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Home , Appian, Cement, Fly ash, Joseph Aspdin, Lime mortar, Portland cement

THE SECRETS OF ROMAN IMAGINE BUILDING STRUCTURES THAT LAST 2,000 YEARS. HOW DID THEY DO IT?

Photo by Lakisha Campbell BC Nightly News, August 7, 2002, Matt Lauer anchoring: It was one of ROMAN CONTRACTORS & CONTRACTS The , or Flavian Amphitheater, sits Nthose catchy, uplifting, end-of-the “Aside from the employment of soldiers near the southeast end of the , between broadcast stories. It seems a man has been from the Legion, and government slaves, the Palatine and Esquiline hills of . stealing coins for 30 years out of a public which were common in the ancient states, Begun by the Emperor Vespasian in circa 75 . Not just any fountain, mind you, but the main construction force behind the A.D., and completed by his son Titus in 80 the Trevi fountain, in Rome—an icon of building of large projects, excluding the A.D., it is the most imposing of Roman antiq- romanticism immortalized in the Fellini film many military roads, and fortifica- uities. The vast, four-storied oval is 617 feet “La Dolce Vita”and the American classic, tions, were contractors….in fact they pos- by 512 feet, much of which is still standing. “Roman Holiday,” with Audrey Hepbu r n . sessed the same basic function of our Lost to the ages are tier on tier of marble seats Lovers and tourists are seen frolicking about modern contractors,” writes David Moore. that originally accommodated some 45,000 an old-world fountain complex of spectacular They even had the same gripes. He spectators, but were looted by succeeding beauty, the looking as clean and pure quotes the Roman engineer , as generations. The Colosseum encloses an and effervescent as if poured from a million follows: “things of this sort should be arena measuring 250 feet by 151 feet, the bottles of Perrier. known to , so that, before they site of gladiatorial combats until 404 A.D. It is said, the reporter intones, that if you begin upon buildings, they may be careful The structure has been damaged several turn your back to the fountain, make a wish not to leave disputed points for the house- times by earthquakes and fire, but those por- and flip a coin over your shoulder into the holders to settle after the works are fin- tions built with endure. water, your wish will come true—and indeed ished, and so that in drawing up contracts — Stephani Miller the video captures people doing so. The the interests of both employer and con- money, the reporter continues, is supposed to tractor may be wisely safe-guarded.” morning some 32 years prior, on which I first go to a Catholic charity, but now this man— As to construction contracts, says encountered Roman construction. It was in the video shows a suitably crazed-looking Moore, the Romans employed highly Mrs. Olaette Cerny’s I class, and the Roman first taunting police, then being carted sophisticated oral and written contracts subject was Via Appia—the Way— away—has been arrested for stealing it! that “were explicit in assigning detailed that most famous and important of Roman It is never said how he got away with it for responsibilities” for all parts of the job, roads, portions of which are still in use today. 30 years. But no matter: n ow comes the including labor and materials—and there Begun in 312 B.C. by the Roman censor denouement, the silver lining:“He can take were even arbitration clauses. Appius Claudius Caecus, it was the main away my money,” a pretty young woman says route from Rome to Greece, stretching some to the television camera, “but he can never to the Aqueducts of . “Just like 350 miles. Roughly 20 feet wide, it was large take away my wish.” they conquered other people, they would con- enough to permit two chariots, one per lane, quer nature with their . In the end, to travel simultaneously. It even had “rest THE REALLY ROMANTIC STORY for this city of a million people, they had 11 areas” every 10 miles or so—horse changing Hmmm. Not bad—unless you know the aqueducts, 11 channels of over 300 miles, stations with taverns and, of course, latrinae. really romantic story NBC missed. From delivering perhaps 150 to 200 gallons per But back to Roman Bath: “This car- whence, might you suppose, does the water person per day, an amazing amount for the ried two aqueducts,” the narrator continues, for the Trevi fountain come? The municipal ancient world.” “the Aqua Claudia on the bottom and the water supply? Nope. It comes directly from The most stunning footage of all wa s mostly missing channel of the Anio Novis the Salone springs, some 11 miles outside of devoted to the Romans’ Aqua Claudia aque- on