Describe two diagrams

There are two diagrams: the left one illustrates how the cement is made and the other one shows how the concrete is produced. (This would sound more natural to me if "the" was removed as shown.)

There are six stages and two substances to make a bag of cement, whilst it needs four ingredients are needed to make concrete.

To produce cement, limestone and clay are the main materials. In the first stage, they are put them together through a crusher to make them into powder. Then this powder is transmitted to a mixer and goes through a tube to reach a rotating heater where it will be rotated and heated. After being heated, this hot powder is ground by a grinder to produce cement. In the final stage, the cement is packed into bags.

The diagram on the right shows that concrete is a mixture of four ingredients. Each has a different percentage to make concrete. Cement is made makes up 15% of the mixture, water accounts for 10%, sand constitutes 25%, and gravel (i.e. small stones) 50%. Put all of them into a rotating mixer, then concrete is produced.

(172 words)

This is an essay for IELTS exam writing task 1.
Hope someone could give me advice on what I did.
Your help is greatly appreciated!