by fulltimestudent 8 Replies latest social current
These concrete walls in Trajan's markets in Rome are nearly 2000 years old and survived a major earthquake in 1349 CE.
Caption: The concrete walls of Trajan's Markets in Rome have stood the test of time and the elements for nearly 2,000 years. They have even survived a major earthquake in 1349.
Credit: Photo courtesy of Marie Jackson, Berkeley
And, slightly before that, between 23 and 15 BCE, Herod instructed his engineers to build this harbour - claimed as the largest ever built (to that point in time)
(See aerial view of the harbour at Link, and notes at : http://web.uvic.ca/~jpoleson/ROMACONS/Caesarea2005.htm )
Named Sebastos (the Greek equivalent of Augustus), the harbour of Caesarea Palaestine, also known in Greek as Caesarea on the Sea,was founded on a shifting sand beach devoid of any mitigating physical features. The shoreline was exposed to the longest fetch in the Mediterranean and scoured by a strong long-shore current that carried sand from south to north. The site had been selected primarily for political reasons, not because nature favoured the construction of a port at this location (Holum and Hohlfelder 1988). Once the royal decision had been made, it was up to King Herod’s builders to execute his desires, even though they faced design and construction challenges never before encountered by Mediterranean harbour engineers (Hohlfelder, 2000 and 2003). Underwater excavation and exploration have been carried out in the submerged ruins of Herod’s vast harbour complex almost continuously since 1960 in an effort to understand how this daunting ancient engineering project was executed so quickly and expertly in the face of seemingly insurmountable obstacles. The bibliography on the underwater excavations at Caesarea Palaestinae is considerable. Most published works relevant to this article are listed in the references section of Oleson et al. 2004, 228-9. This archaeological research has produced a vast literature that has revealed some, but not all, of the secrets of Sebastos.
Since 2002, the Roman Maritime Concrete Study (ROMACONS) has been conducting fieldwork in Italy, collecting cores from maritime structures constructed of Roman hydraulic concrete, and building an underwater reproduction of a pila or pier using materials and tools that would have been available to Roman builders (Oleson et al., 2004a, 2004b; Hohlfelder et al., 2005; Oleson et al., 2006). So far, we have collected cores from Roman maritime structures at Portus, Anzio, Cosa, Santa Liberata, and Baia. Roman hydraulic concrete consisted of a mortar made from lime, pozzolana (a sand-like volcanic ash naturally rich in aluminosilicates), and water, to which various types of rubble aggregate was added. The resultant mixture was a hard and durable concrete that could solidify underwater
Today, scientists are researching the techniques that made Roman concrete so superior.
A major centre for the at research is the Lawrence Berkeley National Laboratory and here's part of their findings:
Back to future with Roman architectural concrete
Research at Berkeley Lab's Advanced Light Source reveals key to longevity of imperial Roman monuments
No visit to Rome is complete without a visit to the Pantheon, Trajan's Markets, the Colosseum, or the other spectacular examples of ancient Roman concrete monuments that have stood the test of time and the elements for nearly two thousand years. A key discovery to understanding the longevity and endurance of Roman architectural concrete has been made by an international and interdisciplinary collaboration of researchers using beams of X-rays at the Advanced Light Source (ALS) of the U.S. Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab).
Working at ALS beamline 12.3.2, a superconducting bending magnet X-ray micro-diffraction beamline, the research team studied a reproduction of Roman volcanic ash-lime mortar that had been previously subjected to fracture testing experiments at Cornell University. In the concrete walls of Trajan's Markets, constructed around 110 CE, this mortar binds cobble-sized fragments of tuff and brick. Through observing the mineralogical changes that took place in the curing of the mortar over a period of 180 days and comparing the results to 1,900 year old samples of the original, the team discovered that a crystalline binding hydrate prevents microcracks from propagating.
