Sample Specification For - Formwork & Reinforcement For Concrete

13.1 The specification given in the chapter are sample specification only and shall not be used as such. Fresh specifications should be drawn for each work depending upon the type and requirements of structure, environmental conditions prevailing etc.

13.2.0 Sample specification for Formwork for inclusion in tender document.

13.2.1 Scope: This Part contains requirements which, where relevant to this Contract, shall apply to formwork and reinforcement for concrete.

13.2.2 Reference standards: Unless otherwise specified, formwork and reinforcement shall comply with the relevant IS Codes and in absence of IS Codes ASTM/BS/DIN Codes.

13.2.3 Submissions by the contractor: Submissions required from the contractor in relation to formwork and reinforcement shall include the following where relevant:

• calculations for design of formwork
• drawings of formwork
• manufacturers data on accessories and mechanical couplings.
• relevant quality standardreinforcement and prestressing steel tendons, as required by the · manufacturers test certificates for each delivery of steel
• details of proposed welding procedures and welders qualifications
• test certificates for mechanical couplings
• samples of steel reinforcement for testing.

13.2.4 Formwork

13.2.4.1. Materials for formwork: Formwork shall be constructed of timber, sheet metal or other approved material. Ties shall be of the rod and cone or other approved proprietary type. Ties for use in water-retaining structures 300mm thick or less shall incorporate a diaphragm not less than 50mm dia. welded to the mid point of the tie, designed to prevent water passing along the tie.

13.2.4.2 Design and layout of formwork: The design and construction of formwork shall take account of safety and of the surface finish required. The formwork shall be sufficiently rigid and tight to prevent loss of grout or mortar from the fresh concrete or the formation of fins or other blemishes on the concrete. The contractor shall appoint a Falsework Coordinator to carry out work on behalf of the contractor.

Formwork and its supports shall maintain their correct shapes and profile so that the final concrete structure is within the limits of the specified dimensional tolerances. They shall be designed to withstand the worst combination of self-weight, reinforcement weight, wet concrete weight, concrete pressure, construction and weather loads, together with all incidental dynamic effects caused by placing, vibrating and compacting the concrete. Formwork shall not be tied to or supported by the reinforcement.

On formwork to external faces which will be permanently exposed, all horizontal and vertical formwork joints shall be so arranged that joint lines will form a uniform pattern on the face of the concrete. Where the contractor proposes to make up the formwork from standard sized manufactured formwork panels, the size of such panels shall be approved by the Engineer before they are used in the construction of the works. The finished appearance of the entire elevation of the structure and adjoining structures shall be considered when planning the pattern of joint lines caused by formwork and by construction joints to ensure continuity of horizontal and vertical lines.

13.2.4.2 Design and layout of formwork: The design and construction of formwork shall take account of safety and of the surface finish required. The formwork shall be sufficiently rigid and tight to prevent loss of grout or mortar from the fresh concrete or the formation of fins or other blemishes on the concrete. The contractor shall appoint a Falsework Coordinator to carry out work on behalf of the contractor.

Formwork and its supports shall maintain their correct shapes and profile so that the final concrete structure is within the limits of the specified dimensional tolerances. They shall be designed to withstand the worst combination of self-weight, reinforcement weight, wet concrete weight, concrete pressure, construction and weather loads, together with all incidental dynamic effects caused by placing, vibrating and compacting the concrete. Formwork shall not be tied to or supported by the reinforcement.

On formwork to external faces which will be permanently exposed, all horizontal and vertical formwork joints shall be so arranged that joint lines will form a uniform pattern on the face of the concrete. Where the contractor proposes to make up the formwork from standard sized manufactured formwork panels, the size of such panels shall be approved by the Engineer before they are used in the construction of the works. The finished appearance of the entire elevation of the structure and adjoining structures shall be considered when planning the pattern of joint lines caused by formwork and by construction joints to ensure continuity of horizontal and vertical lines.

13.2.4.3 Erection of formwork: Faces of formwork in contact with concrete shall be free from adhering foreign matter, projecting nails and the like, splits or other defects, and all formwork shall be clean and free from water, dirt, or other foreign matter.

Except where the surface is subsequently to be rendered, formwork in contact with the concrete shall be treated with a suitable non-staining release agent before the steel is fixed or the concrete placed to prevent the concrete adhering to it. Care shall be taken to prevent the release agent from touching the reinforcement or concrete at construction joints. Surface retarding agents shall not be used unless specified.

All exposed exterior angles on the finished concrete of 90 degree or less shall be given 20mm by 20mm chamfers. Formwork shall be provided for the top surfaces of sloping work where the slope exceeds fifteen degrees from the horizontal unless otherwise specified, and shall be anchored so that the concrete can be properly compacted and to prevent flotation. Care shall be taken to prevent air being trapped.

