Hand Book on Foundation, Formwork, Rebar &...

Hand Book on Foundation, Formwork, Rebar & Concrete

Building Structure Competency Center

PREFACEConstruction industry in India is growing at faster pace and the Buildings & Factories Operating Company (B&F OC) is no exception in terms of number, size and volume of projects. This growth throws challenges in terms of delivery without compromising on Quality, Safety and Sustainability. To meet this challenge, human resource is the prime mover and it is essential to upgrade the skill and knowledge level of engineers and front line supervisors to the latest technology that our company adopts to sustain our leadership in the market.

B&F OC’s entire business is grouped into three disciplines namely Structure, Finishes and MEP. Building Structure Competency Cell (BSCC) of B&F OC is created to provide total solutions to structure discipline in the areas of Foundation, Formwork, reinforcement, Concrete and Pre-stressing.

BSCC has come out with a reference hand book on the methods and processes adopted in construction of structure. I have gone through the book and found it very useful for site engineers especially in

Understanding the basics

Application in respective field

DOs & DON’Ts

Specifications & Standards

With this handbook they will be able to largely address the day to day issues that they face and thereby become self-sufficient.

I am sure that the BSCC site engineers and Supervisors will make use of this hand book to improve the operational efficiency which should translate into improved quality at optimum cost.

I appreciate the entire BSCC teams who have put inefforts to make this book a comprehensive tool.

(A.L.Sekar) Vice President & Head RBBU.

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INDEXCONTENTS Page No.

ALUMINIUM FORM WORK

Introduction ...........................................................................................6

Worksite Management ...........................................................................6

Assembly & Dismantling Process .............................................................9

Flowchart for Aluform ..........................................................................32

SLIP FORM

Introduction .........................................................................................34

Type of Slipform ...................................................................................36

Assembly procedures ...........................................................................36

Tapering Slipform ................................................................................38

Assembly of stair tower .........................................................................39

Dismantling procedure .........................................................................40

Summary of Labour Productivity Norms .................................................43

Slipform Planning ................................................................................44

TUNNEL FORM

Aluminium Formwork Refurbishment .....................................................47

Plywood ..............................................................................................71

Form Release agent .............................................................................73

Formwork lift .......................................................................................74

Automatic Climbing System ..................................................................75

Hand tools required .............................................................................76

Guidelines for Formwork Engineer .......................................................33

Guidelines for Foreman/Charge hand ..................................................78

System Formwork Functions, applications& Safety. .................................79

REINFORCEMENT WORKS

Category of Reinforcements ..................................................................91

Reference Indian standards ..................................................................91

Reference International Standards .........................................................91

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Hook & Bend Allowance .......................................................................92

Bar bending Schedule Format ...............................................................93

Minimum diameter required for Bending Former ...................................98

Cross-sectional area & Mass of Rebar ...................................................99

Checks ..............................................................................................100

Testing of Rebar .................................................................................101

Nominal cover ...................................................................................104

Tips on Cover ....................................................................................104

Tolerance of cover ..............................................................................104

Material for cover ..............................................................................105

Photographs (Rebar) ..........................................................................106

Prefabricated cage photos ..................................................................109

Rebar tying machine ..........................................................................109

Splicing methods ...............................................................................110

Precautions ........................................................................................110

Splicing strengths ...............................................................................110

Reinforcement couplers ......................................................................110

Coupler photographs .........................................................................111

Classification of test for Reinforcement couplers ...................................112

Reinforcement Binding .......................................................................113

Welding of Reinforcements .................................................................115

Precautions in Rebar activity ................................................................117

PILNG WORKS

Pile ...................................................................................................119

Classification .....................................................................................120

Factor governing Pile selection ............................................................112

List of Reference Codes ......................................................................125

Installation sequence

Driven cast in-situ piles ..................................................................126

Bore cast in-situ piles .....................................................................127

Characteristics of Bentonite suspension for BCIS piles ..........................128

Important things to be followed ..........................................................130

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Driven cast in-situ piles ..................................................................130

Bore cast in-situ piles .....................................................................131

Driven precast...............................................................................132

Load test on Piles ...............................................................................134

Types of Arrangements .......................................................................134

Vertical load test Arrangements ......................................................135

Lateral load test Arrangements ......................................................137

Pullout test arrangements ..............................................................138

Pile Integrity test .................................................................................140

PDA Test ............................................................................................140

‘O’ Cell Test. ......................................................................................142

CONCRETE WORKS

Cement .............................................................................................145

Physical requirement of Cement ..........................................................149

Mineral Admixtures ............................................................................150

Fly ash .........................................................................................150

GGBFS .........................................................................................154

Micro silica& Metakoline ................................................................154

Aggregates ........................................................................................155

Mechanical Properties ...................................................................158

Grading Requirements ..................................................................159

Mixing of water ..................................................................................161

Admixture ..........................................................................................162

Concrete ...........................................................................................163

Grades of concrete .......................................................................164

Exposure conditions ......................................................................165

Batching ............................................................................................168

Mixing Time .......................................................................................170

Transporting Concrete ........................................................................171

Planning ............................................................................................172

Compaction ......................................................................................173

Vibration ...........................................................................................173

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Points to remembered in Compaction .................................................174

Finishing ...........................................................................................175

Curing ..............................................................................................177

Common defects in Concrete .............................................................179

Types of Surface defects ......................................................................180

Special concrete .................................................................................186

PRESTRESSING

Introduction .......................................................................................187

Definition ..........................................................................................187

Advantages of Prestressing .................................................................188

Application ........................................................................................188

Materials management ......................................................................189

Reference Standard & codes ...............................................................191

Elongation & Modified Elongation Calculations ...................................192

Jack Pressure calculations ...................................................................192

Losses in Prestressing .........................................................................193

Properties of HT strand (IS: 14268-1995) ............................................193

Methodology of Post Tensioning works ................................................194

Prestressing Equipments. ....................................................................197

Tendon Profile ....................................................................................198

Case study ........................................................................................199

Photos. ..............................................................................................201

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IntroductionFormwork Drawings

Site will be provided with a set of formwork drawings which entailed the followings: -

Shell Plan Layout

Formwork layout drawings,

Wall panel Layout, ¾

Slab Panel Layout, ¾

Starter Block Layout, ¾

Corner Layouts, ¾

Beam Panel Layout, ¾

Soffit Layout, ¾

Staircase Layout, ¾

Bracket and Soldier layout, ¾

Miscellaneous Layout which includes sunken portion, upstand portion ¾etc,

Elevations and sections drawings indicating the location of formwork panels and component,

Typical Fixing Detail drawings,

Location of Box outs and Transfer Box out drawings for transfer of Formwork, etc.

Worksite ManagementLogistic

Prior to the arrival of the containers from the disembarking point to the project work site; a Stock Yard is to be properly allocated and set up for the unloading of the formwork material and accessories.

This Stock Yard should preferably be located at close proximity or within the compound of the project work site, properly fenced up and security

Aluminium Formwork

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shall be of up most priority due to the high residue value in the secondary market for aluminum formwork material.

A Workshop area for maintenance of formwork material is recommended to be set up at the project site to minimize the downtime in requisition of replacement panels.

The proposed Stock Yard and Workshop area shall be flexible and re- adjustable to suit the working environment and project work site. As a result of the far away Stock Yard or Workshop area the project progress will affect the targeted construction cycle time. (Ref Layout Drg No.: )

Upon arrival of formwork panels at Project Site, Site personnel shall ensure that the panels are stacked and stored according to sizes and marking using proper separator such as pallets for easy identification and allocation for subsequent distribution. (Dry Mockup will be assembled as per schemes at factory; this will eliminate the usual problematic discrepancies of odd size panels which need to be fabricated at project site).

Manpower

BSCC - HQ shall provide the estimated manpower requirement for the Project based on the quantity of formwork panels to be supplied to achieve the required cycle time. This manpower requirement shall vary according

to the size of formwork use on the building.

However, the manpower requirement for other supplementary trades which

complement the formwork installation such as Mechanical & Electrical

(M&E) services and rebar works need to be taken into consideration also.

A joint effort of all operations from formwork installer, rebar, plumbing,

electrical and concreting workers need to be synchronized to achieve the

required cycle time.

Segregation and systematically allocation of duties for each formwork team

are required in ensuring optimization of productivity. Hence, each team

shall be delegated or assigned to do specific job tasks on a daily basis to

resemble a manufacturing production line. However, due consideration should be used in determining the level of experience and compatibility of persons when allocating tasks to minimize the risks.

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Safety

Control measures should be taken to identify and minimize the hazards associated with work involving the assembly and dismantling of formwork equipment such as falls from height, slips, falling objects, noise, dust and manual tasks.

The external working brackets/platforms or scaffoldings should not be used to stack materials or equipment. This will lead to the persons working on it expose to additional hazards in relation to trips and slips or collapse of the external working brackets / platforms or scaffolding.

Minimize the working heights for persons performing the assembly and dismantling formwork.

Mixing of formwork components should be avoided to prevent unsafe installation such as mixing pins and braces which may lead to collapse of the formwork.

Do not allow drop stripping of formwork as it is an unsafe practice.

Partially assembled or dismantled formwork should be secured during break time to prevent against overturning or collapsing due to strong wind or accidentally / unintentionally knock over by workers.

Electrical safety should be implemented for the safe use of electrical equipment.

Protruding flat ties or projecting nails should be removed immediately with appropriate tools at dismantling stage.

Use of personal protective equipment by all persons working at work areas (such as safety hardness, safety helmets, eye protection etc) should be strictly implemented.

Accessories & Tools

Accessories (10%) extra will be supplied for the assembly and dismantling of the formwork panels.

Sufficient tools required for assembling and dismantling will also be supplied as per the attached list.

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Setting Up Level & Marking Of PositionThe project surveyor shall mark based on the approved construction drawings to ensure that the gridline and level of the foundation level is properly set up, marked for walls, column etc. Leveling must be checked prior to commencement of formwork installation to ensure accurate positioning.

Formwork Panels

Cleaning of the surface and side panel of the formwork after each usage shall be done immediately using proper tools.

Ensure that all front and side panel of formwork is properly coated with recommended Form release agent that prevents from sticking and concrete buildup aluminium form surfaces. It protects and prolongs the useful lives of the aluminium formwork.

The following precautions shall be taken when applying the Formoil on the aluminium panels.

The best results are obtained when a uniform application of Formoil is ¾applied immediately following stripping and subsequent cleaning of the panels. Always ensure that the coated form surfaces are allowed to dry prior to placing concrete.

Do not over apply. Excess Formoil can adversely affect performance ¾and should be picked up promptly with rags.

Prevent Formoil overspray from contacting reinforcing steel bars and/ ¾or tensioning cables.

Installation Works of Rebar, M&E & Plumbing

The support works such as rebar, Mechanical & Electrical (M&E) and plumbing are to commence immediately once the set up is done. The same is to be ensured before installing the Aluminium formwork.

The support works for the slab section commence after the slab formwork panels are assembled.

Cover Blocks should be fixed on both sides of the rebar section for positioning and eliminate the rebar from resting on the surface of the formwork panels.

Assembly Process

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Positioning of outlets for electrical switch boxes to its correct alignment can be done by riveting the appropriate fit size mould to the formwork panels. The electrical switch boxes are then securely cap to the fit size mould and fasten by way of wiring to the formwork panels. Ensure that it is properly secured to prevent grouting from building up in the switch boxes.

Assembly of Wall Formworks

Always commence wall erection from the external corner of the wall section to ensure both joint external corner wall panels will support each other for standing position. Pin and wedges are to be used to secure the panels together. Always insert the pin from the inside out for easy removal of pin after concreting.

The formwork panels wall positioning is securely placed on the marked gridlines and level by way of fixing timber stoppers at the base of the outer side of the formwork panels at interval of one (1) meter. This would ensure that the formwork panels are not disposition during the concreting process.

Once the initial wall corner panels are assembled, place the wall corner panels on the allotted set up position.

Commence to erect simultaneously the balance of the wall panels from either side of the external wall panel.

Proceed to assemble the internal wall corner. Place these panels into the correct position on the lines which were set up by the surveyor. Proceed to assemble the balance of the internal wall at both sides.

The internal and external walls are to be held together by flat wall tie with wall tie sleeve and PVC cover. These wall tie sleeve and PVC cover are to be cut for the exact length of the wall thickness. Flat wall tie are to be coated with the Form Oil before each usage.

To determine and achieve the vertical accuracy of the formwork panels assembled before concreting process, several methods such as plumb bob, spirit level, theodolite equipment etc can be used. The simplified method of using a plumb bob with a string attached to it which is then suspended from the upper part of the formwork panels is used as a guide to determine the deviation from the vertical alignment of the panels.

Additional wall panels or starter blocks (kickers) are fixed on the external wall panels in accordance to the required height for the formation of the

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slab concrete. Check to ensure that the verticality of the Starter Blocks (kickers) is correctly aligned.

The Starter Blocks (kickers) shall remain at its position for the subsequent forming of next level wall.

Assembly of Beam & Slab Formworks

Fix the slab corner on top of the wall panels with round pins and wedges. The position of the pins should be from top down to ease the dislodging process.

The prop length and prop head is to be connected together for beam and slab support.

Alu span mid beam and Alu span cantilever end beam are connected to the Slab prop head using Beam Splice Bars. They are connected together by long pins and wedges at bottom section.

The Aluspan mid beam sections are accurately position to enable the slab panels to be connected systematically.

Commence to assemble the slab panels from the corner section of the slab. Subsequently, fixed the whole slab area by pinning the slab panels together with the Aluspan mid beam.

Assembly of External Working Brackets

External working platform brackets are used to provide a work area at the external wall section.

Once the first level is completed and external formwork panels are removed, fix the external working brackets to the first floor level at position slightly below the kickers which are fixed on first floor external slab.

The external working brackets are secured to the external wall section from the inside using tie rods, nuts and bolts.

Once all the external working brackets are put in place, timber planks and strips are placed on the floors and railings respectively to create an external working platform for the assembly of the subsequent level of the external formwork panels and kickers.

Another set of external working brackets are later fixed on the subsequent level using the method as prescribed above.

Once the subsequent level of external formwork panels are fixed, the

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external working brackets at one level below are removed and moved to the subsequent level. This process is repeated until the completion of the subsequent floors.

Identification of Formwork Assembled

A numbering sequence / stenciling shall be given for each panel and is identified in accordance to unit area such as living rooms, Kitchens, Bed rooms, bathrooms, common areas etc.

Color identification scheme while numbering on each section or area will also eliminate the confusion that may arise due to the size. It can be identified such that Blue is for Room 1, Red is for Room 2, Green is for Living area etc.,

By practicing the use of numbering system in combination with the color identification scheme, it have been proven to avoid confusion and assist in the process of identification of panels position once they are transferred to the next level/floor.

CONCRETING PROCESS

Pre-Check Before Concreting

Ensure that the position of the walls and column formwork are in accordance with the set up marking.

Check to ensure correct spacing of props for slab formwork.

Check the verticality and horizontality level of the wall and slab panels respectively.

Ensure that all pins, wedges and ties are properly secured and tightened.

Re-check the opening such as door and window panels are correct.

Re-check all propping stands to ensure its height are in accordance to drawings.

Adequate bracing (if necessary) to ensure stability.

Ensure cover blocks are placed correctly.

Monitoring During Concreting Process

Ensure site coordinators are available and on stand-by during the concreting process.

Always ensure that concrete pouring is distributed evenly throughout the

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wall sections before commencing to cast the slab level areas. This is to prevent loading pressure on the formwork panels due to uneven casting.

Recheck the areas whenever cement slurry leakage is noted to determine the cause of it. Remedy work should be done immediately to ensure the concreting process is not affected.

During concreting, always ensure that immediate step is taken to remove / clean all the excess concrete that is stuck on the back of the formwork panels. Non removal will result in the formwork panels getting too heavy and also the scrapping task after the concrete has dried up becomes more tedious.

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Dismantling of Wall, Column & Beam Formwork

Formwork panels shall be removed without damaging the concrete. Reinforcement Bars or other tools shall not be used as a lever against the concrete in removing the formwork panels. Only panel puller shall be used for removing the wall panels.

The appropriate time for the stripping of formwork panels will vary according to the environment and type of concrete used. The formwork panels of the wall, column and beam section can be usually dismantled after 12 hours. However, this process shall subject to approval of the project structural engineer after taking into consideration the grade of concrete used, additional props stand ordered, etc.

Always ensure that the wall section panels are removed first follow by the column and beam sections.

For precautionary step, ensure that formwork panels are removed systematically and due care is to be taken to prevent any damages to the formwork panels and also finish surface of the concrete whenever possible.

For safety reason, ensure that no workers are facing the pin and wedges when removing using hammer. Pin and wedges removed are to be collected and placed in containers to minimize lost and replacement.

The dismantle formwork panels shall be transferred to the next level/floor for subsequent assembly process via the slab opening or staircase areas in an orderly manner and to the appropriate section/area immediately. This will eliminate the confusion and congestion in the dismantling area or level as a result of too many dismantled formwork panels lying on the floor area.

As the formwork panels are pre-numbered and if color identification scheme is implemented, the transfer of panels can be determined and planned ahead according to the various sections / areas of one level/floor to the subsequent level/floor.

Always ensure that all the formwork panels are to be properly cleaned and applied with the Form release agent to protect the surface of the formworks before re-used.

Dismantling Process

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For the external wall section, the Starter Blocks (kickers) on the upper portion of the floor level shall remain intact to support and align the next level/floor of formwork panels that are going to be assembled. The assembly of the external formwork panels can be done by using the external working platforms that are fixed to the wall areas.

Dismantling of Slab Formwork

The appropriate time for the stripping of formwork panels will vary according to the environment and type of concrete used. The formwork panels of the slabs section are usually dismantled after 36 hours. However, this process shall subject to approval of the project structural engineer after taking into consideration the grade of concrete used, additional props stand ordered, etc.

The Aluspans mid beams / end beams have to be removed first after dismantling the wall panels. Proceed by removing the long pins and wedges on the joint bars for the end and middle beams. However, the prop lengths are to remain undisturbed during this process to lend support for the weight of the concrete slab.

There shall be 2 sets of prop lengths to support the concrete slab. The first set of the prop stands will only be removed when the assembly of the third level/floor commences and also upon approval and consultation with the project structural engineer.

Proceed t o dismantle the slab panels by commencing from the end of the slab area. Once the slab panels are dismantled, continue to remove the slab corners.

Removal of Flat Wall Tie & Wall Tie Sleeve

Flat wall Ties are used for the purpose of ensuring the thickness of the walls and column are consistent. Flat wall ties are to be removed by using special called Wall tie remover / extractor.

Subsequently, proceed to remove the wall tie sleeve which is embedded in the walls and columns section by using nose player.

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Sequence No. 1

Form Release agent (Solvent based) to be applied on the surface of all the panels before the assembly process.

Assembly Process

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Sequence No. 2

Outer Corner is fixed to External Wall Corner panel by round pin and wedge.

Assembly Process

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Sequence No. 3

Inner Corner is fixed to the Internal Wall panels by round pin & wedge. The Internal and External Wall Panels are hold by Flat Tie with Tie Bar Shield in between the panels.

Assembly Process

VERTICAL CORNER INTERNAL

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Sequence No. 4

Repeat Sequence No. 3 to complete the assembly of both the Internal and External Wall Panels.

Assembly Process

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Sequence No. 5

Install Slab Corner on the top portion of the Wall Panels with round pin & wedge.

Assembly Process

Slab Corner Internal

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Sequence No. 6

Aluspans mid beams / end beams and Prop head are combined by Beam splice bar with long pin and wedge at the bottom section.

Assembly Process

BEAM SPLICE BAR

BEAM SPLICE BAR

Aluspan

Aluspan cantilever

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Sequence No. 7

Start the assembly of the Slab Panels from the Slab corner Internal. Subsequently, fill out the whole slab area by pinning the slab panels together with the Aluspans (Comprises of Aluspans and cantilevers). Mid Beams / End Beams

Assembly Process

Slab corner Internal

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Sequence No. 8

Additional Wall Panels (or Kickers) are fixed to the external Wall Panels to raise to the appropriate height to contain the slab concrete when it is poured.

Assembly Process

ADDITIONAL WALL PANEL / STARTER BLOCK

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Sequence No. 9

Upon completion of the installation and fixing of the Wall and Slab Panels, a numbering sequence will be made for each of these panels with colour identification scheme to differentiate each of the unit area such as bedrooms, living room, bathroom etc. This numbering and colour identification scheme will ensure that each panels can be determined as to their exact location once they are tansferred to the next level for installation.

Sequence No. 10

Always ensure that wall ties, pins and wedges are properly installed and secured before pouring concrete into the forms. Ensure that concrete pouring is distribute evenly throughout the Wall Panels section before commencing to cast the slabs level area.

Assembly Process

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Sequence No. 1

After 12 hours, remove the Internal Wall panels by knocking out the wedges and pins. The Wall Panels are to be moved to upper floor through the slab opening as shown. The transferring of the panels should be done in a systematically and orderly manner to ensure that the next cycle or level is not affected. Since all the panels are numbered with different colour identification scheme, these transfer process can be determined and planned in advance according to section of the building such as Room 1, Room 2, Bathroom are etc.

