Category: Highway Construction

Introduction: The purpose of this  methodology is intended for the finding out the crust thickness along the road.

Procedure: The procedure of finding out the crust/Pavement composition are under :

1. Decide the chainage from where the sample is to be taken on random basis
2. The first pit shall be selected by the Independent Engineer
3. Make a pit along the direction of the traffic in each stretch with regular interval of 5 km
4. Make a suitable size of pit on shoulder along the movement of the traffic with the help of JCB
5. After digging the pit measure the thickness of each component of the crust
6. Compare this thickness from the original Crust design.
7. Note down the thickness of each layer in prescribed format
8. This above procedure to be adopted along the the direction of the traffic through the project end.

Precaution :

 Road should be barricaded by the safety cone

1. Two flagmen should be deployed with red flag to direct the traffic

Slurry  is a combination or mixture of slow set bitumen emulsion , crusher dust with the addition of cement and water.
Application
It may be used to seal cracks,to provide a more even riding surface or a base for further treatment,before application, pothole and depression to be filled with proper bituminous material.

Material requirements

Aggregates:Suitable aggregate for slurry is graded crusher dust which is clean and free of any clay particles or organic materials.The crusher dust should comply with the specifications as stated in IS-383.A typical grading for suitable crusher dust is shown in the table below.Table 500-33 MORT&H

Sieve Size               % Passing

9.5                             100                                                
4.75                           90-100
2.36                           65-90
1.18                            45-70
0.600                       30-50
0.300                        18-30
0.150                         10-21
0.075                        5-15

Quantity of residual binder :Percentage by mass of aggregate should be 7.5 – 13.5

Water : Water shall be of such quality that the bitumen will not separate from the emulsion before the slurry seal is in place. The pH of the water must lie in the range 4 to 7.

Bitumen Emulsion : The emulsified bitumen shall be a Cationic rapid setting type as approved by the Engineer, conforming to the requirements as per IS: 8887.Slow setting bitumen emulsion is recommended .

Plant & Equipment Requirement :
Below is the list of plant required to mix and lay 5m3 or 700m² of slurry per day practically.

Item                                                           Number of items

Concrete mixer (0.3 m³)                                    1

Wheel barrows                                                       3

Shovels                                                                      5

Pick                                                                             1

Containers (25 litres)                                         5

Container (1 litre)                                                 1

Rubber squeegees                                                5

Hessian sheet (2m x 1.5m)                               1

Watering can                                                          1

Rope (10 mm diameter and 100m length) 1

Labour requirements

Below is the typical composition of a slurry team necessary to mix and lay 5m3 or 700m² per day.

Activity                                                            Number of workers

Loading of crusher dust                                      2

Concrete mixer operator                                     1

Pushing wheelbarrows                                       3

Loading emulsion and water                           2

Spreading with squeegees                                3

Sweeping                                                                  1

Traffic Control                                                       2

Construction

Site Preparation

Slurry should be applied during the day, only in fair weather conditions. Repairs to potholes and depression should have been done prior to resealing with slurry.The surface on which the slurry is to be applied must be thoroughly swept and free of any debris.The surface must be dampened slightly before the slurry is applied.

Mixing by hand

The mix proportions will vary depending on the source and grading of the crusher dust .Before laying the slurry , a trial mix test should be carried out in a small container.Can be adust with water The typical mix proportions are as follows:
Material                             By (Agg)% %              by mass(Overall)
Bitumen emulsion                13.5                                      10.5

Crusher dust                           100                                       77.5

Cement                                      1.5                                           1

Water                                          14                                          11

Total (dry)                              129                                       100

Remarks: % are shown with respect to crusher dust(100%) in 1st column and in 2nd column overall % has been given.

Work Sequences
The following mixing sequence is recommended to obtain a homogenous slurry mixture:
Step 1: Pre-wet the concrete mixer drum with approximately 5 litres of water
Step 2: Add the crusher dust into the concrete mixer
Step 3: Add the cement into the concrete mixer
Step 4: Mix the contents
Step 5: Pour water into the concrete mixer
Step 6: Mix again
Step 7: Pour in emulsion
Step 8: Mix contents
The emulsion must be at ambient temperature. To improve workability of the slurry, a controlled quantity of additional water should be added until the slurry has a creamy consistency . The water quantity will vary depending on the type of aggregate source its moisture content and prevailing air temperature.