"The mortar resists microcracking through in situ crystallization of platy strätlingite, a durable calcium-alumino-silicate mineral that reinforces interfacial zones and the cementitious matrix," says Marie Jackson, a faculty scientist with the University of California (UC) Berkeley's Department of Civil and Environmental Engineering who led this study. "The dense intergrowths of the platy crystals obstruct crack propagation and preserve cohesion at the micron scale, which in turn enables the concrete to maintain its chemical resilience and structural integrity in a seismically active environment at the millennial scale."
Jackson, a volcanologist by training who led an earlier study at the ALS on Roman seawater concrete, is the lead author of a paper describing this study in the Proceedings of the National Academy of Sciences (PNAS) titled "Mechanical Resilience and Cementitious Processes in Imperial Roman Architectural Mortar." Co-authors of the paper are Eric Landis, Philip Brune, Massimo Vitti, Heng Chen, Qinfei Li, Martin Kunz, Hans-Rudolf Wenk, Paulo Monteiro and Anthony Ingraffea.
The mortars that bind the concrete composites used to construct the structures of Imperial Rome are of keen scientific interest not just because of their unmatched resilience and durability, but also for the environmental advantages they offer. Most modern concretes are bound by limestone-based Portland cement. Manufacturing Portland cement requires heating a mix of limestone and clay to 1,450 degrees Celsius (2,642 degrees Fahrenheit), a process that releases enough carbon - given the 19 billion tons of Portland cement used annually - to account for about seven-percent of the total amount of carbon emitted into the atmosphere each year.
Roman architectural mortar, by contrast, is a mixture of about 85-percent (by volume) volcanic ash, fresh water, and lime, which is calcined at much lower temperature than Portland cement. Coarse chunks of volcanic tuff and brick compose about 45-to-55-percent (by volume) of the concrete. The result is a significant reduction in carbon emissions.
Full story at: http://www.eurekalert.org/pub_releases/2014-12/dbnl-bt121514.php
well one thing is it doesn't have rebar which can rust over long periods of time and crack the concrete. was it partly the engineering in arches and
no rebar more than the concrete mix itself?
Is the key volcanic ash? I saw this on tv.
FTS -
Thanks for this- the amazing potential of oldworld materials and methods.
The Pantheon is another long-standing tribute to Roman ingenuity and Roman concrete. Its dome is still the largest unreinforced concrete dome in history.
Concrete, while often not exactly pretty, is a super important tool of city-building today. We've been using Portland cement (an ingredient in concrete) as a binder for nearly 200 years as a building block of modern architecture, but it just can't hold a candle to that old Roman stuff. There are concrete harbors in Italy that are still doing pretty damn well after thousands of years. Meanwhile, a modern-day Portland cement structure is lucky to last 50 years when exposed to saltwater. Now, after years of research in labs across the US and Europe, scientists have figured out that the most robust Roman concrete is a specific mixture of lime and volcanic rock, the details of which have been published in this month's issues of the Journal of the American Ceramic Society and American Mineralogist.
The researchers described it this way in a press release on the subject: The Romans made concrete by mixing lime and volcanic rock. For underwater structures, lime and volcanic ash were mixed to form mortar, and this mortar and volcanic tuff were packed into wooden forms. The seawater instantly triggered a hot chemical reaction. The lime was hydrated – incorporating water molecules into its structure – and reacted with the ash to cement the whole mixture together. And it gets even better. Portland cement is environmentally messy to produce, accounting for some seven percent of the C02 modern industry produces. Roman concrete? Much, much greener. There's still a lot of work to be done in adapting traditional Roman construction techniques to today's needs. But the recipe is as good as ever. We just have to get cookin'. [Bloomberg Businessweek]
Rebar does react with concrete, but they offer coated rebar to reduce this reaction. Reinforced concrete is much safer than unreinforced concrete in beams undergoing tension. Concrete is extremely atromg under compression but not very strong under tensile loads. Adding reinforcement allows r/c beams to be able to handle these loads. Also unreinforced concrete suffers brittle failures, which means it fails suddenly. Properly Reinforced concrete has an elastic failure which is much safer.
The concrete mixture is likely the main reason roman concrete lasts so long. As the article mentions most concrete today is made of Portland cement, coarse and fine aggregate and water.
