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Precast concrete products represent between 10 and 15 percent of the North American cement and concrete market. While the figure in some European markets is 40 percent, most concrete is mixed and poured at construction sites outside the control of a factory setting (and Carbon Sense Solutions' process). "Considering concrete is the most abundant man-made material on earth, and that the precast market is growing, the estimated carbon dioxide storage potential of this is 500 megatons a year," Niven says. "That is on par with other global carbon dioxide mitigation solutions, such as carbon capture and geological storage."
Research professor Tarun Naik, director of the University of Wisconsin-Milwaukee's Center for By-Products Utilization, says that all concrete absorbs carbon dioxide over time if left to cure naturally--but only up to a point. The gas usually penetrates the first one or two millimeters of the concrete's surface before forming a hard crust that blocks any further absorption. Naik says that something as simple as using less sand in a concrete mix can increase the porosity of the finished product and allow more ambient carbon dioxide to be absorbed into the concrete. It's simpler than Carbon Sense Solutions' accelerated curing process and can be applied to a much larger market, he says.
Other groups are taking aim at emissions from the cement-making process itself. Researchers at MIT are seeking new ingredients in cement that are less energy intensive, while companies such as Montreal's CO2 Solution have an enzymatic approach that captures carbon-dioxide emissions from cement-factory flue stacks, converts the greenhouse gas into limestone, and feeds it back into the cement-making process. Calera, backed by venture capitalist Vinod Khosla, even claims that it can remove a ton of carbon dioxide from the environment for every ton of cement it produces.
Nano particles could prevent buildings and bridges from suffering serious structural damage.
New materials provide a potentially cheaper way to reduce carbon dioxide emissions from power plants.
Does this apply to AAC blocks?
Aerated autoclaved concrete is attractive as an inert insulating block, but it obviously requires autoclaving to cure the foamed concrete. The autoclaving not only adds to the cost, but also to the carbon gas emissions from the burning of coal to produce the steam.
AAC blocks and panels can replace standard concrete blocks for many application, and for green construction are getting a lot of attention.
But their cost in dollars and CO2 emissions are short term obstacles.
If concrete is 5% of human CO2 emissions, and this new concrete reduces emissions by 20%, then that's a 1% reduction of total emissions.
Nice - every little bit helps - but not spectacular.
By the time this tech is widely implemented, concrete use will highly likely be much larger than 120% of today's levels, making total CO2 emissions from concrete bigger than today.
I believe it is the manufacturing of cement NOT concrete that is 5% of man-made C02 - can someone confirm?
The Carbonation of Dense Concretes
1. There are no technical or sequestration advantages in using considerable energy to make Portland cement in which silicates and to a lesser extent aluminates predominate only to carbonate them as many researchers are attempting to do.
2. The carbonation of Portlandite which is a minor but significant component formed on the hydration of Portland cement increases strength but lowers the pH resulting in the break down of the passive oxide layer on steel and thus corrosion.
3. How carbonation occurs depends mainly on the maturity of the concrete, the partial pressure of CO2, humidity and permeability.
4. The construction of special carbonation rooms near point sources of CO2 and the logistics involved in moving either fresh concrete or finished product to such rooms or other facilities is and will become increasingly more prohibitive.
5. Because the carbonation of silicate and aluminate phases occurs much more readily in uncured concretes it is not only cheaper but technically much better to optimise natural carbonation. Better microstructure as well as chemical stability is the main outcome.
6. It is also more economical to naturally carbonate concretes provided rate issues and in the case of pre-mix concrete, pH issues if steel reinforcing is to be used, can be overcome.
Manufacturing in the United States is in trouble. That's bad news not just for the country's economy but for the future of innovation.
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jaywetmore
1 Comment
Carbonation of Concrete
For engineers evaluating the condition of concrete to determine remaining life, the extent of carbonation is an important indicator. The closer the carbonation is to the reinforcing steel the shorter the remaining life. Concrete's high alkalinity inhibits the oxidation of the reinforcing steel. Carbonation neutralizes the concrete, resulting in less protection for the metal reinforcement.
Carbonation is contra-indicated for reinforced and prestressed concrete. It is ok in unreinforced concrete like you might find in a sidewalk.
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Siphon
152 Comments
Re: Carbonation of Concrete
Reinforced concrete can be done with other materials, such as composites. They don't oxidize much at all. This is an emerging industry because it's possible to make higher quality reinforced concrete.
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ralph@bfmarch.com
1 Comment
Re: Carbonation of Concrete
"Concrete's high alkalinity inhibits the oxidation of the reinforcing steel." Sounds like more, not less protection for the steel against rusting. What am I missing?
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