7 4 ok CW2C PRESTRESSED GIRDER

ASTM A722M-07 Uncoated High Strength Bars for Pre-stressingConcrete EURONORM prEN Tendons 15.7mm for Pre-stressed Concrete High tensile steel strand with low-relaxation shall be weld fre

CMDRCP / CW2C PACKAGE CW2C KM 18+200 – KM 23+450

CONSTRUCTION METHOD STATEMENT

FOR PRODUCTION OF PRESTRESSED GIRDERS

CMDRCP / CW2C PACKAGE CW2C KM 18+200 – KM 23+450

TABLE OF CONTENTS

I PRESTRESSED CONCRETE

II CONSTRUCTION METHOD FOR SUPER TEE GIRDERS

III CONSTRUCTION METHOD FOR VOIDED SLAB GIRDERS

for Girders, Section 2.5.2.6.2

ASTM A421-91 Un-coated Stress Relieved Steel Wire for Pre-stressed Concrete;

ASTM A416-99 Steel Strand, Un-coated Seven Wire Stress

Relieved Strand for Pre-stressed Concrete

ASTM A722M-07 Uncoated High Strength Bars for Pre-stressingConcrete EURONORM prEN Tendons (15.7mm) for Pre-stressed Concrete

High tensile steel strand with low-relaxation shall be weld free and stressrelieved after stranding and shall conform to the requirements of ASTM A416-

99 or equivalent Steel Strand, Un-coated Seven Wire Stress Relieved Strand forPre-stressed Concrete

High strength steel bars shall confirm to the requirements of ASTM A722M orequivalent for Uncoated High Strength Bars for Pre-stressing Concrete

Testing of pre-stressing reinforcement shall be in accordance with therequirements of the ASTM Specifications for the type of system intended to beused or subject to approval by the Engineer

b)ANCHORAGES FOR POST TENSIONING

All anchorage assemblies shall be subject to the approval of the Engineer

All post-tensioned pre-stressing steel shall be secured at the ends by means ofapproved permanent type anchoring devices The Contractor shall submitinformation and details, including test certifications for by the Engineer

CMDRCP / CW2C PACKAGE CW2C KM 18+200 – KM 23+450

End anchorage devices (stress and dead anchors) shall be designed andmanufactured for the types of tendons to be used They shall have a previousservice record of performance and durability when used on similar type work.All anchorage devices for post-tensioning shall be capable of holding the pre-stressing steel at a load producing a stress of not less than 95 percent of theguaranteed minimum tensile strength of the pre-stressing steel

Fixed anchorages for tendons in pre-cast beams shall be of steel bearing platetype while all remaining anchorages shall be those capable of adjustment bymeans of a threaded anchor head and ring nut

It shall be the responsibility of the Contractor to confirm the required burstingreinforcements in the local zone for the particular shape and design of theanchorage devices proposed

All externally exposed steel parts shall be protected from corrosion All threadedparts and fittings shall be protected by greased wrappings or plugs until used.Anchorages shall be kept free from dirt, mortar, loose rust or other deleteriousmaterials Damaged anchorage parts shall not be used

c)DUCTS (SHEATH)

Ducting for internal tendons shall be fully compatible with the proposedpre-stressing system The ducts shall be fabricated from corrugated galvanizedsheet steel or corrugated thick-walled HDPE conduit

Minimum duct thickness shall be as

d)GROUT FOR DUCTS

Unless otherwise specified in other prevailing sections or subject toapproval by the Engineer as a result of grouting trials, the grout shall:

 Consist only of ordinary Portland cement, water andexpansive admixtures approved by the Engineer and used

in accordance with the manufacturer’s instructions;

 Have a water to cement ratio as low as possible consistentwith the necessary workability, and under no circumstancesshall the water/cement ratio exceed 0.40;

 not contain admixtures containing chlorides, nitrates orsimilar electrolytic conducting materials

