Biện pháp mô tả chi tiết quy trình thi công đúc sẵn dầm I BTCT dự ứng lực. Được biên soạn theo chỉ dẫn kỹ thuật dự án, tiêu chuẩn AASHTO, TCVN
GENERAL DESCRIPTION
Introduction
This method statement provides the details of the procedure, the manpower, the equipment, the materials and relevant documents related to construction box culvert including the quality control verifications, the measurement verifications, and also the safety precautions and environment protection to be implemented for this work.
Project Information
The project road connects Tbong Khmum district to Kratie province of the Cambodia, stretching along the northern, to Kratie province The road passes on a comfortable alignment through flat/wavy terrain along the toe of hilly land Four (4) rather sharp curves along the road are considered non-critical due to adequate super-elevation of the road way and appropriate signage The traffic on the road is a medium mix of private cars and quite heavy trucks that contribute mainly to the road wear The PR.377 and PR377A of RCIP are located in Kratie province The length of the PR377 is 35.00 km and the PR377A is 13.593km The location of the packages is shown in Figure-1
Figure 1.2 Location of Contract Package on CW-3(PR377 & PR377A)
Project Objective
The objective of the project is to ensure continued effective use of the rehabilitated national and provincial road network in support of the economic development in Cambodia It will do so by improving the institutional and technical capacity of the Ministry of Public Works and Transport for road maintenance planning, budgeting and operations as well as by expanding of strengthening maintenance activities.
The project seeks to contribute to cultivating a road asset management culture within the sector by:
(i) expanding maintenance of the national road infrastructure nationwide and facilitating interventions in priority areas, (ii) allocating adequate maintenance funding during the budgeting process; (iii). knowledge building in MPWT on road network management, maintenance technology and contract management; and (iv) private sector involvement in competitive bidding and performance quality.
Project is expected to bring significant benefits to local residents in six Cambodian provinces,Kampong chham, Tbong Phmum, Kratie, Mondulkiri, Ratanakiri and Stung treng province; by reduced travel times and cost, less arduous journeys and better connectivity along the national road network It is intended that the benefits to local populations are maximized, and to ensure that the benefits are shared by local communities.
Topography and Climate
The topography in the project area is mainly flat with some hilly sections and the road elevation varies from minimum 23.52m to maximum 50.95meter The maximum temperature is around 40°C, the annual temperature fluctuates more than 10°C and from 6 – 7°C in a day In hot weather the absolute high temperature may be up to 39°C (in April) By contrast, in January the absolute low temperature may descend to 16°C.
Rainfall Records
Rainfall data from 1980 to 2019 was obtained from Kratie Provincial Department of Water Resources and Meteorology (PDoWRAM) for frequency analysis The highest annual 24hr maximum rainfall was recorded in 1988, followed by 1982 The year 2009 had the highest rainfall after 1992, occurring during the Ketsana storm 2001 recorded the lowest rainfall, indicating a drought period.
Figure 1.5.1 Daily Rainfall Ditribution in Kratie 1980-2019
DESCRIPTION OF WORKS
Scope of Works
This is Method Statement for production of prestressed concrete I-girders (PC-I Girders) for superstructure
Summary table of PC-I Girder:
No Type of I girder Number Bridge Package
Standards and Technical specification related
CAM PW 04-102-99 Bridge Design Standard (Cambodia, 2003) AASHTO, 2002 Standard Specifications for Highway Bridges Other Standards related b) Technical specification
+ Section 5.1: Concrete of Specifications + Section 5.2: Reinforcement of Specifications + Section 5.4: Prestressed Concrete
Construction Schedule
Construction Schedule shall be referred to latest approved Schedule.
ORGANIZATION CHART
Organization Chart is as follow:
MANPOWER AND EQUIPMENT
Equipment
Plants and equipments proposed as in Table below:
No Description Model Quantity Remarks
7 Cement slurry mixer Truck JB-1801.5KW 1
10 Bar Cutter Max dia 32mm 2
11 Bar Bender Max dia 32mm 2
15 Air Compressor 7kg/cm 2 1 Cleaning work
Above stated schedule of equipment shall be increased in quantity if required and necessary Actual equipment mobilized shall be subjected to inspection and approved of the Engineer.
Calibration of pre-stressing Jacks and pumps shall be implemented at least one time per year and after repairing And extra calibration shall be conducted if each pre-stressing result or group control of pre-stressing show abnormal phenomenon or the Engineer’s request.
Manpower
Workforce to be mobilized for construction work as below:
Notes: This manpower will be increased according to the site requirements
MATERIALS
List of main materials used for constructing
1 Portland Cement 2 Course of Aggregate 3 Fine Aggregate
5 Admixtures6 Steel Bars7 Steel Strands8 Steel Duct9 Anchorages10 Other supplies
Technical requirements of the material
Cement shall conform to the requirements of AASHTO Standard Specification M85 The use of high alumina cement is not allowed Cement shall conform to Type I unless specifically otherwise stated in the Special Provisions, or on the Drawings Supply of cement shall be submitted for approval before use, with respect to origin and quality Subsequent deliveries shall be also subject to quality control testing as work proceeds.
