Reinforced Concrete Slab Casting- Work Procedure

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Casting concrete slab is considerably crucial task in building construction and requires great planning and accuracy, in addition to proper execution sequence. This article presents proper procedure on how to prepare and cast reinforced concrete slab.

Materials and Machinery for Slab Casting

• Batching plant
• Transit mixer
• Concrete pump
• Vibrators
• Slump tray
• Slump cone and other associated tools
• Rubber hammer
• Chute and CI Pipes
• power float machine
• shovel

Slab Pre-concreting Checks

There are many checks that need to be performed prior to concreting of reinforced concrete slab:

Checking Slab Formwork

• Check whether the formwork is fixed properly or not for example sleeves and supports.
• Damaged materials employed for formwork or shutter should not be utilized.
• All formwork surfaces in contact with concrete need to be treated with shuttering oil and dampen with water sometime prior to concrete placement.
• check the level of the projected top surface of the slab and place level strips if necessary to mark the exact level.
  

  Fig. 1: Checking level of slab shuttering

Checking Slab Reinforcement

• Check and approve that reinforcements are fixed as per the approved drawings.
• Examine reinforcement spacing (including vertical and horizontal spacing) and cover.
• Ensure that adequate support for reinforcements are provided to prevent any movement during concreting process.
• Loose ties along the splices of reinforcement bars must be tightened again.
• Free end of binding wires shall be bended inward.
  

  Fig. 2: Slab reinforcement checking

Other pre-concreting checks

• Ensure that workers use safety tools and equipment for example safety helmet, safety shoes, goggles, gloves, and vest.
• Safety devices and safety warnings should be provided from site entrance to the casting area.
• Check whether adequate lighting is provided in case of night concreting.

Slab Concreting Work Procedure 

1. Providing Construction Joint

The construction joint shall be pre-decided and fixed prior to start of the concreting. It is planned to have two construction joints for main building as decided. In case of major break down of the Batching plant, the additional Construction joint may be left. The location of the construction joint shall be at the one-third span. Construction joint shall be straight and have profile of ‘L’shape so that successive layer of concrete shall be perfectly bonded with previous laid layer. Preparation of construction joint shall include roughening, removing all laitance adhering to the joint and application of thick slurry before start of the new concrete.

2. Production of Concrete

Stock of material shall be sufficient to start the concrete. It shall be ensured by stores/purchase dept that concreting is not stopped on account of materials. All plant and machinery are checked and made in working conditions.

3. Concrete Pouring

• Proper walkways/platforms shall be arranged so that the supports of the pipeline and manpower are not directly stand on reinforcement.
• Sufficient carpenters along with supervisor shall inspect the behavior of supports below the slab during the casting.
• Extra Props shall be stocked below slab to provide additional supports in case of any failure of supports.
• Before discharging concrete from the mixer, concrete shall be inspected and acceptance shall be conducted like slump tests.
• Required number of concrete specimens shall be taken for compressive strength test and other tests.
• It is recommended to discharge 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.
  

  Fig. 4: Pouring concrete slab

4. Finishing Concrete Surface 

• Use the power float for the smooth finish surface purpose.
• 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.
  

  Fig. 5: Finishing concrete slab surface

5. Curing Concrete

The curing shall be started immediately after thumb set of the concrete laid. Hessian clothe /Plastic shall be covered over the set concrete to reduce moisture evaporation from the concrete during hardening and thus to minimize shrinkage crazy cracks. These cracks are inheriting property of the concrete specially appears during casting of flat surfaces. Final curing shall be done by ponding and stacking water for minimum period of 7 days.