How to prepare and cast reinforced concrete slab

Casting concrete slabs is a critical task in building construction that necessitates meticulous planning and accuracy, as well as a precise execution sequence. This article explains how to properly prepare and cast a reinforced concrete slab.

Slab Casting Materials and Equipment

  • Concrete  mixer
  • Vibrators
  • Safety equipment
  • Slump cone, Cube mould
  • conducting pipes
  • shovel

Pre-concrete Slab Inspections

Many checks must be completed prior to the concreting of a reinforced concrete slab:

Slab Formwork Inspection

  • Examine whether the formwork, such as sleeves and supports, is securely secured.
  • Formwork or shutter materials that have been damaged should not be used.
  • Prior to concrete placement, all formwork surfaces in touch with concrete must be coated with shuttering oil and dampened with water.
  • Check the level of the slab’s projected top surface and use level strips to mark the exact level if necessary.
Checking level of slab shuttering

Slab Reinforcement Inspection

  • Check and confirm that the reinforcements are installed in accordance with the authorised drawings.
  • Examine the reinforcement spacing (both vertical and horizontal) and the cover.
  • Ensure that adequate reinforcement support is provided to prevent movement during the concreting process.
  • Loose ties along reinforcement bar splices must be tightened again.
  • Binding wires’ free ends must be bent inward.
Slab reinforcement checking

Other pre-concrete inspections

  • Ensure that workers use safety equipment and gadgets such as a safety helmet, safety shoes, goggles, gloves, and a vest.
  • From the site entry to the casting area, safety devices and warnings should be provided.
  • Check to see if appropriate illumination is available in the event of night concreting.
Procedure for Slab Concreting Work
  1. Providing Construction Joint

Prior to the start of the concreting, the construction joint must be predetermined and fixed. As previously decided, the main building will have two construction joints. The additional Construction joint may be left if the Batching plant suffers a serious breakdown. The construction junction must be located at the one-third span. The construction joint must be straight and have a ‘L’profile so that each consecutive layer of concrete is perfectly linked to the preceding laid layer. Roughening the construction joint, eliminating all laitance sticking to the junction, and applying a thick slurry before starting the new concrete are all required steps.

Construction joint in slab
  1. Concrete Manufacturing

The material stock must be sufficient to begin the concrete. The stores/purchase department must ensure that concreting does not halt due to a lack of materials. All plant and machinery are inspected and made operational.

  1. Pouring Concrete
Pouring concrete slab
  • Proper walkways/platforms must be installed so that the pipeline supports and labour do not directly stand on reinforcement.
  • Sufficient carpenters and a supervisor must inspect the behaviour of supports beneath the slab during the casting process.
  • Extra Props shall be supplied beneath the slab to offer additional supports in the event of support failure.
  • Before discharging concrete from the mixer, it must be inspected and accepted, just like slump tests.
  • A sufficient number of concrete specimens must be collected for the compressive strength and other testing.
  • It is suggested that the concrete be discharged within 90 minutes of the batching plant loading time.
  • Technical vibrators should be used to appropriately compact the concrete; an extra vibrator should be accessible in case of a shortage or mechanical problems.
  1. Concrete Surface Finishing
Finishing concrete slab surface
  • Use the power float to achieve a smooth finish on the surface.
  • The casted region or member must be secured by erecting a barricade to keep plants and machinery from damaging the concrete.
  • The Quality Engineer will fill up the concrete pour card and submit it to the Engineer along with the concrete delivery remarks as needed.
  1. Concrete Curing
Curing concrete slab by ponding

The curing process must begin immediately after the initial set of the concrete. Cover the set concrete with hessian cloths or plastic to decrease moisture evaporation from the concrete during hardening and thus minimise shrinkage crazy cracks. These fissures are an inherited feature of concrete that occur during the casting of flat surfaces. Ponding and piling water for a minimum of 7 days is required for final curing.

Leave a Comment

Your email address will not be published. Required fields are marked *