Question

different between modern cement and ancient cement

Answer 1

Cementite (Iron Carbide) is a chemical compound whose inclusion hardens steel. Each molecule is made of three iron atoms bonded to one carbon atom to form a crystal lattice structure called orthorhombic. It is a very hard and brittle substance. In its purest form, cementite is classified as a non-oxide ceramic. It is solid and inert, and can withstand crushing force, chemical erosion, abrasion, and temperatures up to 1600 degrees C.

Cement (we normally use hydraulic cements in general building construction) is usually a dry powder, which when mixed with water, reacts with it and the resulting hydration products can bind other materials (aggregate) together. I could go on and on about cement and the history of it’s development. If you are interested in the specifics : 

I hope it will help