VITRUVIUS, BOOK II, CHAPTER 6
On pozzolana



1. Est etiam genus pulveris quod efficit naturaliter res admirandas. Nascitur in regionibus Baianis et in agris municipiorum quae sunt circa Vesuvium montem. Quod commixtum cum calce et caemento non modo ceteris aedificiis praestat firmitatem, sed etiam moles cum struuntur in mari, sub aqua solidescunt. Hoc autem fieri hac ratione videtur quod sub his montibus et terrae ferventes sunt et fontes crebri, qui non essent, si non in imo haberent aut e sulphure aut alumine aut bitumine ardentes maximos ignes. Igitur penitus ignis et flammae vapor per intervenia permanans et ardens efficit levem eam terram, et ibi qui nascitur tofus turgens est sine liquore. Ergo cum tres res consimili ratione ignis vehementia formatae in unam pervenerint mixtionem, repente recepto liquore una cohaerescunt et celeriter umore duratae solidantur, neque eas fluctus neque vis aquae potest dissolvere.

Translation

1. There is also a kind of powder which, by nature, produces wonderful results. It is found in the neighbourhood of Baiae and in the lands of the municipalities round Mount Vesuvius. This being mixed with lime and rubble, not only furnishes strength to other buildings, but also, when piers are built in the sea, they set under water. Now this seems to happen for this reason: that under these mountainous regions there are both hot earth and many springs. And these would not be unless deep down they had huge blazing fires of sulphur, alum or pitch. Therefore the fire and the vapour of flame within, flowing through the cracks, makes that earth light. And the tufa which is found to come up there is free from moisture. Therefore, when three substances formed in like manner by the violence of fire come into one mixture, they suddenly take up water and cohere together. They are quickly hardened by the moisture and made solid, and can be dissolved neither by the waves nor the power of water.

2. Ardores autem esse in his locis etiam haec res potest indicare quod in montibus Cumanorum Baianis sunt loca sudationibus excavata, in quibus vapor fervidus ab imo nascens ignis vehementia perforat eam terram per eamque manando in his locis oritur et ita sudationum egregias efficit utilitates. non minus etiam memorantur antiquitus crevisse ardores et abundavisse sub Vesuvio monte et inde evoluisse circa agros flammam. Ideoque tunc quae spongia sive pumex Pompeianus vocatur excocto ex alio genere lapidis in hanc redacta esse videtur generis qualitatem.

Translation

2. But that there are fervent heats in these districts may be proved by this circumstance. In het hills of Baiae which belong to Cumae sites are excavated for sweating rooms. In these hot vapour rising deep down perforates the soil by the violence of its heat, and passing through it rises in these places, and so produces striking advantages in sweating-rooms. Not less also let it be recorded, that heats in antiquity grew and abounded under Mount Vesuvius, and thence belehed forth flame round the country. And therefore now that which is called "spongestone" or Pompeian pumice seems to be brought to this general quality from another kind of stone when it is subjected to heat.

3. Id autem genus spongiae quod inde eximitur non in omnibus locis nascitur, nisi circum Aetnam et collibus Mysiae quae a Graecis catacecaumene nominatur et si quae eiusdem modi sunt locorum proprietates. Si ergo in his locis aquarum ferventes inveniuntur fontes et montibus excavatis calidi vapores, ipsaque loca ab antiquis memorantur pervagantes in agris habuisse ardores, videtur esse certum ab ignis vehementia ex tofo terraque, quemadmodum in fornacibus ex calce, ita ex his ereptum esse liquorem.

Translation

3. But that kind of spongestone which is taken thence is not found in all places, only round Etna and on the hills of Mysia (which is called Catacecaumene by the Greeks), and if there are in any other places properties of that kind. If, therefore, in these places there are found hot springs, and in all excavations, warm vapours, and if the very places are related by the ancients to have had fires ranging over the fields, it seems to be certain that by the violence of fire, moisture has been removed from the tufa and earth just as from lime in kilns.

4. Igitur dissimilibus et disparibus rebus correptis et in unam potestatem conlatis, calida umoris ieiunitas aquae repente satiata communibus corporibus latenti calore confervescit et vehementer efficit ea coire celeriterque unam soliditatis percipere virtutem.
Relinquetur desideratio, quoniam item sunt in Etruria ex aqua calida crebri fontes, quid ita non etiam ibi nascitur pulvis, e quo eadem ratione sub aqua structura solidescat. Itaque visum est antequam desideraretur de his rebus quemadmodum esse videantur exponere.

Translation

4. Therefore, when unlike and unequal substances are caught together and brought into one nature, the hot desiccation, suddenly satured with water, seethes together with the latent heat in the bodies affected, and causes them to combine vehemently and to gain rapidly one strong solidity.
Since in Etruria also there are frequent springs of hot water, there will remain the inquiry why there also the powder is not found, from which in the same manner walling may set under water. Therefore it seemed good, before inquiry was made on these matters, to seth forth how they seemed to come about.