Premixed grouting material shall be

used

e)CONCRETE

CMDRCP / CW2C PACKAGE CW2C KM 18+200 – KM 23+450

Concrete shall be of the class indicated on the drawings and shall conform tothe requirements of Specification - Concrete and Concrete Structures and therequirements specified below unless otherwise stated on the drawings or asmay be required by the Engineer

The maximum size of aggregate for use in the manufacture of pre-stressedconcrete shall be 25 millimetres

The main properties of concrete such as compressive strength after 28 days,Modulus of Elasticity (Young Modulus), and other properties that were used forthe detailed design shall be confirmed by testing of samples of the approvedmix design The Contractor shall perform the tests in accordance with theappropriate standards, or as may be required by the Engineer

2 CONSTRUCTION REQUIREMENTS

The Contractor shall assign an experienced technician, skilled in the use ofpre-stressing system, who shall supervise the work being performed incompliance with these specifications and to the satisfaction of the Engineer.The Contractor shall provide all equipment necessary for construction and pre-stressing The equipment shall be of a currently manufactured model, andshall be in good working condition A pre-stressing system approved by theEngineer shall be used If hydraulic jacks are used they shall be equipped withaccurate pressure gauges The combination of jack and gauge shall becalibrated and a graph or table showing the calibration shall be provided to theEngineer Should other types of jacks be used, calibrated proving rings or otherdevices shall be furnished so that the jacking forces may be accurately known.The requirements for concrete construction in Specification - Concrete andConcrete Structures shall be complied with, except as may be modified in thisspecification Pre-stressed concrete shall be formed, stressed, placed, cured,and protected at shops, manufacturing plants, and locations where thefabrication of such members may be properly inspected and controlled andapproved by the Engineer

Vertical alignment and girder lengths shown on the drawings representdimensions at the time of final creep Deflection criteria for girders shall be inaccordance with 22 TCN 272-05, longitudinal deflections may be rectified by anappropriate approved method

1.1. PLACING STEEL

All steel reinforcement shall be accurately placed in the position shown on thedrawings and rigidly held in place during placing and setting of the concrete.Distance from the forms shall be maintained by stays, formwork spacers, ties,hangers, or other approved support Formwork spacers for holding units fromcontact with the forms shall be of approved material, shape and dimensions.Layers of reinforcement shall be separated by suitable wire spacers Woodenblocks shall not be used

1.2. PRETENSIONING METHOD

The pre-stressing elements shall be accurately held in position and stressed

by jacks Stressing shall be applied to produce the stresses required in thewires, strands or bars immediately after the anchorage as shown on thedrawings or as directed by the Engineer Suitable allowances shall be made forfriction in the jacks and for slip and yield in the grips or anchorages

Curing shall be by steam methods, or other methods subject to the approval ofthe Engineer

CMDRCP / CW2C PACKAGE CW2C KM 18+200 – KM 23+450

A record shall be kept of the jacking forces and the elongations produced andthe minimum age in hours of the concrete for each unit until the time thetendons were released

No bond stress shall be transferred to the concrete, nor shall end anchors bereleased, until the concrete has attainted a compressive strength of not lessthan 85% of the specified 28-day strength as shown by standard specimenscured in a similar fashion to the element The elements shall be cut orreleased in such an order that eccentricity of pre-stress is minimized subject

to the approval of the Engineer

1.3. POST-TENSIONING METHOD

Post-tensioning shall be carried out in accordance with an approvedmethod, with an approved control method, and in the presence of theEngineer unless permission has been obtained to the contrary

Immediately before tensioning, the Contractor shall prove that all tendons arefree to move in the ducts

Each anchorage device shall be set square to the line of action of thecorresponding post-tensioning tendon and shall be securely fixed in positionand gradient to prevent movement during the placing and compaction ofconcrete

Except where dead-end anchorages are cast in the concrete, tendons shall not

be installed until just prior to stressing Tendons shall be pulled or pushedthrough the duct in such a manner as to avoid damage to either the tendon orthe duct

