3 sc&s3-reinforced concrete

___________________________________________________ CSS3-REINFORCED CONCRETE /1

Section III - REINFORCED CONCRETE

3.1 STANDARDS OF CONSTRUCTION

Refer to Clause 1.1 of this specification, which applies to this section. Specification notes in the Contract Drawings shall generally take precedence over this Specification, and the Contractor shall notify Engineer of discrepancies with normal Vietnam materials, methods and practice. Notwithstanding the above, all materials and workmanship for reinforced concrete works shall comply with the following Vietnam Standards; a. Reinforced Concrete work shall comply with TCVN 4453-95 Monolithic Concrete and Reinforced

Concrete Structures; Code for Construction, check, and Acceptance b. Cement shall comply with TCVN 2682-92 Portland Cement c. Sand shall comply with TCVN 1770-86, Sand used for Construction; technical requirements d. Sand tests shall comply with TCVN 342-86, Sand - methods for determining particle composition and

sizes e. Coarse aggregates shall comply with TCVN 1771-87, Gravel, broken pebble and pebbles used for

construction; technical requirements, and TCVN 1772-87, Stone and pebbles used for construction. f. Analysis for the grading of aggregate shall be as described in QPXD-31-68 (4.8 & 4.18) g. Water quality and testing shall comply with TCVN 4506-87; Water for concrete and mortar. h. Steel reinforcement shall comply with TCVN 1651-85

3.2 NON-CONFORMANCE WITH STANDARDS

Refer to Clause 1.1.2 of this specification, which applies to this section. Any Corrective Action that requires cutting-out and removal of concrete from the works shall be carried back to an approved construction joint before the replacement work.

3.3 MATERIALS

3.3.1 Cement

All cement used to make concrete shall be Portland Cement of approved manufacture, complying with TCVN 2682-92. The Contractor may select to use either Ordinary Portland Cement or Rapid Hardening Portland Cement, but such choice will not entitle him to claim a variation to the Contract Price. Manufacturer's test certificates will generally be accepted as proof of soundness, but Engineer may require additional tests to be carried out on any cement which, in its opinion appears to have deteriorated due to age, damage to containers, improper storage or for any other reason.

3.3.2 Aggregate 3.3.2.1 General

Aggregate shall comply with the general requirements of TCVN 4453. All aggregates shall be hard, durable, clean and free from adherent coatings, and shall not contain harmful materials in sufficient quantity to adversely affect the strength or durability of the concrete or to attack reinforcement.

3.3.2.2 Fine Aggregates (sand) Fine aggregates shall be naturally occurring fresh water sand, complying with TCVN 1770-86. The use of crushed stone shall not be permitted. Fine aggregates shall not contain silt or other fine-grained materials exceeding 3% by volume when tested by the Standard Method prescribed in TCVN 342-86. Fine Aggregates shall not contain organic material in sufficient quantity to show a darker colour than the standard depth of colour No.3 when tested by the Standard Method prescribed in TCVN 342-86.

3.3.2.3 Course Aggregates (gravel) Coarse aggregates shall be hard, crushed stone, complying with TCVN 1771-87 and TCVN 1772-87. For work below ground level, crushed granite shall be used. Course aggregates shall not contain clay lumps exceeding 1% by weight. A representative dry sample of course aggregate shall not show an increase in weight exceeding 8% after immersion in water when tested according to the method in TCVN 1771-87.


Course aggregates shall be well shaped and not flaky, with a maximum flakiness index not exceeding 35. The maximum nominal size of coarse aggregate shall be 20mm.

3.3.2.4 Aggregate Grading The sieve analysis for the grading of aggregate shall be as described in QPXD-31-68, and shall be within the limits specified in Table 3.1 below:

Table 3.1 Grading of Aggregates Fine Aggregate Sieve Size (mm) 5 2.36 1.18 0.6 0.3 0.15 (sand) Retained % 0-5 5-30 15-55 40-75 70-95 90-100 Coarse Aggregate Sieve Size (mm) 25 20 10 5 (gravel) Retained % 0 0-5 45-75 90-100

Grading between the limits specified above shall be subject to the approval of Engineer, and when tested as provided in TCVN 1770-85, shall approximate closely to the grading of the approved samples. If it should be found to be necessary, fine aggregate shall be washed and/or screened to comply with foregoing standards and Engineer’s requirements.

3.3.3 Water

Water for concreting shall be clean, uncontaminated, potable water from a Government main supply, or any other source as approved by Engineer, complying with TCVN 4506-87. The Contractor shall make adequate arrangements to deliver and store sufficient water at the works site for use in mixing and curing the concrete.

3.3.4 Admixtures

Admixtures to concrete mixes, for such as purposes as retarding setting time, increasing workability, waterproofing, surface-hardening agents and the like will be permitted, subject to approval by Engineer. Such admixtures shall be from a reputable supplier who has adequate stocks of material locally and technical staff to advise on product application. The Contractor shall submit admixture proposals to Engineer, including the manufacturer’s name, product name, product specification, and the effects of the admixture on the concrete design strength and workability.