Dismantling Process

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Sequence No. 2

After removing the External Wall Forms (the starter Block (kicker) should remain undisturbed), the dismantled wall forms are moved to upper floor. Access Scaffolding is use for transferring of external wall panels from the ground floor level. For level 1 and above, an external working platform is fixed to the external wall. The external wall forms from level 1onward shall be supported by the kickers. (These steps are to be repeated from one floor to another floor.)

Dismantling Process

Starter Block

Super plate

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Sequence No. 3

After removing the Wall Panels, proceed to the Slab Panels after 36 hours by removing the long pins and wedges on the joint bars the end and middle beam section.

Dismantling Process

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Sequence No. 4

Upon removing the Aluspans Mid Beams and Aluspan cantilevers End Beams, the prop shall remained undisturbed during this process to support the concrete slab.

Dismantling Process

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Sequence No. 5

Proceed to strip the Slab Panels and transfer to the next level according to the designated area and installation sequence.

Dismantling Process

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Sequence No. 6

Strip the Slab Corner.

Dismantling Process

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Sequence No. 7

Pull out Wall flat Tie using Wall Tie puller and remove the Wall tie sleeve using Nose player.

Sequence No. 8

When the cube tests show that the slab concrete is sufficiently strong, the prop together with the prop heads are removed and transferred to the next level.

Dismantling Process

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Flow Chart for Aluform Work at Site

FLOW CHART FOR ALUFORM WORK AT SITE:-

If not suitable

If suitable If not suitable

`

If work front is not ready

If work front is ready

1

2 3

4 4a

2a, 2b

5

6

7

8

7a

9

13

11

15 15a

16a

1a, 1b, 1c

3a

12

14

10

16

19 19a, 19b, 19c, 19d

20 2122 23

17 18

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Activity for the Flow Chart Numbers

1. Receive Aluform materials. 1a. Packing list, BOQ, and Formwork layout. 1b. Tools. 1c. Additional accessories.2. Visual inspection. 2a. Packing list & schemes. 2b. Acceptance criteria.3. Inform concern for any defects 3a. Details of report. 4. Collect modification details. 4a. Fabrication drawings.5. Stock the material as per packing list.6. Room wise segregation.7. Dry mock-up. 7a. Schemes.8. Room wise numbering for identification.9. Dismantling of mock-up.10. Setting out.11. Shift to work location.12. Shift to stock yard.13. Actual assembly at work location.14. Slab rebars & M&E works.15. Final checking (Pre pour check) 15a. Check list.16. Concreting. 16a. Pour card. 17. Post pour check.18. Leveling and finishing.19. De-shuttering 19a. Removing pins and wedges. 19b. Removing wall ties. 19c. Removal of wall panels. 19d. Removal of deck panels.20. Cleaning of panels.21. Fixing of working platforms with brackets.22. Erection of Safety posts / rails.23. Applying Form release agent.

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Introduction Slipform has been accepted as a precise construction technique within a comparatively short period of time – an indication of its considerable popularity. This popularity has in turn encouraged further research ensuring the adoption of new methods and modern materials, which have firmly established slipforming as an economical, rapid and accurate form of construction.

Now that it is properly developed, the technique can be applied to many different forms of structure, including tapering formations with straight or parabolic profiles incorporating constant reductions in wall thickness. Traditional applications for slipforming are silos, chimneys, bridge piers, water towers, special application like construction of pylons, lift core wall of building, lining for tunnel shaft, framed structures etc.,

Principles of Slipform

Slipform construction, also referred to as sliding form construction, is similar to an extrusion process. Plastic concrete is placed in the forms, and the forms act as moving die to shape the concrete. Once the form has been filled with fresh concrete and hardening has started the form is gradually raised by the lifting devices on which it is suspended. The rate of movement of the form is regulated, so that the forms leave the concrete after it is strong enough to retain its shape while supporting its own weight. Pouring of concrete, tying of reinforcement, fixing of openings/inserts etc are performed gradually from a working platform.

An average sliding speed of 200mm an hour is common, rising to 300mm an hour under the best conditions and 100 to 150mm an hour when large or complicated structures are being slipformed.

Design Considerations:

The slipform should be designed so that the loads to which its various component parts are subjected are uniformly distributed, and the yokes are loaded as uniformly and axially as possible to avoid their overturning. The jacks should not be located in wall openings as for as possible. The loading should not exceed the lifting capacity of the jacks. The loads acting on slipform can be classified as follows,

Slipform

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BASIC LOADS

Dead load due to the components

Live loads due to Concrete

Friction between form and concrete

Workmen

Materials

Machinery

Other installations

Auxiliary load due to the way of application of live loads,

Crowds of workmen

Piles of materials

Shocks produced by material unloading

Accidental Loads

Wind pressure

Adhesion between concrete and form due to long interruption.

Friction due to incorrect position of form

Failure of one jack

Extraordinary Loads

Breaking of certain members of the slipform

Failure of two adjacent jacks

Minimum concrete strength required for slipform application,

2 Kgf / cm 2 - when releasing the form.

4 Kgf / cm 2 - when coming out from the form.

20 Kg / cm 2 - after 24 hours since pouring.

200 Kg / cm2 - after 28 days.

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Type of SlipformThe slipform can be broadly classified into,

Straight slipform.

Tapering slipform.

Slipform for special applications

Typical structures that are constructed using straight slipform technique are,

Silos

Cylindrical chimneys

Water tank shafts

Columns

Typical structures that are constructed using Tapering slipform are,

Conical chimneys

Ventilation stack

Tapered bridge piers

Typical structures that are constructed using Special slipform are,

Lift cores

Framed structures

Preheater building

RCC Pylons

Construction of block of flats, lifts and stair- well, bridge piers, preheater and RCC pylons for boiler supporting structure using slipform techniques comes under special applications because of their complex sizes, shapes and loads to be lifted along with slipform, like walkway trusses, etc. which is essential for construction.

Assembly ProceduresStright Slipform

Position the vertical and horizontal reinforcement with correct cover.

Casting of the starter. (min: 150 - 200mm)

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Check starter for the correctness in level and diameter.

Fix the inside and outside staging brackets/erect scaffold pipes, if required.

Fix timber runners connecting the walkway brackets. / Level the surface using cement mortar.

Check the level.

Tie the vertical and horizontal reinforcement upto shutter top height.

Mark the position of inside and outside yokes in the starter, starting from the tower location.

Ensure that three sets of yokes are located in between two tower verticals.

Align the panels and introduce steel washers at regular intervals to maintain

4mm slope both inner & outer faces.

Fix top and bottom waler pipe. Fix external supports, both horizontal and inclined to align the shutter.

Fix filler panels.

Repeat the operation 10 to 12 for outside and make sure that washers are introduced at the bottom of shutters to achieve 4mm slope towards inside.

Fix the waler shoes, inside and outside yoke legs. Adjust waler shoe and check the verticality on both faces

Keep timber supports between top & bottom walers at yoke location.

Align the form panel by external supports.

Fix the yoke beam generally two numbers at the bottom and one number at top.

Check the level of yoke beams with spirit levels.

Fix the inside and outside walkway brackets.

Finish the final alignment by suitably adjusting the waler shoe bolts. Ensure that all walers are touching the form panels. Provide packing wherever required.

Fix the flying tie rod assembly and support the center rings. Ensure uniform tightness is maintained in all the spokes.

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Tapering Slipform Position the vertical and horizontal reinforcement with correct cover.

Casting the starter. (Provide pocket or pipe sleeve in yoke locations to accommodate tapered sleeves )

Check starter for the correctness in inclination level and diameter. Chip and finish the same, if required.

Erect central tower using L&T HDT system and fix planks on the top after aligning the top construction accurately.

Fix the centre frames with the help of scaffold pipes, if required.

Pre assemble the trusses and spiders after marking the location of inside yoke leg, assemble with yoke legs, yoke beams, adjusting screws as per initial setting diagram , erect them and provide support.

Check the level of truss.

Mark the position of inside and outside yokes in the starter starting from the tower location.

Assemble the panels along with form supports with pre assembled condition.

Fix top and bottom waler. Fix external supports both horizontal and inclined to align the shutter.

Fix inside and outside consoles and upper outside console and fix planks.

Fix the yoke beams at top & bottom.

Check the level of yoke beams with spirit levels.

Fix the top platform pipes with guard railings.

Fix the jacks & turnbuckle jacks and finish the hydraulic connections.

Test for leakage in the line and jacks and replace, if required.

Fix water level tubes & check the platform level. Adjust if required.

Check the the final adjustment as per the initial setting diagram.

Fix the handrails.

Fix the tapered sleeves & jack rods.

Energise the slipform before filling the form and removing temporary supports.

38 39

Start the concreting after completion of all activities and checking the availability of all materials as given in the planning for slipform.

Fix the inside and outside hanging scaffold and do the decking.

Tie the safety net.

Assembly of Stair Tower:The verticality of the stair tower shall be checked only with plumb bob.

Stair tower shall be checked for verticality at every support location. If any deviation is found it shall be corrected then and there, by adjusting support length. The deviation in verticality shall not be more than 10mm for every 10M of height and maximum 50mm for the overall height.

CARE DURING SLIPFORM OPERATIONS:

1. Uniform layer of concreting.

2. Regular cleaning of shutters.

3. Penetration testing of concrete, for setting time.

4. Freeness of tapered sleeves.

5. Periodical plumb readings.

6. Adjustment for tilt & twists.

7. Prevent overflowing of concrete.

8. Maintain a free board of 100 mm.

9. Uniform distribution of load on the platform.

10. Lowering of unwanted materials periodically.

11. Proper handling of lasers.

12. Cooling of jacks where the temperature is very high.

13. Protection of high pressure hose.

14. Protection of turnbuckle spindles.

15. Greasing of all moving parts / outside the shutters.

16. Ensure free movement of shutters, walers, intermediate form supports, planks and handrails.

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17. Consistent quality of concrete.

18. Periodical checking of concrete slump.

19. Fixing of required setting time for concrete based on slipping speed.

Dismantling ProcedureStright Slipform:

1. Provide coil nuts in the final layer of concrete approximately 300 mm from top of concrete.

2. Fix dismantling brackets, handrails, finish planking and transfer the load of slipform assembly to the brackets.

3. Remove the flying tie rod assembly and lower the same.

4. Remove the inside and outside hanging scaffold and shift the planks to the staging brackets.

5. Remove the jacks and sleeves.

6. Remove the yoke assembly, which consists of yoke legs, yoke beams and waler shoes.

7. Remove inside & outside walers.

8. Remove the wall forms, while removing the waler.

9. Extract the jack rods and grout the holes.

10. Remove dismantling brackets after completing other works.

Tapering Slipform:

1. Provide coil nuts in the final layer of concrete.

2. Fix dismantling brackets, handrails, and fix the planks.

3. Remove and re-locate the R.G.Hoist to the required location(if it is there).

4. Transfer the load of slipform assembly and main truss to the wall.

5. Remove & re-fix the safety net with the temporary platform.

6. Remove the inside & outside hanging scaffolding.

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7. Remove all the hydraulic hoses, manifolds and the jacks.

8. Remove the intermediate form supports, spindles, turnbuckle, shutters, form supports, wall thickness screws, radius screws and yoke beams.

9. Remove inside & outside yoke legs.

10. Dismantle the truss assembly.

11. Extract the jack rods and grout the hole

12. Lower the materials then and there.

13. Remove the dismantling platform.

Slipform Reinforcement:

The progress of slipform is mainly determined based on the time consuming for concrete pouring speed and reinforcement tying. if any delay in these two the progress will affect drastically. As the space available for tying the horizontal is restricted in slipform, it is very essential to plan all the activities well in advance and to be prepared before starting of slipform.

The following points have to be considered while making the schedule.

The length of vertical/horizontal bars should be restricted to 5 mtr. due to the constraints in lifting and handing at heights.

The diagonal bars around openings should be avoided.

Wherever stirrups are used it should be in 2 pieces only.

It is not possible to have verticals in yoke locations and hence alternate bars should be placed nearby.

Wherever concrete is taken through a chute the verticals below the chutes have to be lapped with smaller lengths by means of welding.

The total requirement of reinforcement should be cut / bent and kept near the slipform structure before starting slipform. The stocks should be kept with proper tag for easy identification.

Refernce Standards And Codes

1. ACI 318- Building code requirements for reinforcement concrete.

2. ACI 304- Recommended practice for measuring, mixing, transporting and placing concrete.

42 43

3. ACI 313-77 R83 - Recommended practice for design and construction of concrete bins, silos and bunkers for storage of granular materials.

4. ACI 347-78 - Recommended practice for concrete formwork.

5. ACI 313-77 - Allowable tolerance.

6. ASTM C 403-70 - Penetration resistance method of concrete setting.

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Summary of Labour Productivity Norms

Sl. No. Type of Work Unit Norms

In M.Hrs

1 Erection of Access Tower (2.5 X 2.5 M) RM 32

2 Dismantling of Access Tower (2.5 X 2.5 M) RM 15

3 Erection of Stair Tower (2.5 X 2.5 M) RM 16

4 Dismantling of Stair Tower (2.5 X 2.5 M) RM 8

5 Straight Slipform Assembly YOKE SET 75

6 Straight Slipform Dismantling YOKE SET 55

7 Slipform Operation - Straight Slipform M2 1.22

8 Assembly of Pre-Stressed Silo YOKE SET 92

9 Slipform Concrete - Manual M3 22

10 Slipform Concrete - Rmc With Pump M3 15

11 Slipform Concrete - Rmc With Hoist M3 25

12 Slipform Reinforcement - Straight Slipform MT 65

13 Extraction of Climbing Rod RM 0.34

14 Taper Slipform Assembly - Upto 24 Yoke Set MT 56

15 Taper Slipform Assembly - 16 To 48 Yoke Set MT 49

16 Taper Slipform Dismantling - Upto 24 Yoke Set MT 49

17 Taper Slipform Dismantling - 16 to 48 Yoke Set MT 46

18 Re-Assembly of Slipform - Taper Slipform MT 78

19 Re-Assembly of Slipform - Straight Slipform YOKE SET 90

20 Slipform Operation - Taper Slipform M2 2.45

21 Slipform Reinforcement - Taper Slipform MT 90

22 Erection of R.G.Hoist NOS. 827

23 Re-Location of R.G.Hoist NOS. 1365

24 Dismantling of R.G.Hoist NOS. 675

25 Pre-Stressing Works in Silos MT 170

Note: The productivity norms will vary based on volume of work involved and number of structures to be constructed in the project.

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The execution of slipform job requires a complete and detailed preparation as many simultaneous and successive operations are involved. The method of construction, preparation of scheme drgs., calculating the requirement of slipform materials, equipment, tools & tackles, consumable, manpower etc needs thorough planning.

It also involve mix design, admixtures to be added for the concrete, reinforcement around openings and planning for other related works on the slipformed structure.

Straight Slipform

On large site with several structures built with the same slipform, planning includes

Work below slip form level

Detailed programme for the wall

Work involved in intermediate floors, if any.

Embedment/ pockets and other installations during slipform

Slipform Materials

The number of yokes for each silo is calculated based on the diameter of the silo. The yoke to yoke distance is normally kept between 1.25 and 1.35 m. Once the number of yokes required is calculated the list of materials can be prepared from the master list. The requirement of jack rods depends on the height of structure. Always keep 5% extra material as spare.

The length of yoke beams = Wall thickness + 1000 mm.

Normally 2Nos. Yoke beams at the bottom and 1 at the top are fixed. Wherever yokes are used for supporting some lifting arrangements, there the top yoke beams also shall be 2 no back to back.

Slipform Equipment:

The capacity of Jacks to be deployed is depends on the following loads:

Basic Loads:

Dead weight of yokes,

Slipform Planning

44 45

Dead weight of Concrete lifting arrangements

Weight of Platform with 40thk plank

Weight of wooden Runners 125*75mm

Total Dead Load = X

Live Loads

Live load over platform @ 200kg/sqm

Weight of Concrete 0.5 cum

Weight of Steel (reinforcement, jack rod stacked on platform)

Weight of Equipment

Total Live load Y

Frictional forces @0.173kg/m (length along the wall sides) Z

Total Load on Slipform L = (X+Y+Z) * t

Required Jacking Capacity (W) should be with 1.4 factor

Note:- Jack shall not be loaded more than 80% of its capacity.

Concrete EquipmentThe quantity of concrete required per meter height should be calculated first. The slipping speed can be assumed based on the quantity of concrete , reinforcement, pre-stressing and other related items. Rate of rise depends on the above and setting time of concrete. Once the slipping speed is assumed the concrete requirement per shift can be calculated.

Once the quantity per shift is known, with 25% spare capacity, the size and number of mixing and lifting equipment shall be decided.

Consumable:The standard list of consumable is given along with master material list. The quantity of electrodes, gas, grease, oil etc. can be given approximately. The

46 47

wire rope required for hoisting to be calculated separately based on height of the structure.

Timber RequirementThe requirement of timber is for the following areas.

1) Working platform 2) Mason’s platform 3) Runners for supports

4) Planks for the bracket platform if assembly is taken up from higher elevation.

Working PlatformsTimber platform consisting of four parts

a) Supporting runners 5”x 3”x7’ long & 6’ long

b) Wooden planks 6” x 1½” x 6’ long.

c) Toe board size: 4” x 1½” x 6’ long

Manpower Requirement:The requirement of labour for various activities can be calculated based on the productivity norms, site conditions and type of structure.It is preferable to engage one single agency for the entire slipform works in a project to have better control over productivity and also optimum use of workmen with multi skill.

46 47

Tunnel Form

Description of Half Tunnel Form

48 49

48 49

50 51

50 51

52 53

52 53

54 55

54 55

56 57

56 57

58 59

Movement of Formwork

58 59




60 61

60 61

Kickers

62 63

62 63

Ties

64 65

Protection Platforms

64 65

66 67

66 67

Aluminium formwork Refurbishment

A) Process involved

a) Manual cleaning

A working table to be made and the Concrete lumps, dirt shall be cleaned by the scrapper and wire brush.

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a.1) Tools Required

Ball Pein Hammer

Chisel

Scrapper

b) Machine Cleaning

b.1) Tools Required

GQ 4 Grinding Machine

4” circular buffing wheel

6” RUBBER BACK UP PAD

c) Dent Removal

Side rails are cleaned with GQ4 Grinding Machine, 4” circular buffing wheel.

Remove the Dents if any in the panel using a hammer and a flat base plate. Make sure that no point contact is there during this process.

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d) Welding

After removing the dents, inspect the panel for any cracks in the welding joints. If found it shall be welded.

Surface cleaning shall be done with the sander disc, ensure that smooth rendering only is done.

d.1) Tools Required

TIG Welding machine

Welding coil spec :Aluminium filler wire 1.2 mm. Er 5356. Make: Indaco

e) Surface cleaning

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e.1) Tools Required

AG7 & AG4 GrindingMachine ( RPM – 5000)

Sander Disc (80/120 Grade)

f) Lacquering and Stenciling

Safety items

Hand gloves

Nose mask

Ear plug / ear muff

Apron

Goggles – white

Brushing viscosity of lacquer can be 30 sec. Surface to be touch dry with in 10 min of application. Allow over night and use. Thinner- MCC 2507.

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PlywoodPlywood is an important commodity which plays a key role in the formwork both in terms of quality and cost (10-13% of formwork cost). The finish of the concrete surface where plywood is used as sheathing members is purely dependent on the quality of the plywood. Plywood is a manufactured wood made up of thin sheets of woods and compressed together with a glue which gives higher strength when compared to a normal wood.

Indian government has put stringent rules for cutting of wood which has initiated the local ply manufactures to import the logs (poplar and birch wood) from various foreign countries for the production of plywood. The performance of the plywood (for formwork application) is mainly based on the glue which they use for binding (mostly wood species used by all the manufactures are common).

Plywood shall be tested at site premises before accepting. The testing facilities are established in all major projects. Incase if the same is not available respective site representative can contact the Cluster BSCC in charge for extending the support.

Plywood procurement is centralized in order to deliver a quality product to the projects at a competitive rate.

Plywood request format shall be filled and sent to the respective cluster BSCC in-charge for clearing the procurement. Cluster BSCC in-charge will in turn take concurrence from Head BSCC.

Now about 60 to 70% of the plywood requirements for the projects are serviced from china and the following are the details pertaining to the same

Item Code – 765610020

Repetitions – 8 to 10

Price – approx 20% cheaper than domestic ply

Delivery period – 60 to 65 days

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72 73

Form Release AgentApproved Form Release Agents

It’s a management decision that apart from these solvet based form release agent other products cannot be used until unless it is approved by Cluster / HQ BSCC.

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Formwork LiftA system which complements the ability of Table form to do faster construction. It is turning out to be one of the most important equipments which will be extremely useful in improving the functional aspect of L&T’s trademark Table form System. Till now, our Table form System was totally dependent on Crane, especially while shifting the Table vertically from one Floor to the next. RCS would not only help in drastically reducing this dependability on Crane but also have a positive impact on the Labour Productivity subsequently helping in reduction of Cycle time. Though the system was procured from the formwork supplier the self climbing equipment was indigenously developed by BSCC-HQ which further eliminated the crane requirement for floor to floor shifting of RCS.

