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What is it about Roman concrete that keeps the Pantheon and Coliseum still standing

Concrete- Lots Of Activity


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By —— Bio and Archives August 12, 2017

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A single industry accounts for around 5% of global carbon dioxide emissions. It produces a material so ubiquitous it is nearly invisible: cement. Cement is the primary ingredient in concrete, which in turn forms the foundations and structures of buildings we live and work in, and the roads and bridges we drive on. Concrete is the second most consumed substance on Earth after water. On average, each year, three tons of concrete are consumed by every person on the planet. Cement production is growing by 2.5% annually.* 1

Ancient Rome’s Buildings

What is it about Roman concrete that keeps the Pantheon and Coliseum still standing?

Modern concrete, used in everything from roads to buildings to bridges, can break down is as few as 50 years. But thousands of years after the Roman Empire crumbled to dust, its concrete structures are still standing. Now scientists have finally figured out why: a special ingredient that makes the cement grow stronger—not weaker—over time.2

Researchers studied drilled cores of a Roman harbor from Pozzuoli Bay near Naples, Italy. When they analyzed it, they found that seawater had dissolved components of the volcanic ash, allowing new binding minerals to grow., Within a decade, a very rare hydrothermal mineral called aluminum tobermorite had formed in the concrete. This material can be made in the lab, but it is very difficult to incorporate in concrete.

So will we be seeing stronger piers and breakwaters anytime soon? Because the mineral take centuries to strengthen concrete, modern scientists are still working on recreating a modern version of Roman cement. 2

Environmental Concerns And Surprises

Though ‘cement’ and ‘concrete’ are often used interchangeably, concrete is actually the final product made from cement. The primary component of cement is limestone. To produce cement, limestone and other clay-like materials are heated in a kiln at 1400 C and then ground to form a lumpy, solid substance called clinker which is then combined with gypsum to form cement.

Cement manufacturing is highly energy and emissions intensive because of the extreme heat required to produce it. A ton of cement requires the equivalence of about 400 pounds of coal and generates nearly a ton of carbon dioxide.

The production of cement releases greenhouse gas emissions both directly and indirectly, while the burning of fossil fuels to heat the kiln indirectly results in carbon dioxide emissions. 1

However, here’s a surprise! Although cement manufacturing is among the most carbon-intensive industrial processes, an international team of researchers has found that over time, this material reabsorbs much of the carbon dioxide emitted when it was made. 3

“It sounds counterintuitive, but it’s true,” said Steven Davis, professor at the University of California, Irvine. “The cement poured around the world since 1930 has taken up a substantial portion of the carbon dioxide released when it was initially produced.”

Researchers tallied emissions from cement manufacturing and compared them to the amount of carbon dioxide reabsorbed by the material over its complete life cycle, which includes normal use, disposal and recycling. They found that cement is a large overlooked and growing net sink around the world—sink meaning a feature such as a forest or ocean that takes carbon dioxide out of the atmosphere and permanently tucks it away so that it can no longer contribute to climate change. 3

Self-Healing Concrete

Many resilient concrete structures like bridges and overpasses could save governments billions of dollars in annual expenses on repairs and maintenance. In recent years, a growing field of research has focused on developing self-healing mechanisms for concrete. 4

The self-healing concrete works in three main ways:

  • The opening of cracks is controlled using fibers which can potentially be made from recycled plastic materials like bottles.
  • A bacteria is incorporated into the concrete which starts to rejuvenate when cracks occur. Once damage starts, the bacteria deposits a biological cement which fills in these areas.
  • Nano and micro-capsules containing a resin or glue healing agent which again is released when damage or cracks start to occur within the concrete structure. 5

The bioconcrete is mixed just like regular concrete, but with an extra ingredient, the ‘healing agent’. It remains intact during mixing, only dissolving and becoming active if the concrete cracks and water gets in. Bacillus bacteria are used for the job because they thrive in alkaline conditions and produce spores that can survive for decades without food or oxygen. 6

 

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Another approach is that of using fibers that shrink in response to water infiltration, effectively squeezing the concrete together. Still others are attempting to embed a concrete kind of vascular network that would send a glue-like healing compound to any cracks in the structure. 7

Researchers have also developed a sunlight induced, self-healing protective coating designed to fix cracks on the surface of concrete structures before they grow into larger ones that compromise structural integrity. This is the first example of a self-healing protective coating for concrete. The next task is to determine the optimal composition of the coating and show that it remains stable over an extended time. So far, the researchers have shown that the coating can remain stable for a year. 4

Concrete From Wood

A type of concrete that largely consists of wood has also been develpped. This material offers the construction industry new possibilities and is based in large part on renewable resources. Houses can be made of wood, as they were in the past, or of concrete, as they are today. To build for tomorrow the two building methods are being combined: these hybrid structures, which contain both wood and concrete elements, are becoming increasingly popular in contemporary architecture.8

Cement bonded wood products have been around for more than a hundred years. Yet previously they were used only for non-load bearing purposes such as insulation. Swiss researchers wondered whether it wasn’t time for a more ambitious use of wood-based concrete. The main difference from classical concrete is that the gravel and sand content is replaced with finely ground wood, in other words, sawdust rather than small stones is mixed with the cement.