Where ties are built into the concrete for the purpose of supporting formwork, part of any such supports shall be capable of removal so that no part remaining embedded in the concrete shall be within 50mm of the surface in the case of reinforced concrete or 150mm in the case of unreinforced concrete. Holes left after removal of such supports shall be neatly filled with epoxy or well rammed dry-pack mortar.

Openings for inspection of the inside of the formwork, for the removal of water used for washing down and for placing concrete shall be provided and so formed as to be easily closed before or during placing concrete. Before placing concrete all bolts, pipes or conduits or any other fixtures which are to be built in shall be fixed in their correct positions, and cores and other devices for forming holes shall be held fast by fixing to the formwork or otherwise. Holes shall not be cut in any concrete without prior approval of the Engineer.

13.2.4.4 Removal of formwork: Formwork shall be so designed as to permit easy removal without resorting to hammering or levering against the surface of the concrete.

The periods of time elapsing between the placing of the concrete and the striking of the formwork shall have regard to the following factors:

• concrete strength;
• stresses in the concrete during construction including for precast units any disturbance and handling stresses;
• curing;
• subsequent surface treatment requirements:
• the presence of re-entrant angles requiring early removal of formwork to avoid thermal cracking.

The time shall be as approved by the Engineer after consideration of the loads likely to be imposed on the concrete and shall in any case be not less than the periods specified in the Code.

Notwithstanding the foregoing the Contractor shall he held responsible for any damage arising from removal of formwork before the structure is capable of carrying its own weight and any incidental loading.

13.2.5 Defects in formed surfaces: Workmanship in formwork and concreting shall be such that concrete shall normally require no making good, surfaces being perfectly compacted and smooth.

Any minor surface blemishes shall be repaired to the satisfaction of the Engineer immediately after removal of formwork. Remedial measures may include, but shall not be limited to, the following:

• Holes left by formwork supports shall be thoroughly cleaned out to remove all loose material and the sides shall be roughened, if necessary, to ensure a satisfactory bond. They shall then be filled with epoxy or dry-pack mortar. 
• Fins, pinhole bubbles, surface discolouration and minor defects may be rubbed down with sacking and cement immediately the formwork is removed.
• Abrupt and gradual irregularities may be rubbed down with carborundum and water after the concrete has been fully cured. 
• Small defects and minor honeycombing shall be chipped out perpendicular to the face of the concrete to a depth of at least 25mm and filled with epoxy or dry-pack mortar.

Where deeper or more extensive defects occur, the Contractor shall obtain the approval of the Engineer to the methods of repair proposed which may include, but shall not be limited to, cutting out to a depth of at least 25mm with a diamond saw to give a regular edge to the repair and further chipping to form a hole with undercut edges to sound concrete or to a total depth of 75mm whichever is the greater. If reinforcing steel is exposed the concrete shall be removed to a depth of 25mm beyond the back side of the reinforcement. Steel mesh reinforcement shall then be sprung into the hole, which shall be refilled with concrete or suitable epoxy resin mortar.

The contractor shall thoroughly clean any hole or defective area that is to be filled and break out any loose, broken or cracked concrete or aggregate.

Where the remedial work is to be carried out using dry-pack mortar or concrete, the concrete surrounding the hole shall be thoroughly soaked after which the surfaces shall be dried so as to leave a small amount of free water on the surface. The surface shall then be dusted lightly with cement by means of a small dry brush until the whole surface that will come into contact with the dry-pack mortar has been covered and darkened by absorption of the free water by the cement. Any dry cement in the hole shall be removed.

Dry-pack mortar shall be mixed and placed as specified.

Where concrete is to be used, the concrete mix shall be as approved by the Engineer and shall be placed and compacted into the hole, using formwork as necessary. 

Where the remedial work is to be carried out using epoxy resin mortar or other special material, the surface of the cleaned hole shall be prepared and primed and the repair material placed, compacted and finished in accordance with the manufacturer's instructions.

Where, in the opinion of the Engineer the defect is too extensive to permit satisfactory repair, either from the point of view of structural integrity or appearance, the concrete containing the defect shall be broken out and replaced.

13.2.6 Dry-pack mortar: Dry-pack mortar for filling holes and repairing surface blemishes shall be made from one part by weight of cement and three parts fine aggregate passing a 1mm sieve. The colour of the mortar shall match that of the surrounding concrete. The mortar shall be mixed with just sufficient water to make the materials stick together when being moulded in the hands.

The dry-pack material shall be placed and packed in layers having a thickness not greater than 15mm. The compaction shall be carried out by use of hardwood stick and hammer and shall extend over the full area of the layer, particular care being taken to compact the dry-pack against the sides of the hole. After compaction the surface of each layer shall be scratched before further loose material is added. Holes shall not be over filled and the surface shall be finished by laying a hardwood block against the dry-pack fill and striking the block several times. Steel finishing tools shall not be used and water shall not be added to facilitate finishing.

