I love the opportunities I have every day to educate others on some of the basics of concrete. Even though concrete applications and finishing can be very complicated, here are some very basic properties and methods that I have learned to help increase our performance as concrete leaders in the NC and SC area.
Concrete cracks, but you can control it mostly by:
1) Strategically cutting relief joints in calculated areas. There is no exact formula for this. The frequency and areas of expansion cuts factor in many different scenarios. Just to name a few; thickness of concrete; temperature during and after pour; thickness of concrete; curves in design; rectangular areas. Our team is very knowledgeable (some of this knowledge has come from trial and error over the years). Although there are some basic guidelines, field knowledge is definitely helpful in preventing expansion cracks with properly placed expansion cracks.
2) Adding the correct additives when weather is not optimal. You can actually pour in just about any weather (the largest building in the world was built in 100+ degree weather, and many colder countries have no choice but to pour in ice and snow). Luckily in the Carolinas, we usually do not have to deal with too many extremes. Unfortunately, we do not have Hawaii weather either! We have wind (which sometimes causes us to use a good surface retarder to prevent spider cracking through plastic shrinkage), heat (we can add retarders in the concrete or surface retarders), and cold (we can add accelerates like calcium chloride in the mix). Using additives allows us to work year round, but as word of caution if you do not have experience with these products they can be very tricky to work with!
3) Ordering the right mix, and pouring the right thickness. Too many times I have been asked to pour 4,000 or 5,000 PSI concrete for a residential driveway 4″ thick by customers thinking they are going to bullet proof their driveway. Although 4,000 and 5,000 psi concrete are generally not a whole lot stronger than 3,000-3,500 PSI, it is designed mostly for commercial and industrial applications of 6″ or thicker. We have found that if you want a really solid residential driveway, usually a good 4″ 3,500 psi concrete with residential fiber will do the trick (rebar/wire mesh strategically placed in potential trouble areas). Commercial driveways can usually get away with a good 6″-8″ 4,000 PSI reinforced pour (residential fiber, mesh, rebar, etc.).
4) A good base with thickened edges where needed. You don’t necessarily always need gravel here in NC. We have great dirt if compacted correctly. Sometimes, when the dirt is not compact-able, you may need gravel. It is a good idea to pour thickened edges by the forms, especially when you build up from natural virgin grade.
5) Keep it wet, and stay off for a couple of days. Ask your contractor how long you should stay off it, and keep heavy moving trucks off it for at least a month. Another good practice is to wet it a couple of times per day to add moisture to the top layer of concrete which is exposed to the weather and hardens before the rest of the concrete.
I know, I know…concrete cracks! No matter what you do, concrete can crack in the strangest areas. Baja Concrete has a commitment to minimizing cracks by following one or a combination of the measures above. We also offer a crack warranty that is extremely competitive with any reliable company. If you do end up with a micro-crack, usually the best thing to do is leave it alone and monitor it every now and then. As soon as you try to repair it (i.e. grinding, sealing, caulking, patching), you are adding and committing to continuous maintenance for the life of your concrete. If it turns into an issue (please see our warranty), give us a call and let us check it out!