Researchers admit it will take several years before we see the first buildings in which lightweight concrete wood plays an integral role construction. The present level of knowledge required for widespread application is still too limited. 8

Concrete From Natural Materials

Researchers at MIT are seeking to redesign concrete by following nature’s blueprints. The team contrasts cement paste, concrete’s binding ingredient, with the structure and properties of natural materials such as bones, shells, and deep-sea sponges. As the researchers observed, these biological materials are exceptionally strong and durable thanks to, in part, to their precise assembly of structures at multiple length scales, from the molecular to the macro, or visible level. 9

Ultimately, the team hopes to identify materials in nature that my be used as sustainable and longer lasting alternatives to Portland cement which, as mentioned earlier, requires a huge amount of energy to manufacture.

 

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De-Icing Roadways

A pinch of steel shavings and a dash of carbon particles to a recipe that has literally been set in concrete for centuries conducts enough electricity to melt ice and snow in the worst winter storms while remaining safe to touch.10

This describes a unique bridge that resides about 15 miles south of Lincoln, Nebraska. It has given designer UNL professor of civil engineering Chris Tuan reason to feel confident. In 2002 Tuan and the Nebraska Department of Roads made the 150 foot Roca Spur Bridge the world’s first to incorporate conductive concrete. Inlaid with 52 conductive slabs that have successfully de-iced its surface for more than a decade, the bridge exemplifies the sort of targeted site that Tuan envisions for the technology.

Potholes often originate from the liberal use of salt or de-icing chemicals that can corrode concrete and contaminate ground water over time, making conductive concrete an appealing alternative with lower operating and maintenance costs. The power required to thermally de-ice the Roca Spur Bridge during a three day storm typically costs about $250 which is several times less than a truckload of chemicals. 10

Deflecting Electromagnetic Attacks

The idea for keeping roads and runways clear of ice may also turn out to be a significant tool in defense against telecommunications infrastructure attacks.

The special conductive concrete protects from intense electromagnetic pulses (EMPs), which can disable electronic systems like data centers and power grids. The threat of such attacks has grown more severe as terrorists consider assaults on digital lines to hamper communications. 11

The key is using magnetite, a mineral that’s a byproduct of steel mining with magnetic properties that absorb and reflect microwaves. This ability to both absorb and reflect EMP waves makes it much more effective than other similar products and at a much cheaper cost.

The team has created an 11 foot by 11 foot building which has now passed military inspection. The technology is ready for commercialization and the University of Nebraska-Lincoln has signed an agreement to license this shielding technology to resistant structures. 12

 

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Concrete on Mars

Sounds a little early, but in anticipation of humans on Mars, a team of Northwestern engineers developed a sulfur-based Martian concrete using materials naturally found on the planet. The Martian concrete can be quickly constructed and, when adjusted for gravity on Mars, is a strong as concrete used for skyscrapers on Earth. It is durable enough to withstand meteorite impacts—an important factor in creating viable shelters for humans. 13


* We edited out the last line of the original version (Sourced materiel was incorrect)

References

  1. Madeline Rubenstein, “Emissions from the cement industry,” blogs.ei.columbia.edu, May 9, 2012
  2. Zahra Ahmad, “Why modern mortar crumbles, but Roman concrete last millennia,” sciencemag.org, July 3, 2017
  3. “Concrete jungle functions as carbon sink, UCI and other researchers find,” news.uci.edu, November 21, 2016
  4. Mike Orcutt,“Self-healing concrete uses sunlight to fix its own cracks,” technologyreview.com, March 6, 2013
  5. “Concrete that can heal its own cracks,” cardiff.ac.uk, September 18, 2013
  6. Andrew Stewart, “The living concrete that can heal itself,” cnn.com, March 7, 2016
  7. Laura Bliss, “The new alchemy: how self-healing materials could change the world,” citylab.com, September 15, 2014
  8. Daia Zwicky, “Concrete from wood,” snf.ch/en, May 7, 2017
  9. Jennifer Chu, “Finding a new formula for concrete,” news.mit.edu, May 25, 2016
  10. 1Scott Schrage, “De-icing concrete could improve roadway safety,” news.unl.edu, January 25, 2016
  11. Matthew Wood, “This Nebraska engineered concrete deflects electromagnetic attacks,” btn.com, December 4, 2016
  12. Gilian Klucas, “Conductive concrete shields electronics from EMP attack,” news.unl.edu, November 14, 2016
  13. “Concrete on Mars,” Northwestern, Summer 2016
Jack Dini -- Bio and Archives |

Jack Dini is author of Challenging Environmental Mythology.  He has also written for American Council on Science and Health, Environment & Climate News, and Hawaii Reporter.

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