Roman Concrete (revised)

[Pertinax]

Some considerable time ago I remarked about having seen a practical construction display of the casting of a roman underwater foundation. Northern Neil's work on the Fortlet models made me turn up the reference I was missing. The Romans had a strong building mortar developed by the third C BC , which in combo with other facing materials could produce walls of great strength.

Slaked Lime was produced in kilns (CaO from burning CaCO3: then slaked to give CA(OH)2and has sand added to it-finally on drying you get crystals of CaCO3 (calcium carbonate) ). Calc carb tends to adhere tenaciously to rough surfaces so it strengthens and plasticises mortar. Vitruvius recommended 3 sand to ! lime-thats a very stiff mix id say.So lime as a commodity was in universl usage, and we can reasonably conjecture its use as wash.

However by Augustan times the pozzolana, red ,volcanic dust became the key ingredient in concrete -it doesnt need to lose water at all to achieve strength,the secret is its silicate aluminate nature combining effotlessley with lime to make hydrated silicate of calcium and other related complexes. So you can work underwater and fast.

http://www.cs.uu.nl/people/wilke/aquasite/...ekopusbreed.htm

 

heres a nice link to give construction phase types.One tends to think of the Opus Testacum as the definitive technique.

 

this image at Glannaventa is instructive:

http://www.unrv.com/forum/index.php?act=mo...&cmd=si&img=491

 

 

http://www.amazon.co.uk/exec/obidos/ASIN/0...8902684-7521431

 

that is the Vitruvius reference (book 2.6.1)

Edited June 4, 2006 by Pertinax

[FLavius Valerius Constantinus]

Only other thing I know is that the Romans also added some type of volcanic ash or rock that helped greatly with the concrete.

[Pertinax]

Only other thing I know is that the Romans also added some type of volcanic ash or rock that helped greatly with the concrete.

Yes , they used the ballast from merchant ships as an additive -which was frequently the volcanic ash from the Pompeii area, and found that it improved the hardness and the setting time of the mix.The feature I saw on the slab casting used some of this "tufa" in the mix.

I would like to add that Sear notes that when reconstruction/overbuilding took place the Roman engineer and architect were quite agreeable to incorporating previous structural elements of older buildings.As an example, a wing of Nero's Golden House ended up as part of the Baths of Caracalla.Vitruvius also gives a clue on population density via reference to use of bricks (De Arch 2.8.17) he expresses concern at the limitations of baked mud brick in supporting the taller housing structures being required ,and he notes the best bricks are made from old roofing tiles because of their great hardness.

 

I should have looped this in before:

http://www.unrv.com/forum/index.php?act=mo...&cmd=si&img=765

Edited June 4, 2006 by Pertinax

[Primus Pilus]

Some excellent articles on Roman Concrete

[Northern Neil]

I am lucky enough to have visited Pozzuoli, near Napoli. It is here that the Romans are said to have invented concrete. Cracking amphitheatre there, by the way! (See gallery)

[Gaius Octavius]

If my memory serves, present day concrete used in road building should be kept wet with straw for months in order to 'age' it properly. The water and concrete form chrystals to harden the road. I think that in order to get a good result, it should only be poured in the early summer.

[P.Clodius]

Wasn't sure where to put this but this section of the forum seems appropriate. Roman Concrete

[P.Clodius]

Whoops..sry didn't know this thread existed already..

[Pertinax]

Whoops..sry didn't know this thread existed already..

Apologies not needed! Just tidying