Question

Which category of materials does concrete belong to and why?

Answer 1

The answer is:

d.It’s a composite because it’s a mixture of cement, sand, and other granular pieces.

The explanation:

Concrete is a composite, since it is composed of various elements like sand, gravel & water.  

Aggregate consists of large chunks of material in a concrete mix, generally a coarse gravel or crushed rocks such as limestone, or granite, along with finer materials such as sand. Cement, most commonly Portland cement, is associated with the general term "concrete.

Answer 2

 I am absolutely sure that concrete  belongs to such category of mterials as composite material because it consists of many processes, where coarse  aggregate bonding with a fluid cement. Hope you still need the answer and do hope you will find it useful.