Permacrete

In the RotS novelization, we hear of the Invisible Hand using "hydrofoamed permacrete" and, later, a note about "a pile of rubble: shattered permacrete, hydrofoamed to reduce weight."   Indeed, Kenobi, unconscious, was Force-launched by Dooku "into the wall so hard the hydrofoamed permacrete buckled and collapsed onto him", though as Anakin found later, "no bones were broken: this was a concussion, no more."

Needless to say, then, this hydrofoamed permacrete doesn't sound like some super-tough, super-dense material.  It would certainly be more substantial than the normal styrofoam we're all used to, but it doesn't seem any more substantial than, say, a sheetrock wall, and given the complete collapse it seems as if it wasn't especially well framed.  (Meaning, a sheetrock wall is anchored to framing studs that are spaced fairly closely, meaning even if you launch a guy through the sheetrock in-between the studs, you'll usually just have a guy-sized hole in the sheetrock rather than a collapsed wall of sheetrock or, worse, collapsed wall altogether.)

I am reminded of other similar techniques used today.  I've seen foam sections used as building material for ornamental purposes, covered in stucco or similar to provide the finishing touches.  And indeed, there is a material commonly referred to as 'eps concrete' where, instead of using sand and rock for the aggregate material of the concrete, simple polystyrene foam is used instead, reducing weight.  "Hydrofoamed" is a word of not perfectly clear meaning, though it suggests something involving water.  Perhaps ice was used as aggregate for a low-temperature concrete mix and then, once hardened, the water is melted, and the wall was dried?   That would be an interesting technique for low-cost, low-weight concrete if your hydrofoamed concrete factory is located in arctic climates, anyway.  Maybe I should patent that.   The last few sentences are hereby copyrighted!

In any case, we know of permacrete from other prequel novelization references, too.  For instance, on Naboo the palace at Theed featured permacrete on the interior that was blasted into shards along with the glass by Panaka's blaster, and the ray shield preventing Obi-Wan from reaching Qui-Gon was said to be as good as a three meter wall of permacrete insofar as keeping Obi-Wan out, suggesting that a wall of such impressive proportions is sufficiently impervious as to keep a Jedi out for an indeterminate length of time.   In the later prequel novelizations, permacrete seems to be referred to as walkway material for Coruscant, the landing pads of Kamino, and the Separatist landing platform of Utapau.  The buildings of Coruscant are said to be durasteel and permacrete canyon walls after the Battle of Coruscant.  The stuff's even slippery when wet.

In short, we have no great reason to suspect permacrete is terribly much stronger than concrete.   Stronger, yes, insofar as it allows for the multi-kilometer buildings of Coruscant, but relatively simple steel-reinforced high-density concrete was used for the base of the Burj Khalifa (formerly Burj Dubai) in this century, and that building is almost a kilometer in height.  I say "relatively simple" because although it was an engineering challenge to get the mix and pours just right, it did not require a totally unprecedented material bearing no resemblance whatsoever to the concretes that had come before.   We might not be able to extend that to a multi-kilometer structure today, but I also rather doubt that it would take a thousand years of development to arrive at such a solution.

There is also reference to "duracrete" in the novelizations, identified as the material of the plaza around the Senate building in the RotS novel, but with no other information provided.  But given the presumable age of the plaza, I would presume it is a lesser material than permacrete.