Unless approved otherwise, concrete shall not be stressed until 2 test cylinderstaken from it have attained a compressive strength of not less than 80% of thespecified 28-day strength as shown by standard specimens cured in a similarfashion to the element unless specifically noted otherwise on the drawings.The test cylinders shall be cured in conditions similar to the concrete to whichthey relate in a manner approved by the Engineer

Where members consist of jointed elements, the strength of transfer of thejointing material shall be at least equivalent to the specified strength of themembers

The Contractor shall establish the datum point for measuring extension andjack pressure to the satisfaction of the Engineer Allowance shall be made forthe friction in the jack and anchorage for pull-in of the tendon duringanchorage

The tendons shall be stressed at a gradual and steady rate until the requiredextension and tendon load are reached or are approved by the Engineer Thesequence of stressing shall be as shown on the drawings or directed by theEngineer

The force in the tendons shall be obtained from readings on a load cell orpressure gauge incorporated in the equipment and the extension of thetendons measured The extension of the tendons under the approved totalforces shall be within the limits given below of the agreed calculatedextension

Transverse Tendons for Segments: ±10% average for onetendon

± 7% for average of onesegment

CMDRCP / CW2C PACKAGE CW2C KM 18+200 – KM 23+450

Longitudinal Tendons for Segments ± 5%

If the measured extensions are not within the specified tolerance then theContractor shall submit to the Engineer his method of rectifying thediscrepancy

When the pre-stressing force has been applied to the satisfaction of theEngineer, the tendons shall be anchored The force exerted by the tensioningapparatus shall then be decreased gradually and steadily so as to avoid shock

to the tendon or anchorage

Full records shall be kept of all tensioning operations including measuredextensions, pressure gauge or load cell readings and draw-in at anchorage.Copies of records shall be supplied to the Engineer within 24 hours of eachtensioning operation

A check shall be made of pre-camber and if significantly different to thecalculated value, the Contractor must investigate before construction of furthergirders

Unless otherwise agreed by the Engineer, tendons shall not be cut less than 2days after stressing

1.4. GROUTING

a. PLANT FOR GROUTING

The grout mixer shall produce a grout of colloidal consistency The grout injectorshall be capable of continuous operation with a sensibly constant pressure up

to 0.70-N/mm2 and shall include a system of circulating or agitating the groutwhilst actual grouting is not in progress All baffles to the pump shall be fittedwith 1.18 mm sieve strainers

The equipment shall be capable of maintaining pressure on completely groutedducts and shall be fitted with a nozzle that can be locked off without loss ofpressure in the duct

The pressure gauges shall be calibrated before they are first used in the Works,and thereafter as required by the Engineer All equipment shall be thoroughlycleaned and washed with clean water at least once every 3 hours during thegrouting operations and at the end of use for each day

During the grouting operation, the Contractor shall provide adequate out plant to facilitate complete removal of the grout in the event of abreakdown of the grouting equipment or other disruption before the groutingoperation has been completed

flushing-b. GROUTING OF DUCTS AND SHEATHING

Grouting trials shall be undertaken when directed by the Engineer Prior to usingthe grout in any trial or in the works the Contractor shall submit a detailedmethod statement for grouting procedures covering proposed materials,sheathing, anchorage and vent alignment equipment, and quality control tothe Engineer for his approval

All ducts shall be thoroughly cleaned out by means of flushing with waterand/or water/compressed air

Grouting of ducts shall be carried out as soon as it is technically practicable, butnot more than 4 weeks after the tendons inside the ducts have beenstressed, and the Engineer’s permission to commence grouting has been

CMDRCP / CW2C PACKAGE CW2C KM 18+200 – KM 23+450

obtained If due to the requirements of the stressing procedure, tendonscannot be grouted within 4 weeks the sheathing shall be sealed to protect thetendons from corrosion

