1. The impact of this work on society is multifaceted and universal. The largest facet lies in the answer to this simple question: how sophisticated and/or energy intensive can a 4500 yr old technology be. The answer in both cases is not very. The sooner we understand how this synthetic limestone was made the sooner we can use it to build affordable housing using an ultra-durable concrete that is indistinguishable from natural limestone. This reconstituted limestone – if made with lime as the Ancient Egyptians made it – would generate roughly 50% less CO2 than a Portland cement-based concrete. The Great Pyramids of Egypt: Cast, Carved or Both?Michel W. Barsoum, Drexel University, DMR 0907430 Researchers at Drexel U in PA have shown that a small fraction of the limestone blocks from the Great Pyramids of Egypt may have been cast, rather than carved. The postulate was that some limestone blocks are a concrete made by mixing diatomaceous earth (a mineral that is rich in silicon dioxide), lime and water with a fine-limestone aggregate. The evidence includes C-dating and microstructural evidence in the form of undigested diatoms. The researchers have also shown that lime will indeed react with diatomaceous earth to form a binder that holds the fine-limestone aggregate together.