NPQS C3-70 - Pre Stressed Concrete Works Ver 1

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NPQS C3-70 Prestressed Concrete Works

National Productivity and Quality Specifications (NPQS)

C3-70 Prestressed Concrete Works

Version 1.0

CONTENTS

1. GENERAL 1.1 Scope 1.2 Related Sections 1.3 Standards and References 1.4 Trade Preambles

2. PERFORMANCE REQUIREMENTS 2.1 Contractor's Submission and Proposals 2.2 Construction

3. MATERIALS 3.1 Concrete 3.2 Reinforcement 3.3 Formwork Material 3.4 Tendons 3.5 Sheaths 3.6 Anchorages 3.7 Tendon Coating 3.8 Spacers 3.9 Debonding Sleeves 3.10 Grout 3.11 Equipment

4. WORKMANSHIP 4.1 General 4.2 Handling and Storage of Prestressing Materials 4.3 Safety Precautions 4.4 Placement of Tendons and Sheaths 4.5 Tensioning 4.6 Anchoring 4.7 Removal of Formwork 4.8 Grouting 4.9 Cutting of T elidons

5. VERIFICATION AND SUBMISSIONS 5.1 Submissions 5.2 Inspection 5.3 Tests

APPENDICES

Ai. GROUT TEST PROCEDURES

A2. GROUTING PROCEDURES


Page

1 1 1 1 2

4 4 4

5 5 5 5 5 5 5 5 5 6 6 7

9 9 9

10 10 11 12 12 12 17

18 18 22 22

1. GENERAL


Read with the General Requirements section, and all other contract documents.

1.1 Scope

This section covers the requirements for carrying out prestressing operations for concrete structures. It applies to both pre-tension and post-tension operations with grouted or un-grouted ducts. For precast prestressed components read this section in conjunction with section C3-60 "Precast Concrete Works".

This document specifies project specific data to be read in conjunction with section C3-70 of NPQS. All modification and additions noted in this document take precedence over clauses noted in NPQS. Clause references in this document tie with those in C3·70 with the same clause title.

1. 2 Related Sections

Read this section in conjunction with the relevant requirements of the following work sections:

C3-10 Concrete Construction Generally C3-20 Reinforcement C3-30 Formwork and F alsework C3-60 Precast Concrete Works

1.3 Standards and References

1.3.1 Standards

Unless otherwise agreed by the SO, ensure all of the Works comply with the relevant requirements of the Standards and Codes listed below or referenced in the body of the Specification. Alternative Standards and Codes may be proposed for approval by the SO, provided it can be demonstrated that the alternative Standards and Codes comply with the requirements of the standards specified. All Standards and Codes quoted are the current version, unless specific year references are noted.

Singapore Standards

SSCP65

SS26

SS78

SS 289

SS 475

Other Standards

BS 4447

Structural use of concrete

Part 1- design and construction

Part 2- special circumstances

Ordinary Portland cement

A11: Testing concrete - method of normal curing of test specimens (27°C method)

A 14: Testing concrete - method for determination of density of hardened concrete

Part 1: Guide to specifying concrete

Part 4: Steel for the prestressing of concrete - strand

Part 5: Steel for the prestressing of concrete - hot-rolled steel bars with or without subsequent processing

Specification for the performance of prestressing anchorages for post-

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BS EN 445 BS EN 446

tensioned construction Grout for prestressing tendons - test methods Grout for prestressing tendons - grouting procedures

BS EN 447 Grout for prestressing tendons - specification for common grout In the event that the Standards or Codes are partially superseded or become obsolete, refer to the latest edition or the approved substitution for the relevant clauses.

1.3.2 Technical References

Refer to the following technical reference for guidance in carrying out the works:

a. Concrete Society Technical Report No. 43, "Post-tensioned concrete floors -design handbook", 1994

b. Concrete Society Technical Report No. 47, "Durable bonded post-tensioned concrete bridges", 1996

c. Post-Tensioning Institute (PTI), "Guide specification for acceptance standards for post-tensioning systems", 1998

d. Post-Tensioning Institute (PTI) "Guide specification for grouting of post-tensioned structures", 2000

e. Post-Tensioning Institute (PTI), "Preprint of chapter VIII, Post-tensioning manual, 6th edition, Anchorage zone design", 2000

f. Federation Internationale du beton (FIB), "Technical Report, Bulletin 7, Corrugated plastic ducts for internal bonded post-tensioning", 2000

g. Federation Internationale de la Precontrainte (FIP), "Recommendations for the corrosion protection of unbonded tendons", FIP Report, Thomas Telford Ltd, 1986.

1.4 Trade Preambles

1.4.1 Contractor's Submissions & Proposals

The intended location and loadings for the prestressing works are indicated in the design drawings. Base on the information, engage qualified and experienced

. personnel 10 propose the following for SO's acceptance and submission for approval if necessary:

1.4.1.1 Design development of the Prestressed Systems

Carry out development of the design to complete the following information:

a. Type, number, distribution, length and profile of the tendons.

b. Required stresses of the tendons at various stages including anticipated prestress losses.

c. All relevant reinforcement details including those to cater for tendon anchors, secondary stresses where indicated in the drawings, and those needed for long term shrinkage and creep control.

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1.4.1.2

1.4.1.3

Produce drawings showing all layout and details of the prestressing works.

Plan and propose the construction sequence including construction joints, stressing sequence and timing.

1.4.1.4 Design all necessary temporary supports for the structural members until all structures are ready to perform as permanent works.

1.4.1.5 Propose suitable grout mix design for grouted tendon works.

Engage a PE (civil) to review and endorse all structural calculations and drawings.

1.4.2 Shop Fabrication Drawings and Site Assembly Drawings

Engage qualified and experienced personnel to prepare coordinated shop fabrication drawings and site assembly drawings, incorporating all designed details.

1.4.3 Maintenance/Replacement Manual

Propose and submit a maintenance manual, covering the long term maintenance of the prestress tendons and accessories to be carried outby'the building owners where applicable. Refer to the General Requirements section. clause 1.4.8 for details.

1.4.4 Supervision

The prestressing and associated works are of a specialist nature. Carry out prestressing and grouting operations under the presence and direction of supervisors with appropriate knowledge, training and experience in carrying out similar operations.