Injection shall be continuous and slow enough to avoid producing segregation ofthe grout The method of injecting grout shall ensure complete filling of theducts and complete surrounding of the steel Grout shall be allowed to flowfrom the free end of the duct until its consistency is equivalent to that of thegrout injected The opening shall then be firmly closed Any air vents shall beclosed in a similar manner one after the other in the direction of flow Theinjection tubes shall then be sealed off under pressure until the grout has set.The filled ducts shall not be subjected to shock or vibration within 1 day ofgrouting Not less than 2 days after grouting the level of grout in the injectionand vent tubes shall be inspected and made good as necessary

The Contractor shall keep full records of grouting including the date when eachduct was grouted, the proportion of the grout and any admixtures used, thepressure, details of any interruptions and topping up required Copies of theserecords shall be supplied to the Engineer within 3 days of completing grouting

c. PROTECTION OF PRESTRESSING ANCHORAGES

As soon as possible after tensioning and grouting are completed, exposed endanchorages, strands and other metal accessories shall be cleaned of rust,misplaced mortar, grout and other such materials

Immediately following the cleaning operation the entire surface of theanchorage recess and all exposed metal shall be thoroughly dried anduniformly coated with an epoxy bonding agent conforming to AASHTO M235Class III in accordance with the manufacturer’s recommendations

The anchorage recess shall then be filled with an approved non-shrinkagemortar The mortar shall not contain aluminium powder, iron particles, chlorides,sulphates, fluorides or nitrates

Where the protection will form part of the exposed works, the anchoragerecess shall be filled with concrete of the same quality and colour as that of theadjacent concrete and shall be applied and cured in accordance with thesespecifications or as may be required by the Engineer

Exposed surfaces of anchorages not in an anchorage recess shall be coatedfor corrosion protection with a coal tar epoxy or equivalent as approved by theEngineer Prior to coating, all surfaces shall be wire brushed to remove all looserust, mill scale or other deleterious substances, and the surfaces cleaned with asuitable solvent to remove oil and grease

3 CURING

Except as specified herein or otherwise approved, wet (water) curing shall beprovided in compliance with the requirements in Specification - Concrete andConcrete Structures If the Contractor elects to cure by any other method, themethod and details shall be subject to the approval of the Engineer

STEAM CURING

A steam curing process complying with the following conditions may beused as an alternative of water curing, if proposed by the Contractor andsubsequently approved by the Engineer

a) The casting bed for any unit cured with steam shall becompletely enclosed to prevent steam from escaping andexclude the outside atmosphere

CMDRCP / CW2C PACKAGE CW2C KM 18+200 – KM 23+450

b) Two to four hours after placing concrete and after theconcrete has undergone initial set, the first application ofsteam shall be made If retarding admixtures have beenused, the duration before application of the steam shall beincreased to four to six hours

c) Water curing methods shall be used from the time theconcrete is placed until steam is first applied

d) The steam shall have a relative humidity of 100% to preventloss of moisture and to provide moisture for proper hydration

of the cement

e) Steam shall not be directly applied to the concrete Duringthe application of the steam, the ambient air temperatureshall increase at a rate not exceeding 22°C per hour until themaximum temperature is reached and shall be held untilthe concrete has reached the desired strength

f) In discontinuing the steam application, the ambient airtemperature shall not decrease at a rate exceeding 22°C perhour until the temperature has reached 10°C above thetemperature of the air to which the concrete will be exposed.g) The maximum curing temperature shall be from 60° to 67°C

4 HANDLING, TRANSPORT AND STORAGE

Pre-cast pre-stressed concrete shall not be moved from the casting position, ortransported, until the concrete has attained a compressive strength of 90%

of the specified 28-day strength

Extreme care shall be exercised in handling and moving concrete

members

Pre-cast girders and slabs shall be transported in an upright position, shock shall

be avoided and the points of support and directions of the reactions with respect

to the members shall be approximately the same during transport and storage

as when the members is in its final position If the Contractor deems itexpedient to transport or store pre-cast pre-stressed units in other positionsthan this, it shall be done at his own risk after notifying the Engineer of hisintention to do so Any unit considered by the Engineer to have becomesubstandard shall be rejected and replaced by an acceptable unit at theContractor’s expense