13.3.0 Sample specification for reinforcement:

13.3.1 Steel for reinforcement shall confirm to any one of the following:

• Mild steel and medium tensile steel bars conforming to IS:432 (Pt.I)
• High strength deformed steel bars confirming to IS: 1786
• Structural steel confirming to grade A and B of IS:2062

13.3.2 Accessories: Spacer blocks for maintaining concrete cover to reinforcement shall be of concrete of the same strength, durability, porosity and appearance as the in-situ concrete. They shall be cast in the form of a truncated cone or pyramid with the smaller face having a minimum dimension of 50mm.

Chairs and other accessories for maintaining reinforcement and prestressing tendons in position shall be of steel. Binding wire shall be No.16 gauge (1.60mm) galvanised iron wire free from corrosion.

13.3.3 Cutting and bending of reinforcement: Bars shall be bent in accordance with the provisions of IS Code. Bending shall be carried out slowly, at a steady even pressure, without jerk or impact. The temperature of the steel at the time of bending shall be not less than 5 0C. If necessary reinforcement maybe warmed to a temperature not exceeding 100 0C to facilitate bending, after which it shall be allowed to cool slowly in air. Hot bars shall not be cooled by quenching with water. Bent bars shall not be re-bent unless permitted by the Engineer.

13.3.4 Storage of reinforcing bars and steel fabric: The contractor shall stack separately and label different types of reinforcement for positive identification. Reinforcement shall not be subjected to mechanical damage or shock loading prior to embedment.

Steel reinforcing bars shall be kept clean and shall be free from pitting, loose rust, mill scale, oil, grease, earth, paint, or any other material which may impair the bond between the concrete and the reinforcement.

All materials shall be stored under cover on wooden or concrete supports at least 150mm clear of the ground.

13.3.5 Fixing of reinforcement: All reinforcement shall be securely and accurately fixed in positions shown on the Drawings using approved concrete spacers, spacer blocks or chairs. These shall be not more than 1m apart and at closer intervals if necessary. All intersections of bars shall be secured with soft iron wire, the ends being turned into the body of the concrete. The contractor shall ensure that all reinforcement is maintained in correct position at all times, particular care being taken during placing of the concrete.

Concrete cover to reinforcement shall be as detailed on the drawings and shall be maintained in accordance with the tolerance. Top reinforcement in slabs shall be maintained in position by chairs, sized and spaced to provide adequate support and fixity for the reinforcement.

No part of the reinforcement shall be used to support formwork, access ways, working platforms or placing equipment, or for the conducting of an electric current other than as pole of an earthing system during the site welding of reinforcement.

13.3.6 Welding of reinforcement: The contractor shall not weld any reinforcement on site except where this has been specified in the contract or is permitted by the Design Engineer in writing who will examine the weldable quality of steel.

Reinforcement which is to be welded shall be welded in accordance with the recommendations of the manufacturer. The contractor shall demonstrate by bend and tensile tests on specimen welds that the strength of the parent metal is not reduced and that the weld possesses a strength not less than that specified for the parent metal. The welding procedure established by successful test welds shall be maintained and no departure from this procedure shall be permitted.

Following the establishment of a satisfactory welding procedure, each welder to be employed on the works shall carry out welder performance qualification tests on reinforcing bars of the same metal and size as those on the works.

Details of welding procedure and welder qualification tests shall be submitted for the approval of the Engineer before welding of reinforcement. Tack or other welds in positions other than those shown on the drawings shall not be permitted, unless specifically authorised by the Engineer.

DURABILITY OF CONCRETE STRUCTURES

13.3.7 Mechanical couplings: Mechanical couplings shall be used where shown on the Drawings, and shall be obtained from an approved manufacturer. The contractor shall demonstrate by tensile tests on sample joints of all sizes required for use in the works, Equipment used for making the couplings shall be supplied by the coupling manufacturer and shall be operated in accordance with the manufacturer's instructions.

13.3.8 Drilled and grouted reinforcement bars: Reinforcing bars for drilling and grouting into existing concrete shall be deformed high yield steel bars. The depth of the holes shall be at least 45 times the diameter of the bar to be grouted except where otherwise approved by the Engineer. The diameter of the hole shall be 7mm larger than the nominal bar diameter.

The hole shall be thoroughly cleaned and the surface wetted before introducing 1:3 cement/sand grout into the hole. The bar shall be pushed into the grout and held in position to maintain a uniform annulus of grout all around the bar until the grout has set. The grouted bars shall not be disturbed for a period of at least 7 days before building them in concrete.

13.3.9 Coated reinforcement: Where shown on the Drawing the reinforcing bars shall be coated. The coating of the reinforcement shall comply with the specifications. Repairs to minor damage to coatings shall be carried out in accordance with the recommendations of the coating manufacturer. Copies of the manufacturer's test certificate shall be provided to the Engineer.

