I have been reading about Roman concrete (300BC-300AD) and how it has greater strength than current concrete mixtures. So far, my research has shown that they did not use re-bar in their structures. But did the Romans use anything external (like fiber, wood, etc) to improve their concrete's tensile strength?
For reference this was the source I was reading:
The Mechanics of Imperial Roman Concrete and the Structural Design of Vaulted Monuments
Drilling Into The Secrets Of Roman ConcreteThe ruins of the Roman Forum. Credit: THINK Global School/flickr/CC BY-NC-ND 2.0
Over two thousand years ago, the ancient Romans built piers, breakwaters, and other structures out of concrete—and some of those structures still stand today. Now, researchers are trying to understand the chemical and geological processes that work together to give that ancient concrete such durability. Using microscopy, x-ray diffraction, and spectroscopic techniques, they’ve developed a map of the crystalline microstructures within the concrete. According to their research, a slow infusion of seawater into concrete made with a type of volcanic ash found near Rome gradually creates crystals of a material called aluminous tobermorite, which actually strengthens the concrete as it ages.
Marie Jackson, a geology and geophysics research professor and one of the authors of a report on the work , says that understanding Roman concrete could give modern materials scientists ideas for how to strengthen modern structures, and could even lead to new materials, such as concretes that soak up and trap nuclear waste.
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Jackson has searched ancient Roman records for the formula to this concrete with no success. The exact formula remains unknown. However, Jackson&rsquos team is experimenting with different combinations of seawater and volcanic ash to make a modern-day concrete with these unique properties. It is possible, too, that fly ash&mdasha problematic byproduct of coal-burning&mdashcould be a worthy substitute for the volcanic ash component, which would be an immense environmental benefit.
A modern equivalent of Roman concrete would be ideal for seawall structures and other marine applications, as well as for encasing high-level wastes in cement-like barriers that protect the surrounding environment. Widespread use of this concrete would also reduce the construction industry&rsquos dependence on Portland cement, the manufacture of which requires high-temperature kilns that emit significant amounts of carbon dioxide.
However, added Jackson, before Roman concrete recipes can be widely accepted by industry, test structures must be built and evaluated long-term to see how they perform compared to similar structures built from steel-reinforced Portland cement.
&ldquoI think people don&rsquot really know how to think about a material that doesn&rsquot have steel reinforcement,&rdquo Jackson said. Mark Crawford is an independent writer.
To improve today’s concrete, do as the Romans did
In a quest to make concrete more durable and sustainable, an international team of geologists and engineers has found inspiration in the ancient Romans, whose massive concrete structures have withstood the elements for more than 2,000 years.
Sample of ancient Roman maritime concrete from Pozzuoli Bay near Naples, Italy. Its diameter is 9 centimeters, and it is composed of mortar formulated from lime, volcanic ash and chunks of volcanic tuff. (Carol Hagen photo)
Using the Advanced Light Source at Lawrence Berkeley National Laboratory (Berkeley Lab), a research team from the University of California, Berkeley, examined the fine-scale structure of Roman concrete. It described for the first time how the extraordinarily stable compound – calcium-aluminum-silicate-hydrate (C-A-S-H) – binds the material used to build some of the most enduring structures in Western civilization.
The discovery could help improve the durability of modern concrete, which within 50 years often shows signs of degradation, particularly in ocean environments.
The manufacturing of Roman concrete also leaves a smaller carbon footprint than does its modern counterpart. The process for creating Portland cement, a key ingredient in modern concrete, requires fossil fuels to burn calcium carbonate (limestone) and clays at about 1,450 degrees Celsius (2,642 degrees Fahrenheit). Seven percent of global carbon dioxide emissions every year comes from this activity. The production of lime for Roman concrete, however, is much cleaner, requiring temperatures that are two-thirds of that required for making Portland cement.
The researchers’ findings are described in two papers, one that was posted online May 28 in the Journal of the American Ceramic Society, and the other scheduled to appear in the October issue of the journal American Mineralogist.
“Roman concrete has remained coherent and well-consolidated for 2,000 years in aggressive maritime environments,” said Marie Jackson, lead author of both papers. “It is one of the most durable construction materials on the planet, and that was no accident. Shipping was the lifeline of political, economic and military stability for the Roman Empire, so constructing harbors that would last was critical.”
