Driveways – Concrete
The Replacement Process
First, the old driveway is removed, and the contractor may put down more gravel or fill to create a better, stronger base for the new concrete. Next, the contractor installs temporary forms to hold the wet concrete in place. The concrete is poured and immediately smoothed, and control joints are cut. Once the concrete hardens, the forms are removed.
Control joints. Control joints help manage any cracks that might occur in concrete. Contraction joints are shallow grooves that are cut into a concrete slab soon after it is placed. As the concrete hardens and shrinks, any separation usually occurs at the contraction joints where the concrete is thinner and weaker rather than across the surface of the slab. Isolation joints, also known as expansion joints, are used to separate a concrete slab from a wall, post, or other structure. These joints extend through the thickness and width of the slab and are filled with a synthetic material and then sealed. Isolation joints help prevent concrete from cracking by providing an area that accommodates and diffuses the surface’s thermal expansion during hot weather. Even with proper control joints, concrete driveways often crack. Due to the variability of materials and terrain, many companies cannot guarantee their driveways against aesthetic cracking.
Setting or curing. Concrete sets or cures through a chemical process called hydration. Water molecules and the cement form tiny crystals that interlock with one another and with aggregate in the mix to give the concrete its strength. Concrete that is cured improperly may fail to achieve its maximum strength and can be marred by aesthetic and structural problems. It is important to keep the surface of the concrete wet and protected from weather extremes during the hardening period. Concrete that is poured in cold weather typically requires a longer curing time. Contractors will often cover the surface with an insulating blanket or surround it with heating elements. In hot weather, the curing period may be shorter, but the contractor must take special care to keep the concrete wet to minimize moisture evaporation in the heat.
Concrete grade is defined by the strength of the concrete and is measured in pounds per square inch (psi). Generally, the higher the psi grade, the more weight the concrete can handle. Residential driveway concrete is usually 3,000 or 4,000 psi.
Residential driveways are usually four inches thick; thinner driveways are more apt to crack. Driveways should be designed and graded to manage water runoff and prevent puddling. Paver driveways are popular because they offer a beautiful variation on the standard, plain concrete driveway. Pavers are brick-like pieces of concrete that can create many different looks, including cobblestone, brick, and slate.