A project site will be debited with a internal hire charges of ` / Month Cycle time – Labour Productivity -

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ACS - Automatic Climbing SystemSelf Climbing System ACS - Fields of Application

Self Climbing System ACS - Hydraulic System

Self Climbing System ACS

76 77

Hand tools required (work place)

76 77

ROLES & RESPONSIBILITIESOF FORMWORK ENGINEER AT SITE

1. Preparation of Formwork programme based on the overall construction programme

2. Finalization and coordination of Shuttering Scheme

3. Ensuring effective and proper utilization of shuttering and staging materials

4. Planning and allocation of materials / labour / Plant & machinery for formwork activities in coordination with concerned persons at site

5. Educating sub-contractors on System formwork

6. Making mock-up of various System formwork

7. Periodical reconciliation of formwork materials

8. Preparing S-6 A schedule (requirement / release) and sending the same to Cluster Office

9. Preparing stock statement of formwork materials both in Units and in Nos., with area of shuttering done category-wise, Plywood / Timber procured during the quarter / till date and Productivity report.

10. Maintain close interaction with stores and site people for proper accounting of materials

11. Despatch and receipt notes to be sent to Cluster Office

12. Making of purchase requisition for Plywood and Timber after thoroughly analyzing the number of repetitions

13. Receipts of plywood / formwork materials to be acknowledged after quality checks to Cluster Office on monthly basis

14. 100% materials reconciliation at the end of the job

15. Looking after pre-despatch maintenance

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16. Ensuring that despatched materials are in usable condition.

17. Sending monthly reports to Cluster office.

ROLES & RESPONSIBILITIESOF SITE FOREMAN / CHARGEHANDS

1. Material Accountability right from the materials receipts at site to despatch to other site after the completion of the job.

2. Small items have to be issued to the sub – contractors from stores and make them responsible for those items. For their sake, tool – box can be issued. These items have to reconcile after the completion of the job.

3. Proper usage of the formwork materials and avoid the misuse (using bracing as leverage) of the same.

4. Ensure proper house – keeping at site as well as the maintenance (greasing / oiling after deshuttering etc.) of the formwork materials

5. Deshuttering right on time to achieve maximum number of repetitions of formwork materials.

6. Optimum use of nails in H – beam.

7. Quality in works carried out at site so that tolerance should within tolerance limit.

8. Formwork labour productivity should be monitored closely to achieve the management goal.

9. Training of Labour and Sub – contractor workmen at site either by mock – up or classroom programme by drawing sketches.

10. Adoption of safety standards while working by fully equipped with PPE and using the complete system at site (do not miss any bracing / connecting pin / locking pin etc.).

11. Use of stocking pallets.

System formwork functions, applications& Safety

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1.Foundation formwork(All steel)Functions/Salient features

1. All the components are made out of steel

2. No timber is used

3. Easy to assemble

4. Higher labour productivity

5. High quality concrete surface finish

6. Suitable for side formwork of sub structures .

7. Capable of withstanding the concrete pressure of 10KN/sq.m

Sequences of assembly

1. Materials stocking near to layout

2. Cleaning and oiling

3. Layout marking

4. Floor forms positioning

5. Accessories fixing

6. Line and verticality checking

7. Concreting

8. Deshuttering

Safety appliances required

1. Safety helmet

2. Manila rope 20 mm or 25 mm

Safety precautions

1. During transporting and stocking the materials proper care has to be taken

80 81

2. While lowering the materials from ground level to down level additional care has to be taken

2.Wall/Column formworkFunctions/Salient features

1. System can be done by Crane and Manual

2. Using standard component wide range of plan configurations are possible

3. High strength tie system bear large concrete pressure and avoid load bearing struts

4. Provisions for fixing scaffolding platform and alignment units built-in

5. Offsetseliminated producing good concrete finish




3. Layout marking/starter casting and layout checking

4. Panel positioning

5. Accessories fixing and alignment

6. Line, level and verticality checking

7. Concreting

8. Deshuttering


1. Safety helmet

2. Safety belt

3. Safetynet for taller structures

80 81

4. Manila rope 20 mm or 25 mm

Safety precautions

Crane operation

1. Sling capacity and quality of sling has to be checked

2. D Shackle capacity has to be checked

3. Experienced signal man has to be engaged for propersignaling to the crane operator

4. Ensure that there is no loose material on the panels or platforms

5. Before lifting the panel, necessary pre checking has to be done on the panels.

Manual operation

1. Use the necessary personal protection appliances such as helmet and belt.

2. Use the proper tool for adjusting the panel height and line

3. Flex systemFunctions/Salient features

1. System can be used up to floor height of 4.40 mtr.

2. Removable folding tripods make selected individual props self -standing

3. Flexibility in adjusting the individual prop height and spacing between props

4. Components are easy to handle manually

5. Steel members can also be used for decking

7. Eliminating the skilled labour at site

82 83



2. Prop layout marking

3. Main Prop positioning with tripod

4. Intermediate props positioning with supporting head

5. Placing of fourway head, primary layer beam and secondary layer beam

6. Levelingof beams with the help of props

7. Placing of plywood.

8. Levelling of seathing and checking


10. Concreting

11. Dismantling

12. Cleaning

13. Transporting and stocking


1. Safety helmet

2. Safety belt

3. Safety net for taller structures whereever it is necessary

4. Manila rope 20 mm or 25 mm wherever it is necessary

Safety precautions

1. All the main props shall be fitted with folding tripod

2. All the indermediate shall be fitted with supporting head

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3. Do not use tor steel in place of locking pin

4. In ground level work , proper earth compaction and necessary bearing below the prop shall be given

4.Heavy duty tower system -HDTFunctions/Salient features

1. Higher loading capacity of 250 KN and needs bracing at every 6 m in height both horizontal directions with permanent other towers

2. Can be assembled in plan dimensions of 1524x1524 mm and 2250x1524 mm, by choosing the type of bracing both configurations with four legs of 62.5 KN capacity each.

3. Height adjustments up to a minimum of 800 mm is possible by utilising both top and bottom tower spindles

4. Easy to obtain plumb using tower spindles

5. Tower as a whole can be shifted(rolled) manually by attaching transport devices to the legs



2. Tower layout marking

3. Frame fixing with necessary accessories at bottom and fixing of bracings between the frames

4. Placing of necessary accessories at top with U head and steel waler

5. Placing of beam span and H-Beams

6. Levelling of beams

7. Placing of bottom/sheathing

8. Leveling of bottm/sheathing

9. Checking of levels and verticality

84 85


11. Concreting

12. Dismantling

13. Cleaning



1. Safety helmet

2. Safety belt



Safety precautions

1. Every 6 mtr interval bracing has to be fixed with permanent structure or tower to tower

2. Ground level earth has to be compacted well for better loading

3. Materials conditions has to be checked and badly damaged frames and bracings to be avoided

4. Do not use tor steel in place of locking pin

5. Stair towerFunctions/Salient features

1. Safe and convenient access up to 100 mtr height in the form of stair with suitablebracing with bracing with permanent structures every 6 mtr

2. Structural skeleton of HDT with a few additional accessories.

3. Can be handled as a single unit with a crane

84 85




3. Frame fixing with necessary accessories at bottom with foot plate , spring locking pin and tower spindle

4. Placing of 1.20 m frame with necessary bracing for one level

5. Checking of level and verticality for one level

6. Fixing of stair brackets ,grid iron ,connection angle , idermediate railing and inner hand railing

7. Every 6 mtr height necessary bracing with permanent structure

8. Dismantling

9. Cleaning



1. Safety helmet

2. Safety belt



Safety precautions

1. Every 6 mtr interval bracing has to be fixed with permanent structure

2. Ground level earth has to be compacted well for safe loading

3. Materials conditions has to be checked and badly damaged frames and bracings to be avoided

4. Do not use coir string or binding wire in place of M 10 bolt and nut with grid iron

5. Do not omit any bracing

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6. Access scaffoldingFunctions/Salient features

1. Exclusively used for scaffolding purpose up to 40 mtr height braced at every 6 mtr with structure

2. Frames are lighter in weight and 1.0 mtr in width

3. This provides free movement for workmen without any obstuction at all levels

4. Bracing 2H-225 serves as an essential bracing for stability as well as hand rail on the face away from the strutures




3. Frame fixing with necessary accessories at bottom with LD foot plate , spring locking pin and LD tower spindle

4. Placing of frame with necessary bracing for one level

5. Checking of level and verticality for one level

6. Fixing of platform hanger and walk way 225

7. Every 6 mtr height necessary bracing with permanent structure

8. Dismantling

9. Cleaning



1. Safety helmet

2. Safety belt

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Safety precautions

1. Every 6 mtr interval bracing has to be fixed with permanent structure

2. Ground level earth has to be compacted well for safe loading

3. Materials conditions has to be checked and badly damaged frames,walkway 225 and bracings to be avoided

4. Do not use coir string or binding wire in place of Platform hanger

5. Do not omit any bracing

7. Lift shaft formworkFunctions/Salient features

1. Provides a platform for shutter and workmen inside the closed area of liftwell and a deshuttering mechanism for stripping of formwork without dismantling the panels and seathing

2. Panels can be lifted integrally in deshuttered position along with platform and erected for next pour

3. A few components are required in addition to all components of wall//column formwork



2. Erect the platform in the pocket loations in the inside wall face with climbing pawl arrangements

3. Level the platform with the help of bolt given in the climbing pawl

4. Erection of inner wall panels with the necessary accessories including tie arrangements

88 89

5. Erection of outer panels with necessary accessories

6. Checking of dimensions,levels and verticality

7. Concreting

8. Releasing of inner panels for minimum of 20 mm on all the four sides

9. Lifting of inner panels with platform for next level

10. Lifting of outer panels



1. Safety helmet

2. Safety belt

3. Safety net for taller structures where ever it is necessary

4. Manila rope 20 mm or 25 mm where ever it is necessary

Safety precautions

1. Sling capacity and quality of sling has to be checked

2. D Shackle capacity has to be checked

3. Experienced signal man has to be engaged for Proper signaling to the crane operator

4. Ensure that there is no loose materials on the panels or platforms

5. Before lifting the panel , necessary pre checking has to be done on the panels.

6. Ensure the gap before lifting the inner panel platform

8.Framed formwork – FramiFunctions/Salient features

1. Sturdy and torsion proof hollow – sectioned steel frame

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2. Hot-dip galvanished for high Durabilty

3. High grade 15 mm thick film coated sheathing for high wear resistance

4. Easy to fasten accessories

5. Integrated handles for easier handling

6. Permissible concrete pressure on formwork 40 KN/sqm

7. Can be used for foundation , column and wall



2. Place the panels with all the necessary accessories as required

3. Check the dimension,level,line and verticality

4. Concreting

5. Releasing of inner panels for minimum of 20 mm on all the four sides

6. Lifting of inner panels with platform for next level

7. Lifting of outer panels



1. Safety helmet

2. Safety belt


Safety precautions

1. Provide the tierod only where the given the provision is given

2. Do not omit any components

3. Framiadj strut 260 is to be anchored properly

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9.Climbing formworkFunctions/Salient features

1. Large area form work can be taken up

2. Any height is possible

3. High degree of safety as on the ground

4. Faster and economical

5. Can be used for inclined structures also

6. Formwork is safely anchored to concrete at all times

7. Simple system of working platforms


1. Safety helmet

2. Safety belt


Safety precautions

1. Platform timbers should be free from cracks ,fungus attack and dead knots

2. Hand rails pipes are to be fixed properly

3. Stop anchor threaded length shall be 55 mm inside the anchor cone

4. Climbing cone threaded bore length shall be ------

5. Plat form shall be free from gap between timber joints

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REINFORCEMENT WORKS

Category of Reinforcements

Carbon steel bars (plain and deformed).

Cold reduced plain and deformed steel wire fabric.

Stainless steel bars and fabric.

Galvanized carbon steel bars and fabric.

Epoxy coated carbon steel bars.

Fiber Reinforced Polymer (FRP) rebar- [Non steel reinforcement]

Reference Indian Standards:

IS 1786 - 2008 - Specification for High Strength Deformed bar and Wires for Concrete Reinforcement.

IS 432 PART 1- 1982 - Specification for Mild steel and Medium tensile steel bars and hard drawn steel wire for concrete reinforcement

IS 432 PART 2 -1982-Specification for Mild steel and Medium tensile steel bars and hard drawn steel wire for concrete reinforcement.

IS 2502 -1963 - Code of practice for Bending and Fixing Bars for Concrete Reinforcement.

SP 34 -1987 Hand book on Concrete Reinforcement and Detailing

Reference International Standards.

BS 4449 Carbon steel bars for concrete.

BS 7295 Fusion bonded epoxy coated steel

BS6744 Stainless steel

BS 4483 Steel fabric

BS 4482 Hard drawn wire

BS 8666 Scheduling dimensioning, bending and cutting of steel reinforcement for concrete - Specification

ASTM A 615 for carbon steel rebar.

ASTM A 706 for seismic rebar.

ASTM A 955 for stainless steel rebar.

ACI 440 for FRP bars

DIN 488 Reinforcing steels

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How to Calculate Hook & Bend Allowance

REBAR TYPE

Bar Diameter, d ≤ 25mm

Bar Diameter, d > 25mm

k Value

Hook Bendk

ValueHook Bend

Mild Steel 2 9d 5d 3 11d 5.5d

Medium Tensile Steel 3 11d 5.5d 4 13d 6d

Cold Worked Steel 4 13d 6d 6 17d 7d

Note:

•AlltheValueistoberoundedofftonearest5mm. •Ifthecalculatedresultis<75mm,thentaketheresultas75mm.

92 93

Calculated Hook & Bend Allowance:

Nom

inal

Size

of

Bar

(D)

Hook Allowance (H) Bend Allowance (B)

Mild Steel

Medium

Tensile

Steel

Cold

Worked

Steel

Mild Steel

Medium

Tensile

Steel

Cold

Worked

Steel

Min

Rec

om

md.

Min

Rec

om

md.

Min

Rec

om

md.

Min

Rec

om

md.

Min

Rec

om

md.

Min

Rec

om

md.

5 75 - 75 - 75 - 75 - 75 - 75 -

6 75 - 75 - 75 - 75 - 75 - 75 -

8 75 - 90 - 105 - 75 - 75 - 75 -

10 90 - 110 - 130 - 75 - 75 - 75 -

12 110 - 130 - 155 - 75 - 75 - 75 -

16 145 - 175 - 210 - 80 - 90 - 95 -

20 180 - 220 - 260 - 100 - 110 - 120 -

22 200 - 240 - 285 - 110 - 120 - 130 -

25 225 - 275 - 325 - 125 - 140 - 150 -

28 250 310 310 365 365 475 146 155 155 170 170 195

32 290 350 350 415 415 545 160 175 175 190 190 225

36 325 395 395 470 470 610 180 200 200 215 215 250

40 360 440 440 520 520 680 200 220 220 240 240 280

45 405 495 495 585 585 765 225 250 250 270 270 315

50 450 550 550 650 650 850 250 275 275 300 300 350

94 95

LARSEN & TOUBRO LIMITED -ECC DIVISION

QUALITY FORMAT

BAR BENDING SCHEDULE PROJECT : DATE : AREA/BUILDING :

DESCRIPTION OF WORK : TIME :

DRG.REF . :

MEMBER BAR NO.

DIA. OF BAR

NO.PER MEMBER

NO.OF MEMBER

TOTAL No. OF BARS

CUT LENGTH

NET LENGTH SHAPE

TOTAL Wt.

REMARKS :

SITE ENGINEER REINFORCEMENT ENGINEER CLIENT

:

94 95

96 97

96 97

98 99

Minimum Diameter Required for Bending Former

Bar diameter ‘d’ (mm)

Bending Former Minimum dia. (mm).

[As per IS 2502-1963] for cold worked steel.

Bending Former Minimum dia. (mm).

[As per BS-8666-2005]

6 48 (8d) 24 (4d)

8 64(8d) 32(4d)

10 80 (8d) 40 (4d)

12 96 (8d) 48 (4d)

16 128 (8d) 64 (4d)

20 160 (8d) 140 (7d)

25 200 (8d) 175 (7d)

28 336 (12d ) 196 ( 7d)

32 384 (12d) 224 (7d)

40 480 (12 d) 280 (7d)

50 600 (12 d) 350 (7d)

98 99

Cross-Sectional Area and Mass of Rebar

NOMINAL SIZE( mm)CROSS-SECTIONAL

AREA (Sq mm)MASS PER METRE RUN

(Kg/m)

4 12.6 0.099

5 19.6 0.154

6 28.3 0.222

7 38.5 0.302

8 50.3 0.395

10 78.6 0.617

12 113.1 0.888

16 201.2 1.58

18 254.6 2.00

20 314.3 2.47

22 380.3 2.98

25 491.1 3.85

28 616 4.83

32 804.6 6.31

36 1018.3 7.99

40 1257.2 9.86

45 1591.1 12.50

50 1964.3 15.42

100 101

CHECKS

During procurement of Rebar

Check the brand isapproved or not. ¾

Check Grade of reinforcement ¾

Check the Quantity requirement and duration ¾

If new vendor collect sample and check for conformity ¾

On receipt at site

Stack various diameter bars separately over wooden sleepers ( avoid ¾contact with soil)

Identify the stack with a tag number ¾

Collect sample for test ¾

Binding Wires for tying rebar should be as per Technical specification / BOQ [black soft annealed wire or GI wire of 16 gauge (1.6mm dia.)]

Rebar Stacking

100 101

Breaking of bars :

If rebars breaks during bending then check the carbon content of the lot. Ensure bars of 25mm and above are free from cracking while bending 90 deg . If observed then straighten the bars again to know they are not breaking. Collect samples and send for chemical analysis. Mark and identify the lot till results available and lot is cleared of doubt.

Sample Testing on receipt at site

Samples of rebars collected from the lots received at site 2 sets of samples ( 3 specimens each) for 100 MT per Lot or Heat number and tested for mechanical properties as above. If one sample fails to meet the requirement 2 additional samples to be collected from the same lot and tested for conformity. If one specimen fails to meet the physical requirement of Table 3 IS 1786 the whole lot is rejected.

Cover blocks

Cover blocks used shall be of same grade of concrete or made up of PVC

TESTING OF REBAR

Sample collection

Samples of 1 m length (quantity as per below table) taken randomly ¾per lot for each diameter.

102 103

Check Rolling margin ( at site lab)

Weigh the mass (measure to a precision of +0.5%) of the rebar samples.

Calculate the nominal mass = Mass of the sample

Actual length of sample

The nominal mass should satisfy the Table 2 of IS1786-2008

Mechanical Properties (To be tested at external Lab).

0.2% proof stress ¾

Elongation ¾

Tensile strength ¾

Bend and Rebend test ¾

Universal Testing machine (Used for finding 0.2% proof stress, Elongation & Tensile strength)

102 103

Rebar Mechanical properties should satisfy Table 3 IS 1786 requirements

For Bend and Rebend test there should be not any rupture or cracks visible in the bent portion.

If any one of the test sample fails then collect 2 more sample of 3 Nos each.

If any one sample fails – LOT REJECTED.

104 105

Nominal Cover for Durability requirement:

Exposure Nominal concrete cover in mm

Mild 20

Moderate 30

Severe 45

Very Severe 50

Extreme 75

Note:

For main reinforcement up to 12mm dia bar for mid exposure the nominal cover may be reduced upto 5mm.

Unless specified otherwise, actual cover should not deviate from the required nominal cover by +10mm

For exposure condition “severe” & “very severe” ,reduction of 5mm may be made, where concrete grade is M35 and above.

TIPS ON COVER:

DESCRIPTION NOMINAL COVER

In no Case Less than Dia of Bar

Column Longitudinal Reinforcing Bar

InnoCase<40mm(or)DiaofBar

COLUMN OF SIZE Up to 200 mm, whose reinforcing bar is <12mmDia.

25 mm

Footings Minimum Cover is 50 mm

TOLERANCE OF COVER

ACTUAL COVER = OF NOMINAL COVER

+10 mm -0mm

104 105

Material for Cover

Concrete cover blocks

PVC Cover block

106 107

Plain Rebars

Deformed Rebars

Photographs

106 107

Stainless Steel Rebar

Epoxy Coated Rebar:

108 109

Hot Dip Galvanised Rebar

FRP Rebar

108 109

Pre-fabricated cages

Rebar Tying machine

110 111

Splicing Methods

Lap Splicing

Welding

Mechanical Coupler

Precautions:

Splicing should not be done at the area where the max. Bending moment is more than 50% of moment resistance.

Lap splicing is not permitted for reinforcing bar > 32mm. (Clause 26.2.5.1(A), is 456 -2000 amendment 3).

Bars >32mm shall be welded or mechanically spliced.

When two different dia. Bars is to be spliced, then the lap length calculation is to be made on basis of smaller dia rod.

