Build a Concrete Driveway the Right Way
You know you need a new driveway. That's the easy part. But you're torn
between using asphalt or concrete. Concrete looks great but does it last 25
or 30 years as promised? The short answer is, yes--a concrete driveway can
last you at least 30 years. But only if it's installed, finished and cured
properly. Here's how.
Concrete is a fickle material and prone to cracking. Although it can be
compressed or squeezed without cracking under the pressure, it doesn't take
stretching or bending very well at all. The goal is to minimize the potential
for cracking by pouring it over a stable, hard surface, and by constructing
it properly with expansion joints and reinforcing steel.
First, make sure your contractor properly grades and compacts the soil before
setting the forms or pouring the concrete. This is absolutely critical to
avoid the stretching or crumbling effect. For example, what do you think
will happen if your driveway is poured over soft, unstable soil? Without a
solid foundation, whole sections of the driveway will crack under the weight
of your car.
Second, your contractor should know how to install control joints. Make sure
you discuss this before your project begins. In addition to stretching, the
other thing concrete doesn't do well is shrink when it dries. The larger the
section, the more it will shrink as it hardens-about 1/16 of an inch per ten
feet. To control cracking caused by the inevitable shrinking, your
contractor will use control joints that actually encourage the concrete to
crack at the control joint. It's done by cutting exact, neatly tooled lines
in the concrete slab, at minimum intervals of fifteen feet or less. These
joints should be deep enough to absorb the stress, preferably at least
one-quarter the depth of the slab. Corners are weak points that must be
protected from cracking. If your driveway will have corners, the control
joint should radiate outward from the corner into the slab.
Your contractor should also consider installing steel reinforcement to
provide extra strength and evenness. Without it, there's nothing to hold
cracked slabs together or keep the cracks from getting bigger. Steel also
helps the slabs to stay level with each other. It should be installed no
deeper than two inches from the concrete surface.
Finally, it's well worth the extra cost to request thicker concrete, a
minimum of five inches is ideal. Although your contractor might say that
four inches is adequate, why not buy yourself an extra inch of strength? The
slightly higher cost in material is not going to inflate the total
installation cost that much.
Sealant may or may not be necessary, depending on the quantity of concrete
poured, its design strength, and if it was already "moist-cured" with a
curing compound. Weak concrete should be sealed.
Sources used to create this article include Tim Carter and the Detroit News.