Concrete is classified as a mixture rather than a pure substance, element, or compound. This classification stems from its composition and how it is formed.
Concrete is primarily made up of cement, water, sand, and aggregate (gravel or crushed stone). When these materials are combined, they undergo a chemical reaction called hydration, which allows the mixture to harden and gain strength. However, because concrete is composed of multiple distinct materials that retain their individual properties even after mixing, it does not fit the definition of a pure substance or a compound.
A pure substance consists of only one type of particle, while a compound is a substance formed when two or more elements chemically bond in a fixed ratio. In contrast, the components of concrete can vary in ratio and type (different aggregates can be used), and they do not undergo a permanent chemical change in the way that compounds do. Thus, concrete represents a heterogeneous mixture, where the original materials can be identified within the final product.