Anderson 7482

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


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)


Assumptions


cement



19% of coal turns to ash




2500 (U.S.G.S. 2007) 2500 (U.S.G.S. 2007) 2500 (U.S.G.S. 2007)


4600 (EIA 2006) 4600 (EIA 2006) 4600 (EIA 2006)


Usable ash (Mt) 150 610 830


(6% = 150/2500 * 100)32% 50%

John Anderson

IABSE Fellow, M.Eng

Projections for 2020


Assumptions


cement







3220 3220 (WBCSD 2007) 3220 (WBCSD 2007)


6020 (EIA 2006) 6020 (EIA 2006) 6020 (EIA 2006)


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


Assumptions


cement







3635 3635 (WBCSD 2007) 3635 (WBCSD 2007)


7200 (EIA 2006) 7200 (EIA 2006) 7200 (EIA 2006)


Usable ash (Mt) 240 960 1300


(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]

Anderson 7482

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