Laying by hand
Slurry can be applied in a layer thickness of 4 mm-5mm.. A rope may be used to ensure straight edges and to control the cover thickness.
For instance to obtain a layer depth of 5 mm slurry, a 10mm diameter rope should be used.

After mixing, the slurry is transported in wheelbarrows to the point of application. The slurry is thenremixed on the road surface and spread with squeegees to obtain a uniform consistency and thickness.
The newly applied slurry layer is finished by dragging a wet hessian sheet over it to achieve a uniformly textured surface.If required rolling can be done with PTR depend upon condition

Traffic control

Slurry takes approximately four hours to set and dry properly under favourable weather conditions and no traffic should be allowed onto the freshly laid slurry before it has dried sufficiently. A suitable means of assessing this is to check whether the slurry can withstand the turning force of a shoe heel under a person’s weight without scuffing.

Quality control
Before construction commences the mix components should be mixed in their predetermined proportions in a small container to determine their compatibility. The resultant mix should be shaped into a patty and allowed to dry in the sun for a visual inspection.

The following tests should be carried out on site during the execution of the works:

•  Daily: Bulking test on the crusher dust to determine whether the mix proportions require adjustment.
• When the water source is changed, dilute the emulsion 50:50 with the water in a glass container to check whether the fluids are compatible.

The key variables that must be checked regularly are the grading of the crusher dust being supplied and the binder content of the final slurry mixture. To this end samples of the crusher dust and wet slurry mixture should be tested in a soils laboratory.

1.0 Purpose
This work shall consist of furnishing and installing reinforced cement concrete pipes, of the type, diameter and length as per design and details and at locations shown on the drawings .

2.0 Scope

The scope of work includes the following
Excavation
Head Wall construction
Bedding for Pipe
Laying of pipes
Jointing
Back Filling

3.0 Equipment

Backhoe loader/excavator
Formwork
Transit Mixer
Vibrator
Batching plant
Dewatering Pump, if required
Dumpers

4.0 Materials
All materials used in the construction of pipe culverts shall conform to the requirements of Section 1000 of MoRTH.
Each consignment of cement concrete pipes shall be inspected, tested before incorporation in the work and should conform to IS 458.

5.0 Responsibility
Section Incharge will be responsible for quality control of the section for the construction of Kerb. Further field engineers, surveyors, supervisors and lab technicians will assist him.

6.0 Procedure

6.1 Excavation
The foundation bed for pipe culverts & Head wall shall be excavated true to the lines and grades shown on the drawings

6.2 Head Wall

PCC of specified grade and thickness shall be laid to the specified dimension and level for leveling course below head walls as per approved drawing
The layout of the Head wall shall be made on the PCC as per approved drawing
The formwork shall be fixed to true line, levels, plumb, etc., rigid, adequately braced both horizontally and vertically. Form joints shall be as much as minimized shall be tight and shall not permit any leakage of slurry from concrete.
• Concreting of head wall shall be carried out in two stages according to site conditions.
• first stage shall be done up to bottom of hume pipe.
• second stage concreting shall be carried out. After placing and aligning all the pipes.

6.3 Bedding for Pipe

The bedding shall be sand / granular material passing 5.6mm sieve. Specified thickness of granular material bedding shall be provided below the pipes as per the approved drawing. The bed shall be compacted/rammed with adequate water.
In case of high embankments where the height of fill is more than three times the external diameter of the pipe, the embankment should be built first to an elevation above the top of the pipe equal to the external diameter of the pipe, and to width on each side of the pipe not less than five times the diameter of pipe, after then trench for pipe bedding should be excavated.

6.4 Laying of Pipes

• The arrangement for lowering the pipes in the bed shall be done carefully so as not to cause damage or undue strain to the pipes, preferably it shall be done by means of tripod, manual labour or by cranes for loading, unloading & setting the pipes.
• The gap between two rows of pipes shall be at least 450 mm or half the diameter of the pipe, whichever is maximum for new culvert and existing gap shall be maintained for widening of the existing culverts.
• The laying of NP4 pipes shall start from the outlet end & shall be completed at the inlet end to specified lines & grades as specified in the approved drawing.

