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Anderson 7482
 

Anderson 7482

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    Anderson 7482 Anderson 7482 Presentation Transcript

    • Sustainable Cement Using Fly Ash An examination of the net role of High Volume Fly Ash cement on carbon dioxide emissions. John Anderson IABSE Anton Tedesko Fellow M.Eng Struc. Eng, UC Berkeley
    • What reduction of carbon dioxide emissions can be achieved through the use of coal combustion products? Can High Volume Fly Ash cement provide the carbon dioxide savings required for long-term sustainability of the cement industry? Questions behind study
      • Main raw ingredients (85% by weight):
      • limestone (mainly calcium carbonate, CaCO 3 ) and
      • silica (silicon dioxide, SiO 2 )
      • Raw materials are crushed and heated in a kiln at 1450°C.
      • (calcinating limestone)
      • Gypsum is then added and the mixture is finely ground  clinker
      • Cement clinker is composed of tricalcium silicate, dicalcium silicate, tricalcium aluminate, tetracalcium aluminoferrite, and gypsum.
      Portland cement
    • Cement clinker is hydrated (addition of water) to form calcium silicate hydrate (C-S-H * ), calcium hydroxide (CH), and ettringite. Concrete is the mixture of hydrated cement paste and aggregates (gravel, crushed stone, or sand). Portland cement *Please note the use of cement chemistry: C = CaO, S =SiO 2 , H = H 2 O
    • The production of cement clinker requires the calcination of limestone (CaCO 3 ) to produce calcium oxide (CaO), an essential ingredient in cement clinker. The production of carbon dioxide results from this reaction. CaCO 3 + heat  CaO + CO 2 The other major source of carbon dioxide from the cement industry is from the burning of fossil fuels to achieve high kiln temperatures. Portland cement
    • The main sources of carbon dioxide are chemical processing (50%) and burning of fossil fuels in kilns (40%). Source: WBCSD (2002) Portland cement
    • CO 2 emissions from cement [1] Gt – Gigatonnes (1 Gt = 10 9 tonnes = 1 billion tonnes); Mt - Megatonnes (1 Mt = 10 6 tonnes = 1 million tonnes) 5 – 8 0.81 – 1.25 RANGE 6.97 Not given 0.932 * Not given Not given 2002 IPCC (2005) 5 Not given 1.37 0.87 1.57 2000 CSI: Substudy 8 (WBCSD 2002) 6.5 21.6 1.4 1 1.4 1995 Malhotra (1999) 5 22.7 1.13 0.81 1.38 1994 IEA GHG (1999); Worrell et al. (2001) 8 Not given 1.45 1.25 1.13 1991 Wilson (1993) CO 2 from cement (%) Total CO 2 from all sources (Gt) CO 2 from cement (Gt) CO 2 /cement (tonne/tonne) Cement Production (Gt) [1] Year Author
    • Fly ash is a by-product of coal combustion. Impurities in coal  bottom ash or fly ash Fly ash -high quantity of reactive silica -particle size 1-100 microns -Class C (high calcium), Class F (low calcium) most common -with calcium hydroxide forms cementitious products Other pozzolans are natural pozzolans (volcanic), slag, silica fume, rice hull ash, and metakaolin. Source: Sindhunata et al. (2006) Fly ash
    • Tricalcium Water Calcium Silicate Calcium Silicate Hydrate Hydroxide Portland cement: C 3 S + H  C-S-H + CH Silica (fly ash) Portland cement + fly ash: S + CH  C-S-H Chemical reaction of Portland cement with fly ash. C-S-H provides strength, CH weak, brittle crystals Fly ash and cement
    • Fresh concrete -reduced water demand, reduced bleed water, increased workability, continuing slump Plastic concrete -extended set times, reduced heat of hydration, reduced plastic shrinkage Hardened concrete - slower rate of strength gain , reduced permeability, reduced drying shrinkage, resistance to scaling from deicing salts Fly ash and cement
    • Future coal and cement production World coal and cement production, 1980-2035 (OECD-Organization for Economic Cooperation and Development) Historical Projected
    • Coal ash production and utilization in 1998 Sources: Malhotra (1999) 8 60 America, United States of 6 10 Great Britain, United Kingdom of 1 8 Spain, Kingdom of NA 38 South Africa, Republic of 5 62 Russian Federation 3 5 Japan 2 >80 India, Republic of 12 28 Germany, Federal Republic of 14 >100 China, People’s Republic of < 1 9 Australia, Commonwealth of Utilization (Mt) Production (Mt) Country
    • Estimated availability of fly ash and blast furnace slag in 2020 Sources: WBCSD (2002) 10 3,219 325 123 205 Total 3 188 5 1 3 Middle East 3 288 8 2 7 Africa 5 341 18 7 11 Latin America 18 79 14 4 11 E Europe 16 175 28 13 15 Russian Federation 9 215 20 4 16 India, Republic of 30 33 10 7 3 Korea, Republic of 7 294 20 3 17 SE Asia 7 1154 81 20 62 China, People’s Republic of 50 8 4 1 2 Aus & NZ 22 88 19 15 4 Japan 20 239 47 27 20 W Europe 64 11 7 3 5 Canada 42 106 44 16 29 America, United States of Potential for CO 2 Reduction in 2020 (%) Est. Cement Demand in 2020 (Mt) Total SCM (Mt) Blast Furnace Slag (Mt) Fly Ash (Mt)
      • Assumptions
      • Up to 60% of ordinary Portland cement (OPC) can be replaced by fly ash (Mehta 1999; Mehta 2002; Malhotra 1999).