the top.” My head spun. An Rome, and it is delivered there by the Aqua duct. Prized for its sweet-tasting mountain underground water main, 40 miles long? An Virgo, a Roman concrete aqueduct built in the spring water, it stretches 50 miles beyond above-ground, 60-foot high, double-decker year 19 B.C. during the reign of Rome, reaching into the foothills of the aqueduct? Equally impressive: the aqueducts . Put another way, Jesus Christ was Apennines. The water travels its first 40 miles ran solely on —so the entire 50-mile not yet born when this aqueduct was built— u n d e rground. “But eve n t u a l l y, mountains length of the Aqua Claudia was built on a and it is still delivering water to the city. come to an end,” said the Roman Bath narra- progressively downward slope. How was this I knew this because I’d seen the NOVA doc- tor. “That’s when aqueducts emerge, in a possible, given the limitations of ancient umentary on public television, Roman Bath, spectacular display of Roman engineering. tools and ? which devoted considerable attention and Graceful arcades of arches, 60 feet high, car- The engineering and construction wa s video footage to the aqueduct—that graceful rying water in channels along the top.” impressive, no question. But like a lightbulb and beguiling monument to Roman ingenu- Spectacular indeed. Watching the show, I going off in my brain, I recalled at that very ity. “The Romans would not take ‘no’ for an became engulfed in a wave of splendid nos- instant precisely what it was that had so cap- answer,” says Peter Aicher, author of Guide talgia, recalling a certain sun-splashed fall tivated me as a schoolboy so many years (continued)

CONSTRUCTOR/September 2002 13 S E C R E T S S E C R E T S S E C R E T S unearth one shiny nugget, how eve r : a n ROMAN LABORERS & GUILDPERSONS intriguing website, w w w. r o m a n c o n c r e t e . c o m, ROMAN CONCRETE PLACEMENT: The Roman construction labor force which in turn touted a book, The Roman Pan - A CLASSICAL CONFRONTATION! consisted of slaves, freedmen, poor citi- theon—The Triumph of Concret e , written by Romans used the same essential con- zens, soldiers from the Legions, and Da vid Moore, P.E. ingredients we use today, but they skilled labor—guild persons—Moore used them in a vastly different manner. writes. “It was the guilds that provided the THE DEFINITIVE STUDY “First a semi-fluid mixture of , poz- skilled labor needed to fasten timber Soon I was on the horn talking with Moore, zolan, and small stones or brickbats was pieces into the scaffolding trusswork that a most courtly and agreeable gentleman, who poured in....” writes J.H. Middelton in spanned large openings in the construc- volunteered to send a copy. When it arrived, I The Remains of Ancient Rome, “Then a tion of arches and . They also pro- found to my great satisfaction that the title layer of larger stones, from 3 to 6 inches vided the metal work and other was misleading. Although it begins with an across, was laid by hand. Then a second refinements of the structures.” exploration of the Pantheon in voluptuous layer of fluid was poured in, and The guilds were not collective bargai n - detail, the overwhelming bulk of this 239- so on.” Moore agrees, with one modifica- ing devices but almost akin to distinct page masterpiece, richly detailed and exquis- tion: he believes that “the -lime social classes much like the caste system itely footnoted, comprises the defi n i t ive was compacted around the pieces of . Once born into a guild, you study of Roman concrete—who, where, of by tamping, which is the p i c ked up the trade and practiced it when, what, why, and how. Moore draws only method of removing the voids and throughout your lifetime. Guilds had their heavily on ancient Roman sources, quoting closing the molecular structure of the own meeting halls and even their own god- extensively the five authors whose writings mortar to make lasting concrete.” There dess, Minerva—the deity of handiwor k . on concrete remain—Cato the Censor, Mar- is a “confrontation” among archeologists Numa, the early second Roman king, orga- cus Vitruvius Pollio, , concerning the Roman placement of nized the following guilds: flute-players, the Poet, and the Emperor . mortar, he explains. “Some say it was goldsmiths, dryers, cobblers, tanners, He also presents a rigorous boil-down of poured. Some say it was tamped. I side wor k ers, potters, and carpenters. Other known contemporary scientific and historical inves- with the latter school which has a scien- guilds included metal wor k ers, for both tigation, quoting such well-known sources as tific basis to obtain lasting concrete. The bronze and ; and cement masons; National Geographic and classical scholars most acceptable method is to use as little timber wor k ers; wagoners; and wrecker s . from Yale University and Oxford () water as possible to get a workable mix- University, as well as such obscure but vital ture and to compact the mortar solidly before: concrete. How in the heck did the documents as The Water Cisterns of Ore into the spaces between the aggregate.” Romans make it to last 2,000 years? What Wa s h e rs in Laurion and Their Special Moore also has Vitruvius on his side, was different about their methods—and what Hydraulic Mortar. who wrote that cistern walls were com- can we learn from them? Long ago, I real- Moore covers every conceivable base, from pacted during construction as a means of ized, I had tied a string around my finger. It Roman construction machinery, tools, train- obtaining sufficient strength to withstand was still there. ing, and construction practices to an essential hydraulic pressures. Speaking of cis- review of Roman society and contracting, to terns, the Romans had 1,352 of them USED BY PATTON’S ARMIES a scientific and historical on strategically located throughout the city, The aqueducts, I knew, were just one exa m - Roman lime and , products and as recorded in the 4th century, A.D. They ple of Roman concrete. In World War II, U.S. mortar, pozzolan-lime behavior—and much even used a special hydraulic cement, Army Gen. George S. Patton, a celebrated more. It was all here. This, indeed, was the known as signinum, to line the inte- mystic who believed himself to be a reincar- animal I had sought, and, further, it was ren- rior surfaces. The exact composition of nated ancient war r i o r , took great satisfaction in dered in clear, lucid prose and a surprisingly this product is not known, but it surely directing the Seventh and later the Third army jaunty style. I knew I was in trouble when I contained pozzolan and possibly cr u s h e d over bridges used by , , found myself reading it on a Saturday night. brick, marble, or charcoal as well. Po m p e y, and other Roman commanders. From the Colosseum, to the Pantheon, to CONCRETE: A BRIEF PRIMER lime in water, and you will observe a bub- the Arch of Constantine, to numerous sites in So—what are the secrets of Roman con- bling, heat-producing , Rome, to the ruins of and Roman crete? One cannot condense a fat book with which will yield a , colloidal paste estates, throughout much of the Mediter- innumerable scientific details into a three- called hydrated lime or slaked lime—which ranean basin, northward to Britain and page article, but there are some general prin- the Romans stored in large clay jars known as throughout much of Europe, there are liter- ciples that can be shared. Let us begin with a amphorae until it was needed. Mix that paste ally thousands of Roman concrete works still brief primer on concrete. Concrete is a com- with clean river and presto: you have a with us today. Many of them are crumbling, bination of aggregates, typically sand and construction mortar that can be used to bind but quite a few, like the Pons Fabricius bridge (although the Romans, notably, used or rocks together or to the sur- in Rome, connecting the left bank of the l a rger stones—see sidebar above, right) face of a wall. Tiber river to Tiber Island, are structurally mixed within a cementitious paste that hard- It’s all quite elementary. , the sound and still in use. ens to create a single mass that can resist British stone mason credited with the inven- Ne wly inspired, I hopped on my computer, great compressive forces. Basic lime-based tion of in 1824, literally logged onto Amazon.com, and typed the mortar, such as that originally used by the whipped up the first batch in his kitchen. But words “Roman Concrete” into the search Romans, is made possible by the unique Aspdin took this simple process one step fur- . Somebody, surely, the scientists— chemical properties of , ther. On the stove he heated finely ground th e y must have figured it all out long ago. But which is found in abundance throughout the and clay. The resulting substance, nothing came up. Next I logged onto world in the form of limestone which conta i n s known as clinker, was cooled and ground into Yahoo.com, typed the same words into the the elements calcium, , and oxygen. a fine powder. The beauty of Aspdin's cement br ow s e r , and bingo: 88,000 references. Most To make a simple , get your and its modern descendants is that it can be of what I found, howe ver , was either sket c h y, hands on some limestone and heat it in a . stored dry in a bag, yet activated merely by boilerplate, repetitive, or