3.3.5 Reinforcement

All reinforcement to be used in the works shall be new, and comply with TCVN 1651-1985. The following types of reinforcement are specified; a. Hot-rolled, mild steel round bars, Grade AIII, Ra = 2,100 kg/cm2, complying with TCVN 1651-1985.

Permitted diameters of these bars are 6mm, 8mm, and 10mm. b. Cold-rolled, high-tensile deformed, round bars, Grade AII, Ra = 2,700 kg/cm2, complying with TCVN

1651-1985. Permitted diameters of these bars are 12mm and greater. The use of high-tensile, welded steel fabric is not specified, and will not be permitted unless the contractor submits a detailed proposal to Engineer for evaluation and approval.

3.3.6 Formwork 3.3.6.1 Formwork panels

All formwork, except where otherwise approved by Engineer, shall be made from steel frame panels with steel or plywood faces, of sufficient strength to ensure complete rigidity throughout the placing, compaction and setting of the concrete. Steel-framed edges of formwork panels shall be straight and true to alignment, within the tolerances specified below. The edges of panels joined together shall be sufficiently tight to prevent the loss of grout during placing and compaction. Plywood or steel faces of formwork panels shall be properly maintained, clean, free of surface imperfections, and have a flat surface within the tolerances specified below.

3.3.6.2 Joints between panels Formwork panels shall be joined together by suitable steel pins & wedges, or other suitable connections, which maintain rigidity and alignment of the forms, and provide for easy removal of panels for inspection. Formwork for beams and columns shall be designed and constructed so that the sides may be removed without interference to remaining formwork. Formwork to one side of each column shall be made from


450mm high removal sections, and shall be taken down and re-fixed as the pouring of concrete proceeds, to facilitate proper placement and compaction of concrete, and for inspection. Where panels join to form a corner, steel backing angles or other approved methods, shall be installed to prevent leakage of grout. Where panels join in the same surface, edges of panels shall make a tight joint, and within the tolerances specified below. Where the work requires formwork infill strips smaller than available panels, these infills shall be made of local hardwood, with smooth surface, free of nails, and wedged tightly between panels.

3.3.6.3 Internal formwork ties Internal ties or struts shall be avoided as far as possible, and if used, they shall be of the ‘snap-off’ steel strap or wire type, capable of removal without damage to the concrete. No part of any metal tie or spacer remaining permanently embedded in the concrete shall be nearer then 15mm to the finished surface of the concrete.

3.3.6.4 Tolerances of formwork panels a. Flatness of face 2mm over full length b. Squareness of frame 2mm across diagonals c. Straightness of frame edge 1mm over full length

3.3.6.5 Inspection of formwork Each delivery of formwork arriving at the Site shall be subject to inspection by Engineer before it is used in the Works. Where formwork does not meet the tolerances specified in Clause 3.3.6.4, those panels or accessories will be rejected. All rejected items shall be stacked in a separate location and removed from Site within 24 hours of inspection. Approval by Engineer does not relieve the Contractor of his obligation to comply with the Standards and the Specification.

3.3.6.6 Re-using formwork panels All formwork that has been approved to be used in the Works, and will be re-used during construction of the project, shall be properly maintained to ensure its quality is preserved. The Contractor shall submit his quality control process to Engineer for approval. Formwork that becomes damaged or is not properly maintained may be subject to rejection by Engineer at any time during the construction of the Works.

3.3.7 Scaffolding

Scaffolding required to support suspended formwork shall consist of adjustable tubular steel props, of the telescopic type, with threaded ends for final adjustment, and suitable steel end-plates. The props may be single, or made into cross-braced frames. The use of wooden props will not be used without the prior approval of Engineer. Bearers for supporting suspended formwork may be of wood or steel. Their sizes shall be suitable to their span and loads to be carried by formwork and freshly placed concrete. Bearers shall be straight and in good condition. Wooden bearers with sags or splits will be rejected. Bracing of formwork to the scaffolding may be of wood or steel. Where wooden bearers or braces are used and are temporarily nailed together, the Contractor shall remove all nails from wood, immediately on removal or stripping of the scaffold. The Contractor shall be responsible for ensuring that all props, bearers and bracing are sufficient to maintain complete rigidity of the formwork during pouring and curing of concrete. Prior to assembling any scaffolding for suspended concrete works, the Contractor shall submit shop drawings, together with calculations (if required by Engineer) of the proposed scaffolding method.

3.4 CONCRETE

3.4.1 Design strength

The design strengths of concrete elements to be used in the works shall be as specified in the Drawings. To achieve these strengths, concrete mixes shall be proportioned by one of the following methods, namely, Nominal concrete mix or Designed concrete mix. The water/cement ratio, workability and the strength of the mixes, when tested in accordance with TCVN 4453-95, shall comply with the following specification.