13.3.10 Testing of samples of reinforcement: The Engineer may require to witness routine testing of steel reinforcement at the manufacturer’s works. When required by the Engineer the contractor shall take samples from reinforcement delivered to site and shall arrange for the samples to be tested by an approved testing agency. Test certificates from that agency shall be submitted to the Engineer.

13. 3.11 Bar schedules: Any bar schedules the contractor shall be entirely responsible for checking the correctness of such schedules before arranging for the supply cutting and bending of steel reinforcement. In the event of any information being apparently missing or incorrect in the drawing the contractor shall promptly refer to the Engineer.

13.4.0 Sample specifications for prestressing steel and sheathing:

13.4.1 The Prestressing steel shall be any of the following.

• Plain hard - drawn steel wire conforming to IS: 1785 )Part I).
• Indented wire for prestressed concrete conforming to IS: 6003.
• Uncoated stress - relieved strand conforming to IS: 6006.
• Uncoated stress - relieved low relaxation seven - ply stand for prestressed concrete conforming to IS: 14268.

DURABILITY OF CONCRETE STRUCTURES

13.4.2 Specification for sheathing: Sheathing Unless otherwise specified, the material shall be Cold Rolled Cold Annealed (CRCA) mild steel intended for mechanical treatment and surface refining but not for quench hardening of tempering.

The material shall normally be bright finished, however, in case of use in aggressive environment, galvanised or lead coated mild steel strips may be adopted.

Sheathings shall be preferably machine manufactured and of large enough bore to allow being easily threaded on to the cable or bar in long lengths.

The thickness of the strips shall be a minimum of 0.24 mm + 0.02 mm for internal diameter of sheathing ducts upto and including 51mm and shall be 0.30 mm + 0.02 mm for diameters beyond 51 mm and upto 91 mm.

The sheaths shall be of such strength as not to be dented or deformed during handling or concreting. They shall conform to the requirements as per tests specified below and a test certificate to this effect shall be furnished by the manufacturer.

13.4.2.1 Tests on sheathing ducts: All tests specified below shall be carried out on the same sample in the order given below. At least 3 samples for one lot supply (not exceeding 7000 m length) shall be tested. The tests are applicable for sheathing transported to site in straight lengths where the prestressing tendon is threaded inside the sheathing prior to concreting.

These tests are not applicable for sheathing ducts placed in position without threading of prestressing cable prior to concreting.

• Workability test: A test sample of 1100 mm long is soldered to a fixed base plate with a soft solder (Fig. 13.1). The sample is then bent to a radius of 1800mm alternately on either side to complete 3 cycles. Thereafter, the sealing joints will be visually inspected to verify that no failure or opening has taken place.
• Transverse load rating test: The test ensures that stiffness of the sheathing is sufficient to prevent permanent distortion during site handling. The sample is placed on a horizontal support 500mm long so that the sample is supported at all points of outward corrugations. A load as specified in Table-13.1 is applied gradually in increments at the centre of the supported portion through a circular contact surface of 12mm dia. Couplers shall be placed so that the load is applied approximately at the centre of two corrugations (Fig. 13.2). The sample is considered acceptable if the permanent deformation is less than 5 percent.

Table 13.1

TRANSVERSE LOAD RATING TEST

Diameter of sheathing (mm)	Load (N)
25-35	250
35-45	400
45-55	500
55-65	600
65-75	700
75-85	800
85-90	1000

Tension load test: The test specimen is subjected to a tensile load. The hollow core is filled with a wooden circular piece having a diameter of 95 percent of the inner diameter of the sample to ensure circular profile during test loading (Fig. 13.3). A coupler is screwed on and the sample is loaded in increments, till load specified in Table-13.2. If no deformation of the joints nor slippage of couplers is noticed, the test shall be considered satisfactory.

Table 13.1

TRANSVERSE LOAD RATING TEST

Diameter of sheathing (mm)	Load (N)
25-35	300
35-45	500
45-55	800
55-65	1100
65-75	1400
75-85	1600
85-90	1800

Water loss test: The sample is sealed at one end. It is then filled with water. After the other end is also sealed as shown in Fig. B-4, it is connected to a system capable of applying a pressure of 0.05 N/mm2 and kept constant for 5 minutes. The sample is acceptable if the loss of water does not exceed 1.5 percent of the volume.

For working out the volume, another sample 500mm long is sealed at one end and the column of hollow space is arrived at by pouring water from a measuring cylinder. The computation of relative profile volume is worked out as follows:

L = length of the specimen
f = nominal internal diameter of the sheathing
Va = pre-measured quantity of water in a measuring cylinder
Vb = balance quantity of water left in the cylinder after completely filling of the test sample.

Actual volume Vp = Va - Vb