      • 1 tonne of fly ash used = 1 tonne of OPC saved = 1 tonne CO 2 saved
      • Reduction requirements
      • Industry experts estimate that global carbon dioxide emissions will be required to achieve reductions of 30% by 2020 and this level could increase to 50% by 2050 (WBCSD 2002).
      • OPC is responsible for 5–8% of global anthropogenic CO 2 .
      Analysis
    • Past data (2000)  18% of coal turns to useable ash
      • 70% of coal ash is usable
      •  13% of coal turns to usable ash
      • Ash is 10% of coal
      • 1/3 ash is usable in cement
      •  3% of coal is usable ash
      Assumptions 3400 (EIA 2006) 3400 (EIA 2006) 4700 (back calculated) Coal consumption (global) (Mt) - 650 468 Coal ash (global) (Mt) 36% 28% 10% (10% = 156/1570 * 100) Possible CO 2 savings 600 455 156 Usable ash (Mt) 1662 1625 1570 Cement Production (global) (Mt) Malhotra (1999) Mehta (1999) WBCSD (2002)
    • Actual results (1999) Actual Results 35 (Mehta 1999) Fly Ash Utilized (global) (Mt) 2% (2% = 35/1600 * 100) CO 2 savings 1600 (U.S.G.S. 2001) Cement Production (global) (Mt)
    • Current data (2007)  18% of coal turns to useable ash
      • 70% of coal ash is usable
      •  19% of coal turns to ash
      •  13% of coal turns to usable ash
      • Ash is 10% of coal
      • 1/3 ash is usable in cement
      •  3% of coal is usable ash
      Assumptions 4600 (EIA 2006) 4600 (EIA 2006) 4600 (EIA 2006) Coal consumption (global) (Mt) - 870 460 Coal ash (global) (Mt) 50% 32% 6% (6% = 150/2500 * 100) Possible CO 2 savings 830 610 150 Usable ash (Mt) 2500 (U.S.G.S. 2007) 2500 (U.S.G.S. 2007) 2500 (U.S.G.S. 2007) Cement Production (global) (Mt) Malhotra (1999) Mehta (1999) WBCSD (2002)
    • Projections for 2020  18% of coal turns to useable ash
      • 70% of coal ash is usable
      •  19% of coal turns to ash
      •  13% of coal turns to usable ash
      • Ash is 10% of coal
      • 1/3 ash is usable in cement
      •  3% of coal is usable ash
      Assumptions 6020 (EIA 2006) 6020 (EIA 2006) 6020 (EIA 2006) Coal consumption (global) (Mt) - 1140 200 Coal ash (global) (Mt) 34% 25% 10% (10% = 325/3220 * 100) Possible CO 2 savings 1080 800 325 (includes slag) Usable ash (Mt) 3220 (WBCSD 2007) 3220 (WBCSD 2007) 3220 Cement Production (global) (Mt) Malhotra (1999) Mehta (1999) WBCSD (2002)
    • Projections for 2030  18% of coal turns to useable ash
      • 70% of coal ash is usable
      •  19% of coal turns to ash
      •  13% of coal turns to usable ash
      • Ash is 10% of coal
      • 1/3 ash is usable in cement
      •  3% of coal is usable ash
      Assumptions 7200 (EIA 2006) 7200 (EIA 2006) 7200 (EIA 2006) Coal consumption (global) (Mt) - 1370 720 Coal ash (global) (Mt) 36% 26% 7% (7% = 240/3635 * 100) Possible CO 2 savings 1300 960 240 Usable ash (Mt) 3635 (WBCSD 2007) 3635 (WBCSD 2007) 3635 Cement Production (global) (Mt) Malhotra (1999) Mehta (1999) WBCSD (2002)
    • CO 2 savings with HVFA cements
      • Significant variance in potential CO 2 emission reductions.