5 MARKING OF PRECAST PRESTRESSED MEMBERS

Each pre-cast pre-stressed member shall be uniquely and permanently marked

so as to show its type and date of casting

6 ERECTION OF PRE-CAST BEAMS

CONFIRMATION OF POSITION

Prior to the erection of the beams the Contractor shall survey the positions of thesupporting columns and confirm with the Engineer on the positions, bothhorizontal and vertical, of the supports

The Contractor shall, at his own expense, make all necessary adjustments tothe bearing seating and beam length to ensure that completed decks are true toline and level

Any proposed deviation of beam length from that given in the drawings shall beagreed by the Engineer before the beam is cast

CMDRCP / CW2C PACKAGE CW2C KM 18+200 – KM 23+450 ERECTION

The method statement shall be submitted to the Engineer for his approvalwithin one month of the commencement date

The statement shall particularly include but not be limited to the use of liftingand transfer gantries supported on the new structure and particular locations.The statement shall include full details of the equipment to be used to handlebeams and to incorporate them into the structure The method statement shall

be accompanied by full structural calculations and appropriate workshopdrawings for each stage of the procedure The calculations shall be appropriatefor such temporary works and shall take into full consideration all temporaryloading cases arising from the procedures, the prevailing conditions at the site,

in particular likely wind loading, and the nature of the existing ground TheContractor shall carry out all additional soils investigation necessary to confirmhis assumptions concerning the nature of the existing ground The calculationsand drawings shall be certified and stamped by a qualified structural engineerexperienced in the preparation of such details

The details shall include consideration of the effect of each stage of theprocedure on the completed permanent works on which the gantry is to bemounted and operated The procedures for lifting and transferring the beamsinto position and the order of erection of the beams shall be such that theeccentricity of loading on the completed permanent works (supporting piersand the foundations) is minimized

When beams are being placed in position they shall be braced againstoverturning before being released by the crane or other lifting devices

Beams shall be prevented from moving laterally during the placing of in-situconcrete

The lifting and placing of beams will not be permitted to commence until suchtime as the Contractor’s method statement, calculations and shop drawingshave been reviewed and approved by the Engineer

II. Construction Method for Super Tee girders.

1 Number of Tensioning pedestals and formwork

SUPER-TEE beams are the pre-stressed concrete beams The prestressing strandwill stressed released on the tensioning pedestals When the concrete beam hasreached 85% required strength to conduct cutting prestressing strand so as toproduce stress in the prestressing strands and concrete of beams

External and inner formworks and shuttering of steel hangers, steel beams andinner formwork shall be fabricated in two sets for each

2 Design of tensioning pedestals and formworks

2.1 Pre-stressed tensioning pedestals

Structure of tensioning pedestals to ensure convenience for placing reinforcingsteel and pre-stressing steel to ensure adequate and convenient space for theerection and removal of formwork, concrete supply, placing concrete and liftingcasted beams then promptly transport to the storage platform

The position of the tensioning pedestal must be in high places to ensure gooddrainage, the tensioning pedestal to ensure absolutely no settlement

2.2 Formwork

Fabrication and erection of formwork shall be in the correct position.It should beeasy to erect and remove the formwork The joints must be parallel or

CMDRCP / CW2C PACKAGE CW2C KM 18+200 – KM 23+450

perpendicular to the beam axis and to be sealed tight enough not to leak mortarand cement laitance

Formwork to cast beams consists of two parts: external and inner formworks

+ After the installation of vibrator into the side formwork iscomplete, trial operation is needed to check the stiffness of theformwork, the state of elimination of the lateral force of thevibrators

+ Technical requirements of formwork:

* The firmness, durable, airtight

Pouring concrete to create even surface for casting pedestal

Segmental construction of the tensioning pedestal by "a step by step method"means concreting the bottom and side walls of each section from this end to theother end of the tensioning pedestal

