IS.1
SPECIFICATION OF ITEMS
IMPORTANT NOTES
CHECK LIST
The contractor in charge of the work shall ensure the following before calling the Consultant for inspection and approval.
1]The respective work on each stage defined is ready for the subsequent stage as described in the technique.
2]Adequate quantity of materials is at site for carrying out the repair work.
3] All the equipment is in working order.
Watch Points :
1]The contractor carrying out the repair and Rehabilitation work shall read and understand the Specifications for Materials, Workmanship, details etc. contained in this manual and as shown on the sketches and take full responsibility for provisions, arrangements, workmanship and care contained therein and maintain scaffolding, propping & shoring and formwork secured in position till the time required as specified.
2]Supervision:
a]It is extremely difficult and costly to alter concrete once it is placed in position and allow to set. Constant and strict supervision is necessary during the progress of the work.
b]Care exercised in removal of the deteriorated concrete, cleaning of the exposed steel reinforcement, its protection from further corrosion, and meticulous preparation of the exposed concrete will determine the longevity and success of the repaired work. Proper preparation of the work for repairs is critical to the success of the repair scheme.
NOTES :
1.Refer to detailing sketches. Work shall be carried out as indicated in the sketches and detailed in the following specifications.
2.Specifications and modes of measurements, not specifically mentioned, shall be as per relevant Indian Standard Codes.
IS.2
SPECIFICATIONS OF ITEMS
A. GENERAL WORK
1.External Scaffolding :
1.1Conventional scaffolding shall be of vertical members of steel/bamboos, spaced and filled by suitable horizontal members secured to each other firmly. This scaffolding shall be double, both connected and braced properly, and secured by connecting with the members of permanent structure, at regular intervals. No holes shall be permitted in external brickwork. Necessary platforms, railings and safety nets, safety belts, helmets, etc. shall be provided to ensure the safety of workers. To reduce the height of falling debris intermediate platforms on the scaffolding shall be erected. Access for labour and staff to the platform from the flats at the relevant levels will be given, if possible. Alternatively, adequate and safe lifting tackle for men and materials shall be provided by the tenderer at his own cost.
1.2Stitched hessian shall be tied to the external face of the scaffolding/platforms in order to avoid lumps of broken concrete flying around and causing accidents. Fencing at ground level shall be erected to dissuade third persons entering the work area.
1.3Any additional arrangement and/or any alterations/additions to the normal scheme of the scaffolding for overcoming obstructions in the plan and elevations of the building shall be thought of and provided for in the quoted rates.
2. Covering :
2.1Windows/doors/openings shall be covered with plywood or tin sheets and properly secured to protect the shutters and glass panes from falling debris, and to keep the dust out.
2.2Any equipment, furniture, fixtures, fittings etc., adjacent to the work area, should be either removed or adequately covered ( as advised by the contractor in writing ) by owners to avoid damage/breakage during the progress of work.
3.Propping & Shoring :
3.1The guidelines outlined on sketches shall be followed.
3.2Steel tube adjustable props are preferred. The sections of timber props, if used, shall be adequate to support the structure temporarily as directed by consultant.
3.3Bracings, base plates and wedging etc. are an integral part of the system. Providing adequate bracings, base plates and wedges is obligatory to have been included in the scheme for propping and shoring.
3.4The propping and shoring shall be kept and maintained in position till required as directed by the Consultant.
SPECIFICATIONS OF ITEMS IS.3
B. CONCRETE REPAIRS
1.Preparatory Work :
1.1.Categories of damage to concrete. Generally, there will be four categories of defective concrete. The defects of design or construction are many times aggravated by corrosion of reinforcement and consequent damage to the concrete.
a.Category No. 1
Core concrete is sound, but the concrete cover is cracked, reinforcement is slightly rusted, but replacement of steel is not required.
b.Category No. 2.
Damage due to corrosion of reinforcement which itself is in tolerable state but core concrete is unsound due to inherent honeycombing, voids, cavitation, deterioration etc.
c.Category No. 3.
Damage where corrosion of reinforcement is severe, the core concrete is compact and sound, but the concrete cover is cracked or spalled and corroded reinforcement is required to be restored by additional reinforcement.
d.Category No. 4.
