Published: August 28, 2019 | Last updated: July 5, 2023

What Does Slabs-On-Grade Mean?

Slabs-on-grade, also known as floating slab, refers to concrete slabs that are directly laid on the ground over a prepared surface.

To prevent groundwater bitumen from entering the slab from the earth, a layer of gravel and bitumen is first laid on the earth. These slabs are popular in areas where ground freezing is not an issue. Depending on the load that the slab has to bear it may have or not have reinforcement.

The minimum thickness of a slab-on-grade is four inches and can be more depending on the soil characteristics such as porosity.


Trenchlesspedia Explains Slabs-On-Grade

Slabs-on-grade is of two types:

  • Supported slab-on-grade.
  • Monolithic slab-on-grade.

The supported slab-on-grade is cast when footings are already framed to raise columns. Monolithic slab-on-grade does not have any footings below it and itself acts as a footing. Slabs-on-grade can be used in places where the load-carrying capacity required is low or in loose soil and soils with varying compressibility. These slabs also efficiently spread vertical loads over a large area.

To cast a slab-on-grade, the earth is first excavated to the required depth and compacted. A layer of gravel and bitumen is first laid over which concrete is poured with or without reinforcement. The thickness of the slab is more at the edges of the slab, with reinforcement rods provided to strengthen the edges.

The slab is allowed to cure to prevent cracks.



Floating Slab

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