>>I've seen the process reproduced (on a video of course) and with the addition of water the mixture started to "boil".<<
Thanks for those links. Without looking further tonight---bad toothache---I'll guess the boiling was from using quick lime, calcium oxide:
1. n. [Drilling Fluids] ID: 1769
A chemical with formula CaO, commonly called quick lime or hot lime. When hydrated with one mole of water, it forms slaked lime, Ca(OH)2. Quick lime is used in preference to slaked lime at oil-mud mixing plants because it generates heat when it becomes slaked with water and therefore speeds up emulsification by the reaction to form calcium-fatty-acid soaps.
(http://www.glossary.oilfield.slb.com/Display.cfm?Term=calcium%20oxide)
The adding of water would convert it to slaked lime, the prime ingredient of 'natural' (as opposed to modern 'Portland') cement.
[Quick lime was also used sparing to sprinkle down the hole of outhouses, to control oder, insects, etc. It is also the lime used to sprinkle on dead critters until [if ever] they can be picked up by the knacker or animal control. It will burn the skin, which is why pre-slaked lime is used for such things as white-wash & plaster; it is safer.]
a few links and quotes:
The Pantheon-- Rome -126 AD
A temple to all gods - by Freda Parker
http://www.monolithic.com/thedome/pantheon/
"Though the Romans had been building with concrete since about 200 BC, work on the Pantheon was difficult and proceeded in gradual stages... Vitruvius (cir. 20 BC), a noted Roman architect, recorded the process followed in his day, that was probably still used by the Pantheon's builders. The ancients hand mixed wet lime and volcanic ash in a mortar box, adding very little water so that they got a nearly dry composition. They carried this mixture to the job site in baskets and poured it over a prepared layer of rock pieces. They then tamped the mortar into the rock layer. The tamping packed the mortar, reduced the need for excess water, but, at the same time, stimulated bonding... Eventually, work began on the concrete dome, constructed in tapering courses or steps that are thickest at the base (20 feet) and thinnest at the oculus (7.5 feet). The Romans used the heaviest aggregate, mostly basalt, at the bottom and lighter materials, such as pumice, at the top. They embedded empty clay jugs into the dome's upper courses to further lighten the structure and facilitate the concrete's curing. In the dome's construction, the Romans probably used temporary wooden centering on which they layered concentric rings of masonry and concrete."
[derivative material at http://www.aviewoncities.com/rome/pantheon.htm ]
http://www.aviewoncities.com/img/rome/kveit0301p.jpg
Pantheon, Rome
Wikipedia
http://www.answers.com/topic/pantheon-rome
http://www.answers.com/main/content/wp/en/thumb/2/28/175px-Ac.pantheon2.jpg
"The building is circular with a portico of three ranks of huge granite Corinthian columns (8 in the first rank and 16 in total) under a pediment opening into the rotunda, under a coffered, concrete dome, with a central opening (oculus), open to the sky. The height to the oculus and the diameter of the interior circle are the same (43 metres), so the whole interior would fit exactly within a cube. The dome is the largest surviving from antiquity, and was the largest dome in western Europe until Brunelleschi's dome of the Duomo of Florence was completed in 1436."
The Pantheon
By David Moore, P.E., 1995
http://www.romanconcrete.com/docs/chapt01/chapt01.htm
"Unrecognized, the design of this ancient concrete building reveals unparalleled features not encountered in modern design standards. Recent studies reveal several major cracks in the dome, but it still functions unimpaired. This condition will surely excite the curiosity of our structural engineers. The building was built entirely without steel reinforcing rods to resist tensile cracking, so necessary in concrete members, and for this concrete dome with a long span to last centuries is incredible. Today, no engineer would dare build this structure without steel rods! Modern codes of engineering practice would not permit such mischief. No investor with knowledge of concrete design would provide the funding."
also:
http://www.geopolymer.org/science_archaeology/roman_cement_concrete/high_durable_buildings.html
