greener cement is a must for the 3rd CO2 polluter of the world

February 2, 2009 § Leave a comment

World needs greener cement industry to fight climate change

Known for its massive CO2 emissions, the cement industry needs a way to get it’s technology greener and less energy-intensive. The 3rd CO2 polluter of the world, after fossil fuels and deforestration, it is also the fastest growing source of greenhouse gas. According to the World Business Council for Sustainable Development (WBCSD http://www.WBCSD.org), “Concrete is the most widely used material on earth apart from water, with nearly three tons used annually for each man, woman, and child.”

Because the constructions are growing every year all over the world – especially in the booming economies from Asia to Eastern Europe -, greening this industry is a must.

China alone makes and uses 45 percent of worldwide output and regarding Eastern Europe, take Ukraine, production is doubling every four years.For now the cement industry is culpable for about 5% of global emissions of carbon dioxide.

The subject of greening cement industry has been on the agenda of many nations and organizations for some time. New York times has a nice article on the subject, called “Cement Industry Is at Center of Climate Change Debate“. As they say, “Cement poses a basic problem: the chemical reaction that creates it releases large amounts of carbon dioxide” and words like sustainable and cement are pretty much contradictory.

There a re a few attempts throughout the world on getting greener cement and I will emphasize a few that popped first on a google search:

1) Ground Granulated Blastfurnace Slag (GGBS)

2) Accelerated Concrete Curing

3) MIT Nanoengineered concrete

4) Seawater cement

5) CO2 negative cement

Ground Granulated Blastfurnace Slag (GGBS)

Professor Jannie van Deventer’s team at the University of Melbourne has rediscovered a cement that is chemically similar to a cement used by the ancient Romans. Because the chemical reaction used to make Portland cement is to blame for 60% of the carbon emissions from cement manufacture.

Jannie van Deventer’s solution is “to change the intrinsic nature of the chemistry. Instead of having a calcium based system – as is the case with normal cement – you have to switch the chemistry to an aluminium silicon system.
You use reactive alumino-silicate materials such as ash that comes from power stations when you burn coal ash is generated in huge quantities, and you can also use slag which is a by product from the manufacturing of iron.”

Combining the ash, ordinary sand, water and also a little bit of alkaline solution, the mixture turns into a concrete that hardens over time, “and has been shown to double its 28 day strength over periods of 10 to 12 years” (source).

The process goes as follows: “the activator” (alkaline solution?) “dissolves out aluminium and silicon molecules from the slag and ash.These molecules then link together, forming much longer molecules…they’re the geopolymers. The geopolymers themselves link together, creating a vast three dimensional network. That’s what gives the cement its strength. And no carbon dioxide is produced.” (source)

Accelerated Concrete Curing

A process developed by canadian environmental consultants Carbon Sense Solutions and applied only for precast concrete, could reduce global CO2 emissions by as much as 1% a year.

The technology is based on a naturally occuring process of reabsorbing CO2 during the life of a concrete structure, process called concrete carbonation. Once concrete has returned to fine particles, full carbonation occurs, and all the CO2 released by calcination is reabsorbed. A recent study indicates that in countries with the most favorable recycling practices, it is realistic to assume that approximately 86% of the concrete is carbonated after 100 years. During this time, the concrete will absorb approximately 57% of the CO2 emitted during the original calcination. About 50% of the CO2 is absorbed within a short time after concrete is crushed during recycling operations. (Nordic Innovation Centre Project 03018).

Carbon Sense Solutions says it has developed a faster way to store more CO2 in concrete, using off the shelf technology, which uses dramatically less energy. They also claim the concrete is more durable, more resistant to shrinking and cracking, and less permeable to water. (source)

MIT Nanoengineered concrete

This is just a study at this time but has great potential in the near future. Studying the nanostructure of the concrete, MIT scientists noticed that concrete’s strength and durability lies in the organization of its nanoparticles.  They found that at the nano level, cement particles organize naturally into the most densely packed structure possible for spherical objects, which is similar to a pyramid-shaped pile of oranges.

The MIT team’s project is a work in progress and they estimate a period of 5 years until it will get them to a production-ready solution. As a replacemnt of calcium, the current chemical element at the base of cement, they are looking at magnesium, considered a waste material in many industries and also in electronic devices that people must pay to dispose of.

Seawater cement

Stanford Professor Brent Constantz has invented a method of making cement that takes half of the CO2 released by making Portland cement and turning it to another sort of cement that naturally occurs when corals are making their shells and reefs, taking the calcium and magnesium in seawater and using it to form carbonates at normal temperatures and pressures:”We are turning CO2 into carbonic acid and then making carbonate,” Constantz says. “All we need is water and pollution.”

Basically by bubbling exhaust fumes through seawater the resulting chemical reaction creates the key ingredient for Brent’s green cement.

The same process can also be used to make an alternative to aggregate – the sand and gravel – that makes up concrete and asphalt, which would sequester even more carbon dioxide from power plants. (source)

CO2 negative cement

Finally there’s a project that seemingly is pretty close to the market and companies around the world are watching what’s new about it. British Novacem company has developed a CO2 sucking cement that absorbs over its lifecicle more CO2 that it produces. In figures this is 0.66 tonnes absorbed while modern cements produce half a ton while produced. Due to the fact that Novacem cement requires less heat in the process, it has an output of 0.44 tonnes of CO2, so it absorbes 150% CO2 while hardening, making it carbon negative.

Novacem has already attracted the attention of major construction companies such as Rio Tinto Minerals, WSP Group and Laing O’Rourke, and investors including the Carbon Trust.

Neither technology from the ones described above is perfect and all need a whole lot of further study and perfecting but they represent a world’s battle over a disease that threatens the health of the planet itself. When any of these technologies gets comercialisation-ready they would have passed many other hurdles like building codes, building facilities next to the relevant supplier and so on.

After all, any bit is better than nothing.

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