3.4.2 Nominal Concrete Mixes

Unless otherwise approved by Engineer, the concrete shall be proportioned as shown in Table 3.2 below. The quantities of cement, fine and coarse aggregates shall be determined by weight and that of water by volume. The fine and coarse aggregates shall be measured separately. A weigh batcher shall be used for the


purpose of weighing cement, fine and coarse aggregates. The accuracy of the weights indicated by the weigh batcher shall be regularly checked and shall be maintained within ±2.5 % of the actual total weight of all aggregates & cement in one batch. The weight and volume of fine and coarse aggregates given in Table 3.2 refers to the materials in a dry state. Tests on the aggregates shall be carried out twice daily or more frequently if required by Engineer. Allowance shall be made for the water contained in the aggregates when calculating the quantity of water to be added to the mix. The quantity of water to be used in nominal mixes shall be as shown in Table 3.2 The water/cement ratio shown in the table is expected to produce cube strengths greater than the requirements of the specification workability, sufficient to ensure that the concrete can be worked and fully compacted using the methods of variation specified here. However, if it is found during the course of work that the concrete mix is stiffer than can be placed satisfactorily, an adjustment of up to 5% may be made in the water/cement ratio, but any further adjustment of the mix shall be made by increasing the proportions of both the water and the cement without increasing the water/cement ratio. The cement proportions shall be increased if the works cube strength falls below those specified.

Table 3.2 Nominal Concrete Mixes Slump = 25 – 50 mm Compacting factor = 0.88-0.94

Proportions of materials to add to 50kg cement Mix Weight of Weight of Water/ Amount Min Strength Proportion dry sand gravel Cement of water Strength 28 days (kg) Ratio (litres) 7days kg/cm2 1:1:2 65 110 0.45 22.5 200 300 1:1:3 80 135 0.50 25.0 170 255 1:2:4 90 155 0.55-0.6 27.5 140 210 1:3:6 155 222 As Approved by Engineer

3.4.3 Designed Concrete Mixes

Designed concrete mixes may be used, and shall comply with TCVN 4453-95. The grades of concrete shall be proportioned as shown in Table 3.3 below: The cement content of any concrete mix shall not exceed 550 kg/m3 of the compacted concrete. The total chloride content of the mix shall not exceed 0.35% of the mass of cement in the mix. If the Contractor chooses to use designed concrete mixes, he shall employ a competent and suitably qualified person to design the mix, to supervise and direct all stages of the preparation and placing of the concrete. The sampling, making, curing and testing of the works cubes shall still be carried out by Engineer or its representative, and the Contractor shall provide all facilities. The Contractor may be present while the cubes are being made and tested. The Contractor shall submit the following information to Engineer for approval of design mix a. Nature and source of each material b. Full details of trial mixes, all in accordance with TCVN 4453 c. Proposed quantities (by weight) of each material to produce 1m3 of fully compacted concrete.

Table 3.3 Designed Concrete Mixes Equivalent Strength Strength Max. aggregate Min. cement in Nominal Mix Concrete Concrete size (mm) finished concrete 7days 28days(kg/cm2) (kg/m3) 1:1:2 Grade 300 200 300 20 380 1:1:3 Grade 250 170 255 20 361 1:2:4 Grade 200 140 210 20 321

3.4.4 Ready-mixed Concrete

Ready-mixed concrete may be used in any part of the works, subject to Engineer’s written approval, which may be withdrawn at any time. If the Contractor proposes to use ready-mixed concrete for the works, he shall submit to Engineer, for approval, the following information;


a. The name and business license of the supplier’s company b. Number of batching plants, their age and maximum mixing rates (m3/hr) c. Number of trucks and their mixing bowl capacity (m3) d. Travel time from the batching plant to the Site e. Log book showing the maintenance control of all equipment used for measuring, weighing, agitating of

the materials and control of water flow. All materials used for making ready-mixed concrete shall comply with Clause 3.3 of this specification in all respects. The Contractor shall satisfy himself that the manufacturing and delivery resources of the proposed supplier are adequate to ensure proper and timely completion of each concreting operation. The method of designing concrete mixes for making ready-mixed concrete for each of the concrete strengths specified, shall comply with this specification in all respects. Before any ready-mixed concrete is delivered to the site, the supplier shall prepare Trial mixes and tests as specified in Clause 3.4.6 below. The Contractor shall provide, at his own cost, all necessary facilities for the supervision and inspection of the batching, mixing and transporting to site of ready-mixed concrete.

3.4.5 Workability

Workability of concrete mixes shall be controlled by direct measurement of water content, making allowance for any water in the aggregates. The Slump Test or the Compacting Factor Test shall be used as a guide to measure the workability of concrete.

3.4.6 Trial mixes and tests

As soon as possible after receiving possession of site, and before any concrete is placed, the Contractor shall prepare a series of trial mixes totaling not more than 4 m3 of concrete under the direction and supervision of Engineer. Test cubes shall be made from samples of these trial mixes, then cured and tested in accordance with the Standard Method in TCVN 4453 to determine the cube strengths at 3, 7, 14, 21and 28 days after casting. The cube strengths of these samples shall be at least equal to those specified in Table 3.4 below. The mix proportions specified above may be adjusted as necessary by Engineer on the basis of these tests without additional cost to the Employer.

