The document discusses a study on the feasibility of using geopolymer as a coating material. The experimental program involved testing different raw materials and molar ratios to determine optimal properties. Results showed that a polysialate-siloxo type geopolymer with a Si/Al ratio of around 4.0, Na/Al ratio of 0.4-0.6, Si/Na ratio of 0.8-1.2, and H2O/Na ratio of 13-17 provided good workability, fast strength development, and potential as an environmentally friendly coating material. The conclusions determined composition ranges that achieved these qualities. Further studies could continue optimizing geopolymer for coating applications.

1. Feasibility Studies of Geopolymer
as a Coating Material

2. Contents
1. Introduction to Geopolymer
2. Experimental Program
3. Results and Analysis
4. Conclusions
5. Further Studies

3. 1. Introduction

4. New coating materials is needed?
 Surface protection and decoration
 Most commonly used interior/exterior painting
are organic materials
 Pigments, solvents and additives
 However, organic materials are harmful to
human beings
 A new kind of environmental friendly coating
material is highly desirable

5. Geopolymer
 Geopolymer is a new generation of inorganic
binder. It is a 3-D amorphous alumino-silicate
polymer.
 Dissolution and
polymerization
of SiO2 and Al2O3
containing materials

6. Formation Mechanisms
1. Dissolution in strong alkaline condition
2. Reorientation
3. Polymerization of silico-oxo-aluminate
(sialate)

7. Theoretical Formula
Mn [ – ( Si–O2 )z – Al–O ]n .wH2O
n – degree of polymerization
 In geopolymer, the sialate (Si-
O-Al-O-) is a cross-linking or
networking element

8. Types of Geopolymer
 Si:Al = 1:1 Polysialate / PS type
(-Si-O-Al-O-)
 Si:Al = 2:1Poly(sialate-siloxo) / PSS type
(-Si-O-Al-O-Si-O-)
 Si:Al = 3:1 Poly(sialate-disiloxo) / PSDS type
(-Si-O-Al-O-Si-O-Si-O-)

9. Raw Materials
 Al-Si source materials
- Metakaolin, slag & fly ash
 Alkaline activators / reagent
- Dissolves silica oxide (SiO2)
- Dissolves aluminum oxide (Al2O3)
- Provides Na+
/ K+
- Sodium / Potassium silicate (Na2SiO3)
 Water

10. Advantages over Cement
 Much less energy consumption
 Almost no CO2 emissions
 Raw materials are low price and can be easily
obtained
 Strength can be attained in a very short time
 Lower drying shrinkage

11. Advantages over Cement
 Strong resistance to chemical attacks
 Excellent fire resistance, low thermal
conductivity and low water permeability
 Immobilization of toxic and heavy metals
 A potential cost effective and environmental
friendly coating material

12. 2. Experimental Program

13. Raw Materials
 Metakaolin obtained by calcining kaolin at
700 for 12 hours℃
 Slag and fly ash from CLP (HK)
 Sodium silicate solution (water-glass) with a
molar ratio of 3.2
 Chemical grade NaOH
 Distilled water

14. Chemical Compositions
SiO2 Al2O3
Metakaolin 63% 27%
Slag 31% 15%
Fly Ash 50% 31%

15. Specimens Preparation
 Well mix the alkaline activator and water
together, then cooled down to about 40 deg
 Dry-mix the solid powder
- Ensure consistency of binders mixture
 Vibration compaction into 40mm cubes
 Setting time by Vicat Test
 Curing – (1) steam curing 60 deg, 12 hrs
– (2) in curing room for 3 days

16. Oxide Molar Ratios
 For PSS type geopolymer, the corresponding
theoretical oxide molar ratios are
[Si/Al]=4.0 [Na/Al]=1.0 [H2O/Na]=6~8
 Effectiveness of dissolution of oxides not
equal to sodium
 Water usage is much higher for coating
materials to be able to flow freely

17. Influencing Factors
Oxide molar ratios Alkalinity
Al-Si source materials
Properties
of geopolymer
Nan [ – ( Si–O2 )z – Al–O ]n .wH2O

18. 3. Results and Analysis

19. Al-Si Sourcing Materials [Si/Al]
Code
Weight Ratio
MK SL FA NaOH Na2SiO3 Water
1 1 0 0.3 0.097 0.139 0.31
2 1 0 0.5 0.097 0.139 0.31
3 1 0 1 0.097 0.139 0.28
4 1 0.25 0.75 0.097 0.139 0.32
5 1 0.33 0.67 0.097 0.139 0.34
6 1 0.25 0.5 0.097 0.139 0.32

