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John Anderson
IABSE Fellow, M.Eng
Sustainable Cement Using Fly Ash
An examination of the net role
of High Volume Fly Ash cement
on carbon dioxide emissions.
John AndersonIABSE Anton Tedesko Fellow
M.Eng Struc. Eng, UC Berkeley
John Anderson
IABSE Fellow, M.Eng
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
John Anderson
IABSE Fellow, M.Eng
Main raw ingredients (85% by weight):•limestone (mainly calcium carbonate, CaCO3) and•silica (silicon dioxide, SiO2)
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
John Anderson
IABSE Fellow, M.Eng
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 =SiO2, H = H2O
John Anderson
IABSE Fellow, M.Eng
The production of cement clinker requires the calcination of limestone (CaCO3) to produce calcium oxide (CaO), an essential ingredient in cement clinker.
The production of carbon dioxide results from this reaction.
CaCO3 + heat CaO + CO2
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
John Anderson
IABSE Fellow, M.Eng
The main sources of carbon dioxide are
chemical processing (50%) and
burning of fossil fuels in kilns (40%).
Source: WBCSD (2002)
Portland cement
John Anderson
IABSE Fellow, M.Eng
CO2 emissions from cement
Author YearCement
Production(Gt)[1]
CO2/cement
(tonne/tonne)
CO2 from
cement (Gt)
Total CO2
from all sources (Gt)
CO2 from
cement (%)
Wilson (1993) 1991 1.13 1.25 1.45 Not given 8
IEA GHG (1999);
Worrell et al. (2001)
1994 1.38 0.81 1.13 22.7 5
Malhotra (1999)
1995 1.4 1 1.4 21.6 6.5
CSI: Substudy 8 (WBCSD
2002)2000 1.57 0.87 1.37 Not given 5
IPCC (2005) 2002 Not given Not given 0.932* Not given 6.97
RANGE 0.81 – 1.25 5 – 8
[1] Gt – Gigatonnes (1 Gt = 109 tonnes = 1 billion tonnes); Mt - Megatonnes (1 Mt = 106 tonnes = 1 million tonnes)
John Anderson
IABSE Fellow, M.Eng
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
John Anderson
IABSE Fellow, M.Eng
Tricalcium Water Calcium Silicate Calcium Silicate Hydrate Hydroxide
Portland cement: C3S + 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
John Anderson
IABSE Fellow, M.Eng
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
John Anderson
IABSE Fellow, M.Eng
World coal and cement production, 1980-2035(OECD-Organization for Economic Cooperation and Development)
Future coal and cement production
Historical Projected
John Anderson
IABSE Fellow, M.Eng
Country Production (Mt)
Utilization(Mt)
Australia, Commonwealth of 9 < 1
China, People’s Republic of >100 14
Germany, Federal Republic of 28 12
India, Republic of >80 2
Japan 5 3
Russian Federation 62 5
South Africa, Republic of 38 NA
Spain, Kingdom of 8 1
Great Britain, United Kingdom of 10 6
America, United States of 60 8
Coal ash production and utilization in 1998
Sources: Malhotra (1999)
John Anderson
IABSE Fellow, M.Eng
Fly Ash (Mt)
Blast Furnace Slag (Mt)
Total SCM(Mt)
Est. Cement Demand in 2020 (Mt)
Potential for CO2
Reduction in 2020 (%)
America, United States of 29 16 44 106 42
Canada 5 3 7 11 64
W Europe 20 27 47 239 20
Japan 4 15 19 88 22
Aus & NZ 2 1 4 8 50
China, People’s Republic of 62 20 81 1154 7
SE Asia 17 3 20 294 7
Korea, Republic of 3 7 10 33 30
India, Republic of 16 4 20 215 9
Russian Federation 15 13 28 175 16
E Europe 11 4 14 79 18
Latin America 11 7 18 341 5
Africa 7 2 8 288 3
Middle East 3 1 5 188 3
Total 205 123 325 3,219 10
Estimated availability of fly ash and blast furnace slag in 2020
Sources: WBCSD (2002)
John Anderson
IABSE Fellow, M.Eng
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 CO2 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 CO2.
