What is the main composition of concrete?

Concrete is primarily composed of cement, aggregate, and water. Cement acts as the binding agent that holds the other materials together. Aggregate consists of coarse and fine materials, typically sand and gravel, which provide bulk and strength to the concrete mixture. Water is crucial for the chemical reaction with cement known as hydration, which ultimately leads to the hardening of concrete.

While steel is often added to enhance the tensile strength of concrete in structures, it is not considered a main component of the basic mixture. The inclusion of plastic or air, as suggested in some other options, does not form the fundamental makeup of concrete; instead, air can be present as a result of the mixing and curing processes, while plastic may refer to additives but are not part of the essential composition. Therefore, the combination of cement, aggregate, and water defines the standard formulation of concrete and is key to its properties and performance in construction.