SPLICE-STRENGTH:

Reinforcment couplers:

Classification according to IS Code (Draft):

Class L +H

Class L.

Different mechanical splicing systems based on type of reinforcment coupler used:

Threaded couplers

Parallel threaded couplers ¾

Tapered threaded couplers ¾

Upset parallel threaded couplers ¾

Coupler with crimped sleeve

Description Compression Tension

Welded splice 100% of design strength of bar

80% of design strength of bar

Mechanical splice 100% of design strength of bar

100% of design strength of bar

110 111

Coupling with injected sleeve

Molten metal injection ¾

Grout (or) epoxy resin injection ¾

Butt splices

Welded couplers

Other patented type

Mechanical Coupler Photographs:

Couplers Based on Application

112 113

Classification of test for reinforcment couplers

Static tensile test

Slip test

Cyclic tensile test

Low cycle fatigue test &

High cycle fatigue test for ‘L+H ‘couplers only.

112 113

The above data is based on draft published by Indian Standard.

Reinforcement Binding

114 115

Hair Pin Tie:

The hair pin tie, the most secure tie used on all good work for fixing key bars and setting the work securely, before infilling.

A most secure tie used on column, beams and for tying key bars before infilling.

Crown Tie:

The crown tie, again a most secure tie, and is used in much same way as the hairpin tie.

It has one further use that it can be used to tighten bars together that have a tendency to spring.

Splice Tie:

The splice tie, is used exactly as the name indicates for joining laps of splices in bars.

It is in fact, exactly the same as the crown tie. And as the same useful qualities

114 115

Welding of Reinforcments:

References Standards:

IS 9417-1989

SP-34(S&T)-1987

Lap Welding

Rebar Dia. Vs Electrode size

Sl.No. NOMINAL BAR DIAMETER (mm)

SIZE OF ELECTRODE, MAX (mm)

1 Up to and including 10 mm 2.50

2 Over 10 up to and including 18 mm 3.15

3 Over 18 up to and including 28 mm 4.00

4 Over 28 mm 5.00

116 117

Quality Control Test on Welded Rebars

Samples of Lap welded joints to be tested for Mechanical properties like Tensile. The failure should occur in the bars outside weld area and not on the weld.

Samples of Butt weld joints to be tested for Tensile and Bend test. The failure should occur in the bars outside weld area and not on the weld in tensile and no sign of crack in the weld portion in bend test.

116 117

Precautions in Rebar Actvity:

Why is it important to bend the bar around the correct radius?

The tighter the bend, the greater the strains that are created in the bar around the bend. The bend diameters in IS 2502 -1963 have been specified as they have been demonstrated to give a good balance between the need to maintain ductility and provide practical construction solutions. The bend diameter requirements of IS 2502-1963 are mandatory .and they should not be compromised.

Why TMT Rebar should not be cut with Flame?

If a TMT bar is heated and then allowed to air cool, the hardened surface will be lost and the strength of the bar will approach that of the core. This loss of strength is the reason for the restriction on the Flame /Gas cutting of TMT rebar

Cross-Section of TMT Rebar

118 119

Do not position laps in beam column junctions.

Do not position laps in the midspan of the beam at bottom

Ensure sufficient chairs are added at the right spacing

For the bars greater than 12 dia the slope shall not be more than 1 in 6 dia as per the sketch. This is to maintain the structural integrity.

118 119

Piling Works

120 121

What is a Pile?Pile is a conduit through which load from the structure is transferred to soil either by friction or by bearing or by both.

Concrete

Bored cast-in-situ piles ¾

Driven cast- in-situ piles ¾

Driven precast piles ¾

Steel piles

CLASSIFICATION

120 121

Test on piles

Pile load test (vertical compression,lateral & pull out ) ¾

Pile integrity test (low strain dynamic test) ¾

PDA test (high strain dynamic test) ¾

Lateral dynamic test ¾

Ultrasonic logging test ¾

“O” cell load test method. ¾

Sheet Pile Vibro Hammer

Sheet Pile Driving With Guide Frame

122 123

FACTORS GOVERNING PILE SELECTIONFACTORS GOVERNING PILE SELECTION

SL.No.

FACTOR

BORED CAST INSITU

DRIVEN CAST IN SITU

DRIVEN PRECAST

TECHNICAL CONSIDERATIONS I

SOIL BEHAVIOUR DUE TO CONSTRUCTION

a PILE HEAVE

DOES NOT OCCUR

OCCURS

OCCURS

b PILE LATERAL MOVEMENT DOES NOT OCCUR CAN OCCURCANNOT BE CORRECTED

CAN OCCUR CANNOT BE CORRECTED

c LOOSE MATERIALS AT PILE TIP

CAN OCCUR DOES NOT OCCUR DOES NOT OCCUR

d DENSIFICATION OF SILTY FINE SAND

DOES NOT OCCUR OCCURS IMPROVES SHEAR STRENGTH

OCCURS IMPROVES SHEAR STRENGTH

e DEVELOPMENT OF EXCESS PORE PRESSURE

MAY FORM DUE TO TEMPORARY CASING RESULTING OF CEMENT SLURRY AT THE TIME OF WITHDRAWAL

WILL FORM RESULTS IN WASHING OF CEMENT SLURRY AND WASHING OF PILE SHAFT

WILL FORM NO AFTER EFFECT

f SUB SURFACE WATER CURRENTS

UNCASED BORE WILL COLLAPSE AND IN CASED,THE CEMENT SLURRY WILL GET WASHED OFF

WILL WASH CEMENT SLURRY

UNAFFECTED

g STRUCTURAL INTEGRITY DUE TO TEMPORARY CASING

NECKING CAN OCCUR

NECKING CAN OCCUR NOT APPLICABLE

h QULAITY OF CONCRETING QUALITY OF CONCRETE IN PILE SHAFT CANNOT BE GUARANTEED

BOUND TO GET SEGREGATED .QUALITY CANNOT BE GURANTEED

QUALITY CAN BE GURANTEED

II PILE/ SOIL INTERACTION IF BENTONITE IS NOT CIRCULATED CONTINUOSLY SLUDGE CAN BE FORMED AT BOTTOM AND SKIN FRICTION MAY BE AFFECTED

FULL FRICTION AND END BEARING WILL BE MOBILISED

FULL FRICTION AND END BEARING WILL BE MOBILISED

III CORROSION DUE TO SULPHATE AND CHLORIDES

CAN BE AFFECTED CAN BE AFFECTED NO EFFECT PROTECTIVE COAT CAN BE APPLIED

To be inserted in Page 88-(Continued from above)

122 123

SL.No.

FACTOR

BORED CAST INSITU

DRIVEN CAST IN SITU

DRIVEN PRECAST

IV NEGATIVE SKIN FRICTION CANNOT OVERCOME.NET PILE CAPACITY REDUCES.

CANNOT OVERCOME.NET PILE CAPACITY REDUCES.

CAN BE EFFECTIVELY REDUCED TO A VERY LOW VALUE AT MINIMUM COST BY PROVIDING BITUMINUOS COATING

V CAPABILITY TO CATER FOR HORIZONTAL FORCES

ADDITIONAL REINFORCMENT TO BE PROVIDED WHICH MAY CREATE PROBLEM WHILE CONCRETING

ADDITIONAL REINFORCMENT TO BE PROVIDED. THIS MAY HINDER CONCRETING

SINCE CONCRETEIMG IS DONE IN CASTING YARD ,ADDL REINFORCMENT WILL NOT CREATE PRBLEM FOR CONCRETING.

MAXIMUM RAKE 1H :8V

MAXIMUM RAKE 1H :8V MAXIMUM RAKE 1H :4V

VI LENGTH OF PILE LONGER SHORTER SHORTER

PRACTICAL CONSIDERATIONS 1 HAIR LINE CRACKS DURING

DRIVING N.A N.A CAN OCCUR.BUT CAN BE

MINIMISED OR AVOIDED IF MINIMUM M30 CONCRETE MIX AND MIN 2% STEEL REINFORCMENT USED.

2 PILE CONSTRUCTION AND SUB SURFACE INTERACTION OVER-BREAK AND LOSS OF GROUND

CAN OCCUR.BUT PRECAUTIONS AND SUPERVISION CAN MINIMISE THE PROBLEM.

DOES NOT OCCUR. DOES NOT OCCUR.

3 PILE CRUSHING AT HEAD N.A N.A MAY OCCUR DUE TO INADEQUATE REINFORCMENT, OVER DRIVING & POOR DOLLY.

4 ACCURACY IN: a) VERTICAL b) RAKER

ACCURATENOT TOO ACCURATE

ACCURATEACCURATE

ACCURATE ACCURATE

COST-TIME LOGISTICS & OTHER ASPECTS 1 MOBILISATION 1 MONTH 1 MONTH 1 MONTH

2 OPERATOR SKILLS EXPERIENCED OPERATOR & CLOSE SUPERVISION

EXPERIENCED OPERATOR & CLOSE SUPERVISION

PARTICULAR SKILLS NOT NECESSARY.

3 CONSTRUCTION METHOD & SPEED

RATHER SLOW MEDIUM SPEED FASTEST

4 LENGTH OF PILE MOST FLEXIBLE FLEXIBLE FLEXIBLE

124 125

SL.No.

FACTOR

BORED CAST INSITU

DRIVEN CAST IN SITU

DRIVEN PRECAST

5 GESTATION TIME 7 DAYS FOR EACH PILE

7 DAYS FOR EACH PILE ADDITIONAL PRECAUTION NECESSARY.DUE TO SOIL DIFFERENCE HEAVE WHILE DRIVING ADJACENT.

28 DAYS FOR FIRST CASTING FIRST SET UP OF PILES IN YARD AFTER MOBILISATION.

A SITE CONGESTION NOT LIKELY FLEXIBLE FLEXIBLE

B GROUND CONDITION PREFERABLY DRY & LEVEL ABOVE WATER TABLE

DRY & LEVEL GROUND DESIRABLE

DRY & LEVEL GROUND ESSENTIAL

C ENVIRONMENTAL MESSY DUE TO BENTONITE

CLEAN CLEAN

D NOISE LEVEL LOW HIGH(EAR PLUGS/EAR MUFFS IS MUST)

HIGH (EAR PLUGS/EAR MUFFS IS MUST)

6 PILE CONSTRUCTION & SUB SURFACE INTERACTION GROUND HEAVE

DOES NOT OCCUR CAN OCCUR CAN OCCUR BUT CAN BE REMIDED BY REDRIVING.

7 RESTRICTION ON PILE SIZES

A CROSS SECTION ONLY CIRCULAR. DIFFICULT TO CONCRETE LESS THAN 400 MM DIA

DIFFICULT TO DRIVE LARGE DIA > 600 MM DIA

DIFFICULT TO HANDLE > 600MM DIA.

B LENGTH ANY LENGTH DIFFICULT FOR VERY LONG LENGTH

GENERALLY LIMITED TO 20-22 M.GREATER LENGTH CAN BE ACHIEVED BY JOINED SECTION.

COMMERCIAL CONSIDERATIONS 1 TOTAL COST LEAST COSTLIER THAN BCIS COSTLIEST

2 INFRASTRUCTURES AT SITE NORMAL NORMAL NORMAL

3 EQUIPMENT SIMPLE/SOPHISTICATED

SIMPLE/SOPHISTICATED

SIMPLE/ SOPHISTICATED

124 125

List of reference codes

IS 2911 part -1 (sec 1) - Design & construction of pile foundation ¾(DCIS)

IS 2911 part -1 (sec 2) - Design & construction of pile foundation ¾(BCIS)

IS 2911 part -1 (sec 3) - design & construction of pile foundation ¾(Driven precast))

IS 2911 part-4 –Load test on piles. ¾

IS 14593 –Design & construction of bored cast-in-situ piles founded ¾on rocks.

IS 14893 – Non destructive integrity testing of piles ¾

BS-8004 –1996 code of practice for foundations ¾

ASTM d 5882 -07 – standard test method for low strain impact integrity ¾testing of deep foundations

ASTM d 4945 – 00 - standard test method for high-strain dynamic ¾testing of piles.

126 127

INSTALLATION SEQUENCES - DRIVEN CAST-IN-SITU PILES.

126 127

INSTALLATION SEQUENCES - BORED CAST-IN-SITU PILES

128 129

CONCRETING OPERATION IN A BCIS PILE.

128 129

Characteristics of bentonite suspensions for Bored Cast in Situ Piles:

130 131

IMPORTANT THINGS TO BE FOLLOWED

DRIVEN CAST-IN-SITU PILES

Plan movement of rig with respect to group of piles, Based on Priority of the Structure.

Cross check the location of piles with reference points.(Survey)

Check the pile shoe for stiffener welding. Ensure full welding is done instead of tack weld.

Place the pile shoe in the survey locations by excavating 200mm soil and place sand bags above the pile shoe after checking the Point.

Apply Bitumen in the annular space between the casing and pile shoe to avoid water ingress.

Check for verticality of casing during driving and Monitor frequently & Record.

Maintain Height of Fall as per set Calculation .Record the No.of blows and record as per the Format.

Terminate the pile based on set criteria.

Check for water ingress inside the casing before concreting using water level indicator(make AIMIL)

Check for proper welding of rebar lap joints.

Maintain proper cover.

Lower the Reinforcement carefully and hold the reinforcement and monitor the same during Extraction.

Keep the concrete slump between 100mm to 150 mm.

Proper care during withdrawal of casing. (The energy required for withdrawal should be half of driving. This will ensure proper compaction of concrete inside.)

The concrete pressure > overburden pressure always during extraction of casing.

Check for Theoretical Vs Actual concrete consumption for each pile.

Check the Top of concrete after extraction from NGL

130 131

Maintain a gap of “6d” between construction of successive piles.(where “d “= diameter of pile )

Piling sequence is to be followed.

Pile Driving shall normally be from the center to periphery or from one side to other of a pile group.

Backfill the Empty bore (unconcreted portion above COL) of the pile with sand or with approved materials.

BORED CAST IN-SITU PILES

Fix the pile point &Cross check the location of piles with reference points.

Drive the Temporary casing vertically in Location.

Fill the Bentonite slurry inside the bore. Always maintain the head of Bentonite slurry 2M above Water table.

Check for verticality during drilling continuously and Record.

Collect the soil sample from the bore and record.

Check for bentonite slurry quality regularlyby testing the same for flow, specific gravity and density during drilling and after flushing and record.

Check the length of drilling by sounding using chain links.

Terminate the pile as per Drawing. If specified by client, terminate the pile based on SPT.

If socketing in Rock, Terminate the same as per Drawing.

Clean the bore thoroughly before inserting Reinforcement.

Insert reinforcementcage. If length of pile is more, ensure proper splice welding is done on reinforcement cage while insertion.

Check for Tremie pipes cleanliness & threading arrangement before concreting.

Lower the Tremie and continue flushing with fresh bentonitetill we get bentonite slurry specific gravity equivalent to fresh slurry.

132 133

Insert Tremie pipe to the required length leaving a gap of 100mm from pile toe level and Record.

Tremie pipe diameter should be >200 mm for concrete mix having 20mm size aggregates.

Check the Capacity of Concrete Hopper.

Start concrete operation after flushing and after checking the specific gravity of slurry.

Keep the concrete slump between 150mm and 180 mm. Grade of concrete as per approved Mix Design.

Tremie pipe should be always 2 to 3 m inside the concrete during concreting operation

While removal of Tremie shake the same to ensure proper compaction of concrete , ensuring that the Tremie pipe does not leave the concrete surface

Maintain the Record of Tremie Removal during operation.

The concrete pressure > overburden pressure always during concreting with Tremie.

All concrete operation should be completed within six hours.

Backfill the Empty bore if any(unconcreted top portion, i.e., from COLto EGL) of the pile with sand or with approved materials.

Muck shall be disposed at designated area/dump yard.

DRIVEN PRECAST PILES

Prepare a neat leveled casting bed free from undulations.

Check the alignment during and after casting the piles.

The pile shoe should be properly aligned during casting.

Lifting hooks should be properly positioned.

Ensure concrete has flown inside and well compacted near pile shoe and end points.

Use Concrete(grade as specified in GFC drawing) with a slump of 80 to 130mm for casting

132 133

Check whether the precast piles have attained the required strength before lifting it.

Lift the pile with Lifting arrangements (Strand back)

Cross check the location of piles with reference points.

Check for verticality during driving.

Take extra precaution for splice joints.

Pile driving sequence should be properly followed. Pile driving shall be from Centre towards outside or from one end to other end in a pile group.

Use stress band at the top of the pile during pile driving.

If the precast pile length exceeds 22m length, then joints are required

PRECAST PILES JOINTS:

MALE JOINT FEMALE JOINT

134 135

LOAD TEST ON PILES

Vertical Load Test:

Intial Load Test Routine Load Test

Test load = 2.5 times of design load or upto failure whichever is earlier.

Test load = 1.5 times of design load or 12mm whichever is earlier

Load test will be carried on Initial test piles seperately casted especially during beginning of project.

Load test will be conducted on working piles. The quantity will be generally 1.5% to 2% of total number of piles.

Type of Arrangements:

Kentledge Method (Placing of Concrete blocks or Sandbags over platform)

Anchor Method

By Rock anchors. ¾

By Anchor piles. ¾

134 135

VERTICAL LOAD TEST ARRANGEMENTS:

136 137

Arrangement for Vertical Load Test

136 137

LATERAL LOAD TESTS ARRANGEMENTS:

Vertical Load Test Photograph

138 139

PULLOUT (OR) UPLIFT TEST ARRANGEMENTS:

Lateral Load Test Photograph

PULLOUT (OR) UPLIFT TEST ARRANGEMENTS:

138 139

Pull Out Test Photograph

140 141

PILE INTEGRITY TEST:

This test evaluates the pile integrity and pile physical dimensions (that is, cross-sectional area, length), continuity, and consistency of the pile material, although evaluation is approximate and not exact. This test method will not give information regarding the pile bearing capacity.

PDA TEST (HIGH STRAIN DYNAMIC TEST):

This test method is used to provide data on strain or force and acceleration, velocity or displacement of a pile under impact force. The data are used to estimate the bearing capacity and the integrity of the pile, as well as hammer performance, pile stresses, and soil dynamics characteristics, such as soil damping coefficients and quake values.

Good Pile

Defective Pile

140 141

PDA test (High strain Dynamic test)

142 143

O-CELL TEST :

142 143

144 145

O-CELL TEST ARRANGEMENT:

144 145

1. Cement

Types of cement available:

As per IS 456-2000 the cement used shall be any of the following and the type selected should be appropriate for the intended use:

a) 33 Grade ordinary Portland cement confirming to IS 269

b) 43 Grade ordinary Portland cement confirming to IS 8112

c) 53 Grade ordinary Portland cement confirming to IS 12269

d) Rapid hardening Portland cement confirming to IS 8041

e) Portland slag cement confirming to IS 455 ( with slag content –35 % to 70 %)

f) Portland pozzolana cement (fly ash based) confirming to IS 1489 (part 1)–(with fly ash content 15% to 35%)

g) Portland pozzolana cement (calcined clay based) confirming IS 1489 (part 2)

h) Hydrophobic cement confirming to IS 8043

i) Low heat Portland cement confirming to IS 12600

j) Sulphate resisting Portland cement confirming to IS 12330.

Other combinations of Portland cement with mineral admixtures like Fly ash, Silica fume, Rice husk ash, Metakaoline and GGBFS of quality confirming with relevant Indian standards may also be used in the manufacture of concrete provided that there are satisfactory data on their suitability, such as performance test on concrete containing them.

Low heat Portland cement confirming to IS 12600 shall be used with adequate precautions with regard to removal of formwork, etc, Highalumina cement confirming to IS 6452 and Supersulphated cement confirming to IS 6909 may be used under special circumstances with prior approval of Engineer-in-charge. Specialist literature may be consulted for guidance regarding the use of these types of cements.

Cement and Mineral Admixtures

146 147

Test Certificates : Sampling requirements.

a) When the cement has ISI Certification mark, or when it comes with manufactures certificate, no further testing is usually required.

b) If clients still insist, one sample for every 250 tonnes or batch of cement may be tested for physical properties or sent for testing to an external agency.

c) Take the samples within one week from receipt of cement and arrange to test within one week from the date of sampling.

d) Send the sample for testing atleast 10 days before the cement is to be used.

e) A sample should consist of twelve roughly equal portions, each portion taken from different bag. The total weight of the sample should be 4 to 5 kg.

Problems of setting and hardening .

a) False set : Concrete may stiffen too early say with 5 to 20 minutes after mixing. This problem arises because of inadequate cooling during grinding of cement or because cement is fresh and hot from the mill. If false set occurs remix the concrete without adding water. Plasticity will return and concrete will set in the normal manner. ( IS 4031 part 14 – Method of test for determination of false set.)

b) Flash set : If concrete stiffens too early and does not regain plasticity on re-mixing, flash set might have occurred. The cause may be ,

1) Use of hot water ( 60o C to 80o C) for mixing.

2) Presence of calcium chloride, especially in admixture.

3) Contamination with high alumina cement or calcium chloride , possibly stored for emergency repairs.

c) Pozzolana and Slag cement :

Concrete with pozzolana cement and slag cement hardens at slower rate. Therefore, prolonged curing is necessary.