Damage where corrosion of reinforcement is severe and core concrete is also unsound. Reinforcement is to be replenished by additional reinforcement.
2.Defining the damaged area :
2.1.The doubtful area shall be checked. Any loose plaster or coating shall be removed to expose the affected concrete surface.
2.2In case the exposed concrete surface is found to be sound but the plaster having come off due to lack of bond, the area shall be demarcated for replastering only.
2.3In case the exposed concrete is found to be damaged, then the damaged concrete shall be demarcated for repairs as described.
3. Demolition :
3.1 All precautions shall be taken by providing guard rails and covers in the interest of the safety of passers by.
3.2The debris shall be stacked as neatly as possible and carted away as soon as possible.
4.Surface preparation :
4.1All loose, disintegrated and cracked concrete shall be removed carefully by chipping hammer and/or chisel to expose sound concrete and to expose the rusted reinforcement if any. The removal of concrete shall be extended at least 150 mm. beyond the rusted length of reinforcement. Care shall be taken to leave sound and compact concrete undisturbed and to ensure that any good bond between the embedded reinforcement and parent concrete is not broken.
4.2All exposed sound concrete shall be chipped to roughen in order to receive the new treatment.
4.3The peripheral edges of broken concrete shall be cut true and in rectilinear patterns. Re-entrant/angled corners shall be chamfered.
SPECIFICATIONS OF ITEMS IS.4
4.Surface preparation : (Cont...)
4.4Plaster or coating, shall be removed to the extent of 100 mm. beyond the cut edges of the damaged concrete.
4.5Any inherent honeycombing, voids, cavitation etc. shall be noted and marked for grouting.
4.6All unwanted foreign materials shall be removed by wire brushing and washing with a water jet.
4.7Any existing reinforcement reduced in size, beyond acceptable limits and certified as such by the consultant, shall be cut and removed.
4.8The remaining reinforcement shall be cleaned thoroughly of all scales, rust and blemishes by light chipping and scrubbing with wire brush. An approved rust remover shall be used if so instructed by the consultant.
5.Reinforcement :
5.1.Providing New Reinforcement [ in case of category of damage to concrete 3 & 4 }
5.1.1Any dislodged but acceptable reinforcement shall be anchored by means of dowels secured in the parent concrete, locking the reinforcement in position as shown in detailing sketches and/or as directed by the consultant.
5.1.2Where the existing reinforcement has rusted and wasted to an extent where it cannot be accepted, new reinforcement in the form of steel bars or welded mesh shall be provided as directed by the consultant.
5.1.3The new reinforcement shall be clean and free from loose mill scales, dust, rust, paint, oils etc. which may affect bonding between bars and concrete.
5.1.4The reinforcement is represented diagrammatically on drawings and sketches; the same is not necessarily shown in true projection. The reinforcement shall be assembled in accordance to clause no. 11 of IS:456-1978.
5.1.5 The new reinforcement shall be fixed to parent concrete by means of dowels secured in parent concrete as shown on the sketches as or directed by the consultant.
5.1.6Reinforcement shall not be bent after being embedded in concrete. Laps in reinforcement may be allowed only with the prior approval of the consultant. The lap length shall be as specified.
5.1.7Reinforcement may be required to be welded to the existing reinforcement as directed. The welding shall be in accordance with the recommendations of relevant standards for welding of steel bars used in reinforced concrete constructions.
5.1.8The gaps and contact between the exposed steel and parent concrete shall be caulked with a specified epoxy putty.
5.1.9The reinforcement old and new shall then be coated with a specified protective coat.
SPECIFICATIONS OF ITEMS IS.5
B. CONCRETE REPAIRS
6.Making Good the Broken Concrete by new modified Concrete:
6.1Constituents.
a.Cement, sand and metal no. 1 for making concrete.
b.A specified additive for making concrete workable and impervious.
c. Nipples and fixing aids for grouting.
d.Specified building chemicals for bond coat, grouting and finish coats.
[ Enough quantities of these components and clean water for mixing shall be kept ready before proceeding with the application.]
6.2 Bond Coat
The bond coat shall be prepared and applied as per manufacturers specifications or as directed by the consultant.
