greening concrete

[amor de cosmos]

Experts Propose Research Priorities for Making Concrete ‘Greener’

The challenge of making concrete greener—reducing its sizable carbon footprint without compromising performance—is just like the world's most ubiquitous manufactured material—hard!

But, according to a new report* from the National Institute of Standards and Technology (NIST), the potential engineering performance, energy-efficiency and environmental benefits make it a challenge worth tackling.

Many factors determine the overall energy and environmental impact of concrete. However, reducing the amount of portland cement, which reacts with water to bind all the sand, stone and the other constituents of concrete as it hardens, provides the biggest opportunity. Depending on the particular concrete formulation that is used, portland cement accounts for approximately one-quarter of the total mass, and it is the product of a very energy-intensive process.

Nearly a kilogram of carbon dioxide, the main greenhouse gas, is produced for each kilogram of concrete that is constructed. Portland cement manufacturing accounts for more than 5 percent of U.S. industrial carbon-dioxide emissions, according to the report. In addition, the U.S. cement industry consumes 400 gigajoules of energy annually. That's equivalent to the energy required to power more than 3 million homes each year.



Consensus high-priority research topics identified by the experts include:

• Developing tools and metrics for quantifying the advantages and disadvantages of using different materials in concrete.
• Developing and validating computer models that can predict the performance of green concrete mixtures, both during construction and over the long term.
• Improving test methods for characterizing materials such as fly ash, glasses, and minerals and other portland cement substitutes to determine whether they will perform as required.
• Developing a more complete understanding of the water-driven chemical interactions that occur as industrial byproduct materials and other components are incorporated into concrete.

http://www.nist.gov/public_affairs/t...x.cfm#concrete

[M II A II R II K]

To improve today’s concrete, do as the Romans did

Read More: http://newscenter.berkeley.edu/2013/...oman-concrete/

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 now 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.”

.....

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)






Chris Brandon of the ROMACONS project collects a sample of ancient Roman concrete drilled from a breakwater in Pozzuoli Bay, near Naples, Italy. The breakwater dates back to around 37 B.C. (D. Bartoli photo, courtesy of J.P. Oleson)

[jd3189]

^^^ Good idea. We should always look at history for a lot of engineering styles. Structures like the Egyptian Pyramids and Greek and Roman temples and buildings still stand even to this day.

[amor de cosmos]

16 September 2013
Environmentally friendly cement is stronger than ordinary cement

New research from the Niels Bohr Institute shows that cement made with waste ash from sugar production is stronger than ordinary cement. The research shows that the ash helps to bind water in the cement so that it is stronger, can withstand higher pressure and crumbles less. At the same time, energy is saved and pollution from cement production is reduced. The results are published in the scientific journal, Scientific Reports.

Cement is comprised of chalk and clay, which are mixed together and heated at high temperatures in a cement kiln. The mixture is then crushed into a powder. When the cement powder is mixed with water a chemical process takes place, which causes the cement mixture to harden. Cement is used as a building material throughout the world.

In some countries where sugar cane is grown, agricultural waste product from sugar production has been added to the cement mixture for many years. Once the sugar has been extracted from the sugar can you are left with a lot of fibre waste, which is used as fuel for energy production. From the energy production you get a lot of ash, which needs to be disposed of. In some countries, like Cuba and Brazil, the ash is added into cement mixtures.

http://www.nbi.ku.dk/english/news/ne...dinary-cement/

[dchan]

^ The sugar cane ash appears to be just another kind of pozzolan, which have been used for over a millenium in concrete/cement technology since Ancient Greece. The 'green' aspect is the use of a waste material that would have ended up in a landfill, but is now being used to strengthen concrete structures instead.

The basic idea behind the use of pozzolans in concrete is that it (a) reduces the use of energy-intensive and expensive Portland cement, and (b) its chemical reaction with concrete ultimately reduces the pore sizes in the concrete. Smaller pore sizes helps to prevent premature corrosion of the reinforcing steel and the concrete itself by reducing the amount of water/salt/sulfate intrusion.

The same pozzolanic reaction also compensates for reduced strength that would result from the decreased use of Portland cement. The same mechanism that reduces the concrete pore size also increases the concrete's strength by providing a denser bind. Therefore, the reduction in the concrete's early stage strength is less drastic than expected.