6.5 Jointing

• The pipes shall be joined by flush joint. The ends of the pipes especially shaped to form self centering joint with a jointing space 13mm wide. The jointing space shall be filled with cement mortar 1:2 sufficiently dry to remain in position. The jointing shall be made with care so that the interior surface is smooth & consistent with the interior surface of the pipe. The joints shall be kept damp for at least four days till the joints are sufficiently hardened.
• The existing head walls shall be dismantled to the required level and dimension as per the approved drawing. New pipe shall be jointed with the existing pipe as shown in the approved drawing.

6.6 Pipe Encasing

Pipe encasing if any, shall be carried out as per the approved drawings .

6.7 Back Filling

Trenches shall be backfilled after the completion of jointing and encasing. The backfill soil shall be free from boulders, large roots, organic soil and any deleterious material and should be approved from the Engineer.Care should be taken while backfilling upto 300 mm above the top of the pipe , the soil should be thoroughly rammed, tamped or vibrated in layers not exceeding 150 mm, special care should be taken while consolidating the materials under the haunches of the pipe. Approved light mechanical means or tamping equipment can be used this purpose.
Filling of the trench should be carried out simultaneously on both sides of the pipe in such a manner that unequal pressures do not occur.
In case of high embankment, after filling the trench upto the top of the pipe , a loose fill of a depth equal to external diameter of the pipe shall be placed over the pipe then after further layers should be added and compacted.

7.0 Quality Control Testing and Acceptance

Quality control tests shall be done as per Sl. No 10 & 14 of Quality Control Tests and Acceptance Criteria .

8.0 Safety & Environment

While working Safety & Environment Procedure shall be followed as per approved EHS Manual.

This Method Statement provides detail of procedure adopted for the construction of backfilling behind structures and abutment.

• Scope

This work will consist of backfilling behind abutment of bridges and around structures like foundations, underpass, box culvert and other similar structures in accordance with the requirements of these specifications (MoRT&H clause no. 305.4.4) and lines & dimensions shown in the drawing or as indicated by the Engineer.

• Material

Approved material will be used as a backfill material from approved sources. Fill material shall be free from logs, stumps, roots, rubbish or any other ingredients likely to deteriorate or affect the structure.

• Responsibility

Section In charge will be responsible for quality control of the section for the backfilling work. He will liaise with Concessionaire Engineer In Charge. Further he will be assisted by field Engineers, Surveyors, Supervisors and lab technicians.

• Equipment

The following construction machineries will be deployed for backfilling work.

Dumper / trucks

Grader

Small Vibratory Roller

Water tanker

Plate Compactor

• Procedure
  • Backfilling around structures

Backfilling will be done with approved material after concrete or masonry is fully set and carried out in such a way as not to cause undue thrust on any part of the structure. All spaces between foundation, masonry or concrete and sites of excavation will be backfilled. Fill material will be spread in layers manually or by grader in layers of uniform thickness not exceeding 250mm compacted thickness over the entire width of the structure. Each layer of approved materials will be thoroughly compacted after necessary watering by means of small vibratory rollers/plate compactor or thoroughly rammed in small areas where mechanical means cannot be deployed. Successive layers will not be placed until the layers under construction have been thoroughly compacted to the specified requirement of table 300-2, i: e; 95% and 97% of MDD at OMC for embankment and sub grade respectively.

• Backfilling Behind abutment and Wing wall

Filling behind abutments and wing walls for all structures without weep-hole, will be done with approved filling material. The fill material will be deposited in loose thickness and compacted after necessary watering up to a thickness of 250mm, until the required compaction of 95% & 97% of MDD at OMC achieved, for embankment & sub grade respectively. Filling will be carried out in equal layers on each side of the structures to avoid displacement and unequal pressure.

Where provision of any filter media is specified behind abutment (where weep-hole exists), filter media as designed will be laid and compacted after necessary watering up to a compacted thickness of 250mm until 95% & 97% of MDD at OMC achieved, for embankment & sub grade respectively. The material used for filter media will conform to the requirement for filter medium spelt out in clause 2504.2 / 309.3.2.