6.3 Concrete Pack:
6.3.1Mixing: The mixing shall be mechanical unless the consultant allows hand mixing. For hand mixing close boarded steel trays shall be used.
6.3.2The concrete mix shall be by volume. Cement aggregate ratio shall be 1:3 to 1:4. Aggregate shall be 10 mm down stone metal and coarse river sand unless directed otherwise by the consultant. The proportion of the stone metal and sand in the aggregate shall be established by trials at site or as directed by the consultant.
6.3.3Water cement ratio shall normally be 0.45 slightly adjustable depending on the site conditions etc.
6.3.4Proper workability and imperviousness of the resulting concrete shall be obtained by using suitable additives of approved make. Preliminary trials are necessary to determine the optimum dosage to obtain the desired workability for a particular water cement ratio.
6.3.5Batches: Making good the broken concrete is a slow process. In order to use the mix within twenty minutes after mixing, it is recommended that the concrete is prepared in small batches each of 15 kgs. or less of cement content. Metal, sand and cement shall be accurately measured in gauge boxes in exact proportions as specified.
6.3.6Application: Concrete shall be placed in the required position within twenty to thirty minutes of addition of water to the dry mix. Concrete which has taken initial set shall not be used.
Local depressions/cavities if any, shall be cleaned. The prepared concrete surface inside the depressions shall then be coated with a bond coat applied with a stiff brush and taking care to work the bond slurry into the exposed concrete. New concrete shall be placed on the bond coat, wet on wet. The concrete shall be applied by trowel just enough to fill the cavities/depressions, pressing it in place and allowing to rest for 12 to 18 hours.
The entire concrete surface to be repaired including the filled depressions shall then be covered by the specified bond coat before applying the concrete pack. The concrete pack shall be applied by trowel in one continuous operation directly on the bond coat, wet on wet, placed in layers, one after the other. Each layer shall be approximately 25 mm thick and shall be pressed in position with hand and/or by a steel spatula to make it dense. The thickness and final line and level of the concrete pack shall be
SPECIFICATIONS OF ITEMS IS.6
Making Good the Broken Concrete by new modified Concrete: (Cont...)
finished to match the existing surrounding concrete surface and/or to provide adequate cover on the reinforcing bars.
6.3.7 Curing: The new concrete shall be covered with a layer of sacking, canvas Hessian or similar materials and kept constantly wet for ten days from the date of placing of concrete. Screeds and overlays shall be cured by ponding for at least seven days. In situations where the curing is not possible or the water shortage is experienced, use of a curing compound may be considered.
6.3.8Inspection: Concrete shall be carefully inspected immediately after stripping off the formwork or after 48 hours of setting. Any defective work shall either be removed or made good before concrete has thoroughly hardened. Serious defects or honey combing shall be brought to the notice of the consultant for his advice for rectification.
It is exceedingly difficult and costly to alter concrete once laid and cured. Hence constant and strict supervision is necessary during all the stages of repairing concrete.
7.Making Good by in Situ Concrete :
7.1In situ concrete shall be used generally in column and beam jacketing or for recasting thin members. The concrete shall be mechanically mixed and placed between shuttering and formwork. The concrete shall be of M200 grade. The concrete shall be placed and compacted before setting commences and shall not be subsequently disturbed. Method of placing should be such as to preclude segregation. Concrete shall be worked around the reinforcement, embedded fixtures and into corners and thoroughly compacted during the operations of placing.
In case of beam soffits, the bottom shuttering shall be jacked up after thirty minutes from laying concrete so as to squeeze and press the fresh mix in and against the existing surfaces. The form work shall not be removed till the specified period is over.
In case concreting work has to be resumed on a surface which has hardened, such surface shall be roughened. After removing all loose aggregates it shall be swept clean, thoroughly wetted and covered with a 12 mm layer of mortar composed of cement and sand in the same ratio as the cement and sand in the concrete mix. The 12 mm layer of mortar shall be freshly mixed and placed just before the placing of the new concrete.