Table3.4 Trial Mixes Equivalent strength Crushing Crushing Crushing Crushing

Nominal Mix Concrete strength 7 days strength strength strength 3 days (kg/cm2) 14 days 21 days 28 days 1:1:2 Grade 300 125 200 240 275 300 1:1:3 Grade 250 105 155 200 230 255 1:2:4 Grade 200 85 125 160 185 210

3.4.7 Mixing of concrete 3.4.7.1 Machine mixing at site

The concrete shall be mixed in a mixing machine of adequate capacity and complying with the requirements of TCVN 4453, and having a power elevated loading hopper, or other type of mixer approved by Engineer. The mixer shall be equipped with an automatic water measuring tank fitted with a device for locking the discharge setting. The quantity of water added to each batch in the mixer shall be carefully measured, and such quantity shall be approved by Engineer before handling, and can only be varied with Engineer’s approval. The mixing shall continue until there is a uniform distribution of the materials and the mass is uniform in colour and consistency and in no case shall the time of mixing be less than two minutes or more than five minutes after all the ingredients have been placed in the mixer.

3.4.7.2 Hand mixing at site Mixing concrete by hand will only be permitted for small quantities of concrete which are to be used for a special purpose. Where hand-mixing is permitted, 10% extra cement shall be added to the proportions specified in the table above.


3.4.7.3 Admixtures Admixtures such as plasticisers or rapid-hardening agents shall not be used without prior approval of Engineer. Where admixtures are approved, they shall conform to clause 3.3.4 of this specification.

3.5 SAMPLING & TESTING OF MATERIALS

3.5.1 Cement

Where testing of cement samples is required by Clause 3.3.1 above, it shall be conducted in a licensed laboratory, to the approval of Engineer, and comply with the testing procedures prescribed in TCVN 3736-82, TCVN 4029-85, TCVN 4032-85, TCVN 4787-89 as applicable. One copy of all test results shall be submitted to Engineer, and the cost of all testing shall be borne by the Contractor. Engineer may, without tests being made, order that any bag of cement, a portion of the contents of which has hardened or which appears to be defective in any other way, be removed from site immediately.

3.5.2 Aggregates

The method of sampling and the amount of aggregate to be provided for the tests shall be in accordance with Section 4.7 to 4.21 of QPXD-31-68. Samples of the fine and coarse aggregate approved by Engineer shall be kept on site and shall be used to compare the general quality of the aggregates delivered during the course of the work. The tests to be performed on the aggregates shall be as specified above. Engineer may require further tests to be carried out on samples of the aggregates delivered to site at intervals. The tests shall be carried out by Engineer or its representative. Should a sample fail to comply with any of the tests, Engineer may, at its discretion, either reject the batch from which the sample was taken, or order it to be washed and/or screened, or permit it to be used with variations in the proportions of the concrete mixes specified. Any batch of aggregate rejected by Engineer shall be removed from the works site immediately.

3.5.3 Reinforcement

Before any reinforcement steel is brought to site, the Contractor shall submit the Manufacturer's Test Certificates to Engineer for acceptance. In addition, the Contractor shall submit a test sheet from an approved laboratory to Engineer for any batch of bars, giving the results of each of the mechanical tests required under the TCVN 1651-85. During the course of the works, any reinforcement which is found to be not in accordance with TCVN 1651-1985, may be rejected by Engineer, notwithstanding any previous acceptance on the strength of the test certificates, and Engineer may call for additional tests to be made at the Contractor's expense on samples taken from the batch of bars, from which the defective reinforcement came. If the samples do not comply with TCVN 1651-1985, then Engineer may reject the whole batch and instruct its removal from the site.

3.5.4 Concrete 3.5.4.1 General

The method of sampling, making test cubes, curing, and testing of hardened concrete shall all comply with TCVN 3105-93 “HW concrete mix-sampling, making and maintaining specimen” and TCVN 3118-93 “Methods of determining compressive strength” While concreting is in progress, samples of the concrete shall be taken and work test cubes made from them. At the same time, workability tests shall be made and the compacting factors or slumps recorded.

3.5.4.2 Equipment for Sampling & Testing The Contractor shall provide testing equipment which shall include the following : a. 12 Sets of 15mm steel or cast iron moulds with base plates. b. 2 Nos. tamping bar. c. 1 No. slump cone with tamping rod or 1 set compacting factor apparatus. d. 1 No. 300mm steel rule. e. 1 Set of sieves. f. 1 No. Cylinder of 100cm3 capacity for field silt test. g. Scales or balance of 25kg. maximum capacity and weights. h. Trowels, shovels, spanners and other tools.