Analysis
John Anderson
IABSE Fellow, M.Eng
Past data (2000)
WBCSD (2002) Mehta (1999) Malhotra (1999)
Assumptions
•Ash is 10% of coal•1/3 ash is usable in
cement
3% of coal is usable ash
•70% of coal ash is usable
13% of coal turns to usable ash
18% of coal turns to useable ash
Cement Production (global) (Mt)
1570 1625 1662
Coal consumption (global) (Mt)
4700 (back calculated) 3400 (EIA 2006) 3400 (EIA 2006)
Coal ash (global) (Mt) 468 650 -
Usable ash (Mt) 156 455 600
Possible CO2 savings 10%
(10% = 156/1570 * 100)28% 36%
John Anderson
IABSE Fellow, M.Eng
Actual results (1999)
Actual Results
Cement Production (global) (Mt)
1600 (U.S.G.S. 2001)
Fly Ash Utilized
(global) (Mt)35 (Mehta 1999)
CO2 savings2%
(2% = 35/1600 * 100)
John Anderson
IABSE Fellow, M.Eng
Current data (2007)
WBCSD (2002) Mehta (1999) Malhotra (1999)
Assumptions
•Ash is 10% of coal•1/3 ash is usable in
cement
3% of coal is usable ash
•70% of coal ash is usable
19% of coal turns to ash
13% of coal turns to usable ash
18% of coal turns to useable ash
Cement Production (global) (Mt)
2500 (U.S.G.S. 2007) 2500 (U.S.G.S. 2007) 2500 (U.S.G.S. 2007)
Coal consumption (global) (Mt)
4600 (EIA 2006) 4600 (EIA 2006) 4600 (EIA 2006)
Coal ash (global) (Mt) 460 870 -
Usable ash (Mt) 150 610 830
Possible CO2 savings 6%
(6% = 150/2500 * 100)32% 50%
John Anderson
IABSE Fellow, M.Eng
Projections for 2020
WBCSD (2002) Mehta (1999) Malhotra (1999)
Assumptions
•Ash is 10% of coal•1/3 ash is usable in
cement
3% of coal is usable ash
•70% of coal ash is usable
19% of coal turns to ash
13% of coal turns to usable ash
18% of coal turns to useable ash
Cement Production (global) (Mt)
3220 3220 (WBCSD 2007) 3220 (WBCSD 2007)
Coal consumption (global) (Mt)
6020 (EIA 2006) 6020 (EIA 2006) 6020 (EIA 2006)
Coal ash (global) (Mt) 200 1140 -
Usable ash (Mt) 325 (includes slag) 800 1080
Possible CO2 savings10%
(10% = 325/3220 * 100)25% 34%
John Anderson
IABSE Fellow, M.Eng
Projections for 2030
WBCSD (2002) Mehta (1999) Malhotra (1999)
Assumptions
•Ash is 10% of coal•1/3 ash is usable in
cement
3% of coal is usable ash
•70% of coal ash is usable
19% of coal turns to ash
13% of coal turns to usable ash
18% of coal turns to useable ash
Cement Production (global) (Mt)
3635 3635 (WBCSD 2007) 3635 (WBCSD 2007)
Coal consumption (global) (Mt)
7200 (EIA 2006) 7200 (EIA 2006) 7200 (EIA 2006)
Coal ash (global) (Mt) 720 1370 -
Usable ash (Mt) 240 960 1300
Possible CO2 savings 7%
(7% = 240/3635 * 100)26% 36%
John Anderson
IABSE Fellow, M.Eng
CO2 savings with HVFA cements
John Anderson
IABSE Fellow, M.Eng
Significant variance in potential CO2 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 NOx burners reducing suitable ash
Results
John Anderson
IABSE Fellow, M.Eng
Rate of growth of coal and cement also influences results.
If coal growth rate greater than cement, then greater potential for CO2 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
John Anderson
IABSE Fellow, M.Eng
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 CO2 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
John Anderson
IABSE Fellow, M.Eng
Current usage rate of fly ash dismally low.
HVFA cement does allow for noticeable CO2 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
John Anderson
IABSE Fellow, M.Eng
Alkali activated cements
Calcium sulfo-aluminate cements
Calcium sulfate based cements
Magnesia cements
Alternative binders
John Anderson
IABSE Fellow, M.Eng
•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 CO2)
Challenges
•CO2 associated with alkali solution production
•Reduced global fly ash availability
Alkali activated cements
John Anderson
IABSE Fellow, M.Eng
•Product of numerous materials being calcinated at elevated temperatures
•Early strength from ettringite, long-term strength from C-S-H
•High early strength, reduced CO2 emissions, low energy requirements, long-term durability
Challenges
•Rapid setting time
•Varying nomenclature
•Absence of international standards
Calcium sulfo-aluminate cements
John Anderson
IABSE Fellow, M.Eng
•Gypsum based mortar
•Rapid setting, controllable shrinkage, and hardening rate
•Low processing energy, reduced CO2 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
John Anderson
IABSE Fellow, M.Eng
•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
John Anderson
IABSE Fellow, M.Eng
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
John Anderson
IABSE Fellow, M.Eng
Thank you.
Selected References: (EIA) Energy Information Administration, 2006, Internal Energy Outlook 2006, Chapter 5: World coal markets, Report #:DOE.EIA-0484(2006) [online], JuneAvailable 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]
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