http://newscenter.berkeley.edu/2013/06/04/roman-concrete/
To improve today�s concrete, do as the Romans did
By Sarah Yang, Media Relations | June 4, 2013
BERKELEY �
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.
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 published in two papers, one that appears
online today (Tuesday, June 4) 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.�
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.
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.
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Wed, May 01, 2013 5:47:27 PM