SPECIFICATIONS OF ITEMS IS.7
B.CONCRETE REPAIRS
9.GROUTING AND SEALING :
Grouting and sealing shall be adopted at various places as directed by the Consultants. Grout and sealing materials to be used shall be:
a)Ordinary cement grout with additives for expansion and easy flow.
b)Readymade cementatious acrylic polymer modified grout.
c)Solventless epoxy grout and sealant
d)Poly-sulphide/silicone sealant.
9.1 Grouting Concrete Matrix :
a. Purpose :
In case of categories no. 2 & 4 of "Damage to Concrete" and in joints and junctions, and in major dormant cracks in the concrete matrix, the matrix and/or the cracks shall be pressure grouted to fill the voids and make the concrete matrix homogeneous.
b. Preparation :
13 to 18 mm dia. holes shall be drilled in concrete at specified intervals as shown on the sketches. The holes shall be cleaned of all dust and particles by air and water. 6 to 10 dia. nozzles shall be placed in these holes leaving their ends atleast 75 mm away from inside ends of the holes. The nozzles shall be secured in place with a quick setting fixing aid.
c. Process :
Readymade grout of approved make shall be pumped through the nozzles at specified air pressure.
9.2Line Grouting:
This will be done in case of surface cracks developed in a concrete element, brickwork or plaster. The crack to be line grouted shall be minimum 2 mm. wide. The crack shall be widened by cutting a `V' shaped groove. Cleaned and washed thoroughly, the cracks shall be sealed with readymade polysulphide or silicon sealant to levels to match the adjoining surface.
10 WATERPROOFING OF CHAJJAS :
Clean the top of the chajja and chisel extra mortar if any.
Apply thick cement slurry over the top of chajja.
Apply 1:1½:3 metal screen or brickbat coat.
Making rounding of 6”radius on the wall (watta) at the junction of chajja and wall of the building.
Cure this coat for seven days.
Apply finishing coat with C.M. 1:4 with waterproofing compound.
Provide drip mould at the bottom edge of chajja alongwith finishing coat.
Apply cement slurry with water-proofing compound for smooth finish (ghotai). Polish with metal float and make impression by 2mm diameter cotton line dori for avoiding cracking.
Cure the water-proofing for atleast seven days with soaked gunny bags.
SPECIFICATIONS OF ITEMS IS. 8
EXTERNAL PLASTER :
The external plaster shall be applied in two coats and finished sand-faced.
All the precautions such as covering windows by plywood/tin sheets and tying stitched Hessian to external face of the scaffolding shall be taken. The debris shall be taken down and stacked or carted away as directed.
If the existing plaster is defective, the loose and damaged plaster shall be broken and removed carefully by chipping or by light chiseling, so as not to disturb the sound concrete/brickwork inside.
If the plaster is to be applied on unrepaired concrete surface the exposed concrete surface shall be first roughened by close chipping, and then cleaned with brushing and washing. If roughening of concrete is not possible, then a bond coat such as hack aid plast or equivalent at the interface shall be provided.
If the plaster is to be applied on repaired concrete surface, the base shall be kept rough to provide a key to the plaster.
If brickwork is to be plastered, the joints shall be raked out atleast 8 mm. deep and cleaned.
The surface to be plastered shall be cleaned of loose materials, is thoroughly watered and kept adequately wet during plastering.
If plaster is done in patches, the bond coat must also be applied on the edges of old plaster in contact with new plaster.
The external plaster shall be applied in two coats:-
The first coat is mortar in cement:sand 1:4 proportions, with a water cement ratio not exceeding 0.45. The surface shall be even and without any undulations so as to have a thin second coat. The first coat is made rough to provide a key to the second coat. The base plaster shall be thoroughly watered and cured for minimum two days before the second coat is applied. If second coat is not to be done immediately, then minimum seven days curing must be done.
The second coat shall be a thin layer of mortar with cement:sand 1:3, using, fine washed sand and the approved additive, applied evenly by a trowel and finished to required granular texture by a rubber sponge. The final line, level and plane shall match the existing unbroken plaster. The second coat shall be kept wet by watering and shall not be allowed to dry for at least seven days.
INTERNAL PLASTER :
Plaster on internal areas, which are not exposed directly to rain and weather, is applied in one coat and finished smooth with Neeru if curing is not possible. The base surface shall be prepared as explained in the specifications for external plaster and a bond coat is applied on the interface if required.