CEMENT

1. Evaluation of 2 fly ash samples – Part 1
Stefan Dietz
HGRS-PID
Course for Cement Application 2008

2. 2
04.09.2022/SDI
© Holcim Group Support 2008 Course for Cement Application 2008
 Evaluate 2 fly ashes according to the evaluation tools
 Which fly ash is the better performing one and why?
Workshop objective

3. 3
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© Holcim Group Support 2008 Course for Cement Application 2008
Properties
Fly ash

4. 4
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© Holcim Group Support 2008 Course for Cement Application 2008
Coal-fired power plant and its products
Boiler
Coal
Coal bunker
Coal mill
ESP
DeSOx
FGD-gypsum Fly ash Bottom ash
Bottom ash
Fly ash
Gypsum

5. 5
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© Holcim Group Support 2008 Course for Cement Application 2008
Quality and quantity of fly ash determined by…
 Coal
 Coal type
 Ash content
 Bed rock material
 Boiler
 Boiler Type, Temperature
 Dedusting equipment
 Electrostatic precipitator
 Baghouse
 Zyclones
 Environmental installation
 High dust equipment for DeSOx and DeNOx

6. 6
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© Holcim Group Support 2008 Course for Cement Application 2008
Impact of Coal type
Component
in weight %
Hard Coal Fly Ash
Germany USA
Lignite/ Subbit. Fly Ash
Germany USA
Class F Ø Class C
SiO2
AI2O3
Fe2O3
CaO
CaOfree
MgO
SO3
LOI
40 - 55
23 - 35
4 - 17
1 - 8
0 - 0.5
0.8 - 4.8
0.1 - 2.0
1 - 5
54.9
25.8
6.9
8.7
n.d.
n.d.
0.6
2.8
20 - 70
1.5 - 20
1 - 15
8 - 40
1 - 20
0.5 - 7
1.5 - 15
0.1 - 3
39.9
16.7
5.8
24.3
1.0
n.d.
3.3
0.9

7. 7
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© Holcim Group Support 2008 Course for Cement Application 2008
Impact of Boiler type
Fluidized Bed
Combustion
Dry Bottom Furnace Slag Tab furnace
(Wet bottom furnace)
Pozzolanic
Spheres
1300 - 1500
50 – 80%
1500 - 1700
70 – 100%
850 - 900
0%
Temp. (°C)
Workability
Water demand

8. 8
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© Holcim Group Support