Provide evidence of past experience to the SO prior to commencement of the Works. Do not remove or replace the supervisor(s) without the prior agreement of the SO.

The supervisors are to be responsible for all safety precautions relating to the operations. Take responsibility and ensure that all personnel operating the tensioning and grouting equipment are competent as verified by the system supplier.

1.4.5 Quality Control Plan

Submit and work to a quality control plan as agreed with the SO. Refer to the General Requirements section, clause 1.4.10 for guidance.

Also refer to Federation Internationale de la Precontrainte (FIP), Guide to good practice, "Quality management systems for post-tensioned concrete structures according to ISO 9001".

1.4.6 Accredited Laboratory

Engage a laboratory accepted by the SO and accredited under the Singapore Laboratory Accreditation Scheme (SINGLAS) to carry out tests and checks as required by this Specification.

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2. PERFORMANCE REQUIREMENTS

2.1 Contractor's Submission and Proposals

When carrying out the design proposals in clause 1.4.1, take account of the following requirements:

2.1.1 Design Intent

The design intent including location, structural elements and design loads are shown in the design drawings. Additional requirements are indicated in the PSD.

Additional design input considerations are as follows:

General loading to comply with Building control regulations. Additional load considerations:

distributed load: kN/m2

concentrated loads: kN

Deflections: mm at location

Basic fire resistance (as determined without regard to finishes): __ hours

finish to soffit:

finish to top surface: __

other requirements: __

Verify the design intent and other requirements from the authorities and from the SO.

2.1.2 Codes

Carry out design development in accordance with SS CP 65: Part 1: Section 4 (Design and Detailing: Prestressed Concrete). unless otherwise agreed.

2.1.3 Serviceability Classification

Take into consideration of serviceability classification in accordance with SS CP 65: Part 1: Clause 4.1.3 (Serviceability Classification). Refer to the PSD for the design class specified.

The structures are to be designed for class __ in accordance with SS CP 65: Part 1: Clause 4.1.3 (Serviceability Classification).

Refer to clause 5.1.2(Design Submission) for items to be included in the design submission.

2 .2 Construction

Take responsibility to ensure that the construction methods and sequence comply with SS CP 65 and that various factors considered in the design of the system is achieved.

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3 . MATERIALS

3 .1 Concrete

Refer to section C3-10 "Concrete Construction Generally". clause 3.0 for requirement of concrete and constituents.

3.2 Reinforcement

Refer to section C3-20 "Reinforcement". clause 3.0.

3.3 Formwork Material

Refer to C3-30 "Formwork and Falsework". clause 3.0.

3.4 Tendons

Tendons are to conforll) to SS 475: Part 5 for bars and SS 475: Part 4 for wire or strand. Use stabilized strands with restrictions en relaxatien lesses in accerdance with CP 65 Part 1, clause 4.8.2. All tendens are to. be free from leese rust, eil, tar, paint, seap and ether lubricants er any harmful matters.

3.4.1 Straightness

Comply with the requirements of SS CP 65: Part 1: Clause 8.4 (Straightness).

3.4.2 Supply ef Wire er Strand

Supply wire er strand in coils with sufficiently large diameter so. that the material is reasonably straight when unwound.

3.5 Sheaths

Material of sheaths are not to. react adversely and chemically with concrete, grease or steel, are strong eneugh to. retain shape and resist damage during construction and able to prevent the entrance of cement paste from the concrete.

For bonded tend ens use spirally wound galvanized steel tubing.

3 • 6 Anchorages

Anchorages are to cemply with BS 4447 and SS CP 65: Part 1: Clauses 8.7.5.2 (Anchorages).

3 .7 Tenden Coating

Provide permanent protectien to. unbonded tendens using a coating of mastic material accepted by the SO. The ceating is to.:

a. remain ductile and free ef cracks

b. be chemically stable

c. adhere to the entire tendon length to. be unbendedl

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3.8 Spacers

For general requirements refer to section C3-20 "Reinfercement", clause 3.4.

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Cable spacers tied to the tendons to prevent relative movement of spacer and tendons are to be of type and at spacing recommended by the Prestress specialist, and able to hold the tendons in true positions and prevent displacement during concreting.

3.9 Debonding Sleeves

Debonding sleeves are to be chemically neutral to the steel, the grease and the concrete. The material is to be either High Density Poly Ethylene or Poly Propylene. Paper and Poly Vinyl Chloride (PVC) are not permitted. The minimum thickness is to be 0.75 mm.

3.10 Grout

Comply with the basic requirements in SS CP 65: Part 1: Clause 8.9 (Grouting of Prestressing Tendons) and Annex A (Informative - Grouting of Prestressing Tendons). Test the grout used in the Works in accordance with clause 4.8.4(Grout Testing).

3.10.1 Cement

Unless otherwise agreed, cement is to be Ordinary Portland Cement to SS 26. At the time of mixing the grout the cement is to be freshly bagged, less than two months old, and is to have a temperature range compatible with that expected on the site. The source and quality of cement used in the works is to be the same as that used in the grout mix and grouting trials.

When using Ordinary Portland Cement for grout, apply the following additional control criteria:

a. Blaine value of cement: 320-380 m'lkg

b. Chloride, CI content ';;0.05% of cement weight

c. Tri-calcium aluminate, CoA content ,;;10% of cement weight

d. Calcium Sulphate, CoA content ,;;60% of cement weight

e. No false set in the cement

f. Loss of ignition, LOI ,;;3%

g. Free lime ,;;1 % of cement weight

3.10.2 Sand

Do not use sand. ./

3.10.3 Water

Use potable water supplied by PUB unless otherwise agreed.

3.10.4 WaterfCement Ratio

Propose suitable WIC ratio giving due regard to the required plastic properties of the grout and taking account of environmental and material influence (e.g. temperature, configuration of the tendons and properties of the materials used), and SS CP 65 A5.

3.10.5 Admixtures

Use admixtures to meet requirements for low bleed and acceptable fluidity.

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Admixtures are to comply with the requirements of SS CP 289 Part 1 Clause 4.4 (Admixtures).

