SCOPE & PURPOSE
This method statement describes the practices and methods to be used with regards to placing, curing and defect rectification of concrete works & blinding concrete.
PROCEDURE OF GENERAL CONCRETE WORKS
PLACING OF CONCRETE
Prior to the placing of any concrete all quality checks are to be completed and the “approval to concrete” instruction issued by client/consultant.
Once delivered to site the concrete will be placed in one of three manners:
a) Direct (or chute) discharge,
b) Crane and bucket, or
c) Concrete pump
The method to be used shall depend on site conditions and pour volume.
The concrete shall be placed in accordance with the Specification for Concrete cast in place and the main points being:
a) Concrete is to be placed as close as possible to its final position and not moved laterally by vibration.
b) Concrete is not to be over vibrated.
c) Concrete is not to be dropped from a height exceeding 2m.
d) “Cold joints” of more than 40 minutes shall be avoided.
e) Concrete shall be placed not later than one hour after the addition of the mixing water.
f) Pumping of concrete shall only be permitted after approval from Company.
If during concreting, rain is imminent sufficient plastic/canvas sheets should be on hand to cover the entire casting area. If seepage water is coming into the excavation in a significant volume or again if rain is imminent a water pump must be in place ready to operate.
CURING OF CONCRETE
After the initial set of the concrete and when the concrete is hard enough to not be damaged by such an action, the exposed concrete surface shall be covered with drenched hessian sacks. These sacks shall be left in position and maintained in a soaked condition for seven days. For formed surfaces the curing shall be applied as described above after the formwork has been removed, or a curing compound shall be applied (refer to 2.5 above).
Laitance may be removed once the concrete is hard by light chipping wire brushing.
Preparation of construction joints shall be done by mechanical chipping taking care not to dislodge the coarse aggregates. This is to be done at least 24 hours after the completion of placing or a concrete surface retarder may be used (refer to 2.6 above).
INSPECTION AND REPAIR OF CONCRETE
After the removal of formwork the element shall be checked for level, dimensions and surface defects, any non-conformity will be brought to the attention of Company before rectification.
The action to be take to resolve any non-conformity will be proposed by MEDMAC and subsequently approved by Company.
Any patching, grouting or other such compound to be used for rectification works shall be submitted to and approved by Company prior to its use.
Curing compounds if used shall be approved and of the clear type.
Construction joints shall be in the locations as indicated in the drawings, or as submitted in a proposal and always at right angles to the structural member’s axis.
Kickers shall be used at the base of all columns and walls.
Blinding Concrete Works
Below is the equipment involved in blinding works:
- Air compressor
- Hand tools, hand saw, wire cutter, brush, and measuring tapes
- Concrete Pump
- Wooden float
Blinding Concrete Procedure:
All the related documents such as shop drawings, method statements, material approvals, subcontractor’s approvals, test certificates, etc must be available on the site
Ensure the source of supply of ready mix and grade of concrete.
Compaction test/plate load test of the Substrate shall be approved and available.
One layer of 1000 gauge polythene sheet shall be laid prior to arrangement of any blinding.
All the concrete encased ducts installation shall be approved from the Engineer.
Ensure the MEP clearance is obtained prior to start the concrete blinding works.
Polythene sheets, hessian cloths and sweet water arrangements shall be arranged for the proper curing.
- All materials used for form-works should be clean strong and clear from any deflection.
- Install form-works to its dimensions correctly and ensure that alignment and levels of form-works are within the tolerances.
- The shutters will be side supported by steel bars to maintain the proper alignment of the forms.
- Level Guides shall be installed for the level maintenance of concrete.
- Blinding concrete for the structures and trenches will be placed using a pump. Grade of concrete will be according to approved concrete design mix.
- Concrete shall not be placed more than 1.5 m height.
- After completion of casting, enough number of workers must be available for the finishing works, cleaning and protection of the casted concrete.
Curing Of Concrete
Concrete have to be cured by sweet water as instructed by the client/consultant. All the surface of foundations will be covered by wet sack cloth to maintain this.