@Walter Hinteler,
Quote:Have you ever put one brick on the other using concrete?
Actually, when bricks are used to build a house, they use mortar as the binding agent between bricks, not cement or concrete.
Mortar is mostly sand and water, with some cement used as a binding agent.
Cement is not used on its own because the cement is to brittle to use.
Quote:And how do you make concrete without cement?
You cant, but you still dont use strictly cement to build.
Concrete is a mixture of cement, flyash, water, sand, aggregate, and chemicals.
Concrete is harder, stronger, more durable, and has more flexability then straight cement.
And yes, the ancient Romans used a form of concrete, but we still arent sure how it was made.
Yes, we know what the ingredients are, but science still hasnt figured out why it is still holding the Pantheon together.
Yes, there are some good theories, but those theories deal mostly with molecular composition and chemical reaction...
http://www.romanconcrete.com/docs/spillway/spillway.htm
Where the ancient Roman mixture has been used today, it has proven to be stronger and more reliable then modern concrete.