Approval of origin and quality require test results demonstrating the cement factory's ability to consistently meet specified physical and chemical properties Regular quality control tests on each cement delivery determine characteristics such as fineness, soundness, setting time, and strength.
+ Specific gravity+ Specific surface by means of air permeability
+ Hot and cold expansion properties + Compressive strength at 3, 7 and 28 days + Setting time
The Contractor shall provide suitable means of storing and protecting the cement agains dampness that shall be subject to the approval of the Engineer.
The Contractor shall store consecutive deliveries of cement separately and shall ensure that cement is used in chronological order of delivery.
The Engineer may reject cement which is more than eight weeks old or which has become partially set or which contains lumps of caked cement The use of cement reclaimed from discarded or used bags will not be permitted b) Water
Water used in mixing and curing concrete shall be subjected to approval of the Engineer and shall be clean and free from oil, salt, acid, alkali, sugar, vegetable, or other substances injurious to concrete or steel Generally, water that is suitable for drinking is satisfactory for use in concrete.
Water shall be tested by methods described in AASHTO T26, and shall not contain concentrations of dissolved solids, chlorides expressed as Cl, and sulphates expressed as S04 in excess of the following limits:
Application Dissolved Solids Concentrations in ppm
Water which contains a high content of suspended solids shall be allowed to stand in a settling basin before use The value of Cl (Chloride Ion) for Prestressed Concrete shall not exceed 500 parts per million (ppm). c) Coarse Aggregate
Coarse aggregate shall consist of clean, hard, durable rounded natural aggregates or crushed rock It shall comply with the requirements of AASHTO M80, Coarse Aggregate for Portland Cement Concrete, in respect of bulk density, unit mass, water absorption, stability, soundness, material finer than 75 microns, deleterious materials, sulphur content, physical properties and particle shape If required, aggregate shall be washed to satisfy these requirements.
The coarse aggregate shall have a Los Angeles abrasion coefficient, after 500 revolutions, below 35
% (AASHTO T-96) and a water absorption capacity < 5 % (AASHTO T-85)
The aggregates shall include as few as possible of flat and elongated particles The testing for checking the amount of particles with an incorrect shape shall be carried out either by determining the average volumetric coefficient of the aggregate, or by any other equivalent method approved by the Engineer
The coarse aggregate for use in concrete structures shall not contain any materials that are deleteriously reactive with the alkalis in the cement in an amount sufficient to cause excessive expansion of mortar or concrete, except that, if such materials are present in injurious amounts, the coarse aggregate may be used with a cement containing less than 0.6 percent alkalis calculated as sodium oxide or with the addition of the material that has been shown to prevent harmful expansion due to alkali-aggregate reaction d) Fine Aggregate
Fine aggregate shall consist of either a sand resulting from the crushing of the rock used for the fabrication of coarse aggregates with a Los Angeles abrasion coefficient lower than 35 % at 500 revolutions (AASHTO T 96) and a water absorption capacity lower than 5 % (AASHTO T 84), or a natural river sand The use of marine sand is not allowed
Fine aggregate shall conform to all the requirements of AASHTO Standard Specification M6 e) Admixtures
Admixtures or any other additions shall not be used except with the written approval of the Engineer
The Contractor shall submit specifications and samples of any admixtures or additive that he proposes to use, to the Engineer at least 28 days before the commencement of construction or manufacture of the particular structure on which he intends to use such admixtures f) Concrete Mix
The concrete mix is tested under the supervision of a supervisory consultant and meets the project's technical requirements
The design testing of concrete mix composition is carried out in the field laboratory.
Before designing concrete mix, must submit to the consulting engineer the origin of the materials, together with the factory certificate as well as the material test results When taking samples for testing, they must be witnessed by the supervision consultant, make a record of taking samples for testing and fully signed by the parties before they can be tested.
Concrete mix design results must be reported in writing.
The composition and strength of concrete must satisfy the requirements in the following table:
Note: The air content for concrete Class A1, A2, B1, B2 and B3 shall not be more than 4, +/- 1 percent
Table 5.2.2: Trial Mix Characteristic Properties
Minimum compressive strength (Mpa) Minimum flexural strength
Slump (mm) 3-Day 7-Day 28-Day 3-Day 7-Day 28-Day Non vibrated
The flexural strength is expressed as the modulus of rupture MR = K* √ f ' c ,with K=0.7 to 0.8, and f’ c in Mpa. g) Reinforcement
The Contractor shall submit the name of the proposed supplier (or suppliers) of the reinforcement and necessary information concerning the supplier as soon as possible to the Engineer for his approval.
Bars for concrete reinforcement shall conform to the material properties specified in AASHTO M 31M, Deformed and plain billet-steel bars for concrete reinforcement, Grades 300 and 400 Deformed bars shall be of Grade 400, plain round bars shall be of grade 300
Wire and Wire Mesh: Wire shall conform to the requirements of AASHTO Standard Specification
M 32 –Cold Drawn Steel Wire for Concrete Reinforcement Wire mesh shall conform to the requirements of AASHTO Standard Specification M 55 - Welded Steel Wire Fabric for Concrete Reinforcemen.
