The document examines the potential for reducing carbon dioxide emissions through the use of high volume fly ash cement. It finds that full utilization of fly ash today could achieve reductions of 10-36% but would not be enough to meet reduction targets of 30% by 2020 and 50% by 2050. Alternative cementitious materials beyond fly ash will be needed to achieve sustainability in the cement industry. The location of increased cement demand aligns with areas of increasing coal production, providing opportunities for greater fly ash use.
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Anderson 7482
1. 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
2. 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
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4. 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
5. 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
6. The main sources of carbon dioxide are chemical processing (50%) and burning of fossil fuels in kilns (40%). Source: WBCSD (2002) Portland cement
7. 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
8. 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
9. 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
10. 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
11. Future coal and cement production World coal and cement production, 1980-2035 (OECD-Organization for Economic Cooperation and Development) Historical Projected
12. 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
13. 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)
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16. 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)
24. 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
25. Alkali activated cements Calcium sulfo-aluminate cements Calcium sulfate based cements Magnesia cements Alternative binders
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30. 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
31. 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]