3.10.5.1 Combinations

Check for compatibility for admixtures used in combination to ensure that all of the specified properties are achieved.

3.10.5.2 Dosage of Admixtures

Determine the optimum dosage of any admixture(s) by trial mixes with the cement to be used in the grout, under climatic conditions representative of the site. Express this dosage as percent by mass of the cement. This is to be within the range recommended by the supplier and in compliance with SS CP 65 A4.5. Agree the method of measuring dosage and checking weights of pre-packed dry materials with the SO.

3.10.5.3 Test for Admixtures

Notwithstanding the product information provided by the manufacturer, if verification is required, select and send samples ·of all admixtures to ·accredited laboratory for chemical content testing, e.g. chloridel;, nitrates and sulphates. - .;

3.10.6 Proprietary Grouts

Proprietary, pre-bagged, pre-packed "special" grouts may be used as.an alternative to site batched grouts provided they meet the specified performance requirements and accepted by the SO.

3 .11 Equipment

3.11.1 Grouting Equipment

Grouting equipment is to consist of:

a. Mixing device to accurately weigh the grout constituents, which will be used to prepare a special mix.

b. Mixing reservoirs with a high-speed mechanical mixer to assure continuous production and flow of grout into the tendon, at the anticipated speed of grout flow.

c. Pumps of sufficient capacity to inject the grout at the anticipated speed into a tendon of a given size and geometry.

d. Calibrated water tank to ensure constant wlc ratio in grout mix content.

3.11.2 Mixing Equipment

The mixing equipment is to be capable of producing a grout of homogeneous consistency and is to be capable of providing a continuous supply to the injection equipment. The capacity of the equipment is to be such that the duct can be filled and vented without interruption and at the required rate of injection. The large volume of grout may entail the use of a double mixing drum.

3.11.3 Injection Equipment

The injection equipment is to be capable of continuous operation with little variation of pressure and include a system for re-circulating the grout while actual grouting is not in progress. The equipment is to have a constant delivery pressure of not less than 0.3 MPa. It is

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to be equipped with a pressure gauge to prevent pressures above 0.5 MPa. The system is to be capable of maintaining pressure on completely grouted ducts and can be locked off without loss of pressure in the duct. All piping to the grout pump are to have a minimum number of bends, valves and changes in diameter and incorporate a sampling tee with locking-off valve.

Calibrate pressure gauges to the satisfaction of the SO before they are first used in the Works and thereafter as directed by the SO. Calibration procedures are subject to review and comment by the SO prior to their use.

3.11.4 Tensioning and Load Measuring Equipment

3.11.4.1 General

Check accuracy of tensioning and load measuring equipment to the satisfaction of the SO prior to commencement of the Work. All gauges, load cells, dynamometers and other devices used for measuring the stressing load are to have a reading accuracy of +/-2%. All pressure gauges are to be capable of reading loads directly, <Jr accompanied by a chart from which the dial reading can be converted into force.

The gauges are to have a full pressure capacity of approximately twice the working pressure and the loads to be gauged is to be not less than Y.. and not more than Y.. of the total graduated capacity of the gauge, unless the calibration data clearly establishes consistent accuracy over a wider range.

3.11.5 Equipment Maintenance

Maintain all equipment in optimum condition with its highest performance. Provide back-up equipment and keep spare parts e.g. hoses and valves on site for ready usage in the event of breakdown during the Works.

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4 . WORKMANSHIP

4.1 General

4.1.1 Code of Practice

Workmanship is generally to comply with SS CP 65: Part 1: Section 8 (Specification and Workmanship: Prestressing Tendons)

Refer also to other references listed in clause 1.3.2 for good practices.

4.1.2 Use of Equipment and Materials

Use all materials and equipment strictly in accordance with the recommendations of the manufacturer of prestressing system.

4.2 Handling and Storage of Prestressing Materials

4.2.1 General

Take all necessary precautions to prevent the corrosion, contamination and physical damage of prestressing materials from manufacture to encased in concrete, i.e. during transportation, handling, storage and installation. Protect and grease wrap all threaded parts and tapped holes of prestressing steel.

4.2.2 Storage

Store prestressing materials in clean and dry conditions, clear of ground and protected from weather. Prestressing steels is to be clean and free from pitting, loose rust and loose mill scale at the time of fixing in position and subsequent concreting. Keep prestressing bars straight during handling and storage. Provide supports to prevent excessive bending stresses.

4.2.3 Transportation

Package prestressing materials in containers or shipping forms for the protection against physical damage and corrosion during transportation.

4.2.4 Installation

Provide protection for prestressing steel for post-tensioning installed in members prior to placing and curing of the concrete, against aggressive corrosion if any, until grouted, to the acceptance by SO. Replace the steel if unacceptable rust conditions are found.

After stressing, complete grouting within 28 days after installation of the prestressing steel, otherwise re-inspect exposed section of steel and replace the steel if unacceptable rust conditions are found.

For both stressed or unstressed prestressing steel in duct that are not grouted within 28 days, apply approved water soluble oil to provide corrosion protection to strand.

4.2.5 Rejection

Reject prestressing steel as unsuitable for use if either of the following conditions occurs:

a. The steel exhibits evidence of corrosion such as may reduce its strength or ductility.

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b. The steel has been in contact with deleterious substances or subject to splashes from the cutting operation of an oxy acetylene torch or arc-welding processes such as may reduce its strength or ductility or bond characteristics.

c. The steel has pitting visible by eye on external or within strand surfaces or other physical damages at any time.

Prestressing steel, which exhibits a light brown surface coating of rust without flaking or pitting may be deemed suitable for use subject to acceptance by the SO.

4 _ 3 Safety Precautions

Take precautionary measures to ensure safety of the construction activities during and after stressing operations and during grouting. Set out appropriate procedures in the method statement.

Secure jacks in such a manner that they will be restrained should they lose their grip on the tendons. Position warning signs to caution that the operation is in progress. No person is allowed to stand behind the jacks or close to the line of action in front while stressing operation is in progress. .. .

The site operations are to comply with the Factories (Building Operations and Works of Engineering Construction) (Amendment) Regulations .