anecdotal. Certainly The limestone will undergo a chemical reac- the of water on the jobsite—a luxury there were some tantalizing snippets, univer - tion in which the carbon and some of the oxy- the Romans did not enjoy. And there were sity postings in particular, but nothing com- gen will be driven off as , other advantages. When concrete made with p r e h e n s ive, not one discrete publication leaving a highly reactive product known as a simple lime mortar dries, carbon dioxide wholly devoted to Roman concrete. I did quicklime, or . Place the quick- from the air recombines with the calcium to (continued on page 16) 14 CONSTRUCTOR/September 2002 S E C R E T S S E C R E T S S E C R E T S create again, a solid mate- and engineering. He devotes an says Moore. There were three more critical rial—in essence, an . The cal- entire chapter in his second book to pozzolan, elements, as follows: cium in the lime, how eve r, does not stating that “there is also a kind of powder ■ Rigid quality control, chemically interact with the either the aggre- which from natural causes produces astonish- ■ L ow water to cementitious materials gate or the sand it is mixed with, but merely ing results. It is found in the neighborhood of ratio, and holds them in suspension. and in the country belonging to the ■ Expert placement and compaction. In Portland cement, the silica in the clay towns round about . This Superior concrete starts with superior lime, bonds with the calcium in the lime through substance, when mixed with lime and rubble, the whiter the better, as impurities will appear the application of heat, which creates a far not only lends strength to buildings of other as dark spots or mottling. While the Romans more durable concrete than that which can be kinds, but even when piers of it are con- had no knowledge of present-day chemistry, made from a simple lime mortar, and one that structed in the sea, they set hard under water.” they nonetheless knew how to distinguish a is hydraulic—meaning that it will set and Scientists today know exactly what Vitru- good quality lime and other concrete ingredi- harden underwater. Although the Romans vius’s “powder” was: —and the ents through empirical observation. As Vitru- never stumbled onto this scientific break- Romans had it in prodigious abundance. Both vius wrote, “We must be careful that it [lime] through, they nonetheless created a durable, Rome and were surrounded by volca- be burned from stone which, whether soft or high-strength concrete with the same proper- noes, including the most famous of all, hard, is in any case white, and lime made of ties, thanks to the help of...Mother Nature. Mount Vesuvius, which destroyed the resort close-grained stone of the harder sort will be city of Pompeii, on the Bay of Naples, in 79 good in structural parts; lime of porous stone, THE SECRET ROMAN RECIPE A.D. Further, they were connected by the Via in .” The Romans also selected the Lime-coated mud walls were constructed in Appia, facilitating ready transport of building other ingredients with care, and were rigidly central India as early as 2,500 B.C., and materials. precise in using the same volume measure- many early civilizations, including that of the What is the secret of the special ingredient? ments for each batch, which they mixed in Romans, used it as a sort of stucco covering Let’s begin by looking at the modern techni- small batches with a hoe and a trough. for mud walls and other crude structures. cal definition of pozzolan, which is as fol- Low water to cementitious materials ratio and When it comes to actual concrete, the Greeks l ows: A siliceous or aluminous material c o m p a c t i o n . Through trial and error the used a highly durable mix as early 1,700 w h i ch in itself possesses no cementitious Romans also came to understand what scien- B.C., as revealed by Italian archeological value, but will, in a finely divided form, and tists like Dolen know as gospel today:a low digs. “We removed this very hard concrete, a in the presence of moisture, chemically react water to cementitious materials ratio, exact- process which caused the breaking of hun- with at ordinary tempera - ing placement, and compaction are also criti- dreds of our picks,” notes author D. Livi in tures to form compounds possessing cementi - cal to attaining maximum concrete strength. The Italian Excavations in Crete and the Ear - tious pro p e r t i e s . Translated: By using Roman mortar, says Moore, was comparable liest European Civilization. volcanic ash in the place of river sand in their to a modern-day zero-slump concrete like It is not known exactly when the Romans concrete, the Romans