Marie Jackson holds a 2,000-year-old sample of maritime concrete from the first century B.C. Santa Liberata harbor site in Tuscany. (Sarah Yang photo)
The research team was led by Paulo Monteiro, a UC Berkeley professor of civil and environmental engineering and a faculty scientist at Berkeley Lab, and Jackson, a UC Berkeley research engineer in civil and environmental engineering. They characterized samples of Roman concrete taken from a breakwater in Pozzuoli Bay, near Naples, Italy.
Building the Empire
Concrete was the Roman Empire’s construction material of choice. It was used in monuments such as the Pantheon in Rome as well as in wharves, breakwaters and other harbor structures. Of particular interest to the research team was how Roman’s underwater concrete endured the unforgiving saltwater environment.
The recipe for Roman concrete was described around 30 B.C. by Marcus Vitruvius Pollio, an engineer for Octavian, who became Emperor Augustus. The not-so-secret ingredient is volcanic ash, which Romans combined with lime to form mortar. They packed this mortar and rock chunks into wooden molds immersed in seawater. Rather than battle the marine elements, Romans harnessed saltwater and made it an integral part of the concrete.
The researchers also described a very rare hydrothermal mineral called aluminum tobermorite (Al-tobermorite) that formed in the concrete. “Our study provided the first experimental determination of the mechanical properties of the mineral,” said Jackson.
This scanning electron microscope image shows crystals of a rare mineral, Al-tobermorite, magnified about 25,000 times. UC Berkeley researchers characterized Al-tobermorite in samples of Roman concrete. (Image courtesy of UC Berkeley)
So why did the use of Roman concrete decrease? “As the Roman Empire declined, and shipping declined, the need for the seawater concrete declined,” said Jackson. “You could also argue that the original structures were built so well that, once they were in place, they didn’t need to be replaced.”
An earth-friendly alternative
While Roman concrete is durable, Monteiro said it is unlikely to replace modern concrete because it is not ideal for construction where faster hardening is needed.
But the researchers are now finding ways to apply their discoveries about Roman concrete to the development of more earth-friendly and durable modern concrete. They are investigating whether volcanic ash would be a good, large-volume substitute in countries without easy access to fly ash, an industrial waste product from the burning of coal that is commonly used to produce modern, green concrete.
“There is not enough fly ash in this world to replace half of the Portland cement being used,” said Monteiro. “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.”
The research began with initial funding from King Abdullah University of Science and Technology in Saudi Arabia (KAUST), which launched a research partnership with UC Berkeley in 2008. Monteiro noted that Saudi Arabia has “mountains of volcanic ash” that could potentially be used in concrete.
In addition to KAUST, funding from the Loeb Classical Library Foundation, Harvard University and the Department of Energy’s Office of Science helped support this research. Samples were provided by Marie Jackson and the Roman Maritime Concrete Study (ROMACONS), sponsored by CTG Italcementi, a research center based in Bergamo, Italy. The researchers also used the Berlin Electron Storage Ring Society for Synchrotron Radiation, or BESSY, for their analyses.
Scientists Have Figured Out How Ancient Rome's Concrete Has Survived 2,000 Years
S cientists have solved the mystery of the durability of Ancient Rome‘s concrete and in the process may have learned something that could influence modern day construction.
The research, published this week in the journal American Mineralogist, details how ancient Roman sea walls built roughly 2,000 years ago managed to stand up to the elements due to a rare chemical reaction that seemingly has strengthened the concrete over time.
Modern cement mixtures tend to erode, particularly in the presence of seawater, but the Roman recipe of volcanic ash, lime, seawater and a mineral called aluminium tobermorite actually reinforces the concrete and prevents cracks from expanding, researchers found.
The reaction was caused by the seawater continually ramming into the structures for hundreds of years, allowing the mineral mixture of silica oxides and lime to grow between the volcanic rock aggregate and mortar to develop resistance.
“Contrary to the principles of modern cement-based concrete, the Romans created a rock-like concrete that thrives in open chemical exchange with seawater,” lead author Marie Jackson from the University of Utah said in the journal.
“It’s a very rare occurrence in the Earth,” she added.
While the Romans benefited from more access to natural volcanic ash, the concept could one day be used as a more environmentally-friendly alternative to modern cement mixing, which emits a significant amount of carbon dioxide into the atmosphere.
&ldquoRomans were fortunate in the type of rock they had to work with,&rdquo Jackson said. &ldquoThey observed that volcanic ash grew cements to produce the [mortar]. We don&rsquot have those rocks in a lot of the world, so there would have to be substitutions made.&rdquo
Jackson is working to create a replacement recipe that she proposed using in place of steel for a planned tidal lagoon in the United Kingdom.