. ~ 4 _ 4 Placement of Tendons and Sheaths

4.4.1 Tendon Identification

Keep clear records of the traceable coil number and test certificate of the wire or strand used for each specified pour.

4.4.2 Welding of Tendons

Welding of tendons is not permitted.

4.4.3 Sheaths Fixing or Support

Fix or support sheaths within the forms at intervals of no more than 1 OOOmm to maintain a smooth profile. Protect the sheaths properly from damage or puncture. Splice to sheathing is to be mortar tight.

4.4.4 Grout Holes/tubes

For grouted tendons provide grout tubes at both ends of the sheathing at least 10mm in diameter. Equip each grout tube with a plug valve or similar, capable of withstanding a pressure of 1 N/mm2 without loss of water grout or air. Provide additional grout holes at high and low points and at other critical locations such as column as necessary to bleed air and water and ensure the ducts are completely filled with grout.

4.4.5 Soffit Marking

Mark tendon positions on the soffit to indicate locations in both plan and elevation within the slab. Agree the system to be used with the SO and record on the as-built drawings.

Where soffits are to be exposed in the completed structure, agree with the SO, the method of recording the locations.

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NPQS C3,..70 Prestressed Concrete Works

4.4.6 Tolerance for Tendons and Sheaths

Position tendons and sheaths in accordance with SS CP 65: Part 1: Clause 8.6 (Positioning of Tendons and Sheaths), and to the following tolerances:

a. Horizontally, ± 5mm for beam width up to 300mm, ±1 Omm for beam width up to 1 OOOmm, ±20mm for slab and beam width more than 1000mm.

b. Vertically, ± depth/40 for slab and beam depth up to 200mm, ±5mm for slab and beam depth up to 1 OOOmm, ±10mm for slab and beam depth more than 1000mm.

4.5 Tensioning

Carry out tensioning operations in accordance with SS CP 65: Part 1: Clause 8.7 (Tensioning the Tendons). Do not cut or remove stressing ends in any way without first obtaining agreement from the SO. Do not start tensioning prior to carrying out the following to SO's satisfaction:

a. All required tests have been completed and accepted by the SO.

b. The method statement has been accepted by the SO.

c. The stressing sequence has been accepted by the SO.

d. The concrete of the structure to be stressed (including any joints) has achieved the specified strength.

e. Allowance has been made for formwork to accommodate shortening, bending or uplift during stressing.

f. All tendons are free to move between jacking points and that members are free to accommodate the horizontal and vertical movements due to the application of prestress.

g. The calculations of the total force and elongation for each tendon have been accepted.

h. Details of any grout mix proposals have been accepted.

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4.5.1 Pre-Tensioning

Where pre-tensioning methods are used, refer to SS CP 65: Part 1: Clause 8.7.4 (Pre-tensioning).

4.5.2 Post-Tensioning

Where post-tensioning methods are used, refer to SS CP 65: Part 1: Clause 8.7.5 (Post-tensioning).

4.5.3 Tendon Loads

Prior to stressing demonstrate that all tendons are free to move in the ducts. All slack is to be taken up before measurement of the elongation commences. Continue stressing of each tendon until both the required load and the calculated elongation have been reached, provided that:

a. The initial load in the tendon does not exceed 80% of the specified characteristic breaking load.

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b. The stressing operation is to cease unless otherwise directed by SO, if the measured elongation of the tendon under its specified load differs from the calculated value by more than

i. 12% forls 10 m

ii. 10% for 10 m < l s 24 m

iii. 8% for 24 m < l < 40 m

iv. 6% for l > 40 m

where l = total horizontal length of tendon

Stress tendons initially to about 10% of final jacking force to remove slack, then spray with paint and stress progressively to full force. Obtain tendon elongation by measuring the length from the end of wedge to the paint mark. Refer to PTI Specifications for further guidance.

4 • 6 Anchoring

locate anchorages within the following tolerances:

a. Horizontally ± 25mm

b. Vertically ±5mm

Anchorages including buried dead anchorages are to be fixed with regard to cover requirements for corrosion resistance and fire protection.

Anchor the tendons when the prestress load has been applied to the satisfaction of the SO. If the draw-in of the tendons at completion of anchoring is greater than the design value shown on the drawings, inform the SO who will decide whether tensioning is to be repeated. After anchoring, decrease the force exerted by the tensioning equipment gradually and steadily to avoid shock.

4.7 Removal of Formwork

Refer to section C3-30 "Formwork and Falsework", clause 4.5 for general requirement of removal of formwork. Remove formwork only when the concrete has attained sufficient strength and tendons have been stressed to support the own weight and any likely constructional loads of the structure. Where necessary, provide props in approved manner after the removal of formwork.

Take the following as a guide to the minimum period before removal under normal circumstances, unless otherwise agreed by the SO:

Location Period after casting

Soffits of slabs After stressing Re-propping to slab if construction loads exceed

After streSSing or 7 days, whichever is later design superimposed loads Sides of beams with props left under After stressing Props to soffits of beams After streSSing or 9 days, whichever is later

4 • 8 Grouting

In general grouting is to comply with SS CP 65: Part 1: Clause 8.9 (Grouting of Prestressing Tendons) and Annex A (Informative - Grouting of Prestressing Tendons). Take guidance from also BS EN 445, BS EN 446 and BS EN 447 and other references listed in clause 1.3.2 for good practices.

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4.8.1 Preparation

Identify all injection and vent tubes of the ducts.

During the grouting operation, provide adequate flushing-out plant to facilitate complete removal of the grout in the event of a breakdown of the grouting equipment or other disruption before the grouting operation has been completed and demonstrate that this equipment is in full working order. Keep all equipment free from build up of adhering materials by washing.

4.8.2 Flushing

Provide standby flushing equipment capable of developing a pumping pressure of 2 N/mm2 and of sufficient capacity to flush out any partially grouted ducts.

Carry out flushing using compressed air before grouting to check for blockage.

4.8.3

4.8.3.1

Batching and Mixing of Grout

Batching

Batch all materials by mass except mixing water and liquid admixtures, which may be batched by mass or volume. Weigh bagged materials before use and mark the weight on each bag.

