The purpose of this safework method of statement is to provide a standardized framework for the control of cast-in place concrete, including formwork, reinforcing operations to ensure compliance with the project requirements. Method statement is applicable to all cast-in place concrete, including formwork, reinforcing to permanent and temporary structures.
HSE engineer will ensure that the work being carried out in accordance with the project heath and safety manual. A safety fence will be erected all around the perimeter of edge beams & slabs in order to avoid accidents. Other necessary warning signs will be placed at right places. All machinery will be calibrated and maintained well at all times.
Following tools and materials shall be arranged for the purpose of the RCC works.
- Tower Cranes
- Mobile Pump Car
- Transits Mixers
- Poker sizes 2”, 1 ½”, 1” petrol automated
- Concrete buckets
- Hand tools shovels & trowels
- Safety scaffolding & ladders
- Wet absorptive covers
- Water stops
- Premoulded joint filler
- Joint sealants
- Imbedded items
- Form oil
- Water supply
- Other materials as per contract documents.
Method for the Cast-In-Place Concrete
Concrete placement will be in compliance with ACI 304. Contractor will cast the concrete separately between vertical and horizontal members considering various aspects, because casting concrete of horizontal members with vertical members together will result in heavier manpower loading and safety problem. Furthermore, it is structurally not allowed.
When the difference of concrete strength is 1.4 times between vertical member and horizontal member, high strength concrete should be casted first. Therefore column head, beam and slab together will be poured in same concrete grade (G28 Mpa) simultaneously. Grade of concrete for column head should be G40 or G45.
For curing method, use moisture curing for all concrete works. Curing compound will sprayed for 7 consecutive days on concrete upon removal of the forms.
Regarding to spacer, the concrete spacer blocks will be used for the soffits of foundations, slabs & beams. The plastic spacers will be used for the sides of all structural members.
“Zoning & Construction Joints” are mentioned as below.
Considering the volume of concrete to be casted one time and efficient manpower planning, Zoning Plan for construction joints is proposed for each floor as per approved drawings. A sketch of a typical vertical construction joint arrangement shall be available at site.
The vertical construction joint shall be formed using Hy-rib mesh with rebar support to be tied in place to the reinforcing cage. A sketch of a typical horizontal construction joint arrangement shall be available at site.
Hy-rib mesh shall be used to form the horizontal construction joint in raft foundations and slab pours. Careful measure will be taken to prevent leakage of concrete, throughout the mesh in all construction joints. All construction joints will be cleaned and all loose or foreign materials shall be removed before new concrete is casted against them. Additional shear steel bars at construction joints instead of shear keyways shall be installed as per the project specification in all locations.
Bonding agent will be applied on existing concrete surfaces at construction joints that will be joined with fresh concrete.
During casting all construction joints shall be monitored to ensure no movement occur.
“LOT NO SYSTEM” is proposed in order to record and take an inspection conveniently.
Concreting will commence after final inspection or receipt of inspection information by consultant as follows:
Inspection and approval of forms and rebar works prior to pour concrete.
Notify concrete supplier by method of Concrete Fax Order, with Site Manager Approval signature by 24 hours prior to pouring the concrete.
Concrete grade requirements
Notify test laboratory (QA/QC Manager faxes Test Laboratory)
Cube moulds, measuring equipment’s, concrete and ambient temperatures thermometers and slump cone with accessories available.
Vibrators and stand-by vibrators are available in case of emergency.
Tower Cranes, concrete hoppers and buckets are available as a reserve means of concrete placement.
Construction joints are properly prepared.
Access to place of pour confirmed & ready.
Temporary form opening and chutes will be provided to discard waste materials.
All embeds installed and checked.
Checking all procedures for pumping concrete in place.
All forms will be cleaned prior to casting & all foreign materials shall be removed.
No concrete shall be casted before inspections have been completed by the project engineer and approval has been received by the Engineer.
Safe working platforms will be constructed for use by the workers and inspection staff.
Access ladders and scaffold shall be provided & maintained.
During Pour All alignment, elevations and supports will be checked during casting operations to ensure movement will not occur.
Date and location of the pour is recorded. Cubes are casted and cured properly as per contract documents.
Obtain approval for concrete curing at site. Prepare finishing equipment’s and chemicals where required.
Pokers shall penetrate through concrete to the full depth of the wet layer for each portion of pour to ensure full consolidation and prevention of Honey Comb, and other defects.
The standard curing method will be arranged by wet absorptive cover and spray water.
Loading and traffic will be controlled over surfaces newly concreted.
Verify finishes, such as exposed aggregate, smooth etc.
No travelling is allowed while bleed water is on surface of the RCC concrete
In order to minimize Tower Crane loading, various system of forms are proposed. :
- Using CS (Climbing System) for wall above the ground floor, it is easy to deliver other materials and keep safety.
- System form (like Peri form) will be used for Concrete column.
- Prefabricated large panel form will be used for retaining wall at the basement floor.
- Metriform formwork system will be used for Slab and perimeter beam as much as possible.
Lifting of Climbing Forms to Upper Floors:
This system form will be used for wall to be formed quickly and safely. Two tower cranes will be used for lifting formwork materials to the upper floors. The standard height of climbing form is 4,500 mm and it can be adjustable to some extent by using additional panel.
Stage 1: Form poured ready to strip
Stage 2: Removal ties, pull away shutter on climbing bracket using sliding unit. Install climbing cone.
Stage 3: Lift form to next level. Set the form on the climbing cone and lock with safety pin.
Stage 4: Pull landing platform shutter away from wall and lift to next level. Landing platform automatically locates into box-out.
Stage 5: With shutters in “set back” position they can be cleaned and oiled, (landing platform shutter is cleaned from climbing bracket). Reinforcement can also be fixed.