3.5.4.3 Compressive Strength Tests Generally, six test cubes shall be made; three cubes for each of two samples taken in each day of concreting, or for each 30m3 of concrete poured, whichever is the lesser. However, where the mix or any of its constituents are changed either in quantity or quality, Engineer may order additional test cubes to be made. All cubes shall be clearly marked with indelible paint with the date of casting and serial number. A record shall be kept to identify each cube by date and by serial number relating to the part of the work from which they are taken, Three cubes, one from each sample, shall be tested at 7 days and the other three at 28 days. The cube strength at testing shall be calculated from the maximum load of concrete load sustained by the cube at failure. The appropriate strength requirement may be considered to be satisfied if none of the strengths of the three cubes is below the specified cube strength, and the average strength of the three cubes is not less than the specified cube strength and the difference between the greatest and least strength is not more than 20% of the average. If the 7 day test results do not meet the strength requirement, Engineer reserves the right to order work in concreting to stop until after the remaining cubes are tested at 28 days. If the 28 day test results do not meet the strength requirements, Engineer shall determine the action to be taken in respect of the concrete member represented by the test cubes concerned, which may include its demolition. The Contractor shall, if required by Engineer, take cored samples from the hardened concrete member and carry out strength tests. All costs incurred in carrying out such sampling, testing and remedial works shall be borne by the Contractor irrespective of whether the tests proved the structure to be sound or otherwise. The strength requirement for nominal mixes shall be as shown in Table 3.2 above

3.5.4.4 Workability Tests While concreting work is in progress, tests on workability of the mix shall be carried out twice daily and, in addition, whenever any materials or the proportions of the mix are changed, or when directed by Engineer. The tests shall be either Slump Test or a Compacting Factor Test. The Slump shall be as small, and the Compacting Factor as low as practicable, consistent with efficient working and full compaction of the concrete mix in the formwork, using the specified methods of compaction.

3.6 DELIVERY, HANDLING & STORAGE

3.6.1 Cement

Cement shall be delivered to the site in covered vehicles adequately protected against water. It shall be stored in a weatherproof cement store to the approval of the Engineer and shall be taken for use in the work in the order of its delivery into the store. Cement delivered in bulk shall be stored in silos of approved design.

3.6.2 Aggregate

Aggregates shall be stored in such a manner as to prevent contamination by undesirable substances. Different types of aggregate shall be stored in separate bins and not be allowed to intermingle.

3.6.3 Reinforcement

Reinforcement shall be delivered to the Site or fabrication yard directly from the manufacturer’s mill or an authorized distributor of the manufacturer. All reinforcement shall remain strapped in bundles or rolls, each with the manufacturer’s tag attached. Reinforcement shall be stored in groups according to Grade and size, and supported in such a way as to avoid contamination by dirt, mud, oil or grease.


3.6.4 Ready-mixed concrete

Concrete mixed at the batching plant shall be put directly into the mixing bowl of the transport truck, and the truck shall proceed directly to the site. The maximum time for transportation of concrete to the site shall conform to Table 3.5 below.

Table 3.5 Time to Transport concrete Temperature: ( oC ) > 30o 20o-30o 10o-20o Time (minutes) 30 45 60

Every truck of concrete that arrives at the site shall bear a delivery note, which describes the properties of the mix, and the date and time of mixing.

3.7 CONSTRUCTION PROCESS

3.7.1 Scaffolding

All scaffolding, including props, frames and bearers, shall be erected using materials specified in Clause 3.3.7, The Contractor shall ensure that all props and frames are supported by suitable base-plates of wood, rock or steel so that adequate bearing pressure is applied to the supporting material, and that the scaffolding is adequately braced to maintain stability.

3.7.2 FORMWORK 3.7.2.1 Installing formwork

All formwork, including panels and accessories as specified and approved in clause 3.3.6.2 shall be installed according to the levels and locations shown on the Drawings. Where joints between panels are not tight enough to prevent the leakage of grout, they shall be filled with solid wooden wedges.The use of metal, plastic or wooden cover pieces on top of formwork panels is prohibited.

3.7.2.2 Oiling and cleaning of formwork Unless otherwise approved by Engineer, the inside surface of all forms shall be coated with an approved, non-staining mould oil before placing reinforcement. After the mould oil is placed on the forms, care shall be taken at all times to keep the reinforcement free from the oil. There shall be no excess oil coating material in the form before concreting. After reinforcement is installed, and before concrete is placed, the forms shall be thoroughly cleaned and shall be free from sawdust, shavings, dust, mud, wire, nails, and any other debris, by hosing with clean water. Temporary openings shall be provided in the forms to drain away the water and rubbish.

3.7.2.3 Tolerances of formwork The maximum tolerances when installing the formwork shall be as follows: Item Tolerance Along Gridlines (axes) 5 mm Level of soffit forms ±5 mm Cross-section (foundations) ±10 mm Cross-section (beams, columns) ±5 mm Slab/beam sag (rooms < 5m high) 6 mm Slab/beam sag (members > 5m long 8 mm Joint surface 2 mm Surface flatness (using a 2m ruler) 3 mm

3.7.2.4 Inspection of formwork All formwork shall be inspected by Engineer after it is prepared, and before the installation of any reinforcement. The Contractor shall provide sufficient survey marks to permit proper inspection and measurement of the formwork. Where formwork fails to meet the tolerances specified in clause 3.7.2.3 above, work shall stop until the repairs are complete and have been re-inspected by Engineer. No reinforcement shall be installed during the time of repair and re-inspection.


