Not a fan of the molded concrete stone idea. The remains don't support it to me. I am however a huge fan of some previous technology to be able to soften stone. But first let me substantiate the first claim.

What we have left over all over the world are remains of structures of complicated shape and massive scale most of which are natural stone of some kind. And by natural stone, I mean they have the crystal structure of material that is typically formed from volcanic, or sedimentary processes and can be verified as such by geologists quite easily. In some cases, they can even tell us where that stone is from. Most importantly, we can tell the difference between natural stone and concrete.

However, lets presume there is some ancient technology that allows us to liquefy stone so that it might be formed into shapes for artistic or structural purposes. At present, to imagine that, with our present material science limitations, we can only see that being possible by the use of extreme heat. So lets say we consider this hypothetical technology generated extreme heat, enough to effectively melt stone. If so, then what ever the mold material was that was used to form the shapes we see today, had an extremely high melting point. Much higher than granite. Also, we can presume that a higher melting point implies a much harder material, (see link below):

[www.gly.uga.edu]

So its safe to say if melting stone was necessary to form it through extreme heat, then what ever material they used for the molds would easily survive today as its hardness would greatly exceed granite and therefore be virtually indestructible. Then of course this scenario begs the question of how they made those molds, but that's an unnecessary digression.

So, lets now consider a larger leap and presume they had some magical technology that could melt stone to liquid, but without that limiting process effect of extreme heat. Lets presume it could be done with totally manageable temperatures allowing mold material to be fairly simple stuff that early man could easily work with like wood.

What I've suggested many times about the possibility of liquid mold able stone is that this technology would allow them to create far more elaborate shapes. Imagining and creating the shapes was never the hard part for early man. 3D visualizing and the artisan skill of sculpture is inherent as an ability in the modern human brain. Its not an advanced form of intelligence that we've only recently developed. Its simply a skill that's been there since the beginning. So if we some how figured out how to liquefy stone at a manageable temperature allowing us to make molds to form it, we'd see countless sculptural and architectural designs that vastly exceed what remains today. It would be almost commonplace, considering we're talking about granite remember. So the absence of those findings tells me that its highly unlikely they were ever able to make molds for stone.

When considering the technological advancements of ancient civilizations, you can break it down into different disciplines and different degrees and stages of advancement of those separate disciplines. For one, with respect to the discipline of material science, it seems that they were certainly able to soften stone. And I believe that advancement came earlier than the ability to create architecturally complicated structures.

The walls in South America would be a good example of early structural application of this stone softening. In the absence of that leap, the seamless connections of the stones in those walls is extremely confounding. But if you presume they could soften or loosen the material bonds of granite to the point that it would sag like Plasticine, then those connections begin to appear as a rudimentary and early application of that tech.

Yada yada yada. I could go on and on, but I'd be interested to see if anyone else is thinking along these lines.