At construction joints, reinforced steel shall be overlapped 30-40 d

The right in place buried details in the tensioning pedestal to link betweentensioning pedestal and jacking beam, link the pedestal with internal formworkwhile installing them on pedestals before pouring concrete to determine theexact location

After placing concrete tensioning pedestal, curing of concrete takes at least for aperiod of 7 days

3.2 External formwork

Manufactured to full designed length and size At junctions, the connecteddetails are filleted 45o and connected by butt welding, and then grinding weldssmoothly Welding process to link all details shall comply with the order ofwelding technology and avoid warping

After welding done to check the detailed dimensions and flatness of eachindividual plate, fix the error before installing the tensioning pedestal

3.3 Inner formwork

Processing of the middle and the border frames and stiffeners To avoid warping,the frame is processed in the fabricating mold Inspection of detailed dimensionsfor each frame

Link the frames together by longitudinal bracing frames Check the overall size

of the frame Resetting to ensure permitted tolerance

Check the overall size of the entire inner formwork

Installing the vibrators to the frame by bolts with lock washer

The steel plate covered on the top of the frame is arranged to be able to getinside to install the vibrator as well as checking and maintenance of vibratorsduring use

4 Installation of external formwork with tensioning pedestals

CMDRCP / CW2C PACKAGE CW2C KM 18+200 – KM 23+450

Each plate of the external formwork is linked with tensioning pedestal, mayplace and pump cement grouting linking for each section before the jointwelding and then pumping cement grouting for the next section, or put theentirely then pumping cement grouting The sequence of construction asfollows:

+ After fabrication of the external formwork plate meets therequirements then each plate will be installed on the tensioningpedestal Link all external formwork plates by butt weld thengrinding welds smoothly Use the turnbuckles to tighten theexternal formwork with the tensioning pedestal Check theoverall size of the external formwork installed

+ Pumping cement mortar into the gap between the externalformwork and the tensioning pedestal

+ Repeat the above sequence of construction for the next segment

- Set and associate support structures for wall wing together withtensioning pedestal

- Set and associate jacking beam with the tensioning pedestal

- Check the overall size of the entire external formwork with tensioningpedestal

5 Installation of inner formwork

Inner formwork is only installed when the steel frame and cable have beenput in place and prestressed cable has been stress released

Inner formwork is installed support system parallel to the upper surface of thetensioning pedestal Before installation of the sections of formwork inside steelcages, it is needed to check, measure size, and apply release agent

Use a steel girder to lift the sections of the formwork sections Measuring andadjustment of cross-arm supporting formwork to ensure size

6 Girder and beam fabrication yard

Fabrication yard should have a suitable length Beam and girder fabrication yardare compacted to K95 The beams are chocked with concrete sleepers

Moving or transfering girders from casting pedestal to stock yard by gate gantry,with the lifting

7 Checking, inspection and removal of formwork

7.1 Checking formwork, scaffolding for tensioning pedestal

The stages during the construction process is supervised and inspected by thetechnician

Formwork, scaffolding for the tensioning pedestal should be checked carefullybefore placing concrete as well as in the process of placing concrete Promptlyrepair the damage

While tensioning of the prestressed steel wire on the tensioning pedestal tocheck the deformation and displacement of the tensioning pedestal as well as allassociated parts, welds to ensure safety and quality of tensioning work as well

as the loss of stresses in the prestressed steel wire

7.2 Removal of formwork and scaffolding

The inner formwork shall be removed ater 36h of placing concrete

8.2 Febrication of reinforcing steel

- Reinforcing steel cage is processed at the site on the support system

- Longitudinal joints are staggered how on a cross-section quantity ofthe joints of <25%

- Tendons are cut adequate length, apply the adhesive tape at the innertube with steel strand to prevent concrete mortar to flow into the tubewhen placing concrete

- These steel strands are hung loose in the reinforced steel cage untilreinforced steel cage is placed into formwork Due to the tensioning,the steel strands will stretch, to ensure that the non-cohesive length

of the steel strand is correct with the design, the outside of the plastictube is extended to the inner surface of beam jack so as not to let theplastic pipe move while steel strand being stretched

