Concrete is so ubiquitous in our urban landscape today that it’s rarely given the credibility it deserves. Concrete is one of the most versatile, durable, and widely used building materials, whose earliest roots even date back to 6500BC – not to mention fire-resistant and low maintenance. No wonder why it’s the material of choice for foundations, buildings, driveways, walkways, bridges, and more.

What is Concrete Made Out Of?

Underneath its drab gray exterior, concrete has some hidden complexity into how it’s constructed. What is concrete made of that makes it so durable and versatile? Concrete is made up of these simple components: cement, water & air, coarse aggregates, and fine aggregates. These different ingredients each have very important functions and roles, so let’s dive a bit deeper.

The Main Ingredients in Concrete

1. Cement

Cement is a component of concrete that serves as a powerful binding material capable of setting, hardening, and remaining stable underwater. There are eight ingredients involved in the chemical manufacturing of cement: lime, silica, alumina, magnesia, sulfur trioxide, alkaline, iron oxide, and calcium sulfate. These ingredients can be extracted from limestone, clay, marl, shale, chalk, sand, bauxite, and iron ore. When cement mixes with water, it becomes a paste that is used to fill up void space between aggregate particles binding them into a strong, solid, not impenetrable mass.

2. Water & Air

Water acts as a lubricant and plays an important role for the mixing, setting, laying and compaction and hardening of concrete. The quantity and quality of water used in mixes that directly affect the strength of concrete. Water is the only concrete ingredient that reacts chemically with cement so that setting and hardening process can take place.

For a mixture to be effective, some level of air entrainment needs to exist within the concrete. Air-entrained concrete contains microscopic air cells that work to relieve internal pressure on the concrete by providing space for the concrete to expand and contract when it freezes and from the heat in the summer.

3. Aggregates

The major concrete ingredient that takes up the most volume are aggregates. Aggregates bound together by hydrated cement make an artificial rock. Aggregates are typically divided into two categories depending on sizes, because there are fine aggregates such as sand and coarse aggregates such as gravel and crushed stones.

4. Admixtures

In addition to cement, water, and other aggregates, there are additional optional ingredients that can be added to concrete such as admixtures, polymers, air entrapment, accelerators, fibers, and reinforcements. These ingredients can be used to modify the properties of the fresh and hardened concrete.