If impracticable to use conventional rollers, the compaction will be carried out by mechanical means like small vibratory roller/plate compactor. Care will be taken to see that, the compaction Equipment does not hit or come too close to any structural member, so as to cause any damage to them or excessive pressure against the structure.

• Quality Control and Testing

Quality control tests shall be done as per Sl. no. 1 of Quality Control Tests and Acceptance Criteria

• Safety & Environment

While working Safety & Environment Procedure shall be followed as per approved EHS Manual.

Transportation, unloading and erection of the precast prestressed concrete girders shall be done under the direction of  experienced  engineer  he should be present for all stages of girder loading, unloading and erection. We have divided all these process into 7 sections

1.OBJECTIVE:

This methodology describes a detailed procedure for the erection of PSC Girders. Minor changes to the methodology would be adopted to suit the site conditions.

2.SCOPE OF WORK:

The scope of this methodology covers Lifting, Transportation and Erection of PSC Girders for all Flyovers & Bridges.

3.RESPONSIBILITY:

The responsibilities of the entire operation shall be assigned to a Senior Officer of the company who shall take care as an In-charge regarding all

4.MANPOWER: 

1. A) Personnel to be deployed for smooth conducting work
2. Section In charge-01 No’s
3. Site Engineer/Site Supervisor-01 No’s
4. Fore Man-01 No’s
5. Segment man-02 No’s
6. Rigman-04 No’s
7. Kalasi-06 No’s
8. Crane Operator-2 No’s
9. Hydra Operator-2 No’s
10. B) Personnel to be deployed for safety during work 

1. Officer Safety-01 No’s
2. Supervisor Safety-01 No’s
3. Marshal Man -02 No’s

5. MACHINERIES :

1.  Modular Trailers with capacity of 60 MT (2 Nos.).
2. Tyre mounted 180 MT crane with Telescopic or Lattice Boom (2 Nos.)
3. Tyre mounted mobile 80 MT service crane (1 Nos.)
4. Pilot van (1 No.)

6.0 CONSTRUCTION METHODOLOGY

6.1     PREPARATION OF SITE AT ERECTION POINT:-

Following points to be ensured:-

1. The site of erection and the approach to be leveled, dressed and rolled (if required) so that the machineries viz; cranes and trailers move and can be placed on s firm ground in correct position.
2. Overhead obstruction (if any) to be removed.
3. Adequate Area lighting to be provided for work at night.
4. Proper and safe access to be arranged for supervisory staff to climb up to the top of Pier Cap to check correct alignment/ level of girder when erected.
5. All lifting tackles viz; Slings, D- Shackle, U clamp ropes and temporary packing viz. wooden block etc. to be checked regarding the Quality/ Soundness and kept near site.

6.2     LOADING OF GIRDER AT CASTING YARD:-

Following points to be ensured:-

1. The girders are to be loaded at the casting yard either by the help of Mobile Cranes.
2. The site where the girders are to be loaded on to the trailer to be dressed leveled and rolled (if required) for smooth and safe movement of trailers and cranes.
3. After girder is loaded on to the trailers, the same is to be securely tied at two ends (near support) so that the same doesn’t tilt during transportation.
4. Girders to be loaded for erection are to be identified and checked carefully regarding length etc. so that there is no mistake regarding the sequence to erection.
5. The engineer shall check the identification mark, length and finishing of girders before loading on to trailers.
6. Lifting tackles viz; slings etc. to be checked and sleepers/ packing are to be kept in correct position before placing the girders on to the trailer.

6.3     ERECTION OF GIRDER:-

1. Before starting erection work the positions of trailer and the cranes are to be ascertained carefully to ensure that during lifting, swinging and placing on to the pier cap is done smoothly.
2. Before lifting the girders, the Radius and Angle of the crane booms to be checked to ascertain safe lifting capacity during erection.
3. The outriggers of the cranes must have proper supports/ packing so that during lifting, swinging and placing the girder, cranes remain stable.
4. Once the girder gets lifted from the trailer, it is to be moved out from the erection site so as to provide adequate space during erection.
5. The girders thus being erected to be placed directly on the Neoprene Bearing (which are to be fixed prior to erection in correct position and level). In-case the girder cannot be placed directly on the bearing the same is to be placed on Pier Cap on wooden sleepers and shifted to correct location by changing the position of the cranes.
6. Before removing the slings from the erected girders it is important to temporarily support the girders by the help of proper diagonal supports. When the second girder is erected in position immediate arrangement is to be made to tie two girders at the support and at the middle by proper tie member (i.e. Channels, Angles etc.).
7. The position of the cranes is to be changed for erection at each girder suitably as required.
8. Once all girders for one carriageway are lifted and placed in positions, cross diaphragm are to be cast so that temporary ties can be removed.