[Allan83]

Lots of things can be done in terms of greening concrete. You can use all kinds of recycled material in the mix design. The manufacturing of the cement itself is very energy intensive, but cement kilns operate at such high temperatures that they will burn all kinds of things completely without any toxic by-products. Most notability you can burn used tires in cement kilns, using them fuel that replaces natural gas. Fly ash is another waste product that is used as a pozzolan in concrete mixes.

[amor de cosmos]

Green Cement Made From Toilets and Bathtubs May be Stronger Than Traditional Mixtures
by Ross Brooks, 04/07/14

An international team comprised of English, Spanish, and Brazilian researchers may have developed a new type of cement made from ceramic waste such as toilets, bathtubs, and basins. And the new mixture has the potential to be even stronger than conventional cement used worldwide. The team is also experimenting with a mixture that uses rice husks instead of chemical compounds, a process that would result in a cement made entirely from reclaimed waste materials.

To create the cement, scientists first grind up old ceramics and mix them with water and an activator solution, which currently uses sodium hydroxide or sodium silicate. This solution is then poured into a mold, and exposed to extreme heat, resulting in a solidified mixture. If the activator solution can be replaced with rice husk ash, it would take yet another material out of the waste stream, provide a way for suppliers generate additional income, and create cement made purely from recycled materials.

The rice husk method has delivered positive results so far, but the team hasn’t been able to generate anything conclusive just yet. Tests on another mixture made with red clay brick have also proven that this new “green” cement could actually be stronger than other common types currently employed around the world.

http://inhabitat.com/green-cement-ma...onal-mixtures/

[scalziand]

Advanced Concrete Means Little Maintenance For A Century

April 16th, 2014 | by Michael Keller


A new water-repellant concrete impregnated with tiny superstrong fibers promises to leave roads and bridges free of major cracks for up to 120 years.

University of Wisconsin-Milwaukee civil engineers have developed a concrete mix that is durable and superhydrophobic. They call it Superhydrophobic Engineered Cementitious Composite (SECC). Preventing normally porous concrete from absorbing water means that liquid can’t get inside, freeze and cause it to crack. The concrete’s unusual characteristics, including being significantly more ductile than traditional concrete, means that cracks that do form do not propagate and cause failure.

“Our architecture allows the material to withstand four times the compression with 200 times the ductility of traditional concrete,” said associate professor Konstantin Sobolev, whose lab created SECC

http://txchnologist.com/post/8290983...ntenance-for-a

[dchan]

^ I didn't see any mention of how resistant this hydrophobic concrete will be to salt corrosion.

[amor de cosmos]

• Video Link

[scalziand]

Originally Posted by dchan

^ I didn't see any mention of how resistant this hydrophobic concrete will be to salt corrosion.

Salt needs to be dissolved into water to penetrate the concrete. If the water can't get in, then the salt can't either.

[dchan]

Originally Posted by scalziand

Salt needs to be dissolved into water to penetrate the concrete. If the water can't get in, then the salt can't either.

That's right, good point. If it works as well as advertised, I'm wondering whether it can durable cost-effective enough to be used in large scale.

There's a sidewalk section in my neighborhood that can really use this hydrophobic concrete. Several years ago, the city DOT decided to create a dead-end at the end of a diagonal street that had previously ended at an intersection between two normal grid streets. At the dead-end, they plopped in a garden and sidewalk bulbout. The first time they poured in the sidewalk, they used normal concrete. When winter came around, the snowplows pushed the snow and salt directly onto the bulbout. So by the time spring came around and all of the snow had melted, the sidewalk emerged very deteriorated and pockmarked, with spalled concrete chips everywhere.

This phenomenon isn't limited to new concrete sidewalks. This year's large snowfall amounts and extended below-freezing periods did a number on sidewalks which normally don't see that much snow and salt. But it does affect newly-poured sidewalks much more than older sidewalks that have mostly cured already.

After seeing the badly damaged concrete surface, the DOT decided to replace the deteriorated sidewalk bulbout with new concrete, this time putting on a shiny coating or paint of some sort (not sure what it is) that I'm guessing is meant to seal the concrete. Long story short: it didn't work this winter. It's not as badly damaged as the previous concrete sidewalk, but it's still pretty badly pockmarked and has exposed concrete that hasn't been coated.