Below is a safework method of statement that covers first the production of wall panels in a precast factory and then erection of precast concrete boundary wall for any kind of the project.
In a precast factory moulds are used for casting precast units or precast wall panels as per the required sizes.
Precast elements are constructed properly to achieve required finishes and dimensions in accordance with the approved shop drawings.
These moulds where possible shall be fixed on mould pallets.
Completing each cycle the mould and production pallets shall be visually inspected by production staff to identify any wear and deformation.
Steel reinforcement to be provided as per approved shop drawing details.
As applicable provide the openings/provisions for the MEP services, properly coordinated checked and approved by quality team.
Reinforcement cage shall be prepared as per approved shop drawings and placed inside the mould after applying mould release compounds.
Prior to casting of the elements QA/QC inspector will ensure that reinforcement cage and moulds are as per the approved shop drawings.
Placing the Concrete for Wall Panels
Concrete shall be placed as to retain no appreciable amount of entrapped air other than entrained air and to avoid detrimental segregation.
Concrete is produced from the fully atomized batching plant which ideally should be near or attached to the precast factory.
For flat elements the placed concrete shall be compacted using clamp on vibrator (also known as external vibrators) at the casting station.
Use needle vibrators for compacting the concrete for footing.
All surfaces of newly cast concrete shall be protected against drying out.
The protection against drying out shall be maintained until achieving the minimum concrete strength expressed by the cube strength at the end of curing (10N/mm²).
Protection against drying out is carried out without addition of water by keeping the formwork in place and covering the concrete surface with vapour resistant sheets that are secured at the edges and joints to prevent through draughts.
On achieving required strength the finished precast products are lifted out of the production pallets using the demolding crane.
These are later water cured for 72 hours at stockyard.
After demolding the wall panel precast products will undergo final inspection.
The precast wall elements are then marked /labeled to ascertain that the consignment is as ordered & with relevant position of each precast element within the works.
Measuring of dimensions to be done in order to ensure conformity with the requirements of the standards and the specification requirements.
Erection of Precast Concrete Wall Boundary
All the mandatory safety precautions and procedures shall be implemented and followed on the project site.
Personnel involved in the precast wall erection shall wear PPE (Personnel Protective Equipment) at all times.
Any personal without necessary safety equipment shall not be allowed to enter the work area.
Competent and trained erector, foreman, banks man and slinger shall be allowed to carry out all the site activities related to boundary wall construction.
Safety shall be the first priority during the wall installation operations.
It is important that precast components are loaded in such a way that unloading is easily done in appropriate sequence.
However, this must never be at the expense of the safe transit of the complete load and therefore some double handling may be required at the point of installation.
Components must be unloaded in such a manner that the stability of the delivery vehicle is not adversely affected.
Prior to erection the Site Safety Officer shall inspect the mobile crane work area including its setting up and duly sign off the suitability of the area for erection.
All the erection equipment (chains, belts etc.) shall be thoroughly checked by the foreman before commencing erection.
All operatives shall be given safety instructions and training prior to arriving on the site.
No one is allowed to stay or work below the hoisted precast concrete elements.
Prior to arriving on the site / work area, the area on a site or building where precast components are being erected, will be inspected.
This includes the area covered by the radius of a crane from lifting off a lorry (or stack) to the final position of unloading.
If any, corrective measures are required should be informed and completed in timely manner.
After inspection of the work area, a sequence of onsite installation shall be agreed with the Client/Main Contractor.
This includes the site access route and the mobile crane capacity (responsibility of Client/main contractor).
It is recommended that crane operator himself should inspect the work area before finalizing the crane capacity.
Note: The manufactures rating capacity for crane refers to its safe load carrying capacity at a minimum radius and often bears little relation to its actual capacity at a working radius when lifting precast elements.
Precast concrete elements shall be erected by mobile crane of adequate load carrying capacity.
Erection shall be carried out as per approved drawing consisting of plans and sections showing the position and connections of the precast elements/products in the completed works.
Erection team shall use leveling shims if required to assist in final positioning of the wall panels.
Any cracks or damage of non-structural nature that do not require replacement shall be left in place and repaired on site subject to consulting engineer’s approval.
Corners of the footing shall be marked on the blinding.
The main contractor to mark the coordinates along the length of the wall.
Footing shall be placed in designated location.
If required for final positioning crow bar will be used.
Panels shall be erected on the footings and shall by supported by supporting jacks.
Panel footing connection shall be then completed with non-shrink grout/concrete screed (40N/mm2 or as per the design), which shall be supplied by client / main contractor.
The next day the jack shall be released by the construction team.
At the end the work inspection request shall be submitted to obtain the client/consultant approval.