If it wasn't for the fact that many megalithic structures were made of stone that wasn't sedimentary, I'd suspect there were other means of making concrete.

However, I have seen marks on stones that are absolutely certain to have been made when the stone was plastic, as if it had been heated. I strongly suspect that directed energy tools were used to plasticize the stone, making it easily shaped. Many of the stones in various megalithic structures bear peculiar marks, which would seem to be caused by a particular mold being used on that structure.

There is no doubt that copper chisels were NOT used to carve the stones the Pyramids were made of. That would be like using silly putty knives to cut steak. In many places you can see 'run out' caused by circle saw blades on the stones. You can't make a useful circle saw blade from copper.

As a result of this, I have actually worked on devices to do exactly that - heat stone using EMF until it's plastic and easy to cut.