were able to mimic the RCC: so stiff and firm that it would not flow first began mixing lime with other substances process by which Portland cement chemi- into the spaces between the rocks in the to form concrete, but “archeological studies cally bonds lime to clay through the applica- aggregate. The Romans even used a special ha ve noted that a wall of rubble in Pompeii tion of heat. But finely divided pozzolan must tool called a beetle to tamp it and pound it was held together with a firm po z z o l a n be amorphous (glassy) to chemically react. into place. The Romans also used wooden and lime mortar dating to the late third century How was this possible? Because the volcano forms, much like those of today, the before Christ,” notes Moore, citing archeolo- had already heated the pozzolan for them! In tell-tale impressions of which can still be gist M.E. Blake. It is also known from ancient the words of Tim Dolen, a pozzolan expert seen on Roman buildings. writings that by 199 B.C. the Romans were and research at the U.S. Bureau already using hyd r a u l i c concrete to line the of Reclamation, “the pozzolan was calcined A PLUNGE INTO DARKNESS harbor works at Puteoli, which indicates a by the volcano,” enabling it to chemically After the emperor passed away in striking degree of sophistication. react with calcium hydroxide in slaked lime, 138 A.D., the Romans ceased building new Use of Roman concrete reached its zenith no heating required. towns, much less cities. Further, says Moore, during the reigns of the Emperors and Dolen and other scientists are working with the Romans neglected to maintain their infra- Hadrian, Moore says, covering the period of a r t i ficial , such as —a structure, a costly mistake that holds lessons roughly 98 to 138 A.D. By that time, he byproduct of -fired electrical plants—to for the modern age. Nature also wreaked writes, “the craftsmen were well trained with reap dramatic improvements in modern-day havoc. “Floods of the Tiber, fires, and earth- many tools and they were sufficiently edu- concrete. In 1987 the Bureau of Reclamation quakes injured the aqueducts, buildings, and cated to attain teamwork.” A striking exam- built the Upper Stillwater in the Uinta roads. Broken aqueducts prevented the deliv- ple of concrete construction from this period Mountains of north-central Utah with roller- ery of vital , and without funds is Trajan’s Forum, the forerunner of today’s compacted concrete (RCC), a stiff, zero- for repairs, the system gradually fell into dis- shopping mall, which was a large complex of slump concrete. The cementitious use,” he writes. 150 stores in the middle of old Rome. The consisted of 70 percent fly ash and 30 percent The final blow came in 410 A.D. when ruins of this landmark can still be observed Portland cement. When used in such high Alaric the Goth sacked Rome. The world today, including its centerpiece, the Great concentrations, says Dolen, pozzolans can would soon enter a Dark Age, and the mira- Hall, whose vaulted roof is still intact. decrease concrete , create greater cle of concrete would be lost until 1824, The Romans had two distinct types of con- long-term strength, and help to reduce the when Joseph Aspdin concocted his fi r s t crete mortar. One was made with simple lime deleterious effects of alkalai aggregate reac- stove-top brew. and river sand, mixed at a ratio of three parts tion and attack. So—have we discovered all the secrets of sand to one part lime. The other type used Roman concrete? Perhaps—but we’ll have to pozzolan instead of river sand and was mixed MAKING THE REALLY GOOD STUFF wait 2,000 years to know for sure! at a ratio of two parts pozzolan to one part Not all Roman concrete was good stuff— —By Benjamin Herring, editor-in-chief. Stephani Miller, lime. There was no doubt as to which was there are notable failures referenced in ancient CO N S T R U C T O R ’ s former editorial assistant, contributed s u p e r i o r : the pozzolanic mortar. Pozzolan writings. But the Romans learned from their copy pertaining to roller compacted concrete and to the sec- (pozzuolania in Latin) took its name from the mi s t a k es, and it’s useful to note that by the tion “MAKING THE REALLY GOOD STUFF.” Pozzouli region by the Bay of Naples, where year 1 A.D., they had been working with their it was found, and it was a truly magical sub- concrete far longer than modern man has been Get more information at stance. Vitruvius, an engineer and working with Portland cement! Pozzolan was WWW.ROMANCONCRETE.COM for the Emperor Augustus, wrote 10 books on only one of the secrets of Roman concrete,

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