Bar Mat Reinforcement: Bar mat reinforcement for concrete shall conform to the requirements of
AASHTO Standard Specification M 54 - Fabricated Steel Bar or Rod Mats for Concrete Reinforcement. h) Pre-Stressing Reinforcement
High Tensile Strength Steel Strand - High Tensile Strength Steel Strand shall conform to the requirements of AASHTO M203 Uncoated Seven-Wire Low Relaxation Stress-Relieved Strand for Prestressed Concrete Strand shall be delivered in coils of sufficiently large diameter to ensure that it pulls off straight They shall be stored clear of the ground and protected from the weather and any other potentially harmful effects. i) Anchorage Assemblies
TESTING AND SAMPLING
Lab
The contractor will submit to the consultant a qualified testing unit The profile will be submitted separately by the contractor The experimental unit will serve the project with the approval of the consultant.
Experimental Work
Contractor will provide full test certificates, origin of all supplier's materials.
The material criteria shall conform to the requirements in item “5: Materials” and the requirements of the technical instructions.
All tests shall be conducted in a manner approved by the engineer and shall be conducted in the contractor's laboratory. a) For concrete mix:
According to the specifications outlined in AASHTO Testing Specifications T-22, T-23, T-97, T-126, T-119, and T-141, all concrete utilized in the project must undergo rigorous sampling and testing procedures These tests are crucial for ensuring concrete quality and adherence to the specifications detailed in the Technical Specifications.
During concrete placement, random samples are collected from separate batches These samples are used to create at least two cylinders per batch using standardized steel molds Each cylinder is clearly labeled with batch or lot information and its location within the structure For precast concrete, cylinders are marked for easy identification with their corresponding structural unit.
Samples of the steel lot delivered to the site will be taken for testing at the request of the engineer.
The frequency of testing for reinforcement shall not be less than the following frequency: 1 time/ each type of diameter/ each batch of steel delivered to the site Additional tests may be required by the engineer.
All rebar tests shall conform to the requirements and specifications of the AASHTO standards. c) For Pre-stressing Reinforcement:
High Tensile Strength Steel Strand - At least one specimen for test shall be taken from each 20 tons production lot of finished strand Test specimens shall be cut from the outside end of reels or either end of coils of strand Any specimen found to contain a wire joint should be discarded and a new specimen obtained.
The specimens shall be tested to determine compliance with the requirements of the relevantAASHTO Specifications.
CONSTRUCTION REQUIREMENT
Reinforcement
Each bundle of steel shall be tagged at the mill with an identifying mill tag showing the name of the mill and the melt or heat number The Contractor shall also make available for review, when requested by the Engineer, a copy of the certified mill test report for each heat and size of reinforcing steel showing physical and chemical analysis
Reinforcement for structures shall be handled and stored in a manner that will prevent bending out of the desired shape and the unnecessary accumulation of dust, oil and paint
All reinforcing steel shall be stored under cover and protected from the weather, and no reinforcing steel shall be stored in direct contact with the ground nor with water.
Before concrete is placed, the reinforcement to be embedded shall be free of mortar, oil, dirt, loose mill scale and loose rust, and other coatings of any character that would destroy or reduce the bond. b) Cutting and Bending
Bars shall be cut and bent cold to the dimensions indicated and with equipment and methods approved by the Engineer.
Stirrups and tie bars shall be bent around a pin having a diameter not less than two times the minimum thickness of the bar Bends for other bars shall be made around a pin having a diameter not less than six times the minimum thickness except for bars larger than 30 mm in which case the bends shall be made around a pin of eight bar diameters Hooks shall conform to American Concrete Institute Standard Building Code Requirements for reinforced concrete (ACI 318), Section 906, or as shown on the Drawings.
Reinforcement shall conform accurately to the dimensions shown on the Drawings Bars shall not be bent and straightened in a manner that will injure the material In particular it shall not be authorized to straighten back deformed bars which have been previously bent Bars with kinks or improper bends shall not be used.
All reinforcement bars shall be sheared; flame cutting will not be permitted unless approved by the Engineer c) Placing, Supporting, and Fastening
All bar reinforcement shall be placed, supported, and secured before the beginning of concreting operations The reinforcement shall be checked and approved by the Engineer before placement of concrete begins The minimum spacing of bars shall not be less than 1.33 times of the maximum particle size of the coarse aggregate Laying or driving bars into the concrete after placement will not be permitted All horizontal reinforcement shall be supported on metal supports or mortar blocks of approved shape with tie wires embedded in them made out of Portland cement and sand in the ratio of 1 to 3 by weight Supports that are in contact with the external face of the concrete will all be mortar blocks The use of small stones or wood blocks will not be permitted The reinforcement shall be held securely in place at the exact position and at the exact spacing as indicated on the Drawings by the use of wire ties at bar intersections, supports and spacer blocks.
