Concrete Floor Slab Construction

Concrete Floor Slab Construction
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Reinforced concrete slab is a common and significant structural element that provide flat, useful surfaces. It is a horizontal structural component, with top and bottom surfaces parallel or near so. This article presents design and construction of reinforced concrete one-way slab.

Concrete Floor Slab Construction Process

  1. Assemble and Erect Formwork
  2. Prepare and Place Reinforcement
  3. Pour, Compact and Finish Concrete
  4. Curing Concrete and Remove Formwork

1. Assemble and Erect Formwork

The formwork shall be designed to withstand construction loads such as fresh concrete pressure and weight of workers and operators and their machines. Guide to Formwork for Concrete ACI 347-04 shall be followed for the design of formworks.

Moreover, there are various construction aspects that need to be considered during the erection of formworks. For example, it should be positioned correctly, lined and levelled, joints sealed adequately, and prevent protruding of nails into the concrete etc…

Furthermore, different materials such as wood, steel, and aluminum can be used for the formworks of slabs.

Slab formwork
Fig. 1: Slab formwork

Finally, there are several common formwork construction deficiencies that site engineer needs to be aware of and prevent their occurrence otherwise formwork failure may occur. These construction deficiencies are provided below:

  • Poor or lack of formwork examination during and after concrete placement to identify uncommon deflections or other indications of possible failure that could be corrected
  • Inadequate nailing, bolting, welding, or fastening
  • Improper lateral bracing
  • Construct formwork that does not comply with form drawings
  • Lack of proper field inspection to ensure that form design has been properly interpreted by form builders
  • Use of damaged or inferior lumber having lower strength than needed.

2. Prepare and Place Reinforcement

Prior to the reinforcement placement, inspect and check Forms to confirm that the dimensions and the location of the concrete members will conform to the structural plans. Added to that, the forms shall be properly cleaned and oiled but not in such amount as to run onto bars or concrete construction joints.

Design drawings provides necessary reinforcement details, so it only needs understanding to use designated bar size, cutting required length, and make necessary hooks and bents.

After preparation is completed, steel bars are placed into their positions with the provision of specified spacings and concrete cover.

The concrete cover and spacing can be maintained by introducing spacers and bars supporters. Wires are used to tie main reinforcement and shrinkage and temperature reinforcement (distribution reinforcement).

wires used to tie reinforcement and supporters used to maintain concrete cover
Fig. 2: wires used to tie reinforcement and supporters used to maintain concrete cover

It should be known that incorrect reinforcing steel placement can lead to serious concrete structural failures. Improper concrete cover exposes reinforcement bars to danger and jeopardize concrete-steel bond.

Finally, after all requirements of reinforcement placements (positions, concrete cover, spacing, and correct bars size; length; hooks; and bending) are finalized, then site engineer can order concreting.

Provision of concrete cover for reinforcement bars in slab
Fig. 3: Provision of concrete cover for reinforcement bars in slab

3. Pour, Compact and Finish Concrete

Mixing, transporting, and handling of concrete shall be properly coordinated with placing and finishing works. In slab, begin concrete placing along the perimeter at one end of the work with each batch placed against previously dispatched concrete.

Concrete placement started from one end of the slab
Fig. 4: Concrete placement started from one end of the slab

Concrete should be deposited at, or as close as possible to, its final position in order to prevent segregation. So, Concrete placement in large and separate piles, then moving them horizontally into final position shall be prevented.

Moreover, site engineer shall monitor concreting properly, and look for signs of problems. For example, loss of grout is the indication of improper sealing and movement of joints. Added to that, cracking, excessive deflection, level and plumb, and any movement shall be checked and tackled to prevent further problems.

Concrete placement using pumps
Fig. 5: Concrete placement using pumps

Furthermore, fresh concrete should be compacted adequately in order to mold it within the forms and around embedded items and reinforcement and to eliminate stone pockets, honeycomb, and entrapped air. Vibration, either internal or external, is the most widely used method for consolidating concrete.

Lastly, slabs could be finished in many ways based on floor application. Helpful information about forms before, during, and after concreting can be found in ACI 311.1R.

Placing and vibrating fresh concrete
Fig. 6: Placing and vibrating fresh concrete

4. Curing Concrete and Remove Formwork

After finishing ended, suitable technique shall be used to cure the concrete adequately. Slab curing methods such as water cure; concrete is flooded; ponded; or mist sprayed.

In addition to water retaining method in which coverings such as sand; canvas; burlap; or straw used to kept slab surface wet continuously, chemical Membranes,and waterproof paper or plastic film seal.

Regarding curing, it is recommended to remove formworks after 14 days. For detailed formwork removal time, Please click here.

Curing concrete slab by ponding
Fig. 7: Curing concrete slab by ponding

All construction process of concrete floor slab are illustrated in Fig.8 and Fig.9.

Illustration of reinforced concrete slab construction
Fig. 8: Illustration of reinforced concrete slab construction
Wire used to bind main and shrinkage and temperature reinforcement
Fig. 9: Wire used to bind main and shrinkage and temperature reinforcement (Detail ‘A’)

Read more:

Formwork Safe Practices Checklist during Design and Construction

Concrete Formwork Design Considerations – Basis for Concrete Formwork Design

Common Defects in Concrete Formwork Systems

Formwork (Shuttering) for Different Structural Members -Beams, Slabs, Columns, Footings

Concrete Formwork Loads and Pressure Calculations

Concrete Cover Specifications for Reinforcement in Different Codes

Types of Formwork (Shuttering) for Concrete Construction and its Properties



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