3.7.3 Reinforcement 3.7.3.1 Cleaning reinforcement

Before being placed in position, reinforcement shall be clean, free from loose mill scale and rust, and shall be free from oil, grease or other harmful matter at the time when the concrete is placed. Starter bars from a previous concrete pour shall be free of adhering concrete or grout.

3.7.3.2 Cutting & bending reinforcement The bending angle, radius, and dimensions shall be in accordance with TCVN 1651-1985 and the Drawings. Reinforcement shall be bent cold with an approved bar-bending machine, and heating the bars by oxy flame or other methods shall not be applied to make bending easier. Reinforcement shall not be re-bent without the approval of Engineer. Straightening of previously bent High-Tensile deformed bars shall be allowed. Bars for use in foundations shall not be cut or bent until the size and depth of the foundations have been approved by Engineer, and the base of the foundation has been prepared with lean-mix concrete.

3.7.3.3 Placing reinforcement The reinforcement shall be placed in the forms and held firm against displacement by approved types of small precast, cement mortar spacer blocks and wire ties, in their exact position. Thickness of spacer blocks shall be the clear cover dimension as shown on the drawings for beams, slabs and columns. Spacer blocks shall be 50mm x 50mm made from cement mortar in the proportions 1:1, and shall be tied to stirrups and column ties as follows; a. Columns, on 4 sides at 500mm maximum centers b. Beams, on 3 sides at 600mm maximum centers c. Slabs, at 750mm maximum centers in both directions, for both top and bottom reinforcement. Top

reinforcement for slabs may be of concrete spacer blocks or approved mild-steel chairs. Bars intended to be in contact when passing each other shall be securely held together at intersection points with tie wires. Stirrups and column ties shall fit tightly against the longitudinal reinforcement to which they shall be securely wire-tied or spot welded. Wire ties used for tying reinforcement shall be 1.6mm diameter, soft annealed iron wire; the ends shall be turned in from face of the formwork and shall not be left projecting beyond the reinforcement. The exact clear cover to reinforcement shall be obtained when the reinforcement is placed and shall be maintained during concreting. The Contractor shall ensure that the reinforcement will not move during placing of the concrete and under effect of vibration.

3.7.3.4 Welding reinforcement Welding on site may only be done with the approval of Engineer. The Contractor shall demonstrate the competence of all welders prior to, and periodically during welding operations . Welding may be used for; Fixing reinforcement in position, e.g. laps to reinforcement, and between reinforcing bars and other steel members such as embedded plates, bolts Structural welds involving transfer of load between reinforcing bars, or between bars and other steel members. Welding shall be by metal-arc welding complying with QPXD-31-68 for mild steel and for carbon-manganese steel whichever is applicable. Welded joints shall not be placed at bends of reinforcement. Joints in parallel bars shall be staggered in the longitudinal direction. For staggered joints, the distance between them shall not be less then the end anchorage length for the bar. The Contractor shall prove by test that the strength of a welded joint is as strong as the parent bar before Engineer will approve the use of such joint.

3.7.3.5 Tolerances for reinforcement The maximum tolerances for placing reinforcement shall be as follows: Item Tolerance Spacing of main bars, column, beam, arch ±10 mm Spacing of main bars, slab, wall, foundation ±20 mm Spacing of secondary bars, slab ±25 mm


Spacing of side bars to beams, foundation ±20 mm Spacing of side bars to slab>100mm ±5 mm Spacing of stirrups & column ties ±10 mm Embedded items (center-line) ±5 mm Embedded items (level) ±5 mm Clear cover to main rebars (foundation) ±10 mm Clear cover to main rebars columns, beams ±5 mm Clear cover to main rebars slab, wall ±5 mm

3.7.3.6 Inspection of reinforcement All reinforcement shall be inspected by Engineer after it is prepared. Where reinforcement fails to meet the tolerances specified in Clause 3.7.3.5 above, work shall stop until the repairs are complete and have been re-inspected by Engineer. No concrete shall be delivered to the Site during the time of repair and re-inspection.

3.7.4 CONCRETE 3.7.4.1 Moving concrete into position

After mixing (for site-mixed concrete) or after delivery to the site (for ready-mixed concrete), concrete shall be moved from the mixer to its location in the forms as quickly as practicable, and by means which will prevent segregation of the materials or loss of ingredients. Concrete shall be placed as near as practicable to its final position to avoid re-handling or flowing. The method of moving concrete shall be by concrete pump, crane-operated hopper (skip), chutes or other methods approved by Engineer. Moving concrete by hand using buckets, etc. will not be permitted, except under special circumstances and only by approval of Engineer. Without such approval, any concrete which is placed by hand will be rejected, and will be taken out of the works.