Proper reinforcement measures in construction involve securing wire ties tightly and making sure they do not extend beyond the reinforcing bars' planes These ties ensure the reinforcement is secure, and the adequacy of both supports and ties is subject to the Engineer's approval, ensuring the project meets industry standards and safety requirements.
The concrete cover shall be in accordance with the requirements of the AASHTO LRFD Bridge Design Specifications, Section 5, Table 5.12.3-1, unless otherwise indicated in the Drawings. d) Splicing
Reinforcement shall be furnished in the lengths indicated on the Drawings Lap splicing except where shown on the Drawings will not be permitted without written approval from the Engineer, and if additional lap splices are used the additional weight occasioned by such lap splices with not be included in the measurement of reinforcement for payment.
Lap splices in reinforced concrete structures require specific dimensions for tensile and compressive reinforcement Tensile reinforcement must have a lap length of at least 40 bar diameters, while compressive reinforcement requires a lap length of 32 bar diameters or as specified in construction drawings Lap splices should be positioned at locations with minimal tensile stress Typically, bars in lap splices are placed in direct contact and secured with wire ties, unless specified otherwise in the drawings.
Welding of reinforcing steel shall not normally be permitted and shall only be done if detailed on the Drawings or approved in writing by the Engineer Before the Engineer will approve of welding, theContractor shall submit such samples as the Engineer may require for testing and make allowance for the time elapsing before test results are available.
Welding of reinforcing steel, if permitted, shall conform to the Structural Welding Code AWS Dl.4 of the American Welding Society and applicable special provisions and shall only be done where shown, specified, or permitted by the Engineer Every welder shall possess a welding certificate issued by an internationally recognized authority acceptable to the Engineer e) Substitutions
Substitution of different size bars will be permitted only with specific authorization by theEngineer If steel is substituted, it shall have a cross sectional area equivalent to the design area or larger.
Formwork
Formwork shall include all temporary or permanent moulds for forming the concrete All formwork shall be of wood or metal and shall be built mortar-tight and rigid enough to maintain the concrete position during placing, compaction, setting, and hardening.
Formwork for exposed surfaces shall be made of dressed lumber of uniform thickness with or without a form liner of an approved type or shall be of metal sufficiently rigid in itself with no surface blemishes that will impair the quality of the concrete surface finish No rusty or bent metal forms shall be used Formwork shall be chamfered on all sharp edges and shall be given a bevel in the case of all projections.
Rough lumber may be used for surfaces that will not be exposed in the finished structure All lumber shall be sound, free from warps and twists, sap, shakes, large or loose knots, wavy edges or other defects affecting the strength or appearance of the finished structure.
The shape, strength, rigidity, water tightness and surface smoothness of reused formwork shall be maintained at all times Any warped or bulged lumber must be resized before being reused Formwork which is unsatisfactory in any respect shall not be reused.
Internal ties shall be so arranged as to permit their removal to a depth of at least 25 mm from the concrete face without injury to the concrete No permanently embedded metal shall have less than 25 mm cover to the finished concrete surface.
Formwork shall be so constructed that easy cleaning out of any extraneous material inside the formwork can be achieved without disturbing formwork already checked and approved by the Engineer.
Formwork shall be treated with approved non-staining oil or saturated with water at the discretion of the Engineer before placing concrete Form oil will only be used after the approval of the Engineer has been given The Engineer may require trials to be carried out before approval is given for the use of a particular form oil, to ascertain that the form oil proposed by the Contractor will not discolor or injure the finished concrete face in any way.
Removal of Formwork and False-work
General - Formwork shall be constructed such that the side forms of members can be removed without disturbing the soffit forms and, if props are to be left in place when the soffit forms are removed, the props shall not be disturbed during striking All formwork shall be removed without damage to the concrete.
Time of removal - Forms and false-work shall not be removed without the approval of the
Engineers must approve construction plans, but this approval does not relieve contractors from the ultimate responsibility for worker safety Safety precautions include removing blocks and bracing simultaneously with forms to prevent debris from compromising the concrete's integrity Adherence to these safety measures ensures the well-being of workers and the durability of the finished structure.
Forms used on exposed vertical faces shall remain in place for periods that shall be determined by the Engineer.
Structures reinforced with regular cement must have formwork and falsework supporting slabs, beams, girders, and arches for 14 days after concrete placement Conversely, structures utilizing high early strength cement may have formwork removed earlier than 14 days, but only with written approval from the Engineer The Engineer will determine the appropriate removal time based on test results.
Formwork and false-work for the whole of suspended span bridges and other special structures shall remain in place until such time as the Engineer will decide after all concrete has been poured.
Patching - As soon as the forms are removed, all wire or metal devices used for securing the formwork which project from or appear on the surface of the finished concrete shall be removed or cut back at least 25 mm from the finished surface of the concrete All holes and pockets so formed shall be filled with cement mortar mixed in the same proportions as the fine aggregate to cement of the concrete mix used for that particular section of the structure, after the surface to be patched has been thoroughly cleaned and wetted to receive the patch.
