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In Search of... Ancient Concrete

July 1, 2013

In between the original Star Trek television series and the later upsurge in Star Trek popularity, Leonard Nimoy hosted a syndicated television series entitled, "In Search of..., from 1976-1982." The show presented information about controversial, mysterious and paranormal phenomena in both historical times and the present day.

Extraterrestrial visitors to Earth were a common topic in this series, and there were episodes about the Bermuda Triangle, the Loch Ness Monster and the Lost Colony of Roanoke. Each episode contained the subject in its title; for example, "In Search of... Ancient Astronauts." It was very entertaining, in a supermarket tabloid sort of way, and I watched nearly all of them.

One part of the series I remember is the disclaimer, which could be appended to many of today's scientific publications.

"This series presents information based in part on theory and conjecture. The producer's purpose is to suggest some possible explanations, but not necessarily the only ones, to the mysteries we will examine."

Nimoy was especially dedicated to his new television series. He even wrote an episode (Season 4, Episode 16, January 10, 1980) about the life of the artist, Vincent van Gogh. Nimoy's research uncovered van Gogh's medical records, which suggested that the artist may have suffered from epilepsy, and not insanity. I think that a severed ear counts as insanity, especially when it's your own.

Vincent van Gogh, self-portrait with pipe and bandaged ear, 1889

Vincent van Gogh (1853-1890), self-portrait with pipe and bandaged ear, 1889, oil on canvas.

(Via Wikimedia Commons.)

One possible episode could have been entitled, "In Search of Ancient Materials." As one example, our ancestor materials scientists had a good understanding of metals. After all, someone in the distant past was the first to smelt iron, which is a considerable technical feat.

Unfortunately, iron tends to rust, so modern metallurgy has produced stainless steel; and also weathering steel (trade name, CORTEN Steel), which develops a protective rust-like coating that prevents further corrosion and is a favored medium for many sculptors.

Untitled 1967 sculpture in CORTEN steel by Pablo Picasso.
The sculpture is located in Daley Plaza, Chicago.

The sculpture cost about $350,000 to make, and Picasso refused an offered $100,000 commission, instead gifting it to the people of Chicago.

(Photograph Copyright 2006 by Jeremy Atherton, published under the Creative Commons Attribution-Share Alike 2.5 Generic license via Wikimedia Commons.)

Lest we feel too smug in our ability to make non-rusting iron, there's a 6.5 ton iron stele in Delhi, India, known as the Iron pillar of Delhi, that's stood uncorrupted for about 1600 years.[1] This huge pillar, which is about seven meters (23 feet) high and tapers from a diameter of about a meter at its base to about 0.7 meters at the top, was created by forge welding individual pieces. The key to its corrosion resistance is the iron's high phosphorous content. Phosphorous is one of the ingredients of CORTEN steel, added in a similar proportion as carbon.[2]

Another example of ancient metallurgy is Japanese swordsmithing, in which blade steel is purified, decarburized and hardened by repeated forging, folding and quenching. The process, which was presented as a lengthy segment in the fourth episode of the 1973 BBC television series, The Ascent of Man, by mathematician, Jacob Bronowski, takes many days.[3] The excellent properties of this steel derive from its microstructure in which a blade is fashioned from tens of thousands of layers.

If you look around our modern world, most of what you see isn't metal, it's concrete. As I mentioned in another article (People Who Live in Concrete Houses..., June 30, 2011), members of the Minerals, Metals & Materials Society, mostly known as The Materials Society (TMS), declared that concrete was the sixth most important material in history.[4] John Smeaton is credited with inventing modern concrete in 1775, but the ancients were using concrete mixtures long before that. Some of this ancient concrete was superior to modern concrete in durability, surviving 2,000 years of seawater attack and wave action, and it's manufacture was environmentally friendly.

