Geopolymers

1
Geopolymers

• An environmental alternative to
• CO2-producing Portland Cement

2
Outline

• CO2 and Global Warming
• Ordinary Portland Cement
• Geopolymers
• Components
• Mechanism
• Experimental Data
• X-ray Diffraction
• MAS-NMR
• Structure
• Geopolymer Cement Properties
• Conclusion

3
Global Warming

• Global Warming is caused by green house gases
  (GHG)
• Carbon dioxide is the main contributor to GHG
• Cement industry contributes 5 of all CO2
• Second fastest growing source of CO2 emissions
• Reasons
• Manufacturing process
• Ordinary Portland Cement (OPC)
• Cement Sustainability Initiative
• 30 reduction by 2020

4
Ordinary Portland Cement

• 5CaCO3 2SiO2 ? Ca3SiO5Ca2SiO4 5CO2
• 1 ton of OPC produces 1 ton of CO2 gas
• Alternative process vs. alternative chemistry

Gartner, E. Cement and Concrete Research 2004,
34, 1489-1498.
5
Geopolymers

• Amorphous macromolecules that result from the
  alkali activation of aluminosilicate minerals at
  relatively low temperatures
• Al3 and Si4 IV-fold coordination with oxygen

PS
PSS
PSDS
Davitovits, J. Journal of Materials Education
1994, 16, 91-139
6
Components

• Sources of silica and aluminum
• Metakaolin
• Dehydroxylated kaolinite
• 2(Si2O5Al2(OH)4)n ? 2(Si2O5Al2O2)n 4n H2O
• Fly Ash
• Silicon Dioxide
• Slag
• Aluminum and Silica Oxides
• Alkaline Activator
• Alkali hydroxide or alkali silicate solution
• Usually Na, K

7
Geopolymerization Mechanism
Step 1 alkalination and formation of tetravalent
Al in the side group sialate -Si-O-Al-(OH)3-Na
Step 2 alkaline dissolution starts with the
attachment of the base OH- to the silicon atom
8
Geopolymerization Mechanism Cont.
Step 3 cleavage of the oxygen in Si-O-Si through
transfer of the electron from Si to O.
Step 4 further formation of silanol Si-OH groups
and isolation of the ortho-sialate molecule, the
primary unit in geopolymerization.
9
Geopolymerization Mechanism Cont.
Step 5 reaction of the basic siloxo Si-O- with
the sodium cation Na and formation of Si-O-Na
terminal bond.
10
Geopolymerization Mechanism Cont.

• Step 6a condensation between reactive groups
  Si-O-Na and aluminum hydroxyl OH-Al, with
  production of NaOH, creation of cyclo-tri-sialate
  structure, further polycondensation into
  Na-poly(sialate) nepheline framework.

11
Geopolymerization Mechanism Cont.
Step 6b in the presence of soluble Na-
polysiloxonate one gets creation of
ortho-sialate-disiloxo cyclic structure, whereby
the alkali NaOH is liberated and reacts again
12
Geopolymerization Mechanism Cont.
Step 7 further polycondensation into
Na-poly(sialate-disiloxo) albite framework with
its typical feldspar crankshaft chain structure.
The Geopolymer Institute http//www.geopolymer.or
g/science/about-geopolymerization/2 (accessed
January 3, 2009)
13
X-Ray Diffraction

• Single diffuse halo peak at 3.05-3.30A
• Amorphous with short range order

Davitovits, J. Journal of Thermal Analysis 1991,
37, 1633-1656
14
27Al MAS-NMR

• Single sharp peak at 55ppm
• One IV-coordinated species
• Only species present
• Excludes diamers/triamers

Davitovits, J. Journal of Thermal Analysis 1991,
37, 1633-1656
15
29Si MAS-NMR

• Broad peak at 94ppm
• Three separate signals
• 85ppm
• 92ppm
• 99ppm
• Presence of three Si species

Davitovits, J. Journal of Thermal Analysis 1991,
37, 1633-1656
16
Si Species
Davitovits, J. Journal of Thermal Analysis 1991,
37, 1633-1656
17
Geopolymer Structure
Davitovits, J. Journal of Thermal Analysis 1991,
37, 1633-1656
18
Properties

• Resistance to many chemically aggressive species
  incl. sea water, acid, alkali and sulfate
• Fire resistance up to 1000C
• Rapid setting without loss of compressive
  strength
• Does not experience damage due to water loss like
  hydraulic cements

19
Hurdles for Geopolymer Cement

• Different source materials
• Properties of soluble silicate
• Varying results and physical parameters
• Contaminants
• Industry regulations
• New material

20
Conclusion

• The reduced CO2 emissions of Geopolymer cements
  make them a good alternative to Ordinary Portland
  Cement.
• Geopolymer cements structure is determined from
  X-ray Diffraction and MAS-NMR data.
• From this predicted structure a mechanism for the
  geopolymer is determined.
• Produces a substance that is comparable to or
  better than traditional cements with respect to
  most properties.

21
Special Thanks

• Geopolymer Institute
• Dr. Davidovitz
• Dr. Van Deventer
• Dr. Barkatt
• CUA Faculty

22
References

• Gartner, E. Cement and Concrete Research 2004,
  34, 1489-1498.
• World Business Council for Sustainable
  Development 2002. Towards a Sustainable Cement
  Industry Climate Change. http//wbcsd.org/DocRoot
  /oSQWu2tWbWX7giNjAmwb/final_report8.pdf
  (accessed January 3, 2009).
• World Council for Sustainable Development 2002.
  The Cement Sustainability Initiative Our Agenda
  for Action. http//www.wbcsdcement.org/pdf/agenda.
  pdf (accessed October 20, 2008).
• Phair, J.W. Green Chemistry 2003, 8, 763-780.
• Davitovits, J. Journal of Thermal Analysis 1991,
  37, 1633-1656.
• Davitovits, J. Journal of Materials Education
  1994, 16, 91-139.
• Materials Research Laboratory, Introduction to
  X-Ray Diffraction. http//www.mrl.ucsb.edu/mrlcent
  ralfacilities/xray/xray-basics/index.html
  (accessed January 3, 2009).
• Hornak, J.P. The Basics of NMR http//www.cis.rit.
  edu/htbooks/nmr/inside.htm (accessed January 3,
  2009).
• The Geopolymer Institue http//www.geopolymer.org
  /science/about-geopolymerization/2 (accessed
  January 3, 2009).
• Duxson, P. Provis, J. Lucky, G. van Deventer,
  J. Cement and Concrete Research 2007, 37,
  1590-1597.
• Kosmatka, Steven H. Kerkhoff, Beatrix Panarese,
  William C. The Design and Control of Concrete
  Mixtures. Portland Cement Association Skokie,
  Illinois, 2002.
• Duxson, P. Fernandez-Jimenez, A. Provis, J.L.
  Lukey, G.C. Palomo, A. Van Deventer, J.S.J.
  Journal of Material Science. 2007, 42, 2927-2933.