General Concrete Problems
After having carefully accepted the formwork, reinforcement and approved by the consultant and supervisory engineer, the contractor is allowed to proceed with the concreting work.
Inspection of the exact position of the heart, the core, the waiting details to ensure that after the concrete is poured, the formwork and the rear formwork are installed without deviation.
The concrete used is supplied from the “cement concrete batching plant”: Concrete trucks are transported to the construction site, then the concrete will be pumped with Dedicated pump truck.
Mixing and transporting concrete must comply with the requirements of technical specification.
The thickness of the concrete layers is suitable for the size of the structure and compaction tools but must not exceed 30cm according to the pouring speed (v < 25m3/h).
Workers will pour concrete under the guidance of field staff to ensure that the concrete work is performed in the correct order, reasonable specifications, and regulations.
Do not distort position of reinforcement, formwork, position of waiting details and thickness of protective concrete layer.
If the reinforcement is bent or warped, it must be straightened before concreting.
Make a working platform for officials and workers to walk during the concrete pouring process without stepping on or stepping directly on the reinforcement, causing damage to the reinforcement.
Concrete structures require meticulous attention to concrete surface levels Prior to pouring, fixed landmarks should be established to ensure accuracy in elevation compared to design specifications Additionally, the concrete surface should be finished with precision, particularly with respect to its cardboard By adhering to these measures, the integrity and longevity of poured structures can be maximized.
Concrete mix fabrication, concrete mixing and concrete transportation:
These works shall be in accordance with the directive section 5.1 “Concrete” – in the TechnicalSpecifications of the project
Post-Tensioning Method
Stressing shall be applied to produce the stresses required in the wires immediately after the anchorage as shown on the Drawings or as directed by the Engineer Suitable allowances shall be made for friction in the jacks and cable ducts and for slip and yield in the grips or anchorages.
The tensioning process shall be conducted so that the tension being applied and the elongation may be measured at all times A record shall be kept of gauge pressures and elongations at all times and the minimum age in hours of the concrete in the unit at the time the stressing took place Pre-stressing forces shall not be applied to the concrete until it has attained strength as specified above for the pre- tensioning method.
PRODUCTION PROCEDURE
Description of work sequence
Site preparation for production yard shall be carried out before mobilization of necessary materials and equipments for the production of PC I-girder.
The location of casting bed shall be compacted to prevent settlement during the application of load
The working area shall be level as possible and stable for good mobility of equipments.
For foundation of casting bed, existing unsuitable soil such as mud or organic soil shall be replaced to suitable material or and compacted adequately to prevent settlement of casting bed.
Checking condition and elevation of casting bed shall be taken during production of PC I-girder even result of static load is satisfactory with criteria for acceptance.
Material and equipment for the work shall be set up And required approval such as for material testing and calibration of stressing jack and pump shall be confirmed.
Prior to commencement of work, all equipment and workers shall be inspected with attendance of the Engineer.
Approval working drawing for PC I-girder shall be confirmed prior to commence production of PC I-girder. b) Fabrication of reinforcing steel bar
Material test of rebar shall be carried out in accordance with Tecnical Specification of Project.
Reinforcing Bars shall be kept off the ground and stored within a building or provided with suitable cover.
Rebar shall be fabricated in accordance with the shape and dimension as shown on approved working drawing.
Bar cutter equipment, bending equipment shall be used to cutting rebar, bending rebar.
Fabrication of rebar shall be carried out by cold cutting and cold bending Rebar fabrication by application of heat shall be in accordance with the Engineer’s instruction. c) Setting bottom form
Bottom form shall be prefabricated wood form with 18mm thickness
Bottom form for casting bed shall be installed on the wood bars with distance 200mm internal.
These wood bars shall be installed on concrete beam at headbeam location and wood bars (100x100mm) at middle location.
Triangular fillets 25mm x 25mm to form smooth straight chamfers shall be installed to all sharp edges of the exposed surface of bottom of PCI girder.
All form shall be cleaned free from dust, grease or other foreign matter and shall be treated with approved form release agent before installation. d) Installation of rebar
Rebar including embedded rebar for diaphragm shall be installed in accordance with approved working drawing
Concrete blocks with whip shall be installed at bottom and side of rebar in order to keep the appropriate concrete covering
Fixing and splicing of rebar shall be done by iron wire 0.9mm or larger diameter
Splicing length and location shall be in accordance with working drawing
Rebar shall be tied at all intersections to prevent dislocation during casting.
Fixing by welding shall only be carried out if it is shown on approved working drawing or as instructed by the Engineer.
Installed rebar shall be free from rust, dirt, oil or other material that might reduce the bond.
Temporary embedded materials, such as PVC pipes used to support deck slabs, must be installed correctly After the materials have served their purpose, their locations should be neatly filled in with cement mortar, as per the relevant clause.
Inspection and approval by the Engineer shall be carried out prior to setting of forms. e) Installation of Steel Ducts with End-Anchorage devices
Steel ducts shall be installed in accordance with designed alignment and location shown on
Steel ducts shall be fixed and supported by rack rebar and adequately tied to prevent dislocation during concrete casting
Ducts shall be tied at all intersections by using annealed iron wire ỉ=0.9 mm or larger diameter, and shall be supported by using rebar ỉmm.