A huge international team of scientists has just published a study of two-thousand-year-old Roman maritime concrete from the Pozzuoli Bay region of Italy, near Naples.[5-9] The research team was led by Paulo Monteiro of Lawrence Berkeley National Laboratory, who is also a professor of civil and environmental engineering at the University of California, Berkeley.[7] Other institutions contributing to this study are the State University of New York (Stony Brook), CTG Italcementi S.p.A. (Bergamo, Italy), the King Abdullah University of Science and Technology (Saudi Arabia), the Middle East Technical University (Ankara, Turkey), the Helmholtz-Zentrum für Materialen und Energie GmbH (Berlin, Germany), and the Université Pierre et Marie Curie and the French National Centre for Scientific Research (CNRS), Paris, France.[5]

Study co-author, Marie Jackson, holding a 2,000-year-old sample of maritime concrete from the Santa Liberata harbor site in Tuscany.

(University of California, Berkeley, photograph by Sarah Yang.)

One problem with modern concrete is that it's so useful a material that 19 billion tons of it are produced annually. "The problem," explains Monteiro, "is that manufacturing Portland cement accounts for seven percent of the carbon dioxide that industry puts into the air."[7] Improving concrete manufacture would cut greenhouse gas emissions significantly. Also, more durable concrete structures would last longer, extending the beneficial environmental impact.[7]

The large carbon dioxide footprint of concrete comes from the essential chemical reaction needed to create Portland cement, the stone-like "glue" that holds concrete together. A mixture of limestone and clay is heated to 1,450 °C (2,642 °F), which releases CO₂ from the limestone, which is calcium carbonate (CaCO₃).

The research team found that the calcium carbonate ("lime") used for Roman concrete was roasted at a considerably lower temperature, 900 °C (1,652 °F), and 10% less of it was used for their concrete mixture, the balance of which was volcanic ash.[7-8] This recipe was was disclosed by Vitruvius, who wrote the c. 15 B.C. treatise, De architectura; and also by Pliny the Elder, who had firsthand experience with volcanic ash, having died in the 79 A.D. eruption of Mount Vesuvius. The best ash was noted to be found at Pozzuoli, and ash with similar mineral characteristics is called pozzolan.[7]

The Roman maritime concrete was cast in place by packing the mortar mixture and loose rock into wooden molds. When immersed into the seawater, the exothermic hydration reaction formed the concrete piece.[7-8] The key to the material robustness is the resultant molecular structure in which aluminum from the volcanic ash combines with the lime and seawater to form tobermorite, a highly stable mineral.

Analytical tools, including the Advanced Light Source at Lawrence Berkeley National Laboratory, revealed the binding agent to be the stable hydrosilicate, calcium-aluminum-silicate-hydrate (C-A-S-H).[7] C-A-S-H is an exceptionally stable binder. Portland cement does not contain the aluminum, so it's just C-S-H.[7] As a consequence, modern concrete does not contain tobermorite.

Yellowish inclusions in this Roman concrete core sample are pumice, the dark stony fragments are lava, the gray areas are volcanic crystalline materials, and the white spots are lime. The inset is a scanning electron micrograph of the aluminum-tobermorite crystals.

(Lawrence Berkeley National Laboratory image.)

Roman concrete was essentially a lost art until this study.[7,9] The only problem with the Roman mixture is its longer setting time, which is incompatible with most modern construction practices.[8] Still, volcanic ash might be a substitute for fly ash, the remains of coal combustion commonly used to produce environmentally-friendly concrete.[8] Says Monteiro,

"There is not enough fly ash in this world to replace half of the Portland cement being used... Many countries don't have fly ash, so the idea is to find alternative, local materials that will work, including the kind of volcanic ash that Romans used. Using these alternatives could replace 40 percent of the world's demand for Portland cement."[8]

One interesting item about this research is that it started with initial funding from King Abdullah University of Science and Technology in Saudi Arabia, which started a research partnership with Berkeley in 2008. Saudi Arabia has "mountains of volcanic ash" that could potentially be used in concrete.[8]

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