For those interested in pre-Roman concrete (and buildings made of it), may I recommend this?
As long ago as 50 BC Diodorus Siculus wrote in his book Bibliotheca Historica about the Nabataeans, "They are conspicuously lovers of freedom and flee into the desert, using this as a stronghold. They fill cisterns and caves with rainwater, making them flush with the rest of the land. They leave signals there which are known to themselves and not understood by anyone else. They water their herds every third day, so that they do not constantly need water in waterless regions, if they have to flee." The information that Diodorus gathered was already common knowledge in the Middle East. The Nabataeans had been building hidden water cisterns for years.
As with the Romans, the Nabataeans secret to waterproof cement was the material known as pozzolan. Where the Romans used volcanic ash to create their waterproof cement, the Nabataeans had a much easier source. In the Hisma desert near Wadi Rumm are major surface deposits of silica, which geologists today claim is nearly 100% silicone.
B. Mason, in his book Principles of Geochemistry provides a technical discussion of research into geology to explain rock composition. For instance, he explains how a pozzolan material can be created by ground water seeping through silica. While the Romans had to search for this key component of ancient waterproof concrete, the Nabataeans simply had to locate places where water had seeped through the silica and scoop it up and add it to their lime plaster. (B. Mason, Principles of Geochemistry. John Wiley and Sons, New York, 1966, p. 160)
And so on.
http://nabataea.net/cement.htmlNow, this
pozzolan material is interesting in its own right.
Natural pozzolanas are abundant in certain locations and are extensively used as an addition to Portland cement in countries such as Italy, Germany, Greece and China. Volcanic ashes and pumices largely composed of volcanic glass are commonly used, as are deposits in which the volcanic glass has been altered to zeolites by interaction with alkaline waters. Deposits of sedimentary origin are less common. Diatomaceous earths, formed by the accumulation of siliceous diatom microskeletons, are a prominent source material here.
Are there any natural pozzolanas in Britain? Well yes, it turns out that wood ash is a good pozzolan material.
Ashes of organic origin. Coal cinders generally have an acceptable balance of silica and alumina, and have been used historically as a pozzolanic additive, but their physical structure tends to weaken the mortar and to absorb excessive water. Coal ash is widely used, in the form of PFA (pulverised fuel ash) as an additive to cementitious mortars and in lime-based grouts. The use of coal-based products carries a risk of sulphate contamination and the materials should always be selected from low sulphate coals. The residue of fuels from lime burning, whether from coal-, coke-, or wood-fired kilns, known as lime-ash, is well known historically as a pozzolan and is still available.(8) Other vegetable ashes, such as rice husk ash, are used as pozzolans in other parts of the world. Bone ash is also known to have been used.
http://www.buildingconservation.com/art ... /pozzo.htm
If you were burning wood to smelt metals (and so producing tons of wood ash), and you were also in a chalk or limestone area (so able to make lime), you would have all the ingredients to make your own polymer concrete. Or megaliths as some like to call them.