Anchorage device shall be installed in accordance with the location and arrangement show on approved working drawing.
Anchorage device shall be fixed firmly with end form by 3nos of diameter 8mm bolt The hole for grouting shall be protected by plastic cap to prevent inflow obstruction.
Any obstruction shall not be allowed to be in PC duct before, during and after installation of steel ducts. f) Installation of side forms
Pre-fabricated metal form panels shall be used for side form
Formworks shall be installed by Truck-Mounted Crane following the layout markings on the bottom form
Layout of panel forms shall be arranged in consideration of diaphragms and fabrication length of PCI girder
Forms shall be properly fixed by braces and support to keep the shape and dimension shown on approved working drawing
All forms shall be cleaned, free from dust, grease or other foreign matter and shall be treated with the proper form-release-agent before installation.
Holes on side from for embedded rebar for diaphragm shall be made at proper location with proper dimension in accordance with approved working drawings
All joint between the part of side form, between the side form and bottom form, form for girder top should have rubber cushion for preventing leakage cement water.
The gap between metal form and supporting beam shall be also wedged by cleat to prevent form displacement.
Inspection and approval by the Engineer shall be done prior to casting concrete. g) Installation of PC strand into steel ducts
Permanent pre-stressing strand shall be installed manually into ducts.
During the bundle threading process, the steel bunch shall not rotate, and shall pass through the hole straight After threading out, check whether the numbers of the steel strands at both ends correspond to the correct positions If not, adjust them to be consistent After threading, the steel bundle should be able to slide freely in the pipeline; otherwise, the cause should continue to be identified and measures should be taken.
Installed pre-stressing cable shall be extended minimum 60cm over both ends of girders in order to install jack for stressing. h) Installation of girder ‘s end Formwork
Formwork shall be in accordance with the requirements of technical specification of project
2 pieces of formwork shall be installed at the ending of the girder
Completion and preparation of next work i) Concrete casting for PCI girder
This Stage shall be set before casting concrete.
Temporary casting platform shall be set up for the casting of prefabricated girders The platform shall have enough construction space and be easy to operate and safe for workers during construction The concrete is mixed centrally in the mixing batching plant, and the concrete mixing conveyor is used for transportation.
Before casting, Construction education should be made to all operators, and a comprehensive inspection should be carried out on the formwork, rebars and embedded parts Construction can only be carried out after meeting the requirements.
Crane and Bucket shall be prepared before casting.
Water shall be sprayed on form, rebar and surface of bottom form prior to concrete casting
Checking the temperature and slump of concrete.
Casting work shall be carried out layer by layer to ensure that concrete shall be placed and compacted throughout the height of the PCI girder especially at anchor location.
The top of 1st layer shall be on top of haunch of bottom flange of girder And compaction shall be taken care strictly to prevent air void on surface of concrete of haunch.
Firstly, flexible vibrator shall be used to compact concrete for each layer And secondary, static vibrators on side forms shall be operated proper duration for 1st ~ 3rd layer.
The top of 2nd layer will be on middle of girder Static vibrator will be operated to compact concrete after compaction by flexible vibrator same as for 1st layer.
Concrete shall be consolidated by approved mechanical vibrators.
Vibrator shall be penetrated into the previously cast layer through the new casting layer.
Concrete vibrators will not be used to transport concrete like a shovel inside the formwork during casting.
Static vibrators (external vibrator) shall be installed outside the form to compact concrete and prevent honeycomb on concrete surface.
The vibrator shall be of a type apporoved by the Engineer, with a minimum frequently of 3500 implulses per minute and shall be capable of visibly affecting a properly designed concrete with a 2 centimeter slump over a circular area of 45 centimeters radius.
Concrete condition shall be closely monitored to avoid concrete to harden before casting the next layer
During concrete casting, it is crucial to ensure the tightness of formworks Regular inspections and monitoring should be conducted to check for any displacement If any movement or displacement of formworks is detected, immediate adjustments must be made to reposition the forms back to their correct position before continuing with concrete placement These timely adjustments prevent potential defects or compromises in the concrete structure's integrity.
Installed rebar and Steel ducts shall be taken care to prevent dislocation during casting concrete.
Notes: When casting the upper concrete, the vibration of the vibrator is intermittent, the concrete no longer sinks, no bubbles rise, the surface is flat and there is a thin layer of cement slurry Be careful not to vibrate the reserved pore and formwork surface during vibration.
In the process of construction, only the part where the concrete casts vibrate No empty vibration exists.
When the girder top plate concrete vibration completed, it should be levelled with wood wipe in time, and measured with a levelling instrument to ensure the flatness of the concrete surface on the top of the girder In order to reduce shrinkage cracks of concrete, the concrete is levelled with steel wipe before initial setting/hardening. j) Removal of forms and curing of concrete
The girder formwork can be removed when the girder reaches the strength after casting
Removal of form shall be taken with care not to damage or injure the newly cast PCI girder.
