The Concrete Driveway

Driveway replacement process. The first step in replacing a concrete driveway is to break up the old driveway and haul it away. Then, depending on the nature of the ground under the driveway, the contractor may put down additional gravel or fill to create a more solid base for the concrete. Without a good base, the driveway is more likely to settle and/or crack. Next, the contractor installs temporary forms to hold the wet concrete. Once the forms are in place, the concrete arrives and is poured into them. The concrete is smoothed, and contraction joints are cut. The concrete hardens inside the forms. Once the concrete is hard, the forms are removed.

Contraction joints. As concrete sets and hardens, it has a tendency to shrink and therefore crack. Contraction joints are shallow grooves cut into a concrete slab soon after it is placed. This way, when the concrete hardens and shrinks, any cracking that arises should tend to follow the contraction joints, where the concrete is thinner and weaker. In temperate climates, experts recommend cutting contraction joints approximately every 15 feet.

Expansion joints. Expansion joints are placed at intervals of about 75 feet, on very large slabs of concrete. These joints extend through the entire thickness and width of the slab, are filled with fiberboard, and are then sealed. Expansion joints help prevent concrete cracking by giving room for thermal expansion in hot weather. Like a contraction joint, an expansion joint can prevent cracks from propagating across the joint. However, even with proper joints, driveways often crack. Due to the variability of materials and terrain, many established companies will not guarantee their driveways against aesthetic cracking.

Concrete grade. Concrete grade is defined by the strength of the concrete and is measured in pounds per square inch (psi). In general, the higher the psi grade, the more weight it can handle, the more durable it will be, and the better it will hold up when pressure washed. Concrete used in driveways is usually 3,000 or 4,000 psi. The 4,000-psi-grade concrete is slightly more expensive than the 3,000-psi-grade concrete. However, this price difference is small when compared to the total cost of driveway replacement.

Setting or curing. Concrete does not dry; it sets or cures through a chemical process called hydration. During hydration, water molecules combine with the cement to form very tiny crystals. These crystals interlock with one another, as well as with the aggregate in the concrete, to give the concrete its strength. If the concrete or the surface of the concrete dries before hydration fully occurs, the concrete loses its strength and/or becomes flaky. Therefore, it is very important to keep the surface of the concrete wet after it is poured.

Driveway design. In general, water should never puddle on the driveway. If the house is on a hill, the driveway should channel the water down to the street or to a storm drain. Residential driveways are usually four inches thick. In general, thinner driveways are more apt to crack than thicker driveways.

Color variation. Unfortunately, due to variation in the color of the raw materials that make up concrete, colors will vary between batches of concrete. Color variation is usually not a problem in a complete replacement job, since all the concrete usually comes from the same batch. However, when adding to or replacing a section of an existing driveway, you should expect color variation.

Undermined driveways. Misplaced gutters or missing downspouts often dump water alongside a driveway or sidewalk. Over time, the flowing water may erode the ground next to the driveway and then underneath it. As the earth beneath the driveway washes away, the driveway loses its support and is likely to crack and settle. Before replacing such a driveway, first fix the water flow problem.

Pavers. Driveways made out of pavers are becoming increasingly popular because they offer a non-traditional variation to the standard concrete driveway. Pavers are brick-like pieces of concrete that are molded at a factory and shipped to the job site. Pavers can create many different looks, including cobblestone, brick, and slate, which results in unique driveways for homeowners. Pavers come in a variety of colors and styles, but they are usually more expensive than standard concrete. While many driveway contractors offer both concrete and paver driveways, homeowners should be sure to select a company that is experienced in the look that they desire.