 7.0     SAFETY:–

Safety during lifting, loading, transportation and erection is the most important and primary consideration of the entire operation. The following points need to be checked and ensured:-

1. Capacity of cranes, trailers, lifting devices and packing (wooden blocks) to be ascertained before use.
2. The approach for the cranes and trailers both at the loading and erection point must be leveled, dressed and rolled to ensure smooth and safe movement.
3. During transportation/ movement of cranes all care to be taken to ensure smooth traffic flow on the highway.
4. A Pilot van with flag/ batten light must escort the cranes and trailers during their movement.
5. Safety officer along with traffic marshals must be available during the entire operation to ensure safety.
6. All persons engaged must use P.P.Es viz. helmets, belts, gloves, shoes, jackets etc.

The technique of precasting is eminently suited to  bridge girder for quicker construction and minimum interference to traffic below the bridge. The girder my be cast in a central plant or in a temporary yard established near the work site. Girder upto about 40 meter can be precast in a single piece transported to site by means of truck cranes.In this article we will discuss pertaining to stressing and prestressing of girder methodology.

REFERENCE DOCUMENTS/CODES/DRAWINGS

1.MORT&H 5th Revision
2. IS: 14268 Stress Relieved Low Relaxation 7 Ply Strands for Prestressed Concrete.
3. IS: 210 Grey Iron Casting – specification
4. BS: 970 Specifications for Wrought Steels for Mechanical & Allied Engineering Purposes.
5. IRC: 18-2000 Design Criteria of Prestressed Concrete Road Bridges (Post-tensioned Concrete)
6. Relevant Prestressing Drawings (Latest Revisions)
7. Specifications Related to Prestressing Work

PRESTRESSING MATERIALS

• High Tensile Strands
Following are the properties of 12.7 mm Ø Low Relaxation High Tensile Strands. Oiled strand shall be used –

Nominal Area of Strand – 98.7 mm 2
Minimum Breaking Strength – 183.7 KN
Nominal Weight of Strand – 0.775 kg/mtr.

• SHEATHING PIPES

We are giving typical sheathing pipe , use pipe as per your project specification
84 mm ID & 98 mm OD & 2 mm thick HDPE sheathing pipes for 19 DP13
75 mm ID & 90 mm OD & 2 mm thick HDPE sheathing pipes for 12 DP13
51 mm ID & 64 mm OD & 2 mm thick HDPE sheathing pipes for 7 DP13
Sheathing duct shall be made up of HDPE of thickness (2.3 mm ± 0.3) mm with following properties –

• Approved 19 DP 13,12 DP 13 & 7 DP 13 Live end Anchorage System(Use Project approved brand)

The precast segment will be cast in casting yard. After curing is over, the segment will be shifted to the respective position and will be assembled with the help of launching girder. The high strength epoxy will be used for gluing two segment together and it will be stressed by high tensioned bar. After final stressing, temporary stress will be released

Tube Unit (Anchor Cone)

The basic raw material for manufacture of tube unit is gray cast iron. It allows the transfer of prestressing force from the bearing plate to the concrete. The Tube Unit is embedded in concrete and can be easily fixed to the MS cone box by means of bolts and nuts. The design of Tube Unit allows uniform flaring of H. T. Strands while stressing and free access to the injection of grout.
Anchor Head (Bearing Plate)

The basic raw material for manufacture of bearing plate is Steel casting / forged steel. The conical holes facilitate the seating of wedges and holding the strands in stressed condition.