“I think Roman concrete or a type of it would be a very good choice [the lagoon]. That project is going to require 120 years of service life to amortize the investment,” she told the BBC earlier this year.”
Jackson warned that typical cement mixtures wouldn’t stand up the elements as well as the Roman-style concrete could.
“Those will surely corrode in at least half of that service lifetime,” she said.
So you are Rome, and want to build a Pantheon no one can copy. You mix concrete with pozzolan, aka basalt ash and pour building parts. And write THIS part down in detail.
Now. what would prevent people from copying this technique ever after? Nothing. Unless you conveniently "forgot" to mention a second part that's also needed for this recipe to work. Such as, having free army labor to chisel basalt girders that go into this basalt concrete for reinforcement. Scientist in 2000 whips out instrument, looks at the finished Pantheon wall, says "Wow, there's nothing but basalt in this, no steel at all. A monolithic pour with no reinforcement!" While in fact quite likely it's chiseled basalt girders in the wall that are doing the heavy lifting. It's just being discovered that basalt reinforcement has 2x the strength of steel at 20% of steel's weight. Obviously, the Ancient Romans didn't have 2000 degree kilns to manufacture basalt rebar as we do today to reinforce concrete. My hunch is, the Romans just took a big honking basalt boulder and had the free labor (aka Army soldiers) chisel the reinforcement girder shapes out of it. And THIS is why no one continued the recipe after the demise of the Roman Empire. Not because all the masons came down with an unexplainable case of collective amnesia how to mix Roman concrete. But because this recipe also required the free rock chiseling labor of an entire Roman Army detachment.
please look into the works of Hannibal Pianta, he attended the Milan Institute of technology in 1888 and conducted work in concrete from 1902(chicago) till his death in 1937(san antoonio). His works are still standing without much restoration work, to include Nel-stone blocks exposed to the elements.
Recently, there’s been a flurry of news surrounding a new paper which examined the mineral structure of concrete samples taken from a 2000 year-old Roman breakwater. The articles range from measuredly pointing out it’s carbon efficiency, to extolling it’s near-mystical properties. The fact that these structures are still intact after millennia, while ours often decay to the point of uselessness after less than 50 years, obviously raises some questions. Namely, was Roman concrete better than ours? Why does ours fail so quickly?
The answer lies in the different way we use concrete compared to the Romans. Concrete is strong in compression, but weak in tension and bending. This means that by itself, concrete is of limited versatility. It’s easily used in columns, arches, and other things that will only be in compression. But you run into trouble when you try to make long bridges, tall buildings, thin walls, or anything else that wants to bend in the middle. Concrete is also very brittle – when it reaches it’s breaking point, it shatters like glass. Because of this, if it fails, it fails instantly and catastrophically, without giving any warning.
In modern construction, both these problems are solved the same way: by putting steel bars or wire in the concrete at key locations. Steel, unlike concrete, is incredibly strong in tension. A concrete beam reinforced with steel in it will be about a fifth as big as an unreinforced one.
It will also be much, much safer. Unlike concrete, which is brittle, steel is ductile – when it fails, it doesn’t fracture, it stretches. This added ductility gives failed reinforced concrete the ability to absorb a great deal of additional energy before it collapses, and provides ample time for people to evacuate. Because of this, including steel in concrete isn’t just a good idea: it’s the law. Nearly every major building code requires concrete to have a minimum amount of reinforcing steel, outside of a few special cases.
But all this strength has a drawback: steel also severely reduces the durability of concrete. Because concrete is porous, over time chloride ions and other corroding elements work their way into the concrete and begin to corrode the steel inside. The amount of time this takes varies depending on how deeply buried the steel is, but it inevitably happens. This corrosion both weakens the steel and causes it to enlarge, ultimately bursting the concrete from the inside out. Steel corrosion is the primary mechanism behind concrete decay, and one of the major limitations on modern concrete’s lifespan. Because Roman concrete had no reinforcing, it has none of these problems.
Another major difference between Roman concrete and ours is the cure time. Modern concrete hardens and reaches its maximum strength very, very quickly. The “standard” time for concrete to fully cure and reach it’s capacity is 28 days, but it’s not uncommon for it to reach usable strength in just a few hours. This rapid cure time, while helpful for speedy construction schedules, introduces thermal stresses as the reaction heats up. These stresses cause cracking, and ultimately reduced durability. To make matters worse, additional steel must be included to address these thermal stresses, exacerbating the problem of corrosion-induced failure.
