What is cement primarily composed of?

Cement is primarily composed of a finely pulverized mixture of clay and limestone. In the production process, these materials are heated in a kiln at high temperatures, which causes a series of chemical reactions known as calcination. This process transforms the raw materials into clinker, which is then ground into a fine powder to produce cement. This finely ground product is essential for various construction applications, particularly in the making of concrete, where it acts as a binding agent.

The correct answer highlights the foundational components in cement manufacturing, setting it apart from other mixtures or substances used in construction. For example, while clay is indeed a component, a mixture with asphalt does not reflect the chemical processes involved in creating cement. Similarly, a slurry of sand and gravel would be more representative of concrete rather than cement itself, as gravel and sand are aggregates and not part of the cement's composition. Lastly, a combination of air and concrete does not pertain to cement at all, as it misrepresents the fundamental ingredients required for cement production.