Concrete slabs on grade can be found in nearly every single industrial, commercial, and residential building. Whether they exist below a layer of flooring material or are exposed, slabs on grade provide foundation for all building foundations.
Concrete slabs on grade can be as simple as your residential driveway placed and finished by hand or as complex as this super-flat industrial floor installed with laser-guided screeds and power trowels. Regardless of the intended use, the engineering principles remain the same. Essentially, quality materials combined with good design and expert workmanship yield the best concrete slab. The following information and references serve as a guide for all three of these essentials.
Design and Control of Concrete Mixtures, EB001
Concrete Floors on Ground, EB075
Placing a Bonded Floor Overlay
If a floor needs to carry greater loads than it was designed for, it can often be upgraded with a bonded overlay. A well-bonded overlay can give the floor the added thickness it needs to support the additional weight. However, placing a bonded overlay presents many difficult challenges. Here are a few tips to help ensure success:
Keep the water content of the overlay as low as possible to minimize shrinkage and curling. The concrete should have a water-cement ratio of 0.45 or less and a minimum cement content of 600 pounds per cubic meter. The maximum aggregate size should be no more than one-third the thickness of the overlay.
Saw control joints to the full depth of the overlay directly over the underlying floor joints. An overlay joint and an underlying joint may begin and end at the same place, but they often are not aligned perfectly along the entire length of the joint. Sawing the overlay joint to its full depth reduces the chances of reflective cracking in the overlay in areas where the joints are not perfectly aligned.
Proper curing is even more important in bonded resurfacing than in ordinary concrete work because of the potential for rapid, early drying of the thin concrete overlay due to its high surface-to-volume ratio. Use a fog spray immediately after finishing, if necessary, to protect against rapid drying, and cover with wet burlap, plastic sheets, or waterproof paper as soon as they can be placed without marring the surface.
This information was excerpted from PCA's 8-page publication, Resurfacing Concrete Floors.