- Place the drainage pipe at the position of the end sealing by the sealPVC pipe

- Concrete spacers are tied with the reinforcing steel cage, the concretestrength of the concrete spacer is equal to or greater than thestrength of concrete beams

8.3 Fixing reinforcing steel into the formwork

- Prior to installation of reinforcement cage, surface of the externalformwork must be cleaned and the release agent is applied to ensurethat the lifting of the beams from the formwork is easy

- Use a long enough beam and two lifting hooks of the gate gantry tolift the entire reinforcement cage from the fabrication platform to thetensioning pedestal and place into formwork

- Check the reinforcement cage while placing into the formwork, thestraightness of the steel strand, thickness of protective coats ofreinforcement

- Installation of formwork for head beam The steel strand is threadedthrough the holes of the head beam shuttering and the jacking beam,make sure the steel strands are vertical alignment from this end tothe other end, the high strength steel strands are not twisted or crossinterlaced

9 Tensioning prestressed steel

9.1 Allowable tolerance for fabrication of concrete for beam casting

pedestal.

10 Quality Ceritificates

CMDRCP / CW2C PACKAGE CW2C KM 18+200 – KM 23+450

- The Contractor shall provide sufficient anchorage certification of themanufacturer Check the anchor shackles and anchor keys beforeproducing stress

9.2 Preparation work before producing stress

- Check the defect of formwork beams, tensioning pedestals if thataffects the load capacity, the repair shall be conducted

- Check the test results of high tensile strength tendon

- Check the technical certification of the anchorage

- Check the tolerance when placing high tensile strength tendon

- Check and adjustment of the tensioning devices (prestressed jacks),the pressure gauge will be used If beyond the time limit must be re-examined

- Determination of friction coefficient of the jack and anchorage shackle(determined separately for each jack)

- Check the threaded hole for high tensile strength steel tendon (purity,the smoothness)

- Check the operation and safety procedures

9.3 Installation of high tensile strength strand.

- High tensile strength strand is prepared on the tensioning pedestal,ensure the tightness when tensioning, forming shapes of straightstrands The strands need to be preserved from rust due to themoisture from the air Do not adhere oil, grease, and dirt, do not letthe stand deformed or chafed

9.4 Threading anchorage shackle.

- Before inserting an anchorage shackle into the tendon to preparetensioning pre-stressed tendons, it is needed to clean soil, sand andfat protective layer of tendon and anchorage shackle For theanchorage core prior to connecting to anchorage, grease shall be getrid of absolutely until clean dry surface

9.5 Tensioning device and sequences for tensioning:

- Jacks used to tension the tendon is single wire tensioning jack

- Use anchorage

- Jacks and anchorage must be tested before being put into use

- When tensioning, the tendons are tensioned by a single strand, thestrand is tensioned from both ends Tensioning sequence as inaccordance with design method

- When installing prestressed tendon, to avoid dirt into reinforced.

- Deviation of the position of tendon after being tensioned comparedwith the design does not exceed 5 mm

11 CONCRETE WORKS

Concrete is produced by batching plant at construction sites and aretransported to the construction location by agitators Prior to delivery ofconcrete, the quality control and testing of concrete must be conductedalong with delivery records

With different structures: measures for placing concrete are shown in thedrawings of the construction methods

Components of concrete

- Adjusting concrete components at the site: Adjusting concretecomponents at the site are conducted on the principle that does notchange the water / cement ratios of design concrete component.When moist aggregates should reduce the amount of mixing water,keep the required slump

Manufacture of concrete mix

Manufacturing concrete mix by batching plant (or concrete mixer) Mixingconcrete process shall comply with the following provisions:

- When mixing concrete, materials must be weighted accurately.Moisture content of sand and stones must be conducted inspectionregularly to adjust the amount of aggregates and water use

