Concrete slabs are common in building construction. Used for foundations, porches, decks, patios, and driveways, concrete slabs comprise several variations with four main designs: flatwork, the T-shaped foundation, slab-on-ground, and frost protected. Concrete slabs used in building construction often employee such measures as reinforcement with steel rebar and post-tensioning to add strength to concrete slabs.
Concrete flatwork is a type of slab used in the formation of decks, patios, driveways, and porches. Flatwork is usually several inches in thickness, commonly around 4 inches. Flatwork is a floating concrete slab not secured to the foundations of the building, according to the Paradigm Construction, Inc., website, and flatwork slabs are not a load-bearing element of a building.
T-shaped slaps get their name from the T-shape of the footer and block foundation. Often called block slabs as a reference to the foundation using concrete blocks during construction, T-shaped foundations find use in areas where freezing of the ground occurs according to the Concrete Network website. This three-stage process begins with digging footers dug and backfilling with concrete. Stage 2 involves the building of a block perimeter wall on top of the footers. This inverted T-shape is the exterior wall of the foundation. After wall construction, the interior of the block slab receives dirt and gravel to several inches below the top of the block wall before adding a concrete slab over the gravel and dirt completes the T-shaped slab.
Slab-on-ground slabs, called monolithic slabs due to their single-pour design, uses thick outer footings and filled with rebar reinforcement to form the slab. Holes dug for the footer and filled with rebar comprise the thick sides of the slab, and forms make a barrier for the pouring of the concrete. The slab is poured with one pour from the foundation holes to the top of the slab forms.
A frost-protected slab is a monolithic slab that uses the heating within the structure to protect the slab foundation from freezing temperatures. Polystyrene insulation placed along the perimeter of the slab retains heat from the structure to prevent the ground temperature of the ground around the footings from freezing.
Post-tensioned slabs employ the same materials as other concrete slabs, but with the addition of high-strength plastic coated steel cables. Post-tensioning of a slab occurs by placing the cables throughout the slab before pouring and, after the slab has hardened, tension applied to the cables compresses the slab to increase the overall strength of the slab. According to Brian Allred's article in Residential Concrete magazine, the strength of concrete is in compression.