Stage 6: Add box-out former. Move forms back into position.
Check for plumb and alignment.
Forms ready for concreting
This system form will be used for all columns. Two tower cranes will be used for lifting and closing formwork materials to the upper floors.
Early striking. Early striking is a technique whereby the formwork is removed 2 to 4 days after pouring a slab, but the supporting structure of scaffolding or props remains undisturbed until the concrete is strong enough to support its own weight over its full span.
Work sequence is as follows:
- Mark line of position for waffle beam on the floor
- Put the base plate on the marking line
- Install cuplok scaffolding for slab and beam formwork
- Put metriform drophead into the top of scaffolding
- Install metriform primary beam between metriform dropheads
- Install metriform infill beam between metriform primary beam
- Fix the plywood with nail on the metriform formwork
- Mark line of position for waffle mould on the plywood
- Set up the waffle mould on the plywood
- Apply form oil on the formwork
- Fix re-bar
- Install M&E conduit pipe and lighting box
- Casting concrete
Conventional Plywood Forms:
Conventional plywood forms will be erected in compliance with the following ACI 347 limits. Shores and struts will be provided sufficiently and at the required interval to prevent excessive settlement or failure of formwork.
In the case of concrete exposed to view, form ties will be arranged in an orderly pattern and every corner will be chamfered with 20 mm x 20 mm PVC strips to produce uniformly straight lines.
After being stripped from the concrete, plywood panel surfaces will be cleaned and coated with the appropriate amount of form-coating compounds according to the manufacturer’s instructions.
Reshoring of beams and slabs will be done with a maximum spacing in each direction of 3 m right after the original shoring is moved. For reshoring, conventional type supports will be used rather than system forms.
On the floor below the floor being constructed, 100% of reshoring supports need to be maintained according to the specifications. On the second floor and third floor below the floor being constructed, two-thirds and one-thirds of reshoring supports need to be maintained respectively. This means that reshoring is installed to some extent on three floors immediately below the one being placed.
Tolerance: Surveying and adjustment: survey after and before casting and adjust properly.
Camber: maintain ±3mm until vertical support is dismantled.
Finishing line: Before dismantling form and supports, maintain the finishing line within these tolerances.
all dimensions(over 3m) : 6mm
all dimensions(under 3m) : 3mm
column : 6mm
Verticality(total height) : 19mm
Floor: sudden irregularities not permitted.
Requirements for the Reinforcing Bars
The standard height of column form is 3,600 mm. However, form panels will disintegrated into pieces so that it will be possible to be integrated to the desirable height in order to fit into the floor more or less than 3,600 mm. Also plywood will be used as supplementary form for column-beam connections.
Column form shall be a system form like the Peri panel that is composed of 2 pieces of L shape. For the using of metriform formwork system for slab and beam, assembling and dismantling of column form should be very quickly. Application of system form comparing with general conventional type form is quick.
As we believe that the best form work system for slab and beam is system form for this proposed structure (low depth of perimeter beam, waffle slab structure etc.), at this moment, it is recommended concreting separately between vertical and horizontal member considering various aspects, because casting concrete horizontal member together with vertical member will result in heavier manpower loading and safety problem.
Metriform formwork system (SGB – Cuplok support system) for slab form is the best for the project, because beam & slab type is waffle slab and the depth of perimeter beams are not big – the deference between slab thickness and beam depth is not big -, which means that stripping system form will not be difficult.
Metriform formwork system for slab form has an advantage like simplicity, accuracy, safety, design and especially
The most of rebar will be fabricated at the factory. The rebar fabrication area is located at site for the missing and shortage purposes. Rebar’s will be cut and bent to the correct details based on the approved shop drawings.
In case of frustration for supply of rebar’s occurred in market, the rebar fabrication will be implemented at site.
Rebar’s which have a diameter of 12mm or greater will be fabricated by using of bending machines with approved fabrication tolerance under supervision of rebar subcontractors. Fabricated rebar will be stored in a neat and tidy manner and according to contract documents.
The cut and bent rebar will be made up into bundles of the appropriate weight and then transported to the site according to the installation schedule. Each bundle of rebar shall be shipped to the site with a tag indicating the relevant information.
Unloading & Hoisting of Rebar’s on site:
Two tower cranes will be used for the installation of the fabricated rebars. Some of the rebar’s will be hoisted directly to several distributed points on the floor or to the working platforms where rebar installation work is taking place and others will be hoisted after being assembled at site.
The rebar installation procedure will be supervised by the site engineers. Each position of site engineer has a duplicate staff, thus night time rebar’s installation will cause no problem in items of supervision.
Columns and beams rebar’s will be assembled as far as possible mainly at the Stock Yard and then hoisted to the designated place by tower cranes using D-shackles and chains to hold the rebar configuration in place. If necessary, supplement bars or angles will be added temporarily to increase rigidity of the prefabricated rebar. Because of the congestion of rebar’s within column, a part of beam rebar’s still need to be assembled in place.
Column rebar will be also assembled to some extent at the Stock Yard. Column main bars will be tied completely with column ties before being hoisted by tower cranes and positioned to the designated places. To hold pre-assembled rebar’s in place tying shall be done.
Wall & slab rebar’s will be usually hoisted as bundles carried from the stock yard and installed manually by steel fixers. However, if the site condition allows, a portion of wall rebar might be temporarily assembled at the stock yard for efficient installation.
Rebar will be tied firmly with approved wires at the designated spots. Approved supports, chairs and spacers with various shapes and dimensions will be placed underneath or at sides of rebar’s to ensure the correct concrete cover required in the contract documents, for each structural element.
The prefabricated rebar cages shall be tied firmly to keep rebar configuration undisturbed during the hoisting operations.