146 147

Simple Physical tests and Interpretations.

a) Fineness : IS 4031 Part 1 – Determination of fineness by dry sieving.

Sieve about 100 g of cement on a 90 micron sieve. The amount retained should be not more than five percent by weight for Rapid hardening cement and ten percent by weight for other cement types. Usually this requirement is met. If not a better test using Blaine’s apparatus will be necessary to find out specific surface in m2 / kg

b) Standard consistency : IS 4031 part 4 – Determination of standard consistency of cement paste.

The standard consistency of the cement paste is “ as that consistency which will not permit the vicat plunger to penetrate to a point 5 to 7 mm from bottom of mould. In general the consistency ranges between 26 % to 34 %. No limitations as per IS .

c) Setting Time : IS 4031 part5 – Determination of setting time of cement

The cement paste made with 85 % of standard consistency water, the initial setting time should not be less than 30 minutes and final setting time should not be more than 10 hours. However the limits of setting time for different types of cement should confirm to the respective Indian standards.

d) Loss on Ignition : IS 4032 – Method of Chemical Analysis of Hydraulic cement

This shows the amount of moisture and carbon dioxide absorbed by the cement. If cement is stored for a longer time (say three months) or if deterioration is suspected, check the cement for loss on ignition. This test can be done in an outside laboratory. The value should not be more than four or five percent by weight of cement.

e) Insoluble Residue : IS 4032 – Method of Chemical Analysis of Hydraulic cement

Insoluble residue is found by dissolving cement in hydrochloric acid. For ordinary PortlandCement this should not be more than 2 to 4 % by weight of cement. For pozzolana cement this may amount to 15% to 20 %

f) Test for Soundness: IS 4031 part 3 – Determination of soundness for hydraulic cement.

148 149

Le Chatelier test reveals the soundness caused by excess amount of uncombined(free) lime. Autoclave tests reveal the soundness caused by excess amount of percales crystals(MgO)It is not necessary to perform tests for soundness at site.

g) Compressive strength of Mortar cubes: IS 4031 part 6 – Determinationof compressive strength of Hydraulic cement other than masonry cement.-

This is the average compressive strength of three mortar cubes of size 70.7 x 70.7 x 70.7 mm prepared using one part of cement with three parts of standard sand confirming to IS 650 with( P/4+ 3 .0) percent (of combined mass of cement and sand) water.

Where P = Standard consistency of the cement in % ,

Supplementary Notes

a. ISI certification , week and year of manufacture are printed on the bag

b. Bags containing Ordinary Portland cement, Portland pozzolana cement and railway sleeper cements are marked respectively with black, red and green colour prints. Other cement bags are printed with black colour.

c. Percentage of slag in slag cement for pre-stressing concrete works should not exceed 50 %.

d. Do not use high alumina cement for structural use.

e. Concrete mix containing hydrophobic cement should be mixed for a longer time than usual.

f. Portland Pozzolona manufactured by blending or inter-grinding flyash in the range of 15% to 35% maximum

g. Portland slag cement manufactured by inter-grinding slag granules in the range of 25% to 70% maximum.

h. Sulphate resistant cement has C3A content of 5 % max.

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Physical requirements of cement

Type of cement

OPC

33

Grade

OPC

43

Grade

OPC

53

Grade

SRC

PPC

(Flyash

Based)

PSCSleeper

53 S

IS Code No 269 8112 12269 123301489 part 1

455 12269

Fineness (Blaine) (sq. cm / gm ) Min

2250 2250 2250 2250 3000 2250 3700

Setting Time (Minute) Initial (Not less than) Final ( Not more than)

30 600

30 600

30 600

30 600

30 600

30 600

60 600

Soundness 1)Le Chatelier (mm)

10 10 10 10 10 10 5

2) Autoclave (%) 0.8 0.8 0.8 0.8 0.8 0.8 0.8

Compressive strength (Kg/ Sq.cm) Min

3 Days160 230 270 100 160 160 -

7 Days 220 330 370 160 220 220 375

28 Days 330 430 530 330 330 330 -

Drying shrinkage (max %)

- - - - 0.15 - -

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Mineral admixtures:

IS 456-2000 permits the usage of the following pozzolanic materials confirming the relevant standard specification can be used in concrete as admixtures with the permission of the deciding authorities.

Fly ash (pulverized fuel ash ) confirming IS 3812-1981

Ground granulated blast furnace slag (GGBFS) confirming IS 12089 & BS 6699

Silica fume confirming IS 15388

Rice husk ash

Metakaoline having fineness between 700 to 900 m2/kg. confirming IS

In general fly ash , GGBFS and in some cases Silica fume is used depends on project requirement. But fly ash is used in major quantity in concrete making as part replacement to cement.

FLY ASH:

Fly ash is the by product of coal fired power plants. The ash which is very small in size is collected by the ESP’s. The chemical composition mainly depends up on the type of coal used for firing in the boilers.

The details of requirement of Chemical and Physical properties of Fly ash for use as a pozzolana for part eplacement of cement , for use as an admixture is given below.

Grade designation : As per IS 3812- Part 1 - 2003 fly ash is designated as

Siliceous Pulverized Fuel Ash — Pulverized fuel ash with reactive calcium oxide less than 10 percent,by mass. Such fly ash are normally produced from burning anthracite or bituminous coal and has pozzolanic properties.

Calcareous Pulverized Fuel Ash — Pulverized fuel ash with reactive calcium oxide not less than 10 percent by mass. Such fly ash are normally produced from lignite or sub-bituminous coal and have both pozzolanic and hydraulic properties

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Chemical requirements

When tested according to IS 1727-1967 fly ash to confirm the following requirements.

Chemical requirements of fly ash

Sl. No

Characteristic Requirements

Siliceous Calcareous

1Silicon dioxide(SiO2) plus aluminium oxide (Al2O3) plus iron oxide (Fe2O3) percent by mass ( Min)

70.0 50

2Silicon dioxide (SiO2) percent by mass (Min)

35.0 25

3Reactive Silica in percent by mass, Min *

20 20

4Magnesium oxide (MgO) percent by mass ( Max)

5.0 5.0

5Total sulphur as sulphur trioxide (SO3), percent by mass (Max)

3.0 3.0

6Available alkalis as sodium oxide (Na2O),percentbymass(Max)•

1.5 1.5

7Total chlorides in percent by mass, Max **

0.05 0.05

8Loss on ignition, percent by mass (Max)

5.0 5.0

* Optional Test

** For the purpose of this test, wherever reference to cement has been made, it may be read as pulverized fuel ash.

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Physical requirements of fly ash (tested as per IS 1727-1967)

Sl. No. Characteristic Requirements

1Fineness- specific surface in m2 / kg by Blaine Air permeability method (Min)

320

2Particles retained on 45 microns IS sieve (wet sieving) percent Max

34

3Lime reactivity – average compressive strength N/mm2 (Min)

4.5

4Compressive strength at 28 days in N/mm2 (Min)

Not less than 80 percent of the strength of corresponding plain

cement mortar cubes

5Soundness by autoclave test expansion of specimens, Percent (Max)

0.8

Not withstanding to the strength requirements specified above the fly ash incorporated shall show a progressive increase in strength.

In case of fly ash is used as replacement to cement a maximum of 35 % is permitted. But field trials to be conducted to estimate the strength development before the concrete mix is used. An optimum dosage of 20% to 25 % is found to give satisfactory results.

Note : Fly ash in general classified as “ Calcareous ( class C)” & “Siliceous (Class F)”. Fly ash of Class C is obtained from power plant where Lignite is used as fuel and Class F obtained from power plants where bituminous coal is used as fuel. In general in India , majority availability is fly ash of “Class F” .

Advantages of using fly ash in concrete

In plastic state concrete:

1) Improved workability: Fly ash is spherical in shape it produces a paste with superior plasticity and reduces the amount of water needed in a mix.

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2) Reduced Segregation: The improved cohesiveness of Fly ash concrete provides added body to plastic state concrete which resist segregation.

3) Reduces Bleed water: The lower water content required for workability in fly ash concrete reduces bleeding.

4) Increased pumpability : The spherical shape of fly ash acts like a tiny ball bearing, reducing internal friction, thereby producing a mix that is easier to pump.

5) Reduces Equipment wear: Fly ash concrete reduces wear on delivery and plant equipment because of the reduction of friction attributed to the spherical nature fly ash.

Long Term advantages of fly ash :

1) Increases concrete strengths: Fly ash concrete will continue to gain strength past the age of 28 days. With improved workability and a reduction in water needed , fly ash concrete provides a lower water / cementitous ratio there by producing superior strengths and longer life.

2) Reduces drying shrinkage: By providing as much as 10 % water reduction in its plastic state, fly ash concrete maintains workability and reduces drying shrinkage.

3) Reduced permeability: The packing effect of the spherical fly ash particles helps to reduce permeability. The chemical reaction between fly ash and lime forms additional (C-S-H) bonds that block bleed channels and fill pore space.

4) Resistance to Sulphate attack: Fly ash combines with free calcium hydroxide making it unavailable to react with sulphates. In producing a less permeable structure there is increased resistance to aggressive soluble sulphate solutions resulting in longer life.

5) Mitigates alkali aggregate: Fly ash reacts with available alkalis in the hardened cement matrix making them less likely to react with the aggregate.

6) Reduces heat of hydration: Large masses of concrete typically produce high internal temperature and thermal cracking. Fly ash concrete produces appreciably less heat than portland cement concrete.

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GGBFS: (Ground Granulated Blast Furnace Slag)

Granulated slag is a non-metallic product consisting essentially of glass containing silicates and aluminizes of lime and other bases. It is a product developed simultaneously with iron in blastfurnace of pig iron furnace. Granulated slag is obtained by further processing the molten slag by rapidly chilling or quenching it with water or steam and air. Ground granulated blast furnace slag confirming IS 12089 Chemical retirements can be used as an mineral admixture as part replacement to cement .

No IS code reference available for GGBFS as IS 12089 refers to granules of slag. BS 6609 has references to slag and in India GGBFS produced satisfy the requirement of BS 6609.

IS 456 stipulates GGBFS can be used as part replacement of cement in concrete mixes and the range of addition is as stipulated in IS 455. A minimum of 25% and a Maximum of 70 % can be used as part replacement of cement, but an optimum dose of 50% replacement gives maximum benefits to concrete.

Micro silica & Metakaolin

Microsilica and Metakaolin are used in high strength concrete as cementitious material. An optimum addition of 5% to 8 % by weight of cementtious material will produce more durable concrete.

In general addition of these material in concrete will result in

Increased durability

Greater resistance to chemicals

High strength

High resistance to chlorides and sulfates

Protection against corrosion

Silica fume addition usually increases water demand. If it is desired to maintain the same water-to-cementitious materials ratio (by mass), water-reducing admixtures or HRWRA or both should be used to obtain the required workability. In order to maintain the same apparent degree of workability, a somewhat higher slump will normally be required for silica fume concrete because of the increased cohesion.

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Aggregates:

Aggregates in general are inert material and occupy nearly more than 75 percent of concrete volume. The quality of aggregate is more important since it is concerned with the durability of concrete. Aggregates in general are classified into three types as coarse aggregate, fine aggregate and all-in-aggregate. Aggregates used in concrete should satisfy the requirement of IS 383 Specification for Coarse and Fine aggregates from natural sources for concrete.

1. Fine aggregate: Aggregates most of which passes 4.75 mm IS sieve and contain only so much percentage of material passing in 600 micron IS sieve as specified for the relevant Zones, and classified as Zone I , Zone II, Zone III and Zone IV.

The following are the types of fine aggregates in general used for production of concrete

1. Natural Sand : Fine aggregate resulting from the natural disintegration of rock and which has been deposited by streams or glacial agencies.

2. Crushed Stone Sand : Fine aggregates produced by crushing hard stone.

3. Crushed Gravel Sand: Fine aggregate produced by crushing natural gravel.

2. Coarse aggregate: Aggregates most of which is retained in 4.75 mm IS sieve and containing only so much finer material as permitted for the various types specified in the standard.

Coarse aggregates may be described as:

a) Uncrushed gravel or stone which results from natural disintegration of rock.

b) Crushed gravel or stone when it results from crushing of gravel or hard stone.

c) Partially crushed gravel or stone when it is a product of the blending of a) & b).

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3. All-in-aggregate : Material composed of fine and coarse aggregates.

Based on the particle shape aggregates are further classified in to the following types.

1. Rounded : Fully water worn or completely shaped by attrition (e.g. – River or seashore gravel, desert, seashore and windblown sands.

2. Irregular or partly rounded : Naturally irregular , or partly shaped by attrition and having rounded edges. ( e.g. Pit sands and gravel, land or dug flints , cuboid rock)

3. Angular : Possessing well-defined edges formed at the inter-section of roughly Planar faces. (e.g. Crushed rocks of all types, talus, screes)

4. Flaky : Material usually angular, of which the thickness is small relative to the width and / or length ( e.g. Laminated rocks)

Data for storage planning :

a) For calculating the volume of heap of aggregate or sand, assume a natural slope of 1.25 horizontal to 1.00 vertical.

b) For rough calculation assume 0.625 cu.m. per tonne of aggregate or 1.60 tonnes of aggregates per cu.m.

c) A conical heap of aggregate having base diameter D (meters) contains D3 / 6 tonnes of aggregates.

d) A long non-retained bank of aggregate, “L” meter wide at base contains L2/3 tonnes of aggregates per meter.

e) Make appropriate allowance if aggregate is retained against vertical surfaces.

Storage and Handling of aggregate

As per IS 4082 – Aggregates shall be stored at site on a hard dry and level patch of ground. If such a surface is not available , a platform of planks or old corrugated iron sheets, or a floor of bricks, or a thin layer of lean concrete shall be made so as to prevent contamination with clay, dust, vegetation and other foreign matter.

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a) Store sand and coarse aggregates of different size fractions in separate stock piles, on firm ground or platform.

b) If aggregates are stored directly over firm ground, do not use the material in the bottom 10 cm portion( This will be a “Dead storage”)

c) Provide ample space between adjacent stock piles ( about one meter).

d) Build up the stock pile in horizontal or gently sloping layers. Do not allow dumping of aggregates down the sloping sides of big stock piles.

e) Do not allow wheel loaders, trucks and bull dozers over the stock piles.

f) Maintain the amount of under sized fraction in each aggregate with in the limit specified in IS 383.

g) Do not blend two sizes of sand by placing them alternatively in stock piles or trucks. Always maintain additional stock piles and batch them separately in to the mixer.

h) If the aggregates have been washed or received wet, allow atleast 48 hours for the excess water to drain away

i) As far as possible avoid screening and washing of aggregates at the concreting site. The same should be done at the source or crusher if required.

j) Aggregates may be covered with low roofed sheds if concreting is done at temperatures above 40o C

Selection of size of aggregate for concrete :

The nominal maximum size of coarse aggregate should be as large as possible within the limits specified but in not case greater than one-fourth of the maximum thickness of the member, provided that the concrete can be placed without difficulty so as to surround all reinforcement thoroughly and fill the corners of the form. For most work, 20 mm aggregate is suitable. Where there is no restriction to the flow of concrete into sections, 40 mm or larger size may be permitted. In concrete elements with thin sections , closely spaced reinforcement or small cover, consideration should be given to the use of 10mm nominal maximum size.

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Plums above 160 mm and up to any reasonable size may be used in plain concrete work up to a maximum limit of 20 percent by volume of concrete when specifically permitted. The plums shall be distributed evenly and shall be not closer than 150mm from the surface.

For heavily reinforced concrete members as in the case of ribs of main beams, the nominal maximum size of the aggregate should usually be restricted to 5 mm less than the minimum clear distance between the main bars or 5 mm less than the minimum cover to the reinforcement which ever is less.

The aggregate used should satisfy the following requirements given in IS 383

Limits of the content of Deleterious Materials (IS 383)

Percentage by weight of aggregate

Deleterious substance

Fine aggregates Coarse aggregates

Uncrushed Crushed Uncrushed Crushed

Coal and lignite 1.00 1.00 1.00 1.00

Clay lumps 1.00 1.00 1.00 1.00

Soft fragments - - 3.00 -

Material finer than 75 micron IS sieve

3.00 15.00 3.00 3.00

Shale 1.00 - - -

Total percentage of all deleterious materials *

5.00 2.00 5.00 5.00

* Excluding Mica

Mechanical properties

Test Wearing surface Non Wearing Surface

Impact Value 30% Max 45 % Max

Crushing Value 30% Max 45 % Max

Abrasion Value 30% Max 50 % Max

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Grading requirement of Single size coarse aggregate (IS 383)

Grading requirement of Graded coarse aggregates ( I S 383)

I S SieveCumulative percentage passing IS Sieves for coarse aggregate of nominal size

40 mm 25 mm 20 mm 16 mm 12.5 mm

80 mm 100 - - - -

40 mm 95 – 100 100 100 - -

25 mm - 90 – 100 - - -

20 mm 30 – 70 - 95 – 100 100 100

16 mm - - - 90 - 100 -

12.5 mm - 25- 55 25 -55 - 90 – 100

10 mm 10 – 35 - - 30 – 70 40 – 85

4.75 mm 0 –5 0 – 5 0 – 5 0 - 10 0 – 10

IS Sieve

Cumulative percentage passing I S Sieves for coarse aggregates of nominal size63 mm 40 mm 25 mm 20 mm 16 mm 12.5 mm 10 mm

80 mm 100 - - - - - -

63 mm 85–100 100 - - - - -

40 mm 0 –30 85–100 100 - - - -

25 mm - 85–100 100 - - -

20 mm 0–5 0–20 - 85–100 100 - -

16 mm - - - - 85–100 100 -

12.5 mm - - 0– 20 - - 85–100 100

10 mm 0– 5 0– 5 - 0–20 0-30 0–45 85–100

4.75 mm - - 0 – 5 0 – 5 0 - 5 0 –10 0 – 20

2.36 mm - - - - - - 0 – 5

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Grading requirement of sand ( IS 383)

Grading limits for crushed sand used as fine aggregate

I S Sieve Cumulative percentage passing I S sieves for grading zone

I II III IV

10 mm 100 100 100 100

4.75 mm 90 – 100 90 – 100 90 – 100 95 – 100

2.36 mm 60 – 95 75 - 100 85 - 100 95 – 100

1.18 mm 30 – 70 55 - 90 75 - 100 90 - 100

600 micron 15 - 34 35 - 59 60 - 79 80 - 100

300 micron 5 - 20 8 - 30 12 - 40 15 - 50

150 micron 0 - 10 0 - 10 0 - 10 0 - 15

75 micron 0 - 3 0 - 3 0 - 3 0 - 3

Note : If the grading falls outside the limits of any particular sieve other than 600 micron IS sieve by a total amount of 5 percent it shall be regarded falling within the zone. This limit is not applicable for coarser limits of zone I and finer limits of zone IV. For crushed sand 150 microns parsing increased to 20 percent.

I S SieveCumulative percentage passing IS sieve

Crushed Sand Crushed sand + Natural sand

10 mm 100 100

4.75 mm 90 – 100 90 – 100

2.36 mm 75 – 100 75 – 100

1.18 mm 55 – 100 55 – 100

600 micron 30 – 70 30 – 70

300 micron 8 – 40 8 – 40

150 micron 0 – 20 0 – 15

75 micron 0 - 15 0 – 9

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All-in aggregate grading

IS SieveCumulative percentage passing IS sieve

40 mm 25 mm 20 mm 12.5 mm

80 mm 100 - - -

40 mm 95 – 100 100 100 -

25 mm 95 – 100 - -

20 mm 45 – 75 95 – 100 100

12.5 mm - 95 – 100

4.75 mm 25 – 45 30 – 50 30 – 50 35 – 55

600 micron 8 – 30 10 – 35 10 – 35 12 – 40

150 micron 0 – 6 0 – 10 0 - 10 0 – 12

1. The relaxed limits for crushed sand are applicable only if the boulders used for crushing in the crusher are free from natural over burden soil / muck.

2. The following Table13 is the guidance for selecting the percentage 4.75 mm passing in all-in-aggregate grading precisely.

Mixing Water

a) Potable water is satisfactory for mixing concrete.

b) Water should be free from oils, acids, alkalis, salts, sugar and organic materials.

c) In general , do not use sea water either for mixing or for curing . However IS 456-2000 permits use of sea water for Plain concrete and reinforced concrete permanently immersed in sea water.

d) The total requirement of water, for all purposes such as mixing, curing, washing of shutters, washing of aggregates and workmen’s consumption may be estimated on the basis of 370 to 500 litres / m3 of concrete.

As a guide the following concentrations represent the maximum permissible values:

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a) To neutralize 100 ml sample of water, using phenolphthalein as an indicator, it should not require more than 5 ml of 0.02 normal NaOH.

b) To neutralize 100 ml sample of water , using mixed indicator, it should not require more than 25 ml of 0.02 normal H2SO4

c) pH value of water shall not be less than 6.

