Cement is a gray powder made by grinding stone. It
was invented by the Romans for making mortar. They mixed
crushed rock with burnt lime to create a sort of flour.
Water was added to these particles and as it dried, it
strengthened. It had to be kept dry in order to maintain its
strength.
Concrete is cement that is mixed with sand, crushed rock
or gravel. It solidifies and hardens after mixing with water
through a process called hydration. The water reacts with the
cement, which bonds the other components together, eventually
creating a strong stone-like material. Concrete is cheap and
is the most widely used man-made material in the world.
Cement and Concrete, respectively
As shown above, concrete typically has another material mixed with it to give it a distinct appearance, while cement is usually plain ground stone.