Wedges
The basic raw material for manufacture of wedges is alloy steel. The individual high tensile strands passing through the bearing plate is anchored by the wedges. The 3 segments of the wedges are held together around the strand by means of special wire circlips for better functioning, easy placement and storage

Prestressing and Grouting is broadly divided into following activities, viz.,

1. Layout & Profiling of the cables/sheathing.

2. Fixing of tube unit/end block.

3.Concreting

4. Cable cutting and threading.

5.Fixing of Bearing plate & Wedges.

6. Stressing.

7. Cutting and end Sealing.

7. Grouting.

1. LAYOUT & PROFILING OF SHEATHING PIPES

After completion of alignment of bottom shuttering & bottom reinforcement of girder, layout & Profiling of cables shall be carried out in following steps :

• Layout of cables is carried out as per given ordinates & related reference drawings.
• After all ordinates are plotted, tie bars of 10 mm. dia. shall be installed as per ordinates to place the sheathing pipe wherever required. Installation of sheathing pipe is carried out over the tie rods.
• Sheathing pipe shall be supported in the bottom by tie rods & shall be cross bound using double binding wire. It should be ensured that the sheathing pipes are fixed firmly in position so as to prevent displacement during concreting by weight of concrete, vibration or by floatation.
• Connect the sheathing with the help of couplers provided at the end of each pipe.
• Sealing of sheathing joints will be done using PVC tapes. It will be ensured that no joints are remaining unsealed.
• Cable profile shall be checked. Vertical ordinates shall be check from soffit of the bottom shutters. Horizontal ordinates shall be check from the face of the side shutters, which has been already checked for verticality or as in drawing.

2. FIXING OF TUBE UNIT

• Fixing of tube unit shall be carried out after installation of end shuttering plate.
• Fix tube unit to End plate with the help of 4 nos. of bolts.
• Bursting reinforcement shall be fixed according to the drawing.
• Connecting the tube unit to sheathing pipe.
• Joint shall be sealed with the help of PVC tape.
• The face of the tube unit shall be truly perpendicular to the axis of the cable and about 1.5 m of cable before trumpet should be in straight alignment.
• After the fixing of tube unit and cable layout, insert the HDPE pipes Or HTS Strand inside all ducts to avoid the damage of sheathing pipe & ingress of cement slurry inside the duct at the time of concreting.

3. CONCRETING

• Although concreting is not a part of stressing but it has very important role in successful completion of stressing of structure.
• It shall be noted that the needle vibrator is not placed directly on sheathing pipe, which may damage the sheathing pipe.
• HDPE pipe Or HTS Strands in all the cables should be moved in both directions during the period of concreting.
• More attention should be given while concreting in the end block portion. Adequate compaction of concrete to be ensured to avoid any kind honeycombing.

4. CABLE CUTTING & THREADING

After completion of concreting & removing end block shuttering, cable threading shall be done.
• H. T. Strands shall be threaded manually.
• For cutting strands, a portable grinding wheel shall be used.
• H. T. Strands shall be cut as given in drawings, considering site conditions & gripping length of jack.

5. FIXING OF BEARING PLATES & WEDGES

• Fixing of bearings plates & wedges is done before stressing. It is ensured that the tapered holes in bearing plates & wedges are free of rust.
• Insert the strands into the tapered holes provided in the bearing plate.
• Install the wedges over the strands and push them with a pipe into the tapered holes of the bearing plate.

