Slab on Grade Design

The slab on grade design process comes before concrete slab construction needs to consider serviceability, soil type, and concrete slab prices or cost. Though not very common, some architects include slab saw plans in the construction document especially for concrete patio slab that are exposed to view with special designs. In almost every case, the slab crack repairs, unless they happen during construction are left as the owner’s responsibility.

Understanding the purpose of the slab will make a big difference when it comes to slab thickness, reinforcements, and final finish. For example if your slab on grade is for floor that is only subjected to normal occupants foot traffic and storage, there is no need for 5 inch thick slab with rebar or welded wire mesh as reinforcements. Even in commercial structures, I have seen some over kill slab design to the range 6 to 8 inch thick slab to be reinforced with #4 or #3 rebars at 12 to 18 inches on center each way for foot traffic from workers. Unless your slab is for vehicular load such as delivery trucks and forklifts there is no need to go any higher than 4 inch thick slab. For residential homes, I use 3 to 4 inch thick unreinforced concrete slab minimum of 3000 psi mix.

Concrete floor slabs, concrete patio, cement or concrete driveway, and rv pad are all different names for names for slab on grade. When it comes to designing a concrete floor slab, there is not much can be done about the configurations since that is determined by the house or structure layout. Furthermore if the floor is covered by tile or carpet, the final finish of the slab does not matter a lot because it will be covered.

Unlike floor slab, configuration of cement patio or driveway is part of the slab designer’s job which is often influenced by the road and house layout as well as climate. The thickness and reinforcement requirements will be determined by serviceability. If the driveway is just for SUV type vehicle, a 4 inch thick slab unreinforced with 4000 psi mix will do. If your driveway will be frequent by delivery trucks that weigh over 5,000 pounds, 5 inch thick slab with minimum reinforcement will do.

The issue of soil type is very important if you are in an area where the soil behavior can be influenced by water. Expansive and collapsible soils are example of soils that alter their behavior when wet. These type of soil will require reinforcements or may require post tension slabs.

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