Concrete Science
On its surface, concrete seems pretty simple. Just some goop that hardens into whatever shape you pour it into. Right?
Sure, but there is a lot more to it than that. This supremely useful substance can almost take on any shape and hardens to a very strong material able to withstand the forces of nature very well. However, it can be very tricky to work with. There are reasons why people rely on professional installation when they want it to last.
Concrete is made up of a filler (fine or coarse aggregate) and a binder (the “glue” made of cement and water). Adding water to the dry ingredients causes a chemical reaction: causing microscopic crystals to develop, grow and interlock. This chemical process is called “curing” and is considered fully cured after 28 days. Though it will continue to strengthen over the course of it’s lifetime.
The right mixture is the key to the strength of your concrete
If you add too much water, the crystals grow too far apart and weaken the structure. Too little water, and the mixture becomes unworkable. If you overwork or overmix it, this can weaken the structure as well. Because concrete must be both strong and workable, a careful balance of the cement to water ratio is required.
Additives
Because of this balance, temperature and humidity are always a concern when setting up concrete. In an ideal world, the weather would always be dry, with a perfect moderate temperature when we pour concrete. In the real world, people need concrete all year long and we have to make adjustments in order to offset any temperature and moisture changes. We use additives when temperatures are high to slow the curing process, or speed it up when temperatures are too low. Or, if the concrete is overly wet, we can use a plasticizer to increase the “slump” (the structure and workability of concrete before it sets) without impacting strength.
Concrete science is a fine balancing act and requires careful planning and calculations.
Cracks
Cracked Concrete In Hamilton Ohio. December, 1935 from the Library of Congress
First, all concrete cracks. It is our job to make sure it cracks where we want it to by scoring it. Those lines in the sidewalk? Those are the control joints, if you look at them from the side you will see hairline vertical cracks.
Maintaining your concrete
Let’s face it, concrete is expensive to replace. So you want to make sure it lasts as long as it can. The secret to the longevity of your concrete is all in how you take care of it.
- Concrete should be cleaned at least once per year (ideally in the spring) to remove any dirt, salt and grime build up (See the video below of me powerwashing my embarrassingly dirty driveway).
- Add a penetrating sealer every 5 years or less-depending on wear.
- Do not use any de-icing salts or chemicals, instead use sand for traction.
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