5. Omnibus locis et regionibus non eadem genera terrae nec lapides nascuntur, sed nonnulla sunt terrena alia sabulosa itemque glareosa aliis locis harenosa non minus materia, et omnino dissimili disparique genere in regionum varietatibus qualitates insunt in terra. Maxime autem id sic licet considerare quod qua mons Appenninus regiones Italiae Etruriaeque circa cingit, prope in omnibus locis non desunt fossicia harenaria, trans Appenninum vero quae pars est ad Adriaticum mare, nulla inveniuntur, item Achaia Asia omnino trans mare nec nominantur quidem. Igitur non in omnibus locis quibus effervent aquae calidae crebri fontes, eaedem opportunitates possunt similiter concurrere, sed omnia uti natura rerum constituit, non ad voluptatem hominum sed ut fortuito disparata procreantur.

Translation

5. Neither the same kinds of soil nor the same rocks are found in all places and regions, but some are earthy, others of gravel, others pebbly, in other places sandy material; and generally there are found in the earth qualities of unlike and unequal kind with the various regions. But we may regard the matter especially in this way: almost everywhere, where the Apennine range encloses the regions of Italy and Etruria, sand-pits are found; whereas across the Apennines, where the land adjoins the Adriatic, none are found. Generally also it is not indeed even named across the sea in Achaia and Asia. Therefore not in all places in which frequent hot springs boil up can the same conveniences arise; but all things are generated as the Nature of Things has determined, not for the pleasure of man, but disparate as though by chance.

6. Ergo quibus locis non sunt terrosi montes sed tenerae materiae, ignis vis per eius venas egrediens adurit eam. quod est molle et tenerum exurit, quod autem asperum relinquit. Itaque uti in Campania exusta terra cinis, sic in Etruria excocta materia efficitur carbunculus. utraque autem sunt egregia in structuris, sed alia in terrenis aedificiis alia etiam in maritimis molibus habent virtutem. Est autem materiae potestas mollior quem tofus, solidior quem terra, qua penitus ab imo vehementia vaporis adusta, nonnullis locis procreatur id genus harenae quod dicitur carbunculus.

Translation

6. Therefore whereever mountains are not of earth but of a woody kind, the force of fire escaping through the veins burns it up. It burns out what is soft and tender, but leaves what is rough. Therefore just as in Campania, burnt-out earth becomes ashes, so in Etruria, charred stone becomes carbuncular. Both are excellent in walling. But some materials have advantages in buildings on land, and others in piers built into the sea. The nature of wood is softer than tufa, more solid than earth; and when this is burnt deep down by violence of vapour, there is generated in some places that kind of sand which is called lignite (carbunculus).

COMMENT

Vitruvius is again talking from his own experience. As an architect he must have known the qualities of this pulvis Puteolanus. Once again he tries to explain the reasons for this hydraulic qualities from his theories about air and heat which detracts moisture from the material. Although he have seen that only the sand of the volcanic regions around Vesuvius and Etna has these properties it didn't come up in his mind that it was only volcanic sand which had these properties. He even tries to explain why sand from Etruria, where there are also hot water springs, and where the conditions of heat and air are - in his opinion - comparable to those of Campania, has not the same qualities: because the nature of the region is different on different places. But he doesn't relate it to volcanic activity.

The Romans discovered the excellent adhesive qualities of this material during the second century B.C.. They called it pulvis Puteolanus because it was found in large quantities in the region of Puteoli (modern Pozzuoli) near the Vesuvius. When lime, quartz, sand and water were combined with pozzolana dust, the mortared mass became a consistent and coherent concrete which could be poured over a rubble aggregate of stone chips and brick particles, or pumice. Vitruvius allusion to the hydraulic properties of pozzolana accords with the study of harbours and seaside villas along the shores of Campania, Tuscany and Latium. And without this material buildings like the Pantheon or the octogonal dining room of the Domus Aurea would have been impossible.
The material most commonly used for aggregate in the hydraulic concrete was a soft volcanic tufa, often of a yellow-brown variety. The Augustan breakwater pier at Puteoli, the naval installations at Cumae and Misenum, and the Portus Julius at Lake Avernus, used this local material with great success. Baian pozzolana was used extensively throughout Italy until the mid-first century A.D. when fresh sources and new ingredients were discovered.
Concrete was used commonly during Vitruvius' lifetime. Poured or stamped into wooden frames or moulds, it served for conduit pipes, parts of aquaducts, harbourworks, public and private, and, most impressively, for soaring vaults, domes, arches and apses.

BIBLIOGRAPHY

Les dix livres d'architecture de Vitruve, Corrigés et traduits en 1684 par C. Perrault, Paris, 1684.
Vitruvius, De Architectura libri X, ed. F. Granger, London, 1962.
Ton Peters, Vitruvius, Handboek bouwkunde, Amsterdam, 1999.
A.Boëthius-J.B.Ward-Perkins, Etruscan and Roman Architecture, Harmondsworth, 1970
A.McKay, Vitruvius, Architect and Engineer, London, 1978




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