Pyramids made of concrete, not pre-cut limestone blocks

Fascinating article, it seems feasible to me.

The Surprising Truth Behind the Construction of the Great Pyramids

Snippet:
The stones also had a high water content-unusual for the normally dry, natural limestone found on the Giza plateau-and the cementing phases, in both the inner and outer casing stones, were amorphous, in other words, their atoms were not arranged in a regular and periodic array. Sedimentary rocks such as limestone are seldom, if ever, amorphous.

The sample chemistries the researchers found do not exist anywhere in nature. "Therefore," says Barsoum, "it's very improbable that the outer and inner casing stones that we examined were chiseled from a natural limestone block."

More startlingly, Barsoum and another of his graduate students, Aaron Sakulich, recently discovered the presence of silicon dioxide nanoscale spheres (with diameters only billionths of a meter across) in one of the samples. This discovery further confirms that these blocks are not natural limestone.