        • 2000 (10-36%), 2007 (6-50%), 2020 (10-34%), 2030 (7-36%)
      • Differences stem from assumptions of how much coal ash would be usable in blended cement.
        • Technologies available to increase percentage of useable ash
        • Decreasing ash due to carbon limitations
        • Increase of low NO x burners reducing suitable ash
      Results
      • Rate of growth of coal and cement also influences results.
      • If coal growth rate greater than cement, then greater potential for CO 2 savings. Greater potential savings seen early on.
        • 2000 to 2007
        • coal (+35%) > cement (+21%)
        • 2007 to 2020
        • coal (+31%) < cement (+47%)
        • 2020 to 2030
        • coal (+20%) < cement (+29%)
      Results
      • Best case scenario (Malhotra) allows for reductions in accordance in 2020 (30%) requirements.
      • Reduction of 50% by 2050 not likely in any scenario.
      • Most conservative assumptions (WBCSD) would allow for at most 10% savings in any given year.
      • Assuming every industry is responsible for its own CO 2 reductions (30% by 2020, 50% by 2050), HVFA cement alone is not a sufficient solution for the cement industry.
      • Alternative cementitious binder(s) required
      • (or reduced consumption of cement)
      Discussion
    • Current usage rate of fly ash dismally low. HVFA cement does allow for noticeable CO 2 reductions. Location of increased cement demand aligns with location of increasing coal production (developing countries). Further issues of sustainability (raw material demand, habitat destruction, water use, etc.) need to be addressed as well. Discussion
    • Alkali activated cements Calcium sulfo-aluminate cements Calcium sulfate based cements Magnesia cements Alternative binders
      • Alumino-silicate bonding phase (reaction between alumina rich source materials, fly ash, and an alkali silicate solution)
      • Source material 100% fly ash (100% reductions in CO 2 )
      • Challenges
      • CO 2 associated with alkali solution production
      • Reduced global fly ash availability
      Alkali activated cements
      • Product of numerous materials being calcinated at elevated temperatures
      • Early strength from ettringite, long-term strength from C-S-H
      • High early strength, reduced CO 2 emissions, low energy requirements, long-term durability
      • Challenges
      • Rapid setting time
      • Varying nomenclature
      • Absence of international standards
      Calcium sulfo-aluminate cements
      • Gypsum based mortar
      • Rapid setting, controllable shrinkage, and hardening rate
      • Low processing energy, reduced CO 2 emissions
      • Calcium sulfates are by-products of coal and oil power plants
      • Challenges
      • Natural calcium sulfates less widespread than limestone sources
      • Low durability, little protection for corrosion resistance of steel reinforcing
      Calcium sulfate based cements
      • Binding phase is magnesium oxide (MgO)
      • Numerous variations (Sorel, magnesium oxysulfate cements, magnesia phosphate cements, and magnesium carbonate cements)
      • Challenges
      • Possible low resistance to water
      • High cost of phosphate
      • Unproven mechanical performance
      Magnesia cements
    • High volume fly ash must be fully utilized today (regulations?). Sustainability of cement industry requires shifting away from one cement type. Future of cement will be regionally based (engineering characteristics easily communicated). Conclusions
    • Thank you. Selected References: (EIA) Energy Information Administration, 2006, Internal Energy Outlook 2006 , Chapter 5: World coal markets, Report #:DOE.EIA-0484(2006) [online], June Available at: http://www.eia.doe.gov/oiaf/ieo/coal.html, [cited on 10 January 2008] Malhotra, V.M., 1999, Making Concrete Greener with Fly Ash, Concrete International , 21(5), May, pp. 61-66. Mehta, P.K., 1999, Concrete Technology for Sustainable Development, Concrete International , November, pp. 47-53. World Business Council for Sustainable Development. (2002) Substudy 8, Towards a Sustainable Cement Industry: Climate Change. [online] March, Available at: http://www.wbcsd.org/DocRoot/oSQWu2tWbWX7giNJAmwb/final_report8.pdf [cited 10 January 2008]