6. STRESSING

Prestressing of the girder is done as required by the system of prestressing and design. Following points will be observed while carrying out the stressing operation.
Only trained and experienced personnel, under the guidance of  technical Staff, should perform stressing & grouting.
• The required strength of the girder concrete as mentioned in drawings/specifications shall be ensured by cube testing before starting the stressing work.
• Stressing of cables shall be done as per the sequence mentioned in the drawings/specifications.
• The first stage stressing shall be done after the concrete achieves 35 Mpa strength or 10 days after casting, whichever is earlier. In the first stage two cables shall be stressed viz. cable no. 1 & cable no.2  or as shown in the drawing.
• In the second stage stressing balance two cables i.e. cable no. 3 & cable no. 4 shall be stressed after the concrete achieves 45 Mpa strength (28 Days strength ) or 21 days after the casting, whichever is later
• Elongation mentioned in the drawings must be modified for actual value of modulus of elasticity ‘E’ and the area of c/s of strands ‘A’ of the cables as per the results unless otherwise mentioned in the drawings/specifications.
• Actual pressure shall be calculated after applying Jack efficiency factor.
• Stressing shall be done using Multi-pull jacks only.
• Stressing shall be done from both ends, care will be taken to achieve almost equal readings of elongation at both the ends in each step of increment of pressure.
• Readings will be taken preferably at incremental steps of 50 kg/cm2 up to the final pressure.
• After locking the wedges the pressure in the jack will be released very slowly to avoid transfer of prestressing force by impact.
• In every cable instantaneous slip of anchorages must be recorded. It will be within limits prescribed by the designer or by the prestressing agency.
• The pressure applied and elongation achieved will match within the prescribed limits. Normally, the limit is 5% of pressure and elongations.
• No person will be allowed to stand behind the anchorages in any circumstances during the process of tensioning.

6.1 THE FOLLOWING STEPS SHOULD BE PREFERRED FOR JACK MOUNTING 

• Fix the bearing plates at both the ends of the tensions.
• Insert the bearing collar & fix it on tube unit with the help of screws.
• Insert the lock-off plate as per the orientation the bearing plate.
• A rigid runaway beam (ISMC/ISMB) structure shall be made at the end of the bridge girder from where the Jack is to be suspended by means of a chain pulley block. The arrangement will give full flexibility of movement of Jack both transversely and longitudinally.
• Push the Jack over the strands. The axis of the Jack must coincide with the tendon axis. Insert the strand in to the Jack.
• Apply “wax” inside the holes of pulling plate as well as outside of master grip.
• Install the 3-piece wedge (master grip) over the strand into the pulling plate inside the rear of the Jack. Push the grips with a piece of hollow hammering pipe to seat tightly inside the pulling plate holes.
• Ensure all connection of Jack with pump is correct and flexibility of hose pipe for movement of the Jack at the time of stressing.
• It is important that the supporting chain or hook shall be slackened off as soon as the Jack starts to carry load, but they must be ready to support the Jack again when the pressure is released.
• Locking pressure should be maintained approximately 70-80 % of the stressing pressure.

7.0 CUTTING AND END SEALING

Cutting should be carried out after checking the 24 hrs. slip loss. Strand should be cut approximately 40 mm. from the face of bearing plate. End sealing should be done with the help of GROUT CAP or Epoxy & cement  Mortar (Mounting the ends) .

7.1 GROUT CAP :

 The advantages of using Dynamic Grout Cap are used for speedy grouting and saving of sealing material i.e. cement mortar.

 7.2 FIXING OF GROUT CAP

• The stressed strands are cut to the required length i.e. 40 mm. from the face of bearing plate.
• On the inner surface of cap, grease should be applied.
• ‘O’ ring should be placed in the slot provided along the periphery of the cap, which maintains the pressure and prevents the leakage of grout.
• Grout cap is fixed by 4 nos. of allen key bolts by keeping the air vent nut in top position.

8. GROUTING

Neat cement slurry should be filled in the annular spaces between sheathing duct & high tensile (H.T.) steel/strands.

8.1 OBJECTIVES OF GROUTING :

1.To protect the steel against corrosion.

2.Effective bond between the Prestressing steel and concrete.

8.2 MATERIALS FOR GROUTING :

(A) CEMENT:

Ordinary Portland cement should be used for the preparation of the grout. I. The cement shall have no false setting phenomenon and shall be at a temperature less than 40 °C at the time of production of grout. The cement should be free from chemical impurities like chloride and sulphate, which leads to corrosion of steel.

(B) WATER:

Clean potable water, free from impurities shall be used. Sea or Creek water shall be strictly avoided.

(C) ADMIXTURE :

While designing grout mix , we are using Sika (Intraplast N 200) 0.4 % by weight of cement). to reduce shrinkage of grout.

 8.3 WATER – CEMENT RATIO

Choose Water-cement ratio as low as possible , consistent with workability. This ratio should not normally exceed 0.45. We are keeping 0.39 as per site condition.(Can select W/C ratio as per your convenient)

8.4 GROUT TEMPERATURE

Generally, the temperature of the grout must be 25 °C. It is likely to change depending upon the site conditions. When the ambient temperature during the day is likely to exceed 40 °C, grouting shall be done in the early morning or late evening hours.