The accuracy of batching is to be ±2 % for cement and admixtures and ±1 % for mixing water.

In calculating the mass of mixing water, include the water content of liquid admixtures.

4.8.3.2 Mixing

Mix the material to produce a homogeneous grout and keep in slow continuous agitation until pumped into the duct. Unless Manufacturers recommend otherwise, add water to the mixer first, follow by the dry materials as a whole or in part in sequence until the total quantities are added. Adhere to the minimum mixing time determined from grouting trials.

4.8.4

4.8.4.1

Grout Testing

General

Test for suitability of the grout constituents to assure consistent properties and quality of a particular grout mix, prior to use in trials and the Works.

Carry out the following suitability tests in the conditions of temperature and humidity expected on the site to confirm the performance characteristics of an approved grout mix:

a. Fluidity of grout to ensure complete filling of the tendon.

b. Bleed of grout to limit free water inside the tendon duct, which can be re-absorbed by the grout within a specified time.

c. Volume change of grout to be maintained within a specified range around zero to ensure complete filling of the tendon duct.

d. Density test to ensure grout density is above the specified requirement.

e. Strength of grout to assure sufficient bond between the prestressing steel and the concrete structure.

f. Sedimentation of grout to control uniformity of grout in the tendon.

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For acceptance testing, perform the test twice each day. The minimum testing requirements are summarised in the following table.

Suitabilitv Fluidity After mixing one test.

After estimated time to grout duct or minimum of 30 minutes -two tests averaged.

Bleed Volume Change After mixing - three tests averaged. Strength

( Acceptance -~

Fluidity After mixing one test from mixer. After flow through duct - one test from each anchorage outlet. On completion - one test from mixer.

Bleed Two tests per day, one of which is to be from grout after flow Volume Change through duct, taken from end anchorage outlet and the other Strength Density

from the mixer.

Include the temperature of the freshly mixed grout, the ambient temperature and humidity in all test reports for suitability tests, trials and the Works .

. ~ 4.8.4.2 Fluidity Test

Carry out test in accordance with procedure as set out in EN 445.

Acceotance Values' The fluidity is to achieve the values in the table below

At the end of the injection At duct Change Test Immediately period subject to a outlet of flow Method after mixing minimum of 30 minutes Time (in time in 45 Time (in sec) after mixing *

Time (in sec) sec) min.

Cone 025 (see 025 (see note) 010 03 sec not<& * MIxing time IS to be measured from the time when all of the matenals are In the mixer. For special grout the minimum time is to be 90 minutes

b

Additionally, the fluidity at the duct outlets is not to exceed that of the injected grout by more than 10%. The grout is to contain no lumps.

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4.8.4.3 Bleeding Test

Carry out test using cylinder in accordance with procedure as set out in EN 445.

Refer to the PSD for requirement of additional inclined tube test. Where required, carry out the inclined tube test in accordance with the procedures as set out in appendix A 1.1.

Inclined tube test is I is not required additionally.

Acceptance Values: The bleeding is to be less than 0.5% of the initial volume of the grout where special grout is used and the average of 4 successive results is to be less than 0.3%. The water is to be reabsorbed by the grout during the 24 hours after mixing. Where common grout is used values is to be 2% and 1% respectively.

4.8.4.4 Volume Change Test

Carry out test with cylinder method in accordance with procedure as set out in EN 445.

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Acceptance Values: The volume change is to be within the range -0% and +2%.

4.8.4.5 Density Test

Carry out test in accordance with procedure as set out in the appendix A 1.2.

Acceptance Values: The grout density is to be above 1950 kg/m3, ideally at 2000-2100 kg/m3.

4.8.4.6 Cube Strength Test

The compressive strength of 100 mm cubes of grout is not to be less than the value in SS CP 65: Part 1: Clause A.3.4 (Compressive Strength) and design strength of the members. Cubes are to be made, cured and tested in accordance with SS 78: Part A8, All and A14.

Notify the SO if the grout strength cannot achieve the design strength of the members.

4.8.4.7 Chlorides Content Test,

This test is to confirm thatthe grout mix does not contain excessive chloride contents, which could harm the tendons. The total amount of chlorides from all sources (I.e. cement, water and admixture) in grout is not to exceed 0.1 % by mass of the cement. The chloride content is determined by chemical analysis of the grout mix.

An approved analysis method is to be used. Test one ;,>ample sufficient for analysis per grout mix.

4.8.4.8 Sedimentation Test

Grout mix with a tendency to segregation or sedimentation can be detected in an inclined tube test.

Acceptance values: Variation of density D 5%

4.8.5 Grouting Trials

Refer to the PSD for requirement of grouting trials. Where required, carry out full scale grouting trials using the same equipment and procedures as proposed for the Works. Conduct one trial for each type of cables. Check that the trials reflect the actual duct geometry and typical tendon arrangements. Stress the tendons just sufficiently to hold them in proper position with respect to the ducts.

Grouting trial is I is not required. Prior to the stressing operation apply cyclic loading up to 25% of the characteristic strength and back to zero to remove any slack and confirm that snag does not occur. Carry out the trials on specially erected construction, not less than 14 days before construction commences. Determine the efficiency of grouting by cutting out five duct sections from each type of duct at locations chosen by the SO. Each section is to be 300mm long and is to be sectioned longitudinally after removal from the trial. The cut sections of grouted duct are to be completely filled with no voids larger that 5% of the duct diameter and the tendon is to be completely surrounded with grout. Maximum bleed water and air volume at the top section of the inclined tube is not to exceed 0.3% of the volume of grout at the time of grouting. Report to the SO on any signs of segregation.

In the event that a trial fails to demonstrate that the ducts have been successfully grouted, repeat the trial with revised methods until satisfactory grouting is achieved. Also demonstrate in the trial, the proposed measures for flushing and blowing out the grout in the event of unacceptable grouting.

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4.8.6 Grout Injection


Carry out grouting of the tendons as soon as practicable upon stressing operations and acceptance of the stressing records by the SO. For very damp atmosphere or high salt water content, carry out grouting not more than 7 days after stressing the tendons. For moderate and very dry atmosphere, grouting may be carried out up to 15 and 20 days after tensioning respectively.

