1. An evaluation and suggestion for a sustainable concrete industry
Green Concrete
Evolutionary Cement
An evaluation and suggestion for a sustainable concrete industry
John Anderson
CEE, UC Berkeley
Spring 2007

2. Overview of Green Concrete
Environmental aspects of concrete
CO2 in Ordinary Portland Cement
Alternative binders
Alkali activated cements
Calcium sulfoaluminate cements
Other alternatives
Challenges and opportunities for green cement
green cement

3. Environmental aspects
CO2 emissions
Water use
Raw material extraction
Responsibility of engineers
green cement

4. CO2 in Ordinary Portland cement
~50% from the calcination of limestone
CaCO3 → CaO + CO2
(3CaCO3 + SiO2  Ca3SiO5 + 3CO2)
~40% from fossil fuels to heat kiln
(1450 ºC)
alternative fuels- Cement Sustainability Initiative
(tires, plastic insulation, paper)
green cement

5. Alternative binders (1)
Cement compound
Raw material used
Quantity of RMCO2* generated (g/g)
M (magnesia, periclase)
Magnesite
1.092
C (calcia, quicklime)
Limestone
0.785
C3S (alite)
Limestone + silica
0.578
β-C3S (belite)
0.511
C3A (tricalcium aluminate)
Limestone + alumina
0.489
C4AF (calcium aluminoferrite)
As above + iron oxide
0.362
NS (sodium metasilicate)
Soda + silica
0.361
CA (monocalcium aluminate)
0.279
C4A3S (calcium sulfoaluminate)
As above + anhydrite
0.216
* RMCO2- raw material CO2
FDCO2- fuel derived CO2
green cement

6. Alternative binders (2)
Alkali activated cements
Calcium sulfo-aluminate cements
Other options
(calcium sulfate, magnesia, and blended OPC cements)
green cement

7. Alkali activated cements
Alumino-silicate bonding phase
(alumina rich source material and an alkali silicate solution)
Termed geocements, aluminate cements
Source materials can be either pozzolanic or non-pozzolanic
Fly ash, blast furnace slag, metakaolin
green cement

8. Alkali activated cements
Environmental +
Waste as source material (fly ash, blast furnace slag)
Low RMCO2 (except metakaolin)
Low FDCO2 (except metakaolin)
Environmental -
High RDCO2 and FDCO2 for alkali activator
Elevated curing temps
Alkali runoff
Limited source materials
green cement

9. Alkali activated cements
Fly ash alkali activated
Curing (> 30° C)
Activator (10% by mass)
green cement

10. Alkali activated cements
Fly ash alkali activated
Strength development
7 days
28 days
green cement

11. Alkali activated cements
Fly ash alkali activated
Compressive strength (MPa)
Activator
Curing
temperature
(° C)
Activator/fly ash
ratio 0.25 (time of
curing)
2 h
5 h
24 h
Solution 1 65
0.0
21.2 85
9.3
22.0
34.6
Solution 2
8.7
1.4
9.4
23.3
Solution 3
4.3
31.7
52.7
39.8
48.2
54.5
Solution 4
9.5
38.7
7.7
34.3
63.0
NaOH 12 M (solution 1), KOH 18 M (solution 2),
NaOH + sodium silicate (solution 3),
and KOH + potassium silicate (solution 4).
green cement

12. Alkali activated cements
Slag alkali activated
Similar advantageous as fly ash
Influencing factors
Activator, curing temp, specific surface
Production decreasing
Rapid setting time and high shrinkage
Metakaolin alkali activated
Human-made
Thermal decomposition of kaolin
High costs
Significant RMCO2 and FDCO2
green cement

13. Calcium sulfoaluminate cements
Known as sulfoaluminate, ettringite, or belite-sulfoaluminate cements
High alumina, low energy, high early strength, rapid setting, long-term durability
Source material
Limestone, bauxite or alumina clays, and gypsum
Clinker result of calcinated source materials
Hydration products
Early strength: ettringite, long-term strength: C-S-H
green cement

14. Calcium sulfoaluminate cements
Environmental appeal
No elevated curing temperature
Use outside of precast
Reduced limestone used
Reduced kiln temperatures ( ° C)
Lower grinding energy
Gypsum not fired in kiln
High sulfur industrial byproducts
Slag, flue gas desulfurisation sludge, low calcium FA
No alkali solution/ alkali runoff
green cement

15. Calcium sulfoaluminate cements
Strength
Higher long-term strength than OPC
Cured at room temp (20°C), compression strength of ~80MPa
SAC-calcium sulfoaluminate cement,
FAC-ferroaluminate cement,
PC-portland cement
CAC-calcium aluminate cement
green cement

16. Additional alternative binders
Calcium sulfate-based cements
Gypsum based mortars
Hydration of calcium sulfate hemihydrate
Zero RMCO2, low FDCO2
Natural and byproduct source material
Durability weakness of gypsum
Use dense gypsum (alabaster) or additives (calcium aluminates)
No corrosion protection
Use fibers
green cement

17. Additional alternative binders
Magnesia cements
Binding phase- magnesium oxide
Family
Sorel, magnesium oxysulfates, magnesia phosphate, magnesia carbonate
CO2 sink
Recycling
Calcinate at 1000°C, high RMCO2
Possible water durability issues
$, unproven properties
green cement

18. Additional alternative binders
Blended OPC
OPC plus replacement (pozzolan) material
Fly ash, slag, rice husk ash
Initiated by lime
Low heat of hydration, improved workability
90% of market needs < 3,000 (20 MPa)
80% of SCMs go to landfill, low-value applc.
Low early strengths
Characterization of source material
Coal not sustainable product
green cement

19. Future of green cement Opportunities Challenges Market system for CO2
PC faces mechanical challenges
Low strength/ low risk applications
Challenges
OPC well established
Conservative nature of construction/design industry
More research
green cement