Not sure if I've ever mentioned this before, but a while ago I had the chance to talk to a geologist attached to English Heritage, looking after Avebury Stone Circle.
I asked what kind of stones were used at Avebury. The first answer was “
Oh, they’re sarsen stones”.
Yes, but what are the sarsen stones made of? “
Oh, these are concreted alluvial deposits”.
I asked “
Oh, you mean they’re made of concrete, like some of the Egyptian pyramid stones?”.
At this point the English Heritage geologist was starting to look a bit scared, so I stopped asking awkward questions. And yet : some other geologists like Steve Marshall are more enquiring. They’ve noted many curious things about the sarsens at Avebury:
'Silica Glaze' - smooth, shiny patches of silica are found on some stones, resembling a thick, transparent pottery glaze.
'Sticky areas' are rough, with sharp peaks like cake icing. The sarsen appears to have become sticky before it set hard.
For more details, see
http://exploringavebury.com/geologyThey have even made their own geopolymer sarsen stones. For the recipe, see:
http://exploringavebury.com/assets/uplo ... 0Stone.pdfAfter three years:
it resembled mortar made with Portland cement but seemed to be even harder.
If you want to make Egyptian-style limestone geopolymer, there are some good videos online.
https://www.youtube.com/watch?v=znQk_yB ... tion=shareTheir recipe?
they use old disaggregated (rotted) limestone rubble as their major material at 95% of solids. The binder is made from a mixture of kaolin clay, natron (sodium carbonate aka washing soda) and lime in water. The natural limestone in Egypt contains the kaolin already, but their source in the video didn’t have it, so it was added. Natron is found in the Egyptian desert, and lime is made by burning limestone. The water (12-17% of solid volume), natron, clay and lime are mixed in a large tub, then the limestone aggregate is added. As a damp squishable material like wet beach sand, it is dumped in layers into a wooden mold and tamped. In 4 hours it sets up and in a few days it is fully hardened. It looks like real limestone.
Other recipes are available.
And then (of course) there are the Tiwanaku / Pumapunku "Megaliths"
https://www.youtube.com/watch?v=rf9qK9QTlq0