4.8.6.1 Written Acceptance

Obtain written acceptance of the stressing records by the SO prior to grouting. If grouting is not started within 24 hours of the acceptance, obtain a fresh written acceptance from the SO.

4.8.6.2 Preliminary Inspection

Immediately before grouting starts, blow the ducts, vents, inlets and outlets thoroughly with compressed, dry, oil-free air to ensure that the duct system is capable of accepting the grout injection. Check each vent in turn. Clean partial or complete blockage of ducts or vents before. grouting starts. Do not ·flush the system with water. Remove any water found in the duct systems.

Grout is to be used within 30 minutes of mixing unless fluidity test demonstrates a period of at least 15 minutes beyond the intended time of use is acceptable, and with acceptance by the'SO.

4.8.6.3 General grouting of tendons

Refer to procedure as set out in appendix A2.1

4.8.6.4 Vacuum Grouting of ex1ernal tendons

Refer to procedure as set out in appendix A2.2

4.8.6.5 Inspection of Grout

Before the grout set, inspect the level of grout in the injection and vent tubes. If the level of competent grout has fallen below the required final level or the material is degraded due to bleed water or air or segregation, or if there is evidence of inadequate protection, top up the grout. In addition, inspect the end caps at anchorages and demonstrate that they are satisfactorily filled with grout. If there is cause for doubt that the ducts are completely filled with grout, flush the ducts clean of grout and protect the tendons until re-grouting of the duct is possible.

4.8.6.6 Sealing of Vents

On completion of grouting, provide a positive seal to grout vents so as to ensure the encapsulation to the tendons equivalent to that by the concrete and anchorage protection.

4.8.7 Blockages and Breakdown

If a fault caused by blockages or breakdown develops during the injection procedure, remove the grout from the duct using flushing equipment and repeat the injection procedure as soon as practicable.

4.8.8 Protection After Grouting

Protect the filled ducts to the satisfaction of the SO to ensure that they are not subject to shock or vibration for one day after the injection of the grout. Carry out visual inspection on the level of grout in the injection and vent tubes and make good if necessary before the grout set.

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4.9 Cutting of Tendons


Obtain written acceptance of the stressing records by the SO prior to cutting.

Carry out the cutting by using a high-speed abrasive cutting wheel, friction saw or other method accepted by the SO.

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5 . VERIFICATION AND SUBMISSIONS

5.1 Submissions

5.1.1 Tender Submission

Submit the following information with the tender:

a. Technical details of the proposed prestress system including catalogues of the components and intended source of the tendons.

b. Certificates to show compliance with the codes set out in the specifications.

c. Name of the prestress specialist engaged and records of past projects where the proposed system has been successfully adopted.

5.1.2 Designs Submission

Submit to the SO for acceptance, calculations of total forces and elongation of tendons within time frame as directed by the SO prior to commencement of stressing operation.

Include calculations of total forces and elongation of tendons with jack pressure· gauge readings at each stressing stage, taking into account all short·term and long· term losses including creep and shrinkage of concrete, creep of steel, stressing sequence, anchorage friction, wedge pull-in, jack loss, duct friction etc.

Losses due to friction is not to exceed a magnitude which makes it necessary to stress the steel above 80% of the ultimate tensile strength, in order to obtain the required force. In this event, provide additional tendons instead.

In addition, submit drawings showing at least the following information:

a. reinforcement details

b. effective forces

c. tendon profiles and details

d. jointing details

e. anchorage locations and details

f. bearing details

g. stressing sequence

h. tendon elongation calculations

The design calculations and drawings are to be endorsed by a PE.

5.1.3 Method Statements

Submit to the SO for acceptance, method statements prior to commencement of any work. Include all details of the prestressing system with at least the following information:

a. corrosion protection systems

b. corrosion inhibitors

c. friction-reducing compounds for unbonded systems

d. installation procedure

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e. stressing procedure

f. formwork removal

g. drainage, vent and bleed details for grouted tendons

h. grout mix

i. admixture testing procedure

j. grouting testing procedure

k. grouting trials procedure

I. grouting procedure

m. preventive and corrective measurements

n. fire resistance

o. quality control

p. safety precautions

Submit these details and allow sufficient time for review. Where bonded tendons are to be used, carry out grputing trials on representative construction in time for evaluation of the results and any necessary changes to be made.

lb 5.1.4 Shop Fabrication and Site Assembly Drawings

Submit to the SO for acceptance, shop and assembly drawings within time frame as agreed with the SO prior to commencement of any work. Include all details of the prestressing system with at least the following information:

a. Details of reinforcement such as bursting steel

b. effective forces

c. tendon profiles and details including the source of the tendons.

d. fastenings and methods of maintaining tendon profiles

e. jointing details

f. anchorage locations and details

g. block-out, recesses and closure strips in slabs, beams, columns and core walls for anchorage to facilitate stressing operations

h. bursting steel requirement for anchorage

i. formwork details

j. stressing sequence

k. tendon elongation calculations

I. all other fabrication details

5.1.4.1 Assembly drawings

Submit assembly drawings of the prestress system as provided by the prestress specialists for the purpose of verification on site.

5.1.5 Calibration Certificates

Submit to the SO for acceptance, all calibration certificates for the tenSioning equipment, load measuring equipment and grouting equipment prior to

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commencement of the Work. Calibration Certificate of equipment used for prestressing and grouting are to be valid throughout the operations on site.

5.1.6 Records

Submit the following records to the SO after the transfer of stresses:

5.1.6.1 Force in Tendons.

Record the force and elongation in the tendons immediately after they were anchored.

5.1.6.2 Transfer Strength

The strength and age of test cubes demonstrating that the specified transfer strength had been achieved and the minimum age in hours of the concrete at the time the stress was applied to the member.

~ 5.1.6.3 Stressing Record Sheets

Submit a copy of stressing record sheets to the SO at the end of the next working day. Agree the format of the sheets with the SO prior to commencing the trials.