Roman concrete, on the other hand, cured astonishingly slowly. If I’m reading the paper right, the breakwater the concrete was sampled from took two years to cool down completely. This extremely slow cure time means lower thermal stresses, and a corresponding higher durability.
Of course, all this is academic if we couldn’t produce similarly durable concrete today. And it turns out, when the situation calls for it, we’re capable of putting together an extremely durable concrete mix. Modern concrete structures have been built that are designed to have 1000-year lifespans. In fact, the exact mineral that supposedly makes the Roman concrete so durable, aluminum-substituted tobermorite, was patented 30 years ago, for the exact use suggested in the recent paper. Ultra durable concrete is within our reach. But the requirements for making it – no steel, extremely slow cure time, high pozzolans in the mix – are very limiting, and very, very expensive. The trick to making concrete that can last the ages isn’t some lost recipe, but boring old economics.
Corrosive seawater encourages growth of rare minerals
Around A.D. 79, Roman author Pliny the Elder wrote in his Naturalis Historia that concrete structures in harbors, exposed to the constant assault of the saltwater waves, become “a single stone mass, impregnable to the waves and every day stronger.”
He wasn’t exaggerating. While modern marine concrete structures crumble within decades, 2,000-year-old Roman piers and breakwaters endure to this day and are stronger now than when they were first constructed. University of Utah geologist Marie Jackson studies the minerals and microscale structures of Roman concrete as she would a volcanic rock. She and her colleagues have found that seawater filtering through the concrete leads to the growth of interlocking minerals that lend the concrete added cohesion. The results are published today in American Mineralogist.
ROMACONS drilling at a marine structure in Portus Cosanus, Tuscany, 2003. Drilling is by permission of the Soprintendenza Archeologia per la Toscana.
Roman concrete vs. Portland cement
Romans made concrete by mixing volcanic ash with lime and seawater to make a mortar, and then incorporating into that mortar chunks of volcanic rock, the “aggregate” in the concrete. The combination of ash, water, and quicklime produces what is called a pozzolanic reaction, named after the city of Pozzuoli in the Bay of Naples. The Romans may have gotten the idea for this mixture from naturally cemented volcanic ash deposits called tuff that are common in the area, as Pliny described.
The conglomerate-like concrete was used in many architectural structures, including the Pantheon and Trajan’s Markets in Rome. Massive marine structures protected harbors from the open sea and served as extensive anchorages for ships and warehouses.
Modern Portland cement concrete also uses rock aggregate, but with an important difference: the sand and gravel particles are intended to be inert. Any reaction with the cement paste could form gels that expand and crack the concrete.
“This alkali-silica reaction occurs throughout the world and it’s one of the main causes of destruction of Portland cement concrete structures,” Jackson says.
Rediscovering Roman concrete
PHOTO CREDIT: Marie Jackson
Left to right: Nobumichi Tamura, Marie Jackson and Camelia Stan at beamline 12.3.2 at the Advanced Light Source, Lawrence Berkeley National Laboratories. January 2017. Tamura and Stan are scientists at the Advanced Light Souce.
Jackson’s interest in Roman concrete began with a sabbatical year in Rome. She first studied tuffs and then investigated volcanic ash deposits, soon becoming fascinated with their roles in producing the remarkable durability of Roman concrete.
Along with colleagues, Jackson began studying the factors that made architectural concrete in Rome so resilient. One factor, she says, is that the mineral intergrowths between the aggregate and the mortar prevent cracks from lengthening, while the surfaces of nonreactive aggregates in Portland cement only help cracks propagate farther.
In another study of drill cores of Roman harbor concrete collected by the ROMACONS project in 2002-2009, Jackson and colleagues found an exceptionally rare mineral, aluminous tobermorite (Al-tobermorite) in the marine mortar. The mineral crystals formed in lime particles through pozzolanic reaction at somewhat elevated temperatures. The presence of Al-tobermorite surprised Jackson. “It’s very difficult to make,” she says of the mineral. Synthesizing it in the laboratory requires high temperatures and results in only small quantities.
