any other sharp tool can be used to cut the water stop. Joints at inter Sections and at ends of pieces shall be made in the manner most appropriate to the material being used. Joints shall develop effective water tightness fully equal to that of the continuous water stop material and shall permanently retain their flexibility. For straight line connection melting method of connection can be used by pressing two water stops intended for connection against a heated iron or copper sheet. When they are melted, the two are combined.

After joining, the water stop should be allowed to cool.

For all other connections such as T-type or L-type, the welding method of joining should be used. Welding rod of same material as the water stop shall be used. The welding rod & the water stop shall be heated & melt at the same time, by means of heated air jetting from the hot jet gun.

8.13     Measurement and Payment

8.13.1 Material

Measurement and payment for concrete, reinforcement, PVC water Work will be made in accordance with the provisions of this clause specified hereinafter.

Concrete will be measured for the number of cubic feet acceptably placed complete in all respect as per Drawings and in strict accordance with this Section of specification.

Measurement for steel reinforcement will be made of number of kilograms reinforcement steel acceptably placed on the basis of the lengths of bars installed in accordance with the approved Drawings or bar schedules or as directed, converted to weight for the size of bars listed by the use of unit weights per linear foot as given in the following table:

Bar Size	Unit Weight Pounds (lbs) Per Foot
¼ “	0.167
3/8”	0.376
½ “	0.668
5/8”	1.043
¾”	1.502
7/8”	2.044
1”	2.670
1 1/8”	3.775
1 ¼”	4.172
1 3/8”	5.049

                                                                       

Steel in laps and embedment indicated on the Drawings or as required by the Engineer will be paid for at the steel unit price. No measurement for payment will be made for the steel consumed in providing supports and for the additional steel in laps, which are authorized for the convenience of the Contractor.

Polyvinyl chloride and/or metal water stopper of the size gauge as shown on the Drawings will be measured for the number of linear feet acceptably placed in the Work. In computing the quantities, no allowance will be made for laps.

8.13.2 Basis of Payment

Payment will be made in accordance with the unit prices in the Bill of Quantities for the various items in accordance with the specifications and shall constitute full compensation for furnishing all materials, shuttering, equipment and labour and for performing all operation necessary to complete the Work.

S. #	Description	Unit
1	Provide and lay concrete	Cft
2	Furnish and Fix Reinforcing Steel including Cutting, Placing and Binding complete	Kg
3	Furnish and Install Water Stopper
	(i)      PVC	L.ft
	(ii)     Stainless Steel	L.ft