20. Al-Si Sourcing Materials [Si/Al]
Code
Oxide Molar Ratio M Strength (MPa) Setting Time
[Si]/[Al] [Na]/[Al]
[H2O]/
[Na]
[Si]/[Na] [Na+] SC-80 NC-03D Initial Final
1 4.15 0.49 15.0 1.0 6.87 20.4 3.5 2:00:45 2:05:55
2 3.95 0.42 17.0 1.0 6.11 22.5 3.7 1:00:35 1:01:50
3 3.62 0.31 20.0 1.0 5.25 13.6 3.3 0:08:00 0:16:30
4 3.74 0.33 23.0 1.0 4.59 16.4 8.3 0:01:20 0:05:45
5 3.79 0.34 24.0 1.0 4.41 16.7 11.0 0:00:53 0:03:33
6 3.91 0.39 20.0 1.0 5.25 29.9 12.6 0:01:45 0:03:55

21. Alkalinity [Na+]
Code
Weight Ratio
MK SL FA NaOH Na2SiO3 Water
6 1 0.25 0.5 0.097 0.139 0.32
7 1 0.25 0.5 0.073 0.139 0.33
8 1 0.25 0.5 0.131 0.139 0.31
9 1 0.25 0.5 0.157 0.139 0.30

22. Alkalinity [Na+]
Code
Oxide Molar Ratio M Strength (Mpa) Setting Time
[Si]/[Al] [Na]/[Al]
[H2O]/
[Na]
[Si]/[Na] [Na+] SC-80 NC-03D Initial Final
6 3.91 0.39 20.0 1.0 5.25 29.9 12.6 0:01:45 0:03:55
7 3.91 0.32 25.0 1.2 4.21 19.1 9.0 0:00:47 0:01:43
8 3.91 0.49 16.0 0.8 6.56 38.5 16.6 0:02:03 0:04:06
9 3.91 0.55 13.6 0.7 7.70 32.8 12.4 0:01:23 0:01:26

23. Achieving the Alkalinity
Code
Weight Ratio
MK SL FA NaOH Na2SiO3 Water
6 1 0.25 0.5 0.097 0.139 0.32
8 1 0.25 0.5 0.131 0.139 0.31
10 1 0.25 0.5 0.097 0.139 0.27

24. Achieving the Alkalinity
Code
Oxide Molar Ratio M Strength (MPa) Setting Time
[Si]/[Al] [Na]/[Al]
[H2O]/
[Na]
[Si]/[Na] [Na+] SC-80 NC-03D Initial Final
6 3.91 0.39 20.0 1.0 5.25 29.9 12.6 0:01:45 0:03:55
8 3.91 0.49 16.0 0.8 6.56 38.5 16.6 0:02:03 0:04:06
10 3.91 0.39 17.0 1.0 6.10 36.9 14.4 0:02:02 0:03:27

25. Sodium Usage [Na/Al]
Code
Weight Ratio
MK SL FA NaOH Na2SiO3 Water
8 1 0.25 0.5 0.131 0.139 0.31
11 1 0.25 0.5 0.135 0.195 0.31
12 1 0.25 0.5 0.139 0.264 0.31
13 1 0.25 0.5 0.139 0.172 0.33

26. Sodium Usage [Na/Al]
Code
Oxide Molar Ratio M Strength (MPa) Setting Time
[Si]/[Al] [Na]/[Al]
[H2O]/
[Na]
[Si]/[Na] [Na+] SC-80 NC-03D Initial Final
8 3.91 0.49 16.0 0.8 6.56 38.5 16.6 0:02:03 0:04:06
11 4.07 0.54 14.7 1.0 7.01 39.2 20.9 0:04:44 0:07:59
12 4.26 0.61 13.3 1.2 7.53 38.6 18.6 0:07:37 0:10:52
13 4.01 0.53 15.5 0.9 6.71 38.3 15.5 0:03:25 0:06:08

27. Molar Ratio of Reagent
Code
Weight Ratio
MK SL FA NaOH Na2SiO3 Water
13 1 0.25 0.5 0.139 0.172 0.33
14 1 0.25 0.5 0.107 0.172 0.31
15 1 0.25 0.5 0.163 0.172 0.30

28. Molar Ratio of Reagent
Code
Oxide Molar Ratio M Strength (MPa) Setting Time
[Si]/[Al] [Na]/[Al] [H2O]/[Na] [Si]/[Na] [Na+] SC-80 NC-03D Initial Final
13 4.01 0.53 15.5 0.9 6.71 38.3 15.5 0:03:25 0:06:08
14 4.01 0.45 17.1 1.1 6.05 40.0 16.2 0:02:52 0:05:15
15 4.01 0.60 12.8 0.8 8.09 30.6 13.9 0:01:52 0:01:55

29. 4. Conclusions

30. Conclusions
 Working temperature at about 40 deg
 Alkalinity [Na+] of about 6~8
 Al-Si sourcing materials
– [Si/Al] of about 4.0 – PSS type
 Dissolution of Al-Si oxides
– [Na/Al] of about 0.4~0.6
 Molar ratio of reagent (water-glass)
– [Si/Na] of about 0.8~1.2
 Water usage for reasonable workability
– [H2O/Na] of about 13~17

31. Conclusions
 Good workability and fast strength
development
 Geopolymer is a promising candidate of cost
effective and environmental friendly coating
material

32. Thank you very much!