Horizontal slabs of thick reinforced concrete often form the floors and ceilings of highrises around the world. Sometimes, the slab is prefabricated in a manufacturing facility and transported to the site. Prefabricated concrete, also known as precast concrete, is also frequently used as a cladding material.

Creating a reinforced concrete slab, image by Marcus Mitanis

But most construction sites utilize a different method. In slabs of situ concrete — also called cast-in-place concrete — are built directly on the building site using formwork, a mould in which the wet concrete is poured. If the slab needs to be reinforced, rebar is placed within the formwork before the pour is made. The concrete is then compacted to ensure the formwork is completely filled. The process of consolidation is conducted to remove trapped air from freshly poured concrete. The most common practice uses an internal vibrator, which is driven down into the wet pour and slowly lifted to help air bubbles escape. 

Wood formwork awaits a concrete pour atop a finished floor slab, image by Marcus Mitanis

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