Include in the records, at least the following:

a. location of the stressing operations

b. date and time of starting and completing the stressing operations

c. technical personnel supervising and carrying out the stressing operations

d. type and identification numbers of equipment used

e. identification of tendons by numbers with reference to the drawings

f. coil, heat and batch numbers of the tendons used

g. stressing method (single or double end, monostrand or multistrand)

h. initial pressure force where tendons are marked for measurement of elongations

i. pressure force and elongations at each stressing stage

j. final pressure force and elongation on completion of tensioning

k. amount of draw-in

I. elongation remaining after release of jack

m. tendon breakage or details of any interruptions

n. ramming pressure, if applicable

5.1.6.4 Grouting Trials Record Sheets

Submit a copy of grouting record sheets to the SO at the end of the next working day. Agree the form of the sheets with the SO prior to commencement of the trials.


a. location of the grouting trials

b. date and time of starting and completing the grouting trials

c. technical personnel supervising and carrying outthe grouting trials

d. type and identification number of equipment used

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e. identification of the tendons by numbers with reference to the drawings

f. grout mix, including any admixtures

g. method of injection

h. rate of injection

i. pressure of injection

j. details of any interruptions

k. details of any topping up

5.1.6.5 Grouting Record Sheets

Submit a copy of grouting record sheets to the SO at the end of the next working day. Agree the format of the sheets with the SO prior to commencing the grouting operation.


a. location ofthe grOuting operations

b. date and time of starting and completing the grouting operations

c. weather conditions

d. technical personnel supervising and carrying out the grouting operations

e. type and identification number of equipment used

f. identification of the tendons by numbers with reference to the drawings

g. grout mix, including any admixtures

h. method of injection

i. rate of injection

j. pressure of injection

k. details of any interruptions

I. details of any topping up

5.1.7 Quality Control Manual

Submit a Quality Manual containing a QA/QC programme for the Works to the SO for acceptance within directed time frame.

The Quality Manual is to include at least information on the following:

a. Quality policy

b. Organisation charts and responsibilities

c. Internal quality control and audits

d. Facilities and equipment

e. Calibration and testing of equipment

f. Testing and inspection procedures

g. Subcontractors and suppliers

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5.1.8 As Build Drawings

NPQS C3~ 70 Prestressed Concrete Works

Submit to the SO for record, as-built shop drawings on completion of the prestressing works for each stage, showing all details of the approved drawings and deviations or amendments if any.

5.1.9 Maintenance/Replacement Manual

At the end of the project submit a maintenance / replacement manual for all components that require maintenance from the owners of the building if applicable.

5.2 Inspection

Provide equipment and assistance as required to enable the SO to check the soundness of any doubtful grouting by visual inspection and/or by other means. Where unsatisfactory grouting is discovered, undertake such remedial measures as agreed with the SO.

5.3. Tests

5.3.1 Concrete Strength

Submit to the SO for acceptance minimum concrete strength at each stage of stressing and anchorage capacities. Test in accordance with SS 78.

5.3.2 Admixtures

Provide data on suitability of admixtures, including testing and previous experience with such materials. Maintain records of the details and performance of the materials.

5.3.3 Grout

Submit to the SO for acceptance, details of suitability test results of the grout proposed for use in the Works prior to any grouting works. Submit to the SO cube test results of the grout for any grouted tendons.

5.3.4

5.3.4.1

Tendons

Batch

A batch of tendons is any quantity of tendons of the same type, size and grade, manufactured by the same manufacturer, covered by the same certificates and delivered to the site at anyone time.

5.3.4.2 Sampling

Provide samples of tendons from each batch of tendons delivered to the site for testing prior to installation of the tendons. The number of samples to be provided from each batch is as stipulated in the following table.

Description Size of batch No. of samples per batch

0- 20 tonnes 1

Steel wire 20-100 tonnes 5

exceeding 100 tonnes 1 for each 20 tonnes or part

0-20 tonnes 1

Wire strand and 20-100 tonnes 5 Alloy steel bar

exceeding 100 tonnes 1 for each 20 tonnes or part

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The number of specimens in each sample is to be 3. Each specimen is to be 1 metre long and straight, taken from different coils or bars in the batch. Cut ends of the specimens square without unravelling of wires. Remove loose mill scale and loose rust by wire brushing before delivery to the laboratory.

5.3.4.3 Testing

Test each sample of tendons to determine the characteristic breaking load, characteristic proof load, elongation at maximum load, diameter, cross-sectional area, unit mass, modulus of elasticity and ductility.

Method of the testing is to be in accordance with the following:

a. High tensile steel wire: SS 475: Part 4

b. High tensile steel strand: SS 475: Part 4

c. Hot rolled processed high tensile alloy steel bars: SS 475: Part 5

5.3.4.4 Compliance

Characteristic'breaking load and characteristic proof load is to satisfy the values specified in the referenced standards.

5.3.4.5 Non-compliance

If the result of any material property test for elongation at maximum load, diameter, cross-sectional area, unit mass, modulus of elasticity or ductility of tendons does not comply with the specified requirements, provide one additional sample from the same batch and repeat the test. The number of specimens in the additional sample is to be as directed. If the result of any additional test fails again, the entire batch is deemed as not comply with the specified requirements.

5.3.5

5.3.5.1

Duct Friction Test

Sampling

Carry out this test when required as indicated in the PSD.

Duct friction test is I is not required for the project.

If required, carry out __ numbers of duct friction test.

5.3.5.2 Testing

Stress tendons from one end and measure' the tendon force afboth jacking and non-jacking ends. Measure the tendon force at the non-jacking end by direct-reading load cells or by a dummy jack of an approved type. The load-measuring device is to be sufficiently rigid to ensure that the movement of the tendons at the non-jacking end under the specified tendon force is not excessive. The load-measuring device is to be readable and accurate to 0.5 mm.

Stress the tendons to the specified tendon force in equal increments. Measure the tendon elongations at the jacking end and the tendon force and tendon movement at the non-jacking end. Suit the number of load increments to the tensioning operation with at least 5 increments:

5.3.5.3 Compliance

The force at the non-jacking end of the tendons determined in the duct friction test is to be within +10 % and -5 % of the calculated value.

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5.3.5.4 Record

Submit to the SO for acceptance, the record of duct friction tests within agreed time frame.