 8.5  TESTS ON GROUT MIX

The characteristics of the grout are determined on the grout itself or on samples made from the grout in accordance with the following.

• Fluidity
• Bleeding
• Volume Change

8.6 GROUTING PROCESS

 Following points will be observed while doing the grouting.

• Grouting of cables shall be done as early as possible, after completion of stressing.
• All cables that are to be grouted shall be cleaned thoroughly with water & compressed air.
• The grout mix is prepared in the agitator by thoroughly mixing it for 1 min.
• The agitator must be placed at a height such that mortar can flow directly in top second tank placed beneath the outlet of agitator.
• Before flowing in to the second tank mortar must be passed through a 2 mm. mesh screen so as to eliminate impurities and lumps which otherwise cause choking of the pump at the time of grouting process.
• Connect the suction hose of grout pump to the second drum.
• Operate the pump to drain off water from the pump and hoses.
• Allow discharge of a small quantity of grout from delivery hoses to check the correct functioning of pump.
• Connect the delivery hoses to the tube unit’s grout inlet opening and begin grouting.
• Ensure that there is always enough grout in tank so that air is not sucked in to the pump.
• When the grout flows out of the dead end tube unit’s grout opening, open the air vent nut of the grout caps of both the ends.
• Block the outlet of the other end after being assured that the air has been completely bleeded and the duct is filled with grout.
• Close the air vent nut and operate the pump until the desired pressure is achieved.
• After the design pressure is achieved, stop the pump and maintain the pressure of 3-5 Kg/cm² for 1 min. and close the valve of inlet connector.
• Release the pressure in hose. The pump runs idle and returns grout to the tank.
• Clean the grout pump & agitator with clean water to z avoid clogging.

  8.7 END PROTECTION OF ANCHORAGES

 Tendons shall be protected against corrosion by a plug at each end  to prevent passage of air. After grouting is over the anchorages will be  protected for corrosion as under –

1. Clean the exposed anchorage parts for rust and dirt with wire brush manually.
2. Clean the surface with cotton waste & apply a coat tar epoxy (solvent free araldite)

9   SAFETY PRECAUTIONS

 9.1  Safety Precautions While Concreting

Although concreting is not a part of prestressing, it plays a vital role in successful stressing of structure. Following points should be considered while concreting

• Main contractor should ensure that vibration is to be supervised. It should be noted that needle is not directly placed on sheathing pipe, which may damage the duct & thereby blocking the path of strands.
• The portion of the end block of the girder should be properly concreted. Weak concrete leads to puncture of tube unit & hence stressing should be done only if concrete is capable of taking the load.
• It should be ensured that the bursting reinforcement in the end block zone is adequately & properly installed.

9.2  Safety Precautions While Stressing

Very large forces are introduced into the tendons during stressing and the equipment is under high hydraulic pressure. Hence, careful working can avoid accidents.

• Only trained and experienced personnel, under the guidance of Dynamic technical Staff, should perform stressing.
• The equipment, especially the high pressure hoses and the adaptors must be in perfect condition. Damaged hoses must be replaced immediately.
• Jack should never be handled by hoses.
• Stressing should be done according to specified data. The allowed maximum pressure should never be exceeded.
• During stressing, nobody should be allowed behind or underneath the jack, since failure of a strand can cause fatal accidents.
• For stressing close to traffic areas, the jack must be secured by ropes or chain hoist.
• All bars, wires and strands should be stored carefully. Ensure that they are not damaged in any way and should be checked for rust and corrosion before they are used.
• Care should be taken while handling coils of high tensile steel strand as they may ‘whip back’ with force, if not securely bound.
• Hogging of the girder during stressing operation should be observed & recorded.

9.3  Safety Precautions While Grouting

• Protective glasses must be worn during grouting operation.
• Do not start the pump while valves are closed, it may cause damage to the pressure gauge.
• Place the grout tank preferably at the same level of grout pump.
• In case of a longer stoppage (more than 5 min), ensure that the grout does not get set in the pump, if necessary empty the grout and flush the pump with water.