For the new study, Jackson and other researchers returned to the ROMACONS drill cores, examining them with a variety of methods, including microdiffraction and microfluorescence analyses at the Advanced Light Source beamline 12.3.2 at Lawrence Berkeley National Laboratory. They found that Al-tobermorite and a related zeolite mineral, phillipsite, formed in pumice particles and pores in the cementing matrix. From previous work, the team knew that the pozzolanic curing process of Roman concrete was short-lived. Something else must have caused the minerals to grow at low temperature long after the concrete had hardened. “No one has produced tobermorite at 20 degrees Celsius,” she says. “Oh — except the Romans!”
“As geologists, we know that rocks change,” Jackson says. “Change is a constant for earth materials. So how does change influence the durability of Roman structures?”
PHOTO CREDIT: Courtesy of Marie Jackson
This microscopic image shows the lumpy calcium-aluminum-silicate-hydrate (C-A-S-H) binder material that forms when volcanic ash, lime and seawater mix. Platy crystals of Al-tobermorite have grown amongst the C-A-S-H in the cementing matrix.
The team concluded that when seawater percolated through the concrete in breakwaters and in piers, it dissolved components of the volcanic ash and allowed new minerals to grow from the highly alkaline leached fluids, particularly Al-tobermorite and phillipsite. This Al-tobermorite has silica-rich compositions, similar to crystals that form in volcanic rocks. The crystals have platy shapes that reinforce the cementing matrix. The interlocking plates increase the concrete’s resistance to brittle fracture.
Jackson says that this corrosion-like process would normally be a bad thing for modern materials. “We’re looking at a system that’s contrary to everything one would not want in cement-based concrete,” she says. “We’re looking at a system that thrives in open chemical exchange with seawater.”
Modern Roman concrete
Given the durability advantages of Roman concrete, why isn’t it used more often, particularly since manufacturing of Portland cement produces substantial carbon dioxide emissions?
“The recipe was completely lost,” Jackson says. She has extensively studied ancient Roman texts, but hasn’t yet uncovered the precise methods for mixing the marine mortar, to fully recreate the concrete.
“Romans were fortunate in the type of rock they had to work with,” she says. “They observed that volcanic ash grew cements to produce the tuff. We don’t have those rocks in a lot of the world, so there would have to be substitutions made.”
She is now working with geological engineer Tom Adams to develop a replacement recipe, however, using materials from the western U.S. The seawater in her experiments comes from the Berkeley, California, marina, collected by Jackson herself.
Roman concrete takes time to develop strength from seawater, and features less compressive strength than typical Portland cement. For those reasons, it’s unlikely that Roman concrete could become widespread, but could be useful in particular contexts.
Jackson recently weighed in on a proposed tidal lagoon to be built in Swansea, United Kingdom, to harness tidal power. The lagoon, she says, would need to operate for 120 years to recoup the costs incurred to build it. “You can imagine that, with the way we build now, it would be a mass of corroding steel by that time.” A Roman concrete prototype, on the other hand, could remain intact for centuries.
Jackson says that while researchers have answered many questions about the mortar of the concrete, the long-term chemical reactions in the aggregate materials remain unexplored. She intends to continue the work of Pliny and other Roman scholars who worked assiduously to discover the secrets of their concrete. “The Romans were concerned with this,” Jackson says. “If we’re going to build in the sea, we should be concerned with it too.”
Why Has Roman Concrete Lasted So Long?
The Pantheon looks pretty good for a 1900 year old building, considering that it is the largest unreinforced concrete dome in the world. Perhaps it's because it was not reinforced, so there was no iron to rust and expand, or perhaps because Roman concrete was different than the stuff we use today. TreeHugger has noted before that Roman concrete was a whole lot greener than today's mixes now a new study by researchers at the Berkeley Lab shows that the concrete actually gets stronger over time.
Unlike modern concrete which actually shrinks, opening up tiny cracks that propagate and let moisture in, Roman concrete, made with volcanic ash instead of portland cement, is actually self-healing as a crystalline binder forms and prevents the concrete from cracking any further. According to Marie Jackson of UC Berkeley:
So not only would concrete made with volcanic ash have a much lower carbon footprint, It would last a lot longer. Jackson continues in a more comprehensible tone:
The making of cement accounts for as much as 7% of the CO2 produced each year the amount of the stuff being poured these days is extraordinary. Vaclav Smil tells Bill Gates that the statistic shown above is the most staggering in his book, Making the Modern World: Materials and Dematerialization. We use far too much of the stuff and it doesn't last nearly as long as we thought it would. Time for a change.