Include at least the following information in the records:

a. details of prestressing system including tendons, anchorage and sheath

b. stressing sequence

c. method of measuring elongations

d. calculated values of prestress loss, tendon force and tendon elongations

e. type and identification numbers of equipment used

f. identification of tendons by numbers with reference to the drawings

g. anti-corrosive or corrosion protection

h. graph showing tendon forces at jacking end against tendon forces at non-jacking end

i. comparison between the calculated and measured tendon forces at the non-jacking end

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A1. GROUT TEST PROCEDURES

A 1.1 Bleeding Test (Inclined Tube)

A1.1.1 Principle

The test consists of measuring the quantity of water remaining on the surface of grout which has been allowed to stand protected from evaporation.

A1.1.2 Apparatus

For inclined tube bleeding test, the apparatus shall consist of an inclined tube 5m long and 80mm diameter equipped with caps at each end and grout inlet at the lower end and grout vent at the top. The tube is to be able to sustain a grout pressure of at least 1 MPa, or other equivalent set-up as agreed with SO. The tube shall be fully grouted.

A1.1.3 Test Proced u re

Place the cylinder on a surface free from shocks or vibration. The grout used is to be from the same batch as that used for the fluidity test. Pour grout into the cylinder to a height of approximately 150mm and seal the cylinder to prevent evaporation. Note the height to the top of the grout (h) ignoring the meniscus. After 3 hours, measure the depth of water on top of the grout (h,), After 24 hours check whether the water has been reabsorbed. The test is carried out on one sample of grout.

A1.1.4 Reporting of Results

Bleeding at the end of 3 hours is given by (h,/h) x 100% where:-h, is the height in mm of water on the surface of the grout after 3 hours. h is the initial height in mm of grout. The report is to state the range of air temperatures and the grout temperature at the time of test, the bleeding at 3 hours and whether the water has been reabsorbed after 24 hours. For acceptance testing, perform a minimum of 2 tests per day, unless otherwise agreed by the SO.

A1.2 Density Test

A1.2.1 Principle

The density is measured as the ratio of weight to volume in both the fluid and the hardened state.

A1.2.2 Apparatus

The apparatus comprises suitably calibrated equipment for weight and volume measurement.

A1.2.3 Reporting of results

The method of sampling, measuring weight and volume, the equipment used and the density determined shall be reported.

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A 1.3 Sedimentation Test

A1.3.1 Principle


The sedimentation is measured as a percentage difference in density of the grout between the samples taken form the top and bottom of the test cylinder.

A1.3.2 Apparatus

A transparent graduated cylinder 60mm to 100mm internal diameter and approximately 1 m in height.

A1.3.3 Test Procedure

Place the cylinder on a horizontal surface free from shocks or vibration. Fill it with grout to the top and seal the cylinder to prevent evaporation. At least 24 hr after filling the cylinder remove the grout column intact from the cylinder. Take two samples from each end of the grout column of approximately 50mm length. Keep the samples . immersed in water. Measure the density of each of the four samples by an approved method.

A1.3.4 Reporting of results

Sedimentation is the variation in the density of the sample from the top compared with the density of the sample from the bottom, expressed in percent. The variation of the density of the second top sample compared with the density of the second bottom sample shall also be reported.

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A2. GROUTING PROCEDURES

A2.1 General Grouting of Tendons

Procedure of grouting of tendons:

a. Start grouting from the lower end of duct.

b. Apply grout pressure as low as practicable not exceed 1 MPa (10 bar).

c. Grout injection is to be continuous and steady and is to be at a rate, which will avoid grout segregation and the trapping of air in the duct.

d. Allow grout to flow from each of the grout vents until its consistency is equivalent to that of the grout injected.

e. Vent further 5 litres grout at each vent into a clean receptacle.

f. Test representative samples as indicated by the SO in accordance with the specified grout testing procedures and discard the grout.

g. Close all vents one after another inthEi direction of flow.

h. If the grout pressure exceeds 1 MPa (10 bar), close the valve at the grout nozzle, connect the nozzle to the next already filled vent and continue grout injection from there.

i. After the last grout vent has been closed, maintain the pressure at 0.1 to 0.3 MPa (1 to 3 bar) above the maximum grout pressure for 1 minute to check for any leaks.

j. Close the injection vent under pressure.

k. For cables with more than two crests, open all crests in the duct profiles for 10 minutes after completion of grouting one after the other and vent grout through the vent until its consistency is equivalent to that of the grout injected.

I. Record any escape of air, water or grout and immediately report to the SO to agree any further necessary actions.

A2.2 Vacuum Grouting of External Tendons

Procedure of vacuum grouting of external tendons:

a. Connect a vacuum to the far end of duct.

b. Activate the vacuum with all vents closed and run it for not less than 10 minutes prior to grout injection.

c. Maintain a negative pressure of 0.075 MPa (750 millibar) throughout the grouting process.

d. Start grouting from the lower end of duct.

e. Apply grout pressure as low as practicable not exceed 1 MPa (10 bar).

f. Grout injection is to be continuous and steady and is to be at a rate, which will avoid grout segregation and the trapping of air in the duct.

g. Maintain the vacuum until grout is observed at the higher end of the duct.

h. Close the higher end of the duct.

i. Allow grout to flow from each of the grout vents until its consistency is equivalent to that of the grout injected.

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j. Vent further 5 litres grout at each vent into a clean receptacle.

k. Test representative samples as indicated by the SO in accordance with the specified grout testing procedures and discard the grout.

I. Close all vents one after another in the direction of flow.

m. If the grout pressure exceeds 1 MPa (10 bar), close the valve at the grout nozzle, connect the nozzle to the next already filled vent and continue grout injection from there.

n. After the last grout vent has been closed, maintain the pressure at 0.1 to 0.3 MPa (1 to 3 bar) above the maximum grout pressure for 1 minute to check any leaks.

o. Close the injection vent under pressure.

p. For cables with more than two crests, open all crests in the duct profiles for 10 minutes after completion of grouting one after the other and vent grout through the vent until its consistency is equivalent to that of the grout injected.

q. Record any escape of air, water or grout and immediately report to the SO to agree any further necessary actions.

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Documents

NPQS C3-70 - Pre Stressed Concrete Works Ver 1