In the process of formwork removal, it is not allowed to pry with iron objects in case of damaging the concrete surface of the girder After the formwork is removed, the girder should be moved to the storage place, cleaned, repaired, oiled and maintained for next use.
After removal of forms, surface of concrete where diaphragm will be constructed shall be treated with chipping as construction joint.
Exposed surface of girder (top surface of girder) shall be covered by wet burlaps immediately after final finishing of concrete surface.
Immediately after forms have been removed and finishing completed, all concrete shall be cured by one of the following methods:
Water method – the entire exposed surfaces other than slabs shall be protected from the sun and the whole structure shall be covered with the burlap, cotton mats, or other suitable fabric for a period of at least seven days.
Membrane forming curing compound – All surfaces shall be given the required surface finish prior to application of the curing compound During the finishing period, the concrete shall be protected by the water method of curing It can be sprayed or applied to the concrete surface by means of an applicator in one or more coast at the rate instructed by the manufacturer. k) Strand tensioning
In this project, the prestressed tension adopts double tension and double control, and the tension jack adopts through-core jack The tension is mainly controlled by stress, and the elongation is used as the check The actual elongation is compared with the theoretical elongation value, and the error should be kept within ±6%
General sequence of prestressing work is shown below:
Checking the concrete strength, if 80% of design strength is achieved, tensioning is permitted to be execution
Checking the technical certificate of high strength steel
Checking the technical certificate of anchor.
Checking the error when setting high strength steel bunch.
Checking and adjustment tensioning equipment (jack for), pressure gauge will be used If the calibration term is over, new calibration should be done.
Determine coefficient of friction of jack and hooped anchor (separate determination should be done for every jack)
Checking hole for high strength steel bunch (cleanness, through passage)
Checking practice on operation safety
Method of cleaning the inside of steel duct before strand tensioning:
QUALITY CONTROL
Quality control of equipment and materials
a) Strictly control raw material supply quality
The technical indicators of cement used in mixing concrete must conform to the corresponding national standards The cement delivered to the site should include the factory test report provided by the supplier, and be inspected and accepted in batches according to the cement variety, label number and factory number The overdue cement needs to be reinspected and unqualified cement shall not be used.
Mixed concrete should be made of hard, durable natural coarse sand as fine aggregate; fine aggregate to the site, should be stored in batches according to different origin, specifications and varieties The test department should provide the report.
The coarse aggregate used for concrete should be hard and durable crushed stone, and the technical indexes must meet the standard.
The water used for mixing and curing concrete must conform to the relevant provisions All drinkable water may be used for mixing and curing concrete.
In order to improve the technical performance of concrete, concrete can be mixed with appropriate chemical admixtures; a variety of admixtures should be provided by the specialized production companies; admixtures to the site whether solid, liquid, should have appropriate packaging containers And with the product identification certificate, store the admixtures after being classified, to prevent deterioration Before using, the admixtures must be carefully checked, mixed and confirmed.
Steel must adhere to national and metallurgical ministry standards Upon entering the site, steel should have a quality certificate or acceptance report from the manufacturer Site test engineers must inspect steel and document findings in the "Steel Bar Test Identification Report" for batch use During transportation and storage, precautions should be taken to prevent corrosion and pollution, and steel should be stored according to factory name, grade, and specification to facilitate identification.
The formwork's construction ensures accurate shape, dimensions, and placement of structural components, as per design specifications Its robust design ensures adequate strength, stiffness, and stability to withstand construction loads Simplicity and ease of installation and removal facilitate efficient operations and multiple reuses.
The combination should be tight and there should be no leakage Every time the formwork is used, someone should be assigned to clean it up and apply a release agent for the next use.
The steel bar should be straightened before processing, and the oil stains and rust on the surface should be cleaned. c) Concrete Quality Assurance Measures
The concrete shall be stirred evenly and the color shall be consistent, and the mixing time shall comply with the regulations.
Concrete should not segregate, leak and bleed during transportation The inner wall of the vehicle should be flat and smooth, and the road should be as smooth as possible.
Before pouring concrete, various inspections and records should be made according to regulations,and sundries on formwork and steel bars should be removed The pouring thickness is appropriate,and the poured concrete should be compacted with a combination of an attached vibrator and an inserted vibrator During the concrete pouring construction, special personnel shall be appointed to check the status of formwork, steel bars, embedded parts and reserved holes, etc. d) Prestressed Construction Quality Assurance Measures
Arrange experienced technicians to guide the prestressed tensioning operation full-time All personnel operating prestressing equipment shall undergo induction training and conduct standardized training through the use of equipment to master operating techniques.
Before operation, calibrate the tensioning equipment and force measuring facilities, and carry out regular inspection and calibration according to the regulations When the temperature drops below 5°C without insulation measures, tensioning work is prohibited.
Contractor must submit the calibration chart of the tensioning equipment and force measure facilities to the engineer The serials number on stressing devices must match those lists on the calibration sheet and the calibration shall be carried out by a recognized laboratory Contractor shall attach the schedule of PC-I girder production (production rate and cycle) and related record form, such as: elongation record, jacking force, etc.