3.7.4.2 Placing concrete a. For deep beams and main frame beams, concrete shall be placed in the formwork in layers not more

than 500mm deep. Each layer shall be compacted by vibration before the next layer is placed. For shallow beams and slabs, concrete shall be placed to the full depth.

b. For columns and walls, concrete shall be placed in the formwork in layers not more than 1.5 metres in depth. Each layer shall be compacted by vibration before the next layer is placed.

c. No concrete shall be placed such that the free-fall from the pump, hopper or chute to its final position exceeds 1.5 metres. Regardless of these requirements, any cause of segregation or loss of integrity during the placement of concrete will not be permitted.

d. Concrete shall be moved from the pump, hopper or chute into its position by hand using shovels, rakes, etc. Vibrators shall be used only for compacting concrete and not for working concrete into position.

e. Concreting work shall be carried out continuously between approved construction joints in one sequence of operation. The surface of the concrete shall be maintained level during placing.

f. When the continuous concreting in Clause 3.7.4.2 e) above is interrupted, concreting shall be stopped on horizontal layers and against vertical surfaces by using stopping-off boards to make a construction joint.. The time of interruption that requires this construction joint will be at the discretion of Engineer, and the Table 3.6 below may be used as a guide only.

Table 3.6 Time for interrupting concrete pour Temperature: ( oC ) > 30o 20o-30o 10o-20o Time (minutes) 60 90 135

Unless Engineer approves otherwise, construction joints shall be made in the following situations: g. Freshly placed concrete is placed against in-situ concrete that has been in position for more than the

time specified in Clause 3.7.4.2 f) above The total time of transporting and placing concrete from a ready-mixed batching plant, is longer than

the time specified in Clause 4.9.4 above


In the opinion of Engineer, the concrete has stiffened to such an extent that it no longer responds to the action of a pencil vibrator.

h. Where construction joints are formed as specified in Clause 3.7.4.2 above, further concrete shall not be placed against that joint for 24 hours.

i. A record shall be kept on site of the date and time of placing the concrete in each position of the structure and the reference numbers of the test cubes that belong to batches of concrete in particular parts of the structure.

j. After concrete has been placed in its final position in the forms, it shall be thoroughly compacted by both tamping & mechanical vibration, using the types of vibrators specified, and shall be thoroughly worked into the corners of formwork by hand tamping. After tamping into place the concrete shall not be subjected to disturbance other than such as incidental to compaction by vibration.

3.7.4.3 Compacting Concrete a. Concrete placed between walls of formwork shall be compacted by pencil-type vibrators. Concrete

placed in slabs with no formwork on its upper surface shall be compacted either by pencil-type vibrators, pan-type vibrators, vibrating-beam type vibrators, or any other approved Engineer. All vibrators used shall have a power source sufficient for the work.

b. Vibrators shall be operated only by workmen skilled in their use. c. Pencil-type vibrators shall be inserted rapidly and withdrawn slowly and at a uniform pace of

approximately 100mm per second. Compaction shall be deemed to be completed when cement mortar appears in a circle around the vibrator. Over-vibration leading to segregation of the mix must be avoided. Pencil-type vibrators shall be inserted at points judged by the area of mortar showing after compacting with a certain allowance made for overlapping, and they should not come into contact with the formwork or the reinforcement, and should be inserted at a distance of 75mm from the formwork.

d. Pan-type vibrators shall be placed on the surface of the concrete which shall have previously been tamped and leveled, leaving an allowance in height for compaction, until cement mortar appears under the pan. The vibrator shall then be lifted and placed on the adjoining surface and this operation shall be repeated until the whole surface has been compacted.

e. Vibrating-beam-type vibrator, spanning the full width of the surface, may be used, but limited to a maximum span of 6m. The vibrating beam shall make only one pass over the slab surface. Concrete shall be placed higher than the finished level, and the buildup of concrete in front of the screeding board shall be controlled by hand continuously as the work proceeds.

3.7.4.4 Curing & protection of concrete Immediately after final set of the concrete, all exposed surfaces shall be protected from direct sun in a manner approved by Engineer. All concrete shall be well watered after it has set, and shall be kept continuously damp until thoroughly cured. Provision shall be made for adequate water distribution to all parts of the works, so that, if required this treatment can be continued throughout the period of construction. In order to keep the concrete continuously damp, all exposed surface shall be covered with continuously damped hessian bags or any other approved means, for the period of curing, which shall not be less than 7 days. All work shall be protected from damage by shock or over-loading or falling earth.

3.7.4.5 Construction Joints Construction joints shall be made in the locations shown in the Drawings or as approved by Engineer on site. These joints shall be made against stop-end forms, perpendicular to the axis of the member, and rebated where required. Care shall be taken to prevent loss of grout through the stop-end. More than usual compaction shall be given to concrete on each side of construction joints during concreting. Wherever possible, stop-ends for construction joints shall be removed as soon as the concrete has set and the surface shall be brushed and washed to remove excess laitance and expose the aggregates. Alternatively, this must be done by chipping concrete after it has hardened. Before concreting is resumed, the face of the joint shall be well cleaned and wetted. Construction joints in exposed concrete surfaces shall be located and formed to give minimum variation from the specified finish.


