Fly ash for cement

After their coal fly ash spill in December, maybe Tennessee Valley Authority should contact our good friends from Nalco regarding the company’s development of fly ash application as a cement substitute.

Nalco’s subsidiary Nalco Mobotec recently announced a joint venture deal with Canada-based SONIC Technology Solutions to expand the use of fly ash from coal-powered stations as a cement substitute or concrete additive.

Nalco said SONIC’s SonoAsh process can turn low-grade waste fly ash into a valuable high-grade product with carbon credits for both the electric utility and cement industries.

Around 65% of North America’s fly ash is said to be unacceptable for use in the cement industry and just ends up in landfill. Not only will SONIC’s technology reduce landfill waste but it will also reduce carbon dioxide emissions from the cement industry.

Production of cement, which is very energy intensive, is said to contribute 7% global carbon dioxide emissions. Global cement demand, according to Nalco, approaches 3 billion tons/year and has grown rapidly in recent years.

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5 Responses to Fly ash for cement

  1. Pradeep 5 March, 2009 at 10:33 am #

    Around 65% of North America’s fly ash is said to be unacceptable for use in the cement industry and just ends up in landfill.
    Something does not add up here:
    From the ACAA (American Coal Ash Association) Website:

    According to the ACAA, of the 71.7 million tons (MT)of fly ash produced in 2007, 31.6 tons was used in various applications, 17.1 MT was used in concrete products and raw feed for clinker and ONLY 7.7 MT (10%) was used for structural fills/embankments (ex: landfills).

    Is NALCO referring to coal ash or more specifically to fly ash? [Coal combustion residues consist of fly ash (71 MT), bottom ash (18.1 MT), FGD gypsum (12.3 MT), etc...]

    Apart from this, reduction in cement CO2 emissions will be realized if more of fly ash is used/ton of cement. At the moment, the ASTM standard limits fly ash blending at 25% w/w. All the NALCO process is doing, IMO, is to reduce the unburnt carbon in the fly ash. This will make more fly ash available to the cement industry, but it does not necessarily mean that the cement industry would jump at the opportunity and blend more fly ash per ton of cement. Remember that fly ash is always cheaper than clinker (the material out of a cement kiln). Therefore, blending fly ash with clinker always makes economical, and environmental sense for the cement manufacturers given that fly ash increases the durability of concretes. So, my somewhat rhetorical question is: if the cement industry is already doing all it can do, what more do you think this process will enable it to do?

  2. Doris 6 March, 2009 at 12:39 pm #

    Hi Pradeep,
    As far as their press statement says, it seems Nalco is specifically talking about low-grade fly ash that mostly goes to landfill. They did mention that high-grade fly ash are already being used in the concrete industry as a performance-enhancing additive or cement replacement.

    I have no idea behind the chemistry of what makes fly ash high grade or low grade but it sure would be nice for Nalco to answer your question!

  3. Pradeep 6 March, 2009 at 2:39 pm #

    Doris,
    I worked at a cement plant (in India) for a while, and we blended all the fly ash we could into the cement, this is partly because high-grade fly ash (pure white color) was available from a nearby power station. However, low-NOx regulations in the US have resulted in lower flame temperature during coal burning, and this leaves some unburnt carbon in the fly ash. As I understand it, the Nalco process removes this carbon.

    I will try to figure out if there is data on whether US cement industry could use more fly ash..It seems that apart from blending with cement (post-kiln), fly ash could also be fed to a cement kiln as a raw meal with the limestone. The unburnt carbon of the fly ash is burnt in the kiln, in this case. It would sure be nice to get a bird’s eye view of fly ash utilization in the US cement industry.

  4. James Smith 18 May, 2009 at 5:58 pm #

    Fly ash concrete is an “inferior building and structural material in terms of durability, safety, and environmental effects.” “Although recycling fly ash into building materials may seem to be a viable alternative to disposing fly ash into waste dumps where it can leach into the soil, using a hazardous material in building products is actually waste disposal masquerading as recycling. A fundamental rule of recycling is similar to that of medicine, that is, “First, do not harm.” However, the use of fly ash in construction materials is far from safe. For example, some buildings in the United States, Europe, and Hong Kong have been found to have an increase in toxic indoor air contamination which is in direct relation to fly ash that has been used as an additive in concrete to make it more flowable. In a high rise building in Hong Kong, researchers suspect that the combination of fly ash and granite aggregation in concrete causes the building to be “hot” with the radioactive gas radon when the air-conditioning systems are shut down at night and on weekends. As a result, night and weekend workers may be exposed to higher and potentially dangerous radon levels.”
    See website: http://findarticles.com/p/articles/mi_gx5204/is_2003/ai_n19124302/?tag=content;col1

  5. Anonymous 13 October, 2009 at 9:58 pm #

    Can fly ash be mixed with cement to produce inferior concrete for utilizing it as road bed material? I undertsand that in India there are mobile units available for use at numerous coal fired power plants, is that a fact?

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