When stretching, make the line of action of the tension force of the jack coincide with the axis of the prestressed steel strand; for curved prestressed steel strands, the line of action of the tension force should coincide with the tangent line at the end of the center line of the tunnel, and make detailed records.
The prestress should be stretched at a slow and uniform speed, and both ends should be carried out at the same time When the prestress stretches to the specified value of the design and reaches the anchorage of the supervisory engineer.
Construction site quality management and implementation control
In order to achieve quality goals, we will take the following quality assurance measures in terms of project site quality management and implementation:
Establish a sound quality responsibility system for the project manager department, decompose the quality objectives, and decompose them layer by layer according to the specific quality requirements of creating excellence by unit project-division project-sub-item project-construction process, and implement the quality responsibility to the utmost grassroots.
Formulate practical and feasible management systems, including joint review of drawings and technical disclosure systems; on-site quality management systems; process management systems; scheme data management systems;
Strict quality procedural management, including: project quality plan, document and data control procedures, material management procedures, process control procedures, inspection and test procedures, non-conforming control procedures, quality record procedures, and standardize various quality with strict procedures management work.
Strengthen quality process control, including: process control plan, quality inspection plan, implementation rules for acceptance quality control, monthly quality report, summary of new materials and new process quality control procedures.
To ensure the highest quality, a stringent three-level inspection system, meticulous process planning, and strict adherence to standards were implemented Unqualified materials and equipment were unequivocally prohibited, and any deviations from established requirements necessitated immediate reworking.
Strengthen the quality control of incoming inspection and testing of raw materials, strengthen the quality inspection of the construction process and the quality control of testing, strengthen the management of construction technology, and conscientiously implement process standards and operating procedures, so as to improve the stability of project quality and ensure the realization ofAll elements of quality objectives are under control.
Construction Process Quality Control
Before the start of construction, according to the actual situation of the project, the project department will prepare the "Construction Organization Design" (construction plan), which will be approved by the engineering department of the company, and if necessary, by the chief engineer or deputy chief engineer.
The construction organization design (quality plan) should specify the quality objectives, construction period, construction methods, quality assurance measures, inspection and test plans, construction equipment, product material requirements, construction personnel, safety assurance measures, environmental requirements, etc.
Carry out three-level technical disclosure:
According to the "Quality Plan" and the requirements of regulations, before each process starts, the engineering and technical personnel of the company or office shall first disclose to the engineering and technical personnel of the project department, and then the engineering and technical personnel of the project department shall report to the team The leader will explain the truth, and finally the team leader will explain the truth to the operating personnel.
Implementation method of quality control
Prior to construction, a comprehensive review process is conducted The project's technical lead assembles key personnel, including foremen, internal workers, and quality and safety specialists Together, they meticulously examine project specifications, construction techniques, and operational protocols These stakeholders delve into the blueprints, engaging in rigorous joint reviews, ensuring a thorough understanding With this knowledge, they meticulously develop a targeted construction organization design, laying the groundwork for a successful execution of the project.
In view of the key points and difficulties of this project, establish a QC team, formulate a detailed construction process card, and strictly follow the card construction to ensure the quality of the project.
Strictly follow the construction drawings.
The person in charge of technology should always check various records and reports, and deal with problems in time when they are found The data clerk in the office should sort out all kinds of materials, and the foreman should make a construction diary.
ENVIROMENT AND SAFETY CONTROL
Safety Control
Prior to starting of construction works, Warning signs and instruction boards shall be fully installed either inside or surrounding the construction site and the following particular matters are to be through to all members working in the construction site in order to complete the work efficiently without any accident or casualty. a) Joint Meeting
Before commencing any project, a briefing session involving all relevant parties is crucial During this meeting, a comprehensive overview of the project's scope, objectives, and implementation strategy should be provided to ensure a shared understanding and alignment This initial gathering helps lay the foundation for efficient and coordinated work throughout the project lifecycle.
All workers shall always wear Personal Protective Equipment (PPE), such as hardhat (helmet), safety shoes, hand gloves and working uniform. c) Prevention of Accident by Heavy Machine
Only skilled operator shall be allowed to operate equipment on site In case of new operators, a test of skill shall be conducted first prior to his acceptance to the job Preventive maintenance check shall be done regularly at equipment working at site prior to full operation Stability of working area and foundation of equipment shall be checked particularly at locations of outrigger and track pad of cranes. d) Prevention of Accident of Electrocution
Electric generating equipment shall be properly protected and properly installed with earth connection Electric wires shall relate to electrical tapes to prevent electric leakage Only skilled operator shall be allowed to operate equipment on site. e) Prevention of Accident in Night Shift Works
Enough lighting system shall be provided for night shift works especially installed at working platforms If necessary, all the surrounding working area shall be lighted up The people who work on the site must wear reflective jacket, if worked at night. f) Existing Facilities
Existing facilities especially existing overhead electric line, water line, telecommunication line and other important facilities at surrounding area shall be taken with care not to damage.