Foundations of Concrete
Did you know: Concrete is the most widely-used building material in the world.
Why? Because it’s among the strongest, most sustainable, and most economical building material available.
These traits lend to its use in many applications, from the tallest building in the world—Burj Khalifa—all the way to the foundation your house sits on. Concrete is unique because it’s soft and malleable when freshly mixed and extremely hard and sturdy once hardened.
What is Concrete Made of?
In its simplest form, concrete is made of three basic components: water, aggregate (rock, sand, or gravel), and cement.
PS: If you read that and thought, “Wait, I always assumed concrete and cement were the same thing!”—don’t worry, you’re not alone!
Most people don’t realize that cement is in itself a component of concrete!
Let’s break it down: components of concrete
Aggregate: Aggregate usually comprises 60-75% of a concrete mix by volume. Aggregates like rock, sand, and gravel are generally used as stable and non-reactive fillers that stiffen and harden the concrete mix. Changes in gradation, size, unit weight, and moisture content of aggregate can all alter the character and performance of concrete.
Cement: Hydraulic cements (like Portland cements) are composed primarily of inorganic material, most commonly lime or calcium silicates. Hydraulic cements set and harden by chemically reacting with water.
Water: Combining water (H2O) with cement kickstarts the process of hydration (see below).
Supplementary cementitious materials (SCM): SCMs are materials like fly ash or calcium carbonate which, when used in conjunction with cement, contribute to the beneficial characteristics of concrete. They’re often used as a replacement for cement by volume to improve economy and sustainability.
Chemical admixtures: Admixtures are either powder or liquid materials added to the concrete during the batching process that aid in the transport and placement of the fresh concrete and enhance strength and durability of hardened concrete.
Now let’s bring it all together
When mixed together, cement and water create a paste. Through a chemical process called hydration, the paste begins to harden. Hydration of cement is an exothermic reaction that creates several products, the main one being calcium silicate hydrate (C-S-H) which is the primary source of concrete strength.
The hydration process begins immediately and lasts for the life of the concrete, but the first 28 days are crucial.
During this time, the concrete is “curing.” This involves controlling moisture and temperature conditions, which affect strength development, durability, and permeability of the finished product.
Once your concrete is cured, you’re ready for the next adventure! Whether that means cooking on it, driving on it, building on it, or some other creative project… concrete can take you places.
