A uniform subgrade is the key to preventing unwanted settlements. A sand layer is not needed for increased subgrade support, but if it is used as a leveling course, it must be compacted with a vibratory plate compactor.
Durable, long lasting and low maintenance concrete begins with selecting the proper mix design. For exterior concrete to resist the affects of snow and ice, freezing and thawing, and deicing chemicals, the National Association of Home Builders recommends the use of an air entrained concrete mix with a minimum design strength of 3500 psi and a maximum slump of 5". Higher slump concrete can be placed with the addition of water-reducing chemical admixtures.
Joints are used to aid construction and control cracking. Best results are obtained when control joints are spaced twice the thickness of the slab in feet; i.e., 8'x8' joint spacing for 4" thick slab. Maximum spacing should be 2½ times the slab thickness in feet, and never exceed 15 feet. Slab panels should be as square as possible. Joints should have a minimum depth of 1/4 the thickness of the slab. Expansion joint material should be used full depth to isolate slabs-on-grade from building and foundation walls, street connections or any fixed object. Sealing joints will extend the life of slabs-on-grade and prevent water runoff from weakening the subgrade.
The most important and economical step in assuring durable, long lasting concrete is curing. Curing concrete will nearly double its strength. Curing should begin as soon as finishing is completed. Use an accepted curing method. The most common method of curing is applying a spray-on curing compound. Concrete should have at least 30 days of air-drying prior to the onset of harsh winter weather and exposure to deicing chemicals.