- Cement, sand, macadam and liquid admixture to make concrete mix

is weighted by volume Water and admixture weighed by volume.Allowed tolerance when weighing shall not exceed the allowed values

- The accuracy of measuring equipment must be calibrated prior toplacing concrete During weighing, regular monitoring to detect andcorrect promptly

Transportation of concrete mix

- The transportation of mixed concrete from the batching plant to thework should ensure the following requirements:

CMDRCP / CW2C PACKAGE CW2C KM 18+200 – KM 23+450

 Use a reasonable means of transport, to prevent the concretemixture from segregation, loss of cement grout and water lossfrom wind and sun

 Using the equipment, manpower and transportation should bearranged to suit the volume, speed of mixing, pouring andcompacting concrete

 Allowable time to keep the concrete mix during transport should

be determined by experiments on the basis of weather conditions,type of cement and admixture used

Placing concrete

When placing concrete must meet the following requirements:

- Closely monitor the status of formwork during the constructionprocess to settle in time if problems occur

- When it rains, measures to cover in order not to let the rain water intothe concrete

- Only to place concrete when the ambient temperature satisfying therequirement

- Concrete was placed in layers with a thickness not exceeding 60cmand ensure concrete is placed shall be able to bond with the nextplacing concrete layer Placing time between layers does not exceedthe initial setting time of the concrete

- The placing concrete: for each type of structure, placing concrete can

be used cranes or pumps (details shown in the drawings)

- Notes when compacting concrete:

+ When using poker vibrators, moving distance not exceeding 1.5times the radius of the vibrator effects Distance to sideformwork from 5-10cm, penitrating into the under concrete layer5-10cm, when finishing each vibration of a place just to withdrawvibrator up, avoid collision of vibrator into formwork, reinforcingsteel and right in place buried parts

+ When using the vibrator must base on the figure and shape ofthe structure and vibrator functions, through testing todetermine the distance of the vibrators

+ When the concrete to stop subsidence, no air bubbles, surfacewell-compacted, then stop vibrating

- The placing concrete must be conducted continuously If interruptionoccurs, the interupption time must be less than the time of initial

- After completion of the placing concrete and concrete is in the stage

of initial setting if the surface exposes shall promptly repair andscreed smoothly Wait until sedimentation of the grout, scread thesecond time and and finishing or roughening the surface

- During the placing concrte shall regularly check the stable status ofthe supports, formwork, reinforcing steel and right in place buriedcomponents If found loose, deformed, displacement must settledtimely

Curing concrete

- After placing conrette, concrete must be cured in conditions ofhumidity and needed temperature for curing and preventing theharmful effects during curing of the concrete

- Moisture curing: is the process for keeping concrete with moisturenecessary to the setting and hardening after shaping During curing,the concrete shall be protected against mechanical impacts such asvibration, shock forces, loads and impacts, which are likely to causeother damage

Checking of the concrete samples

- The limit compressive strength of concrete must be taken throughtesting samples to determine the standards of current regulations.Each casted beam takes 09 samples, 03 samples tested after 72hours (3 days), 03 following samples is pressed after 7 days, 03remaing samples to determine the remaining 28-day strength Thetesting sample of cylinder 150x300 mm or cube 150x150x150 mm

- The quality of materials used for mixing concrete must be tested, theexperimental methods must conform to the relevant regulations

12 Cutting the tendons and measuring camber of the beams

- To only conduct the cutting tendon to transfer the tensioning force tothe concrete when the concrete of girder reaches the required strenth

as in accordance with the technical specification

- Before cutting strand, paint markers shall be marked on every strand

at both ends of the beams, away from outer surface of the formworkabout 15 cm to measure the lagging of strand inside the beams ateach end The sections of the shuttering of the beam and theformwork is moved out of the concrete beams

- The sequence for cutting strand is conducted simultaneously from theinside to outside and and symmetric to the beam alignment Thestrands are cut each individual strand and simultaneously at bothends by cutting tools in position in the jacking beam of about 30 cm