Proper Slab Construction Concepts – A Challenge to overcome??

What is slab? A RCC (Reinforced Cement Concrete) slab is the most common structural element of any type of building. Horizontal slabs, typically between 4 and 20 inches (100 and 500 millimeters) thick, are most often used to construct floors and ceilings.Here discussion on “flat slab” has not been considered.

Typical loads to be considered for slab design (i) Dead load: Any permanent load acting on the slab e.g. self-weight of slab, weight of floor finish & plaster

(ii) Live Load: Any non-permanent or moving load e.g. weight of occupants, furniture, and partitionon the slab

(iii) Snow load (if any)

Note: Earthquake and Wind loads are not considered in the design of slabs.

Slab construction: Busting myth

S. No. MythActual

Recommended slab construction practices: 1. For lapping/ joining of rebar, a minimum lap length of 57 x diameter of rebar should be provided(a). Thus 1.5ft lap length will be required if you are using 8mm diarebar. Lapping should preferably be avoided at centre of slab panel.

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Note: Lapping refers to the joining of rebars to achieve the desired continuity.

2. The guidelines of minimum period before striking/removal of soffit shutter and vertical props of slab and beam as per BIS are as follows:

3. Slab curing should be done for minimum of 14 days from date of casting, as per BIS. It is recommended to do curing for a period of 28 days.

4. During waterproofing treatment of roof slab, mix standard waterproofing compound with concrete and apply on slab in ½’’ to 1’’ layer in single pour without any time lag between laying the mix (with supporting props in position). This is to avoid any construction joint in the waterproofing layer. (This layer to be poured in a bit slope to ensure proper drainage)

5. To accelerate setting of concrete in heavy rainfall/snowfall prone areas, standard accelerating admixture complying with BIS9103 may be used.

NOTE: (a) Design is suggested considering M20 grade of concrete (cement:sand:stonechips=1:1.5:3)and Fe500(D) grade of HYSD rebar

(b) Slab panel size means the centre-to-centre dimensions of the space enclosed by beams

(c) For slab exposed to severe rainfall, BIS recommends 45mm clear cover.