Q. This spring we added a garage and replaced our driveway. It has only been about five months, but we’ve noticed cracks in the garage floor and a few in the driveway. The garage floor was perfect when the contractor left, flat and smooth, but now the cracks are showing, and in a couple of places I noticed it’s chalky white. I’m concerned that something was done wrong. The concrete was delivered and poured all together, from a big truck. Does it sound like something went wrong?
A. There are a few things in life that are inevitable, other than the obvious. The same goes for concrete. Inevitable cracking can be limited with an understanding of the details. Concrete is a chemical mixture. The chemicals and materials all work in a relationship that either binds, bonds and stabilizes, or various reactions occur.
I was fascinated when I first learned this fact, so much so that I did my fifth-year thesis in Methods and Materials classes on “the effects of salt intrusion on concrete.” I visited worksites, took lots of notes, climbed through condemned bridges and on scaffolds to get an up-close examination of damage, followed repair procedures, studied parking garage structural design and then went to view each step of the parking garage’s construction process. The most interesting thing I took away from all of that was the effects that translate to everything in nature, from our internal organs and outside skin tissue, to the growth of plants, the forming of plastics and every kind of chemical and physical property and process.
Concrete is an ever-changing composition, not a stable compound. It moves with thermal changes, expanding and contracting, elongating and shrinking. As a solid material, most people think it’s waterproof when, in fact, concrete is absorbent. If you put the wrong waterproofing coating on it, it no longer breathes, and will violently react by forcing the surface to split in small eruptions, fighting off suffocation in the same way you would if someone tried restricting your breathing. The reaction is called spalling, which also happens when a liquid penetrates the surface and expands by freezing.
To combat some of the reactions, since concrete isn’t very elastic, steel reinforcing rods, abbreviated as “rebar,” are added. If you place the rebar in the wrong places, they can actually have a negative effect. The ratios are calculated based on a very exact science that has been carefully researched. Engineering concrete isn’t guesswork, yet I see workers regularly setting up reinforcing, before the concrete is poured, in the wrong places and configurations.
You may be missing expansion joints that allow the cracking to happen at the designated weak joints; there may have been too much water in the mix, causing the calcium whiteness to leach to the surface; or the internal heat from the curing of the concrete wasn’t able to dissipate properly if the air temperature was too high. Your concrete is going to have small cracks. Good luck!
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