After backfilling works the next is casting slab on grade (ground), make sure that all the area beneath grade slab have been properly backfilled and compacted.
Approval must be obtained from the Engineer for waterproofing and backfilling works prior to start slab on grade casting.
Here is the method statement of Slab on Grade preparation and concrete pouring.
Method Statement for Casting Slab on Grade
2. Purpose and scope
The purpose of this method statement is to explain the proper procedure on how to prepare and cast slab on grade or any horizontal element or member including fixation of steel reinforcement, MEP embedment’s, fixing of shutter etc. without injuries.
3. Work procedure
- Site planning
- Delivery – fresh concrete shall be batched from the approved supplier of concrete. Concrete will be delivered direct to the site and to be received by assistant Quality Engineer for checking of the required criteria of concrete. The assistant QC Engineer will make sure the concrete delivered is as per the approved design mix for the situated member to be casted.
- All data for testing on fresh concrete at site shall be recorded on the concrete pour card.
- After the blinding is casted and placement of waterproofing is done, the preparation and casting for slab on grade shall be done.
- Fix the reinforcement steel as per the approved drawings, sometimes A393 BRC mesh is indicated in the drawing and most commonly use in 250mm thick concrete grade slab.
- Any loose binder or ties along the splices reinforcement steel shall be re-tightened. Bend inward the free ends of the binding wire or ties.
- Use PVC spacer for vertical bars and concrete spacer for bottom as concrete covers.
- Ensure and coordinate with MEP staff for any MEP works required on the area as per approved drawings.
- Fix the forms such; supports, sleeves etc., if any.
- Any damaged materials used for form work or shutter like plywood shall not be used.
- All surface of forms or shutter facing concrete shall be treated with shuttering oil and dampen with water few minutes before concrete will be poured.
- Clean the slabs on grade using air compressor for dust or any small particles or deleterious materials that may impair the workability of concrete.
- The surveyor will then checked the level of the projected top surface of the slab and place level strips if necessary to mark the exact level.
- The concreting are as must be arranged with necessary equipment or tools for concreting use such as vibrators, power float machine, shovel etc.
- Skilled and unskilled labor shall need to use safety requirements such as safety helmet, safety shoes, goggles, gloves, vest etc.
- Safety devices and safety warnings shall be provided starting from the site entrance gate till the casting area.
- Proper lighting must be available in case of night concreting.
- Concrete pouring
- The concrete mixer must be stopped at the check point for the inspection of slump test and to obtain sample cubes for test.
- One set of cubes shall be taken every 50 cubic meter concrete, each set consist of 6 cubes, 3 cubes to be tested on 7th days and 3 cubes to be tested for 28th days.
- Extra three cubes can be made for re-checking if in case circumstances may happen.
- Unload the concrete within 90 minutes from the batching plant loading time.
- Compact the concrete properly by using mechanical vibrators, extra vibrator shall be available in case of any shortage or mechanical problems.
- Use approved hardener material after casting concrete when required. Make sure applications shall be as per manufacturer’s recommendation.
- Use the power float for the smooth finish surface purpose. Store extra power float near the casting area in case of any mechanical malfunctioning.
- Cure the casted area properly with covering concrete with hessian cloth and polythene sheet on top but before placing the concrete wet the hessian with water.
- Cure the concrete by spraying water three times per day for a period of 7 days.
- The casted area or member shall be protected by placing barricade to prevent plants and machineries damaged the concrete.
- Concrete pour card shall be filled by Quality Engineer and to be submitted to the Engineer including concrete delivery notes, this task will be done whenever required.
- Concrete cube test report shall be submitted to the Engineer
- All works shall comply with safety procedure or instruction set out in project safety plan and municipality rules and regulations.
- Basic PPE to be worn by all staff and laborers.
- Trained operator and banksman would be engaged to control or operate heavy equipment machine.
- Provide sufficient lighting whenever night casting.
5. Equipment and tools
- Concrete Pump
- Concrete Mixer
- Mini truck
- Bob cat
- Concrete vibrators
- Wheel borrow
- Slump tray
- Slump cone and other associated tools
- Rubber hammer
6. Materials and References
- C40/20 Concrete Grade with additives
- Deformed bars or A393 BRC mesh
- Approved drawing