eli5 how does cement and concrete become hard if it’s only rocks and water

Question

eli5 how does cement and concrete become hard if it’s only rocks and water

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Answer 1

Concrete is a mixture of rock “aggregate” and cement. Cement is the special bit. It’s a mixture of limestone and clay that has been “cooked”. When you add water to it, a series of chemical reactions cause it to bind to the water and go hard. Cement is effectively the “glue” that sticks concrete together!