3.7.4.6 Service conduits and pipes Where service conduits and/or pipes are proposed to be located within any reinforced concrete element, including foundation members and structural beams, slabs and columns, the Contractor shall submit all such proposals to Engineer for approval before any installation. For the purposes of submission, the following guidelines will apply, though each case will be evaluated on its merit. a. Wherever a conduit or pipe is proposed, it will be located on the neutral axis of the concrete element b. In every case, the sectional area of the conduit or pipe shall not be more than 15% of the net area of the

structural section. c. uPVC electrical conduits may be placed symmetrically on the neutral axis of a slab, beam or column d. uPVC rainwater down-pipes may be placed symmetrically on the neutral axis of columns. Down-pipes

of metals shall have a protective, insulating casing e. Fresh-water supply pipes of any material will not be permitted to be cast into any structural member f. The Contractor will be responsible for the work of any subcontractor when installing any service

conduits or pipes 3.7.4.7 Slab penetrations

All penetrations (holes) in slabs which are provide to allow service conduits and pipes to pass through, shall be located in the positions shown on the Drawings..Each opening size shall conform to additional reinforcement trimming bars as shown on the Drawings.

3.7.4.8 Removal of Formwork The Contractor shall inform Engineer and obtain approval before removing any formwork, but such approval shall not relive the Contractor of his responsibilities. No props to slab or beam soffits may be removed until the Contractor has submitted 7 days compressive test results to Engineer. For concrete using Ordinary Portland cement, the 7 day strengths shall be not less than 60% of the concrete’s design strength Formwork shall be removed without shock or vibration that could damage the concrete. A period of time shall elapse between the placing of the concrete and the removal of the formwork for various parts of the structure. Table 3.7 below shall be used as a guide to the minimum times of removal of formwork for concrete using ordinary Portland and Rapid Hardening Cement. However Engineer may, at its discretion, increase these times if it considers such an increase to be necessary. This guide is based on the structure supporting construction loads of further storeys.

Table 3.7 Time to remove formwork

Structural Ordinary Rapid hardening Element Portland cement Portland cement Sides of beams, columns & walls 1 day 1 days Slab soffits (props re-installed) 8 days* 3 days Beam soffits (props re-installed) 8 days 5 days Removal of 50% props to slabs 14 days 8 days Removal of props to beams 21 days 10 days Cantilever props to beams, slabs 28 days 14days * = Engineer will consider requests to remove slab formwork and re-prop the slab after 4 days, on condition that calculations be submitted showing the required prop spacing to carry additional construction loads applied during the following 21 days

3.7.4.9 Finished concrete All concrete is to be left as from the formwork. Any defects in the concrete shall be left undisturbed until inspected by Engineer, and such defects shall be repaired by methods approved by Engineer. All fair-faced concrete surfaces shall be properly protected from staining, which may arise during flooring or any other operation by covering with polythene sheets.

3.7.4.10 Tolerances in finished concrete The maximum tolerances of concrete structure shall be as follows:


Item Tolerance Gridlines of foundations 15 mm Gridlines of columns, beams 10 mm Sag in rooms < 5m high 8 mm Sag for members > 5m 10 mm Sag for whole building H/1000 and <30 mm Level of floor -10~+5 mm Level of whole building ±30 mm Cross section -5mm+8 mm Surface (in 2m) 8 mm Center-line of embedded plate 10 mm Center-line of embedded bolt 5 mm Center-line of embedded pipe 5 mm Center line of opening 15 mm

3.7.4.11 Inspection of finished concrete All finished concrete work shall be inspected by Engineer after the removal of soffit forms and re-propping. The Contractor shall provide sufficient survey marks to permit proper inspection and measurement of the finished concrete work Where finished concrete work fails to meet the tolerances specified in Clause 3.7.4.9 above, work shall stop and Engineer shall issue a non-conformance notice to the Contractor. Engineer and the Contractor shall meet to discuss corrective action.

3.8 PRECAST CONCRETE ELEMENTS

Precast concrete shall be 1:2:3 mix with 20mm aggregate, fair finish on exposed surfaces. All precast units shall mature for at least 14 days before being incorporated in the works for non-structural members and for 21 days in the case of structural members. Concrete lintels may be precast or cast in-situ as per the Contractor's quotation, and prices shall be deemed to include for whichever method is adopted.

3.9 FINAL INSPECTION AND HAND-OVER

Where each section of concrete works has been agreed to be handed over , the Contractor shall, at the time of Joint Inspection, submit to Engineer the following documents, certificates, and records of the Works completed; a. Three (3) sets of ‘As-built’ drawings of the work b. Business license of companies which supplied cement, sand, stone and reinforcement c. Business license of the companies which supplied ready-mixed concrete (Vietnamese) d. Original Test Certificates of cement, sand, stone, and reinforcement (Vietnamese) e. Original Test Certificates of Concrete Trial Mixes (only once for the first inspection) f. Original Test Certificates of concrete tests for each time of concreting g. Copy of materials delivery inspection records h. Copy of in-progress construction inspection records, for formwork, reinforcement, concreting and

finished concrete. Copy of non-conformances and approved corrective action Engineer will supply the Contractor with one reference set of the documents, upon request. Where any approved corrective action of a non-conformance will cause a subsequent Contractor or Subcontractor not to accept the concrete work, Engineer will instruct the concrete Contractor to be liable for the costs of rectifying the concrete work to enable acceptance.

3 sc&s3-reinforced concrete

Documents