IS 456 –2000 stipulates the permissible limits of solids shall be as follows

Sl.No Permissible Solids Permissible Limit (Max)

1 Organic 200 mg/l

2 Inorganic 3000 mg/l

3 Sulphates (as SO3) 400 mg/l

4 Chlorides (as Cl)2000 mg/l for PCC and

500 mg /l for RCC

5 Suspended matter 2000 mg /l

In case of doubt regarding the usage of water the same can be tested for setting time and compressive strength test as mentioned below.

1) The average 28 days compressive strength of at least three 150 mm concrete cube prepared with water proposed to be used shall not be less than 90 percent of the average of strength of three similar concrete cubes prepared with distilled water.

2) The initial setting time of test block made with the appropriate cement and the water proposed to be used shall not be less than 30 min and shall not differ by ± 30 min from the initial setting time of control test block prepared with the same cement and distilled water.

Admixture

Admixtures are the fourth ingredients in concrete making, which are added to cement, aggregate and mixing water. Admixtures are added to concrete mix immediately before or during its mixing , to modify one or more of the properties of concrete in the plastic and hardened states. Admixtures used in concrete should satisfy the requirement of IS 9103.

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Admixtures are of four types:

1. Accelerating admixtures

2. Retarding admixtures

3. Water reducing admixture and

4. Air entraining admixtures

Before using an admixture in concrete, the performance of it should be evaluted by comparing the properties of concrete with and without any admixture.

Though the admixtures are intended to modify a single property of concrete, some admixtures available are capable of modifying more than one property of concrete.

Eg. Water reducing admixtures can also be set retarders.

In addition , an admixture can improve the desirable properties of concrete in more than one way. For example , water reducing admixtures can be used : (a) to increase the workability of concrete with the same water and cement contents, (b) to increase the compressive strength of concrete without changing the workability by reduction of the water content in the concrete mix, when the cement content is unaltered, or to effect saving in cement by reduction in both the cement and water contents in the mix, while maintaining the same workability and compressive strength as in the reference concrete.

Every batch of admixture to be tested for compatibility before use. The concrete mix design carried out with the admixture shall be rechecked for increase in slump, slump retention, setting time and strength development. The performance should not defer from initial sample and trial conducted during trial stage.

Concrete

The concrete mix should be proportioned in such a way , it should give a uniform colour, easily transported, handled and placed in its final position with out difficulty and has given the required shape of the member as designed.

According to IS 456-2000 clause 9.2.1, “As the guarantor of quality of concrete used in the construction, the constructor shall carryout the mix design and mix

164 165

so designed (not the method of design) shall be approved by the employer within the limitations of parameters and other stipulations laid down by the standard IS 456-2000”.

Concrete mix design for the grades of concrete used in project site can be designed by considering the durability, Workability, Minimum cement content, maximum water cement ratio, maximum size of aggregate and cement type to used, method of placement, reinforcement congestion etc. Mix designed asper10262, ACI or any other accepted method and mixes so designed should satisfy the parameters laid down by IS 456.

Grades of concrete (IS 456-2000)

Group Grade Designation Specified characteristic compressive

Strength of150 mm cube at 28 days in N/mm2

(1) (2) (3)

Ordinary Concrete M 10 10

M 15 15

M 20 20

Standard concrete M 25 25

M 30 30

M 35 35

M 40 40 M 45 45

M 50 50

M 55 55

High strength concrete M 60 60

M 65 65

M 70 70

M 75 75

M 80 80

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Note :

1. In the designation of concrete mix M refers to the mix and number to the specified compressive strength of 150 mm size cube at 28 days expressed in N/mm2

2. For concrete of compressive strength greater than M 55 design parameters given in the standard may not be applicable and the values may be obtained from specialized literature and experimental results.

Exposure Conditions as Per is 456-2000

S.No Environment Exposure condition

1 Mild Concrete surface protected against weather or aggressive conditions, except those situated in coastal area

2 Moderate Concrete surface sheltered from severe rain or freezing whilst wet, concrete exposed to condensation and rain , concrete continuously under water, concrete in contact or buried under non aggressive soil/ground water, concrete surfaces sheltered from saturated salt air in coastal area

3 Severe Concrete surfaces exposed to severe rain, alternate wetting and drying or occasional freezing whilst wet or sever condensation, Concrete completely immersed in sea water, Concrete exposed to coastal environment

4 Very Severe Concrete surface exposed to sea water spray, corrosive fumes or severe freezing conditions whilst wet, Concrete in contact with or buried under aggressive sub soil/ ground water.

5 Extreme Surface of members in tidal zone, Members in direct contact with liquid / solid aggressive chemicals

Minimum cement content , Maximum water cement ratio and Minimum grade

of concrete for different exposure condition with normal weight aggregates of

20mm nominal size.

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Note:

1. Cement content prescribed in this table is irrespective of the grade of cement and inclusive of additions like fly ash and GGBFS and their content also to be taken into account in the concrete composition with respect to cement content and water cement ratio if the suitability is established as long as the maximum amounts taken into account do not exceed the limit of pozzolana and slag specified in IS 1489 Part I and IS 455 respectively.

2. Minimum grade for plain concrete under mild exposure condition is not specified

Requirement of concrete exposed to Sulphate attack

S.

NoExposure

Plain concrete Reinforced concrete

Minimum

cement

content

(kg/cum)

Maximum

free w/c

ratio

Minimum

grade of

concrete

Minimum

cement

content

(kg/cum)

Maximum

free w/c

ratio

Minimum

grade of

concrete

1 Mild 220 0.60 - 300 0.55 M 20

2 Moderate 240 0.60 M 15 300 0.50 M 25

3 Severe 250 0.50 M 20 320 0.45 M 30

4 Very

Severe

260 0.45 M 20 340 0.45 M 35

5 Extreme 280 0.40 M 25 360 0.40 M 40

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Class

Concentration of sulphates, Expressed as SO3

Type of cement

Dense fully compacted concrete made with 20mm Nominal MSA complying IS 383

In soil In Ground water

Minimum cement content

Maximum free w/c ratio

Total SO3

SO3 in 2:1 water : soil extract

Percent g/l g/l (Kg/cum)

1 Traces (<0.2)

Less than 1.0

Less than 0.3

Ordinary portland cement or Portland slag cement or portland pozzolana cement

280 0.55

2

0.2 to 0.5

1.0 to 1.9 0.3 to 1.2

Ordinary portland cement or Portland slag cement or Portland pozzolana cement

Supersulphated cement or Sulphate resisting Portland cement

330

310

0.50

0.50

3

0.50 to 1.0

1.9 to 3.1 1.2 to 2.5


Portland pozzolana cement or Portland slag cement

330

350

0.50

0.45

4 1.0 to 2.0

3.1 to 5.0 2.5 to 5.0


370 0.45

5 More than 2.0

More than 5.0

More than 5.0

Sulphate resisting Portland cement or supersulphated cement with protective coating

400 0.40

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Notes:

Cement content given in this table is irrespective of grades of cement.

1. Use of supersulphated cement is generally restricted where the prevailing temperature is above 40OC

2. Supersulphated cement gives an acceptable life provided that the concrete is dense and prepared with a water cement ratio of 0.40 or less , in mineral acids, down pH 3.5.

3. The cement content given in col. 6 of this table is the minimum recommended. For SO3 contents near the upper limits of any class cement content above these minimum are advised.

4. For severe conditions such as thin sections under hydrostatic pressure on one side only and sections partly immersed, considerations should be given to further reduction of water cement ratio.

5. Portland slag cement confirming to IS 455 with slag content more than 50 percent exhibits better sulphate resisting properties.

6. Where chloride is encountered along with sulphates in soil or ground water ordinary Portland cement with C3A contents from 5 to 8 percent shall be desirable to be used in concrete, instead of sulphate resisting cement. Alternatively Portland slag cement confirming to IS 455 having more than 50 % of slag or blend of ordinary Portland cement and slag may be used provided sufficient information is available on performance of such blended cement in these conditions.

Batching

Cement

a) Cement should be batched in bags (50 kg each)

b) Fractions of a bag of cement should always be weighed.

c) Whenever a new consignment of cement is received check the weight of several bags individually, for uniformity as well as for average weight.

d) Check the number of bags emptied in to the batch, at frequent intervals. Any irregularity in batching may also be detected from the appearance of concrete.

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e) Keep a record of number of bags consumed. Received and in stock, The stock should be checked regularly.

f) The tolerance limit for batching of cement is ± 1 % by weight.

Aggregates

a) If possible batch aggregates by weight.

b) If the mix proportions, are given by weight (in case designed mixes) but only volume batching could be done at site, then convert the weight to volume by dividing the weights by loose bulk density.

Use only loose bulk density and not rodded bulk density for conversion. Loose bulk density is determined by filling a known volume container loosely without compacting and finding the weight and volume.

Weight of material loosely packed in the container

Loose bulk density = ----------------------------------------------------------

Volume of the container.

c) Do not heap the sand or aggregates in the batch box. It should always be struck level, so that constant volumes are measured out.

d) Use separate batch boxes for different grades of concrete and different aggregates. It is advisable to mark on the box with paint the grade of concrete and type of aggregate, whether fine or coarse, over the respective boxes for easy identification, Marking also helps in avoiding use of wrong boxes.

e) The size of batch boxes should be so arranged that aggregates can be batched in whole number of boxes. When slight changes are required (say for bulkage) nail marks maybe made on the boxes before batching to show the height of filling in the boxes as required.

f) In volume batching, when moist sand is used, allowance must be made for bulking of sand, procedure for determining the bulking is given in Appendix I.

g) Batch tolerance for aggregates is ± 3 % by weight.

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Water:

a) Usually, water is measured by measuring cans or buckets in site mixers and with water meter in batching plants.

b) Batch tolerance for water is ± 3 % by weight as per IS 456

Procedure for Loading the skip

(a) When charging the skip or hopper with dry materials, first place the coarse aggregate at the bottom followed by sand and cement.

(b) If the sand to be used is damp, first place half the coarse aggregate in the skip, then the cement , followed by the fine aggregate and the remainder of the coarse aggregate to prevent the mount of the skip getting choked with the damp sand.

(c) Do not place materials in the skip unless they are to be mixed and used immediately.

Checking batching devices/methods.

(a) See that batching hopper is empty and clean.

(b) See that hoppers, fulcrums, knife edges , and all moving parts are free from binding, rubbing and friction. Knife edge bearing must be centered and knife edges must be sharp.

(c) Balance scales on zero , dial scales should be checked atleast once daily to ascertain that the hand returns to zero when batcher is emptied.

(d) In volume batching check if appropriate boxes are used for feeding the aggregates. Also check if corrected quantity is being batched. Check if correction for bulkage of moist sand is being done.

(e) Check for moisture content in sand and coarse aggregate daily. Do necessary corrections before batching, if moisture is present.

Mixing time

In general the mixing time is 2 minutes. For automatic control plants the mixing time can be as stated by manufacture. At the end of mixing time the concrete from plant should have uniform colour, cohesive and free from segregation.

170 171

If mineral admixtures like microsilica, high volume fly ash , GGBFS used to get uniform blending of the material the mixing time needs to be increased , normal experience shows it is 60 seconds to 90 seconds depend on quantity of mineral admixture used.

In central control plant the mixing time for 0.5 cum batch should not be less than 30 seconds. Refer to the cycle time diagram of the batching plant manufacture for this.

Transporting concrete

(a) The method of conveying concrete should not cause segregation, loss of part of the concrete and loss of slump.

(b) Do not add extra water to the concrete (in addition to what is required as per the W/c ratio) for the purpose of easy handling / transporting.

(c) Properly designed and operated buckets are an excellent means of transporting concrete. But they should be capable of discharging low slump concrete and the discharge rate should be controllable. Cylindrical buckets with proper center discharge gates are the most efficient

(d) When using chutes for transporting , take care to avoid segregation. The chutes should be of rounded cross-section and of smooth metal to avoid sticking of concrete. They should be of correct slope so that concrete of the required slump will slide without flowing. Usually, the slope is 1 vertical to 2 or 2 ½ horizontal but the best slope for a particular concrete can be fixed after a few trials. Control should be provided at the end of the chute so that concrete will drop vertically without segregation.Flush the chute with water before starting to transport the concrete.

(e) Wheel barrows can be effectively used for transporting concrete horizontally over a short distance of about 60 meters. Provide a smooth path for the wheelbarrows using planks or sheets to transport the concrete without shaking or spilling.

172 173

Placing

(a) Preparation

1) Do not place the concrete until the place of deposit has been thoroughly inspected and approved. Check whether the formwork has been oiled and the supports are rigid. Also, check whether the reinforcement , cover blocks, inserts and embedded plates have been properly secured in position.

2) Where concrete is to be bonded to a previous lift of concrete , clean the surface thoroughly and chip the top to a depth sufficient to expose fresh , clean cut concrete without disturbing or loosening the coarse aggregate

3) Keep the dry surface saturated with water for not less than 24 hours . Before placing fresh concrete, remove the standing water from depressions and spread about 1.5 cm thick mortar layer (in same proportion as in original concrete but not greater than 1:2) over the contact surface of the old concrete.

4) When concreting has to be done against earthen surface, compact the base by rolling or ramming and wet the surface by sprinkling water to prevent excessive loss of moisture from the concrete.

b) During Placement

Deposit the concrete at, or as near as possible to its final position

Place the concrete in uniform layers. Avoid placing in large heaps or sloping layers which will lead to segregation.

In walls and columns no layer should be more than about450mm thick. As more layer thickness make the concrete impossible to vibrate the bottom layer and will lead to air entrapment at bottom and surface blemishes on vertical surface.

In thin slabs place concrete thickness of 150mm.

Where good finish is required on columns and walls restrict the pour height to 2m per hour.

Ensure every layer of concrete is fully compacted before placing successive layer.

172 173

Ensure the vibrator head penetrates the previous layer this will eliminate layer lines.

Always make sure that you can see the concrete being deposited.

In columns and walls the placing must be done in such a way that the concrete does not strike the face of the formwork, similarly, avoid heavy impact against reinforcement as the force could displace it.

Compaction

The object of compaction is to get rid of as much as possible of entrapped air, down to less than 1% is the aim.(This does not apply with deliberate air entrainment, but in that case the air is uniformly distributed and stable)

The amount of air is related to workability. Concrete with a slump of 75mm contains about 5% air while concrete with 25mm has 20%.

This is why low slump concrete requires more vibration or longer time or more poker needles compared to concrete with higher slump.

It is important to remove this entrapped air for the following reasons:

Voids reduces the strength of the concrete. Every 1% of entrapped air the strength falls by about 5 to 6 % . So a concrete with 3% voids will be about 15 to 20% weaker than it should be.

Voids increased permeability, which in turn reduces the durability.

Void reduces the contact between concrete and reinforcement and other embedded metals. The required bond will then not be achieved and the reinforced member will not be as strong as it should be.

Voids produces visual blemishes such as blowholes and honeycombing and porosity on the struck surface.

Vibration

Rodding , spading-even using foot- are all ways of removing air from concrete to compact it, but the best and quickest method is vibration.

When concrete is vibrated it is fluidized which reduces the internal friction between the aggregate particle and removes the entrapped air , make them to get packed well to become a dense member.

174 175

With a properly designed cohesive mix, segregation and bleeding will be minimized. With an over-wet mix the larger aggregates may settle during compaction with the result that a weak layer of laitance will finish up on top surface.

Process of compaction

Points to remember in compaction

1. Make sure the concrete surface being vibrated is seen. Light is need for thin section columns and walls.

2. Insert the needle quickly this makes the concrete liquefies and fill the forms and allow the vibrator to penetrate to the previous layer.

3. Compact concrete in place till the Entrapped air expels out

4. Withdraw the needle slowly. The main thing is to see the hole made by vibrator head is closed.

5. Have proper lighting arrangement to see the concrete placed is vibrated

6. Excess vibration not to be done this may lead to Segregate the concrete

7. Place the poker needle in not more than 500mm away from its last position.

8. Avoid touching the form face with poker needle. This will result in colour variation

9. Avoid touching the reinforcement by poker , this will displace the

174 175

reiniforcement and also will decrease the bond between the reinforcement and concrete

10. Avoid moving concrete to flow using poker.

STOP VIBRATION WHEN

The concrete surface takes on a sheen

Large air bubbles no longer escape

You hear the vibrator change pitch or tone

You feel a change in vibration action

VIBRATING DON’TS

Don’t let a vibrator run very long outside concrete; it will overheat

Don’t use a vibrator to move concrete horizontally

Don’t force pr push a vibrator into concrete it won’t remain vertical and may get caught in the reinforcement

Don’t start a job without a spare vibrator

FINISHING

Initial finishing:

Strike off:

Properly done removes excess concrete and brings top surface to ¾grade

Start as soon as possible after placing concrete ¾

End before bleed water appears ¾

Straight edge uses can be of wood or magnesium ¾

Straight edge

Use a side-to-side sawing motion while pulling forward ¾

Tilt it slightly backward to create a single cutting edge ¾

Keep about an inch of concrete in front to fill low spots ¾

Make a second pass if the surface is not to grade ¾

Pull concrete into end edge forms. ¾

176 177

BULL FLOATS AND DARBIES

Use to level ridges and fill voids left by straightedge ¾

Start immediately after strike off and finish before bleed water ¾appears

Use at right angle to the direction of strike off ¾

Push the bull float with the front edge slightly off the surface to cut ¾bumps; pull the bull float with the back edge slightly off the surface to fill voids

Use magnesium tools for sir entrained concrete ¾

Darbies serve the same purpose as bull floats but for smaller areas; ¾use in a sawing arc motion

WAITING PERIOD

Begin further finishing when all the bleed water has evaporated and ¾concrete is firm enough to leave only ¼ inch foot prints

Finishing while bleed water is present can cause surface crazing, ¾dusting or scalling

Final finishing

Edgers

Use to produce a clean slab edge that is less likely to chip ¾

An edger is less likely to dig into concrete or leave a bumpy surface ¾if a trowel is used in a vertical sawing motion to dislodge aggregate particles away from the edge forms

Run back and forth with the leading edge slightly raised ¾

Don’t start in a corner and don’t raise the edger off the concrete unless ¾the tool is in motion

Use a wide edger for the first pass, then a narrow edger for the second ¾pass

Groovers

Use to control crack location by cutting joints to a depth of atleast one- ¾fourth the slab thickness

Push the groover into the concrete then move it forward while applying ¾pressure to the back of the tool

176 177

After joint is cut, turn the groover around, running it back over the cut ¾to give as smoother finish

For a straight cut, use a chalk line or a straight edge as a guide ¾

Floats

Use to remove imperfections and to bring mortar to the surface for ¾troweling

Hold flot flat and at arm’s length, moving it in awide semicircular ¾motion until surface is smooth

Use magnesium tools for air entrained concrete ¾

More than one float pass may be required ¾

Trowels

Use to produce a hard, dense surface ¾

Trowel only after floating, starting with a wide trowel then moving to ¾smaller trowels on the later passes

Hold trowel at a slight tilt at arm’s length and move it in a semicircular ¾motion , overlapping each pass by one half until surface finish is smooth.

CURING

When cement is mixed with water, a chemical reaction takes place, called hydration, it is this reaction which causes the cement and hence the concrete to harden and then develop strength. This strength development can take place only if the concrete is kept moist and at a favorable temperature, especially during the first few days.

A properly cured concrete is superior in many ways. It is stronger and more durable to chemical attack, but it is also more resistant to traffic wear and more water- tight , further more the accidental knocks it is bound to receive well probably cause less damage.

Cure concrete immediately after finishing by

Ponding

Build dike, then fill with water to cover the entire concrete slab ¾

Avoid water or dike material that can stain the concrete ¾

178 179

Use curing water at a temperature within 20 ° F ( i.e -6 deg) of concrete ¾temperature

Avoid premature or sudden release of ponded water which can ¾damage the surrounding environment

Sprinkling or fog spraying

Keep the surface continuously wet, alternate wetting and frying causes ¾craze cracking

Use low water pressure and flow to avoid washing away the fresh ¾concrete surface

Use curing water at a temperature within 20 ° F ( i.e -6 deg) of concrete ¾temperature

Avoid if water runoff can damage the surrounding environment. ¾

Using wet materials

Cover the concrete with wet burlap, straw, sawdust, or sand ¾

Wet continuously, or cover with plastic sheet and wet frequently ¾

Avoid materials that discolor concrete ¾

Prevent materials from blowing away. ¾

Using Plastic sheet or water proof paper

Lay flat , lap edges 6 inches, and cover exposed concrete edges ¾

Use minimum 4 mm thick plastic sheet white in hot weather and black ¾in cold weather

Don’t use on architectural concrete ¾

Secure covering to prevent concrete exposure ¾

Using curing compounds

Apply after finishing when bleedwater disappears in slab or flat surface ¾

In vertical faces apply in two applications, at right angles to from a ¾continuous film

The efficiency will be 80% to that of water curing. ¾

If further painting or surface finishing required select compound which ¾will not harm secondary finishes. Otherwise paints will not stick to the surface.

178 179

COMMON DEFECTS IN CONCRETE

FACTORS CAUSING DEFECTS

Causes of consolidation-related defects on formed concrete surfaces include:

Any defects in the finished concrete surface observed after removal of form work

a. Design and construction-related causes

Difficult placement due to design of a member

Improper design, construction and maintenance of forms

Improper selection of concrete mixture proportions

Failure to adjust concrete mixture proportions to suit

Placement condition

Improper placement practices

Improper vibration and consolidation practices

Improper steel detailing

b. Equipment-related causes

Improper equipment

Improper equipment maintenance

Equipment failure (crane, pump, concrete plant)

Interruption of utility service

c. Material-related causes

Improper selection of release agent

Cement characteristics

Variation in mixture components

Inappropriate use of admixtures

Inappropriate use of release agents

d. Environmental causes

Extreme weather conditions

180 181

Types of surface defects Surface defects which can result from ineffective consolidation procedures are discussed below.

1 Honeycomb

Honeycomb is a condition of irregular voids due to failure of the mortar to effectively fill the spaces between coarse aggregate particles. Where bridging of the aggregate particles or stiffness of the mixture is a cause of honeycomb, vibration may assist in overcoming the bridging by increasing the flowability of the concrete. Factors that may contribute to honeycombing are: congested reinforcement, insufficient paste content, improper sand-aggregate ratio, improper placing techniques, quick setting on hot concrete, and difficult construction conditions. Changes in mixture proportions to improve workability may assist in reducing or preventing honeycombing.

2 Bugholes (Air surface voids)

Bugholes on vertical faces are normally caused by air bubbles, but occasionally by water entrapped between the concrete mass and the form, especially in sticky or stiff concrete mixtures of low workability which may have an excessive sand and/or entrapped air content. Also, the use of vibrators of too large an amplitude or the lack of complete insertion of the vibrator head may result in increased air-void formation. Air voids vary insize from microscopic to about 1 in. (25 mm). Rarely will water create bugholes on formed surfaces. Excess water normally manifests itself in other textural defects such as bleeding channels or sand streaks on vertical formed surfaces. Bleed water voids can form at the top of a column and on battered formed surfaces. Surface voids can be minimized by procedures which are discussed in section 4.

3 Form-streaking

Form-streaking is caused by mortar leaking through form joints and may be aggravated by over vibration from vibrators that are too powerful, or by using forms that vibrate excessively during consolidation. Placing excessively wet or high-slump concrete mixtures will result in more mortar washing out through tie holes and loose fitting forms. Special care is sometimes required when superplasticizers are used, as they tend to increase leakage at form joints and in pump lines.

180 181

4 Aggregate transparency

Aggregate transparency is a condition characterized by a mottled coloring on the surface which results from deficiencies in the mortar. It may result when concrete mixtures have low sand content, dry or porous aggregates, or high slump with some lightweight and normal weight aggregates. Also, high density or glossy form surfaces may cause aggregate transparency.

5 Subsidence cracking

Subsidence cracking results from the development of tension when the concrete settles after or near initial set.

The cracks are caused because the upper concrete bridges between the forms while the lower concrete settles. These cracks may occur when there is an insufficient interval between placement of concrete in columns and placement of concrete for slabs or beams. They may also occur adjacent to block outs or over reinforcing bars with shallow cover.

To prevent subsidence cracking, the concrete can be revibrated. Revibration is most effective when done at the latest time at which the vibrator head will penetrate the concrete under its own weight. Subsidence cracking over reinforcing bars can be controlled by increasing concrete cover during the design phase and by using well-consolidated, low-slump concrete.

6 Color variation

Color variation may occur within a placement if the concrete is not uniform or is incompletely mixed. Vibrators inserted too close to the form destroy the release agent or mar the form surface. External vibration used haphazardly may also cause color variation. Furthermore, color variations may result from nonuniform absorption and/or nonuniform application of the release agent.

7 Sand streaking

Sand streaking is a streak of exposed fine aggregate in the surface of the formed concrete caused by heavy bleeding along the form. It frequently results from the use of harsh, wet mixtures, particularly those deficient in 0.30 to 0.15 mm and smaller sizes. Sand streaking is controlled by the use of tight

182 183

forms and proper mixture proportioning, using well-graded fines to minimize bleeding. Although the characteristics of portland cement and pozzolans, if used, have some influence on bleeding, the grading of the fine aggregate is of greater importance. Streaking tendencies increase when the ratio of sand to cementing materials increases, such as in lean mixtures.

8 Layer lines

Layer lines are dark horizontal lines on formed surfaces which indicate the boundary between concrete placements. Layer lines are caused by stiffening or insufficient consolidation of the lower level due to lack of penetration of the vibrator into the lower level.

9 Form offsets

Form offsets are usually caused by inadequate stiffness or anchorage of the forms and can be aggravated by too high a rate of placement and/or using too powerful a vibrator.

10 Cold joints

Cold joints frequently occur in concrete for many reasons. Cold joints can often be avoided by contingency planning, back-up equipment, working to keep the concrete surface alive, and working to vibrate into lower lifts.

Minimizing surface defects

To minimize the size and number of bugholes and other defects, arising out of the consolidation the following practices should be followed:

Vibration period should be of sufficient duration

Vibrator insertions should be properly spaced and overlapped and the vibrator removed slowly

Each concrete layer should be consolidated from the bottom upward

Vibration periods should be increased when using impermeable forms

Inward sloping forms and other complex design details should be avoided

Depth of placement layers should be limited

Vibrator should penetrate into the previous layer

182 183

Tightening devices and gaskets to prevent leakage at form joints should be provided as necessary

Placing ports should be designed into the forms as necessary

Bugholes can be minimized by the use, where practical, of a 64 mm diameter vibrator of high frequency with medium to low amplitude. The vibrator should be immersed in the concrete around the perimeter of the form without damaging the form wall. Where reinforcement is placed near the form wall, the vibrator must be inserted inside the reinforcement. Care should be taken to insure that the vibrator has a sufficient radius of action to liquefy the concrete at the form wall. Form vibration may be used to supplement the internal vibration. An alternate procedure is to use a high frequency, low amplitude form vibrator. Vibration procedures should be evaluated at the beginning of a project to determine the vibration time for each type of vibrator for a given mixture.

In areas where voids are most prevalent, revibration may be used to reduce bugholes. Revibration is more effective if it is done at the latest possible time at which the vibrator head will penetrate the concrete under its own weight. Greater benefits are obtained with wetter concrete mixtures, especially in the top few feet of a placement where air and water voids are most prevalent.

Other measures, such as altering mix proportions, using super-plasticizers and using smaller maximum aggregate size to improve workability should also be considered as methods of minimizing surface defects. These measures have often been successful, particularly when trying to consolidate concrete in congested areas.

184 185

Def

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184 185

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ssiv

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ith

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rete

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r ex

tern

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fect

s C

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me

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esc

rip

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ks

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ing

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idth

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th

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ical

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rfer

ence

to

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ess

Poor

the

rmal

in

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tion,

irre

gula

r sh

ape

rest

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ing

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lem

ent,

ex

cess

ive

abso

rben

cy

Insu

ffic

ient

in

terv

al b

etw

een

topo

ut o

f co

lum

ns a

nd

plac

emen

t of

sl

ab o

r be

am,

low

hum

idity

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san

d, h

igh

wat

er c

onte

nt

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rap

id

Insu

ffic

ient

vib

ration

Sand

str

eaki

ng

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iation

in c

olou

r or

sha

de d

ue t

o se

para

tion

of fin

e pa

rtic

les

caus

ed

by b

leed

ing

para

llel t

o th

e fo

rm f

ace

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w

abso

rben

cy

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te

mpe

ratu

re,

wet

mix

ture

s

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mix

ture

, ov

er s

ande

d bl

eedi

ng m

ix,

sand

def

icie

nt in

fin

es, lo

w a

ir

cont

ent

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rap

id f

or

type

of

mix

Exc

essi

ve v

ibra

tion

,

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essi

ve a

mpl

itud

e ,

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r m

anip

ulat

ion

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r lin

es

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k co

lour

ed

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s be

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ncre

te la

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rnal

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ce

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suff

icie

nt

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ning

, hi

gh

tem

pera

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mix

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with

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to

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dSl

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emen

t, la

ck

of e

quip

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t or

man

pow

er

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of

vibr

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n,

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re t

o pe

netr

ate

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pr

evio

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yer

Form

off

sets

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upt

to g

radu

al

surf

ace

irre

gula

rities

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adeq

uate

st

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ss o

r an

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age,

w

eak

form

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mat

eria

l, irre

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r lu

mbe

r, p

oor

carp

entr

y

Exc

essi

ve

reta

rdat

ion

of

mix

es

Rat

e to

o hi

gh

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essi

ve a

mpl

itud

e,

nonu

nifo

rm s

paci

ng o

f im

mer

sion

Agg

rega

te

tran

spar

ency

D

ark

or li

ght

area

s of

sim

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ape

to t

hat

of t

he

coar

se a

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gate

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ottled

app

eara

nce

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fle

xibl

e,

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sity

su

rfac

e fin

ish

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w s

and

cont

ent,

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pgra

ded,

ag

greg

ate

dry

or

poro

us ,

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ssiv

e co

arse

ag

greg

ate

, ex

cess

ive

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p w

ith

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wei

ght

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rete

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essi

ve o

r ex

tern

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atio

n; o

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ncre

te

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fect

s C

au

ses

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me

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esc

rip

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king

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ort

crac

ks

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ing

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idth

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n ho

rizo

ntal

th

an

vert

ical

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rfer

ence

to

acc

ess

Poor

the

rmal

in

sula

tion,

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gula

r sh

ape

rest

rain

ing

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lem

ent,

ex

cess

ive

abso

rben

cy

Insu

ffic

ient

in

terv

al b

etw

een

topo

ut o

f co

lum

ns a

nd

plac

emen

t of

sl

ab o

r be

am,

low

hum

idity

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san

d, h

igh

wat

er c

onte

nt

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rap

id

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ffic

ient

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ration

Sand

str

eaki

ng

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iation

in c

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r or

sha

de d

ue t

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para

tion

of fin

e pa

rtic

les

caus

ed

by b

leed

ing

para

llel t

o th

e fo

rm f

ace

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w

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rben

cy

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te

mpe

ratu

re,

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mix

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s

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mix

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, ov

er s

ande

d bl

eedi

ng m

ix,

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def

icie

nt in

fin

es, lo

w a

ir

cont

ent

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rap

id f

or

type

of

mix

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essi

ve v

ibra

tion

,

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essi

ve a

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itud

e ,

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r m

anip

ulat

ion

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r lin

es

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k co

lour

ed

zone

s be

twee

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te la

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rnal

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suff

icie

nt

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ning

, hi

gh

tem

pera

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mix

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with

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ency

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dSl

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emen

t, la

ck

of e

quip

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t or

man

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er

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re t

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ate

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us la

yer

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off

sets

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upt

to g

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eria

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Exc

essi

ve

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rdat

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of

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es

Rat

e to

o hi

gh

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essi

ve a

mpl

itud

e,

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ng o

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rega

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spar

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ark

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se a

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ottled

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nce

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sity

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ish

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w s

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ent,

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ded,

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greg

ate

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ssiv

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arse

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greg

ate

, ex

cess

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p w

ith

light

wei

ght

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rete

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ve o

r ex

tern

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idity

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essi

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ssiv

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rete

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tern

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atio

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ncre

te

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fect

s C

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ses

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me

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rip

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esh

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ort

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ks

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idth

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ore

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n ho

rizo

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an

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ical

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rfer

ence

to

acc

ess

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rmal

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tion,

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gula

r sh

ape

rest

rain

ing

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lem

ent,

ex

cess

ive

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rben

cy

Insu

ffic

ient

in

terv

al b

etw

een

topo

ut o

f co

lum

ns a

nd

plac

emen

t of

sl

ab o

r be

am,

low

hum

idity

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san

d, h

igh

wat

er c

onte

nt

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rap

id

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ration

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str

eaki

ng

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iation

in c

olou

r or

sha

de d

ue t

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tion

of fin

e pa

rtic

les

caus

ed

by b

leed

ing

para

llel t

o th

e fo

rm f

ace

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w

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rben

cy

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te

mpe

ratu

re,

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mix

ture

s

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mix

ture

, ov

er s

ande

d bl

eedi

ng m

ix,

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def

icie

nt in

fin

es, lo

w a

ir

cont

ent

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rap

id f

or

type

of

mix

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essi

ve v

ibra

tion

,

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essi

ve a

mpl

itud

e ,

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r m

anip

ulat

ion

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r lin

es

Dar

k co

lour

ed

zone

s be

twee

n co

ncre

te la

yers

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rnal

in

terf

eren

ce

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suff

icie

nt

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ning

, hi

gh

tem

pera

ture

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mix

ture

with

tend

ency

to

blee

dSl

ow

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emen

t, la

ck

of e

quip

men

t or

man

pow

er

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of

vibr

atio

n,

failu

re t

o pe

netr

ate

into

pr

evio

us la

yer

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off

sets

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upt

to g

radu

al

surf

ace

irre

gula

rities

In

adeq

uate

st

iffne

ss o

r an

chor

age,

w

eak

form

ing

mat

eria

l, irre

gula

r lu

mbe

r, p

oor

carp

entr

y

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essi

ve

reta

rdat

ion

of

mix

es

Rat

e to

o hi

gh

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essi

ve a

mpl

itud

e,

nonu

nifo

rm s

paci

ng o

f im

mer

sion

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rega

te

tran

spar

ency

D

ark

or li

ght

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s of

sim

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size

and

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ape

to t

hat

of t

he

coar

se a

ggre

gate

, m

ottled

app

eara

nce

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fle

xibl

e,

high

den

sity

su

rfac

e fin

ish

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w s

and

cont

ent,

ga

pgra

ded,

ag

greg

ate

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or

poro

us ,

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ssiv

e co

arse

ag

greg

ate

, ex

cess

ive

slum

p w

ith

light

wei

ght

conc

rete

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essi

ve o

r ex

tern

al

vibr

atio

n; o

ver

vibr

atio

n of

ligh

t w

eigh

t co

ncre

te

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fect

s C

au

ses

Na

me

D

esc

rip

tio

n

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sig

n o

f m

em

be

r Fo

rms

Co

nst

ruct

ion

co

nd

itio

ns

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pe

rtie

s o

f fr

esh

co

ncr

ete

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lace

me

nt

Co

nso

lid

ati

on

Subs

iden

ce

crac

king

Sh

ort

crac

ks

vary

ing

in w

idth

, m

ore

ofte

n ho

rizo

ntal

th

an

vert

ical

Inte

rfer

ence

to

acc

ess

Poor

the

rmal

in

sula

tion,

irre

gula

r sh

ape

rest

rain

ing

sett

lem

ent,

ex

cess

ive

abso

rben

cy

Insu

ffic

ient

in

terv

al b

etw

een

topo

ut o

f co

lum

ns a

nd

plac

emen

t of

sl

ab o

r be

am,

low

hum

idity

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san

d, h

igh

wat

er c

onte

nt

Too

rap

id

Insu

ffic

ient

vib

ration

Sand

str

eaki

ng

Var

iation

in c

olou

r or

sha

de d

ue t

o se

para

tion

of fin

e pa

rtic

les

caus

ed

by b

leed

ing

para

llel t

o th

e fo

rm f

ace

Lo

w

abso

rben

cy

Low

te

mpe

ratu

re,

wet

mix

ture

s

Lean

mix

ture

, ov

er s

ande

d bl

eedi

ng m

ix,

sand

def

icie

nt in

fin

es, lo

w a

ir

cont

ent

Too

rap

id f

or

type

of

mix

Exc

essi

ve v

ibra

tion

,

Exc

essi

ve a

mpl

itud

e ,

Ove

r m

anip

ulat

ion

Laye

r lin

es

Dar

k co

lour

ed

zone

s be

twee

n co

ncre

te la

yers

Inte

rnal

in

terf

eren

ce

In

suff

icie

nt

plan

ning

, hi

gh

tem

pera

ture

Wet

mix

ture

with

tend

ency

to

blee

dSl

ow

Plac

emen

t, la

ck

of e

quip

men

t or

man

pow

er

Lack

of

vibr

atio

n,

failu

re t

o pe

netr

ate

into

pr

evio

us la

yer

Form

off

sets

Abr

upt

to g

radu

al

surf

ace

irre

gula

rities

In

adeq

uate

st

iffne

ss o

r an

chor

age,

w

eak

form

ing

mat

eria

l, irre

gula

r lu

mbe

r, p

oor

carp

entr

y

Exc

essi

ve

reta

rdat

ion

of

mix

es

Rat

e to

o hi

gh

Exc

essi

ve a

mpl

itud

e,

nonu

nifo

rm s

paci

ng o

f im

mer

sion

186 187

SPECIAL CONCRETE

Concrete used for ALUFORM and Tunnel form has to be designed considering the following to avoid surface defects and to get form finish

The concrete mix should be slightly over sanded and cohesive

The concrete mix at placement should have a slump of 150mm to 200 mm (like tremie concrete)

The maximum size of aggregate may be 12.5mm or 10mm considering the reinforcement, electrical conduits and electrical boxes and other boxouts provided

The concrete should attain the required strength of 15 N/mm2 at 36 hours for Mivan formwork and 8 to 10 N/mm2 after 18 hours for tunnel forms

The cubes used to check the form removal strength shall be cured along with structure and tested at specified time.

When Self compacting concrete is used the concrete shall have a flow of 600 mm to 700mm flow at placement.

Concrete placement shall be commenced from pouring in walls and finished along with slab covering room by room

When concrete is placed in walls the form work shall be shirked with wooden mallet to ensure air removal from surface

Excess malleting to be avoided after full placement in walls , if continued will lead to formation of mild gap between form and concrete and will entrap bleed water and lead to bug holes.

While placing in walls having windows, electrical boxes concrete need to be placed from one side ensuring the concrete placed flow to the other side and get lifted up passing boxes or cutouts. Both side placement will lead to air entrapment under boxes and lead to void or cavity.

186 187

INTRODUCTION:

The prestressing and precasting of concrete are inter-related features of the modern building industry. Prestressing concrete is the application of compressive force to concrete members and may be achieved by either pre-tensioning high tensile steel strands before the concrete has set, or by the post-tensioning the strands after the concrete has set.

DEFINITIONS:

Prestressing of concrete is defined as the application of compressive stresses to concrete members. Those zones of the member ultimately required to carry tensile stresses under working load conditions are given an initial compressive stress before the application of working loads so that the tensile stress developed by these working loads are balanced by induced compressive strength. Prestress can be applied in two ways.

1. Pre- tensioning

2. Post-tensioning.

1. Pre-tensioning:

Pre-tensioning is the application, before casting, of a tensile force to high tensile steel tendons around which the concrete is to be cast. When the placed concrete has developed sufficient compressive strength a compressive force is imparted to it by releasing the tendons, so that the concrete member is in a permanent state of prestress.

2. Post- tensioning:

Post-tensioning is a method of reinforcing concrete or other materials with high strength steel

Prestressing

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strands or bars, typically referred to as tendons. Post-tensioning applications include office and apartment buildings, parking structures, bridges, stadiums, soil anchors and water tanks.

Post – tensioning is the application of a compressive force to the concrete at some point in time after casting. When the concrete has gained strength a state of prestress is induced by tensioning steel tendons passed through ducts cast in to the concrete, and locking the stressed tendons with mechanical anchors. The tendons are then normally grouted in place.

ADVANTAGES OF PRESTRESSING

Minimizes the concrete crakes. ¾

Allows reducing beam depth. ¾

Allows greater degree of loading than any structural material. ¾

Lighter elements permit the use of longer span. ¾

Ability to control deflection in beams and slab. ¾

Permits efficient usage of steel and reduces cost. ¾

Speed in construction. ¾

APPLICATION

Bridges ¾

Nuclear Structures. ¾

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Building frames and floor slabs. ¾

Marine and waterside Structures. ¾

Ground anchor. ¾

Heavy lifting. ¾

Foundation. ¾Materials

Management1) HT Strand

2) Anchorages

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3) Wedges:

4) Sheathing:

190 191

MATERIAL ORDERING:

The followings are to be specified in MR.

Client Specification ¾

IS code references ¾

Type of material ¾

Delivery schedule ¾

Type of packing ¾

RECEPIT AT SITE:

H.T. Strand:

Check the following:

Size of Strand. ¾

Coil No/Heat No. ¾

IS Specifications and class of strand. ¾

Weight/ Length. ¾

Test certificate. ¾

PT Hardware:

Check for the test/mill certificate ¾

IS Code references ¾

Size/ dimensions. ¾

Quantity ¾

Visual inspection for any crake ¾

REFRENCE STANDARDS &CODES:

HT STRAND : IS : 14268 -1995

IS: 6006 -1983

ASTM A 146 -1998

TEST FOR SHEATHING : IRC : 18 -2000

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TESTING FOR PRESTRESSING SYSTEM : BS 4447 -1973

GROUTING : IRC : 18 -2000

PRESSURE GAUGE TESTING : IS: 3624 -1987

Elongation & Modified Elongation Calculations:

a) Elongation Calculation:

1. Design load in “N”--- P

2. Length of Tendon in “mm” --- L

3. Area of Strand in “mm2” --- A

4. Young’s Modulus in “N/ mm2” --- E

Elongation (e) = PxL / AxE in “mm”

b) Modified Elongation Calculation:

1. Area of Strand in “mm2” --- A

2. Young’s Modulus in “N/ mm2” --- E

3. Elongation in “mm” --- e

4. Modified Area of Strand (as per TC) in “mm2” --- MA

5. Modified Young’s Modulus in (as per TC) “N/ mm2” --- ME

Modified Elongation (Me) = ex AxE / MAxME in “mm”

Jack Pressure Calculation:

a) Single-pull Stressing:

1. Design load per Strand “Kg”

2. Losses due to Jack Efficiency “%” (add as per Jack Calibration Report)

3. Losses due to Anchorages “%” (add as per System Supplier’s Report

4. Load per Strand including losses “Kg” --- P

5. Jack Ram Area “Cm2” --- JA

Jack Pressure (JP) = P/JA in “Kg/Cm2”

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b) Multi-pull Stressing:

1. Design load per Strand “Kg”

2. Load per Tendon (as per the type) “Kg”

3. Losses due to Jack Efficiency “%” (add as per Jack Calibration Report)

4. Losses due to Anchorages “%” (add as per System Supplier’s Report)

5. Load per Tendon including losses “Kg” --- P

6. Jack Ram Area in “cm2” --- JA

Jack Pressure (JP) = P/JA in “Kg/cm2”

Losses in Prestress:

Losses due to Elastic Shortening of Concrete

Creep in Concrete (Creep Strain)

Shrinkage in Concrete

Relaxation of Prestressing Steel

Losses due to seating of Anchorages

Friction Losses

Properties of HT Strand (IS: 14268 - 1995):

Class

of HT

Strand

Nominal

diameter

(mm)

Tolerance in

Dia (mm)

Nominal

Area

(mm2)

Nominal

Mass

(Kg/M)

Breaking

Strength

(KN)

0.2% Proof

Load (KN)

Minimum

Tensile

Strength

(N/mm2)

Modulus of

Elasticity

(N/mm2)

I

9.5 +/-0.4 51.6 0.405 89.0 80.1

1860 195000 11.1 +/-0.4 69.7 0.548 120.1 108.1

12.7 +/-0.4 92.9 0.73 160.1 144.1

15.2 +/-0.4 139.4 1.094 240.2 216.2

II

9.5 +0.66 / -0.15 54.8 0.432 102.3 92.1

1860 195000 11.1 +0.66 / -0.15 74.2 0.582 137.9 124.1

12.7 +0.66 / -0.15 98.7 0.775 183.7 165.3

15.2 +0.66 / -0.15 140 1.102 260.7 234.6

Methodology of Post-tensioning work:

Post-tensioning work is divided into three major activities. The general

methodology is given below.

1. Profiling.

2. Stressing.

3. Grouting.

1) Profiling:

Read the drawings and identify type of tendons, layout, locations, and

number of strands per tendon, sequence of laying, number of tendons per

pour, etc.

Calculate the materials requirement such as Tube Units, Bearing Plates,

Wedges, Sheathing and Prestressing Steel (HTS).

Calculate the cut length of Strand inclusive of Jack Grip length & profile for

each tendon and prepare Strand cutting schedule as per drawing. HT Strand

must be cut by using cut-off wheel/abrasion blade.

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Methodology of Post-tensioning work:

Post-tensioning work is divided into three major activities. The general methodology is given below.

1. Profiling.

2. Stressing.

3. Grouting.

1) Profiling:

Read the drawings and identify type of tendons, layout, locations, and number of strands per tendon, sequence of laying, number of tendons per pour, etc.

Calculate the materials requirement such as Tube Units, Bearing Plates, Wedges, Sheathing and Prestressing Steel (HTS).

Calculate the cut length of Strand inclusive of Jack Grip length & profile for each tendon and prepare Strand cutting schedule as per drawing. HT Strand must be cut by using cut-off wheel/abrasion blade.

H T Strand shall be uncoiled using coil dispenser and it should not contact soil or dust while cutting.

Mark the Tendons as per Tendon layout drawing, after the completion of formwork& reinforcement.

Fix the fabricated tendon support bars (bar chairs) rigidly at every 1m (max.) interval according to the tendon layout and profile drawings.

Lay the sheathing over the tendon support bars as per the tendon layout drawing and jointhe ducts using couplers and seal the joint using self-adhesive tape.

Thread therequired number of Strands into Sheathing according to the Tendon type (strand schedule) and tie thesheathing with Bar Chairs using Binding wires rigidly.

Profiling of Tendons, both horizontally and vertically as per drawingsand arresting it rigidly to avoid any disturbances in profile during concreting.

Fix the Stressing anchorages and make Dead-end anchorages position as per the layout drawing. Fix the Grout vents at end portions and Air vents

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at high profile locations and seal it properly.

Tie Bursting and Spiral reinforcements at the anchorages zones as per the details given in drawing.

Final checking of all Tendons for profiling, supporting and sealing after the completion of reinforcement and formwork works and before concreting.

2) Stressing:

Stressing shall be carried out only after the concrete has attainedthe required Compressive Strength and age of concrete as specified in the drawing.

Check the Stressing equipments and hoses before stressing to ensure proper/smooth functioning.

H T Strand/Wire/Bars shall be completely cleaned (oil, dust & etc.) for gripping of Jacks. Stressing can be carried out stage by stage if required, as per drawing.

Calculate the Elongation or Modified Elongation for each tendon as per the physical values in TC.

Calculate the Jack Pressure for the Design Load including Jack & Anchorage losses.

Stressing shall be carried out only as per the specified sequence. Load shall be applied to the tendons by using calibrated hydraulic pumps and jacks and monitored through calibrated Pressure gauges.

Fix the Bearing plate to the tube unit and lock it by wedges and mark a reference point on Strand to measure elongation. Stressing can be performed in single / multi strokes depend on Jack piston length.

Fix the Hydraulic Jack (Mono/Multi) at stressing end (Single/Double) and ensure proper seating of jack with bearing plate and also connect the Jack & Pump by hydraulic hosepipes.

Apply the calculated pressure (load) gradually in incremental basis on each strand or tendon by using hydraulic Jack and Pump. Apply jack pressure at both ends simultaneously for double-end stressing.

While applying load check for required elongation & jack pressure during stressing and also note the Jack pressure & Elongation reading at every interval / stage in stressing format.

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Compute the total Jack Pressure applied and the total elongation arrived during stressing.

If elongation reached, but pressure not reached apply 5% additional elongation. If pressure reached, but elongation not reached apply 5% additional pressure.

After applying the additional pressure / elongation, if the Stressing result is within +/-5%, release the jack pressure slowly and then proceed for next stressing.

If the stressing result / value is more than +/-5% inform the Design Engineer for further instruction. Same method shall be followed for all other Strands / Tendons.

12 hours after the completion of stressing of all tendons, cut the strands leaving 25mm from the face of wedges by using angle grinder.

After cutting fill the recess pockets (Stressing pocket) in layers using approved materials.

3) Grouting:

After the setting / curing time of recess pockets, flush the tendons (sheathing) completely by water and then by compressed air.

Potable water and OPC Cement should be used for preparation of grout. Suitable admixture (Non-Aluminium / Non-Chloride based) may be added to the grout as per specification.

Fix the valves at all grout and air vents and also fix the pressure gauge.

Mix Water followed by Cement of ratio 0.40 in the grouting machine.

The grout shall be mixed in mixture for 2-3 minutes and until pumping of grout.

Grout should be colloidal mixture and free from any lumps and it should passed through sieve.

Pump the grout into the tendon through grout vent pipe (inlet) and release the air inside the tendon through air vents.

Plug all air vent pipes and also the outlet vent pipe after consistent grout is passed.

After plugging all the vents pipes tightly, built the pressure of 5kg/cm 2

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and maintain for one minute. Then close the inlet valve also. The same method shall be followed for all other tendons.

Grouting should be performed continuously to avoid grout setting. Any breakage occurred during grouting, flush the tendon with water and compressed air and do fresh grouting.

Clean the vicinity by water after the grouting is completed.

Cut all vent pipes projecting outside the surface after the grout is set.

PRESTRESSING EQUIPMENTS

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GROUTING MACHINE

TENDONS LAID IN FLAT SLAB PROFILED TENDONS IN BEAM (MULTI 19T15 SYSTEM)

TENDON PROFILING:

198 199

CASE STUDY

Problem:

Breaking of concrete near anchorage area.

Probable reason:

Poor quality of concrete

Improper vibration of concrete near anchorage zone

Poor workmanship

Dead end slippage

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Strand snap

Actual reason:

Honey comb near anchorage area

Improper vibration.

Correct alignments of anchorage

Remedial action:

De-stress the tendon

Chip the crack area and remove the loose concrete.

Remove the broken anchorage

Fix the new anchorage and connect the duct.

Fill the area with epoxy or approved material

After getting the strength stress the tendon.

Note:

All this remedial works carried out the consultation with

Designer.

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Photos

202 203

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IntroductionLarsen & Toubro , Health, Safety & Environment Department had been certified ISO 9001:2000. We are the first company in India to have such accreditation. The company’s management gives utmost importance to safety in the company’s function. The Safety Engineering Department has bagged many commendations from various clients.

GOALS

Maintaining a safe and healthy working environment.

Preventing fatalities and lost time injuries.

Preventing damage to the equipment, facilities and potential effects on progress.

Eliminating risk to the environment.

No fires.A Safe and Productive Project, in Scheduled time.

Safety Rule and Procedure.

Rules:

Head Protection:-

All personals engaged for this job shall wear Safety Helmet of Class ‘B’ type.

Hand Protection:-

Appropriate Hand Gloves will be used for Materials handling , Concreting, Welding , Grinding , Gas cutting , Chemical Handling & Electrical work.

Eye Protection:-

Suitable goggles must be ensured for the personnel deployed for Welding (Face Shield), Grinding, Gas cutting, Concreting, Chipping etc. Staff should wear safety spectacle.

Ear Protection:-

The personnel engaged in the noise zone such as Compressor Operator. Pneumatic Vibrators & Breakers, DG Operator etc. will be equipped with suitable ear protection.

Environment, Health and Safety

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Protection from Dust & other poisonous gases:-

Suitable nose mask, face shield / cloth are to be used by the individuals to protect them from dust, fumes, poisonous and toxic gases.

Body Protection:-

Appropriate body protection like Boiler Suit, Aprons must be used by the concern personnel at site.

Fall Protection:-

All personnel working at heights must use the safety belt.

Foot Protection:-

Safety Shoe ought to be worn by all who enters the site.

Housekeeping:

1. This is to be maintained by the individual at his work area.

2. Papers, cotton waste or any other rubbish should be thrown in the dustbin.

3. Every gang should keep their materials stacked properly.

4. Do not keep materials obstructing the path.

Electrical:

1. Only electricians are allowed to give electrical connections.

2. Electrical cables are to be kept minimum 7’ high or buried in the ground.

3. Bare electric wire insertion in socket is prohibited.

Plant & Machinery:

a. Only qualified operators are allowed to operate winches, cranes, trailors & any vehicles. They should have license as per local government rules.

b. Cranes & equipments shall be used after inspected & approved by the Safety engg. Dept.

204 205

Others:

It is preferable to have one entrance to enter the chimney. One security ¾guard shall be posted to prohibit anyone entering without helmet and trespassers.

The entrance shall be sheltered to a length of 15m outside the chimney ¾and inside upto R. G. Hoist so that entrant will be saved from falling material.

Barricade is required around the shaft circumference at a distance of ¾10m.

Inside the chimney, at the locations where perpendicularly is checked ¾by laser beam, is to be sheltered with a small hole.

Deploy minimum number of workmen on the platform and as far as ¾possible have them scattered.

Safety posters and caution boards shall be displayed on the platform ¾and at ground level.

Intercom for communication is very much required. ¾

It is important to give a safety talk to workers by the concerned engineer ¾briefing on procedures before the slipform starts.

Aviation warning lights are necessary when the structure reaches ¾height of 50M

It is part of each employee’s job to report all unsafe act / unsafe ¾condition and accident immediately to his supervisor.

At No Smoking areas smoking is prohibited. ¾

Horseplay like practical jokes, running etc. is strictly to be avoided. ¾

Observe all working & hazard notice. ¾

All are requested to follow instructions from their immediate supervisors. ¾If instructions are not clear or are confusing, the employee has a responsibility to clarify with the supervisor and obtain clear instructions before commencement of works.

Appropriate fire extinguishers are to be kept on the platform. The ¾distance to reach a fire extinguisher should be maximum 25m.

206 207

PROCEDURE:

Safety Committee:

Safety Committee is formed at site whose function is to troubleshoot safety problems and conduct a weekly safety walk down . Not more than five to six members would be in the committee and they are mainly section in charges.

Safe Work Method.

A written Safe Work Method for a job is prepared by the Safety Personnel in consultation with the concerned engineers. The Work Method helps to foresee the risk involved in the job, take precautionary action for the risk involved and plan the materials required for the safety cause. The safe work method is methodically done as followed:

a. Approach Safety.

b. Work Method Safety.

c. Work area Safety.

d. Men Material and Machinery.

On receiving the safe work method, the line engineers brief it to their subordinate and implement them.

Safety Meeting:

Safety meeting shall be held once in a week for staff and sub- contracors’ representatives. The meeting is convened by the safety engineer and chaired by the project manager / site superintendent. Minutes of the meeting are minuted in L&T’s Safety Meeting Format. Copies are sent to GM/ DGM/ RSC, PM/ Site staff, once in a fortnight.

Screening System:

All workmen before deploying at site shall be screened by the site in charge/ engineer and safety engineer.

Orientation :

Orientation on safety is given to the new staff and workmen before they go to work place.

206 207

Training:

Training programmes conducted by the Safety engineer for staff and workmen

General Safety ¾

Safety in Welding & Gas Cutting Operation ¾

Material Handling ¾

Fire Safety ¾

Working at Heights ¾

Electrical Safety ¾

Work Permit systems ¾

Personnel Protective Equipments & Job based training programmes ¾

Safety Inspection:

Daily Safety Inspection is conducted by safety engineer. .Weekly Safety Inspection by the safety committee and the findings are minuted.

Tool Box Meeting / Safety Task Assignment (STA):

Tool box meeting is conducted everyday by gathering the workmen before starting the job. Concerned engineer talks for 5 to 10 minutes on Safety to the workmen. In Tool Box Meeting, general safety, case studies or job knowledge is imparted to the workmen.

STA is conducted whenever a new activity is taken up and the concerned engineer details the workmen the safe work method to carryout the job. This safety procedure helps to keep the safety consciousness among the workmen at constant level.

Ladder Inspection:

The ladders used in the site are numbered and inspected once in a month. The inspection is recorded in a register.

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Scaffolding:

Scaffolding is erected by an experienced scaffolders and under the supervision of a competent authority. Tag system shall be followed to indicate whether the scaffold is permitted to use or not. Red tag indicates, only scaffolders are allowed to work on it and the scaffold is not ready to use. Green tag indicates the scaffold is for use by all.

Wire ropes, Tools & Tackles inspection:

A competent person identified at the site first inspects the above materials. The said materials are coded and coloured to indicate whether they are good for use. Visual Inspection is carried out once in a month and recorded the findings.

Electrical Inspection:

Monthly Inspection is done for the total electrical installation at the site and recorded.

Equipment fitness certificate:

Any equipment arriving to the site is inspected and authorized by the P & M engineer and safety engineer on its fitness to use. Based on their recommendation the equipment is deployed / rejected / used after a minor repair. The inspection is recorded.

Fire Safety:

1. Once in three months the fire extinguishers installed in the site premises shall be maintained and recorded in a register.

2. Monthly inspection shall be conducted for the smoke detectors in the portocabin / Site Office, to ensure its working condition.

Work Permit System:

All the relevant work permit systems shall be followed as per L&T / Client’s procedure. viz,

a. Excavation Permit.

b. Electrical work Permit.

c. Confined space entry permit. Etc.

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Accident Reports, Investigation and Analysis:

All minor injuries should be brought to the notice of the Site management and recorded.

Lost Time Accidents, fatal accident, vehicle accident or damage to L&T plants, facilities or equipment should be reported to the site management. The contact phone nos. is given in Emergency Response Program. Subsequently, reports of the accident shall be given in the L&T format.

All accidents and near misses shall be investigated by the Safety engineer & Safety committee of the site and recorded.

Safety Motivations:

The company has the following reward schemes to encourage the employees to follow safety.

1. Million Safe Manhours: The jobsite which achieves One million safe manhours or more a certificate of merit is given to the jobsite signed by the President of the company.

2. Annual Safety Award: Given to the Best Safety performed jobsite in the Company as a whole.

3. Best safety workman: This is given at site level on monthly basis. The site safety committee selects the most safety conscious workman among the workforce , for the month and rewards him

HEALTH AND WELFARE

a) First Aid : First Aid Facility to be available in accordance with L&T policy requirement. It is intent of the L&T management that the project is self sufficient in terms of dealing minor first aid injuries and medical requirements. In the event of a Serious Injury or an individual requiring professional medical advice and care, are referred immediately to the local hospital.

b) Sanitary Facilities: Adequate sanitary facilities are provided for the number of personnel present at site. Administration department will maintain it in hygienic condition.

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c) Working hours: Working hours may vary due to time of year and particular peak workloads. In general work will be restricted to a ten hours day with one-hour lunch break. Working on Fridays, the normal rest day is discouraged but may be required from time to time.

Welfare facilities encompass both the site facilities and those of the company accommodation.

SAFETY IN SLIPFORM:

GENERAL:

1. Wearing safety helmet by all will be imperative.

2. Preferably one entrance will be there to enter the structure.

3. The entrance will be sheltered to a length of 5 mtrs, from outside the structure so that entrants will be saved from falling objects.

4. Barrication will be there around the structure to a distance of 10 mtrs.

5. Minimum number of workmen will be deployed on the platform and as far as possible have them scattered.

6. SMOKING IS PROHIBITED on the platform.

7. Fire extinguishers will be kept on the platform and the distance to reach a fire extinguisher will be max. of 25 mtrs.

8. Safety posters and caution boards will be displayed on the platform and at ground level.

PLATFORM:

1. The working platforms will be checked by a competent person, for its stability and reliability.

2. Platforms will have handrail and toe board.

3. The recommended size of plank is 1800 x 250 mm width x 50 mm thick - preferable variety is hardwood, for working platform and hanging scaffolds.

4. Both inside and outside hanging scaffold platforms will be covered with safety nets.

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5. Access ladders will be provided to access top platform and hanging platform.

ELECTRICAL:

1. All electrical equipment will be earthen.

2. Earth leakage circuit breaker (ELCB) will be fixed.

3. The electrical cable will be neatly traced along the platform and handrail.

REINFORCEMENT GANG:

1. Experienced and designated operator for winch operation will be deployed.

2. The access to pick the rebar from the winch bucket will be safe and easy reach.

3. Rebar will be uniformly distributed on the platform and they will be placed on sleepers such that the load is transferred to the spider beam and not to the planks.

4. The quantum of RF rods stacked will not be more than a shifts requirement.

HOUSE KEEPING:

1. Housekeeping on platform will be maintained stringently. No material will be dropped from height.

2. The shutter cleaning gang will be instructed to clear the platform at the end of the shift and the collected debris will be brought down.

3. Bit rods cut by gas cutter or electrode bits generated by welders will be collected by the respective helpers and brought down at the end of each shift.

Safety is everybody’s business. Slipform in-charge, in co-ordination with site safety engineer should conduct safety demonstration / meetings.

1. Daily pep talk.

2. Weekly safety meeting for staff, departmental, subcontractor and other workmen.

212

3. Fire extinguisher demonstration.

4. Check on all safety appliances.

PLANT & MACHINERY:

Trial run for all plant and machinery before starting slipforming. ¾

Operators for all machinery and training the operators. ¾

Sufficient spares to run the machinery on a continuous basis. ¾

Mandatory safety checks on machinery. ¾

Back up in case of breakdown. ¾

Maintenance record for machineries duly checked and counter signed ¾by the concerned staff and operator.

GENERAL SAFETY

Toe boards. ¾

Tying of safety nets. ¾

Hand rails. ¾

Fire extinguishers (DCP) at top and bottom. ¾

First aid box at top. ¾

Emergency lights. ¾

Safety signboards. ¾

Protective shed. ¾

Prevent overloading of safety nets. Periodic cleaning is necessary. ¾

Wind protection cloth. ¾

Safety belts, safety helmets, goggles and gloves to be used properly. ¾

Proper earthling. Earthing for lights (ELCB) ¾

Proper illumination at the top as well as around the slipform ¾structure.

Built in safety systems in the equipment to be tested. ¾

Lightening arrestors./ Aviation lamps wherever required. ¾

This Handbook is the property of Larsen & Toubro Limited Construction Group and must not be passed on to any unauthorized person or body for reproduction or reference without prior permission sought in writing from L&T ECC Division.

Engineering Construction & Contracts Division Mount Poonamallee Road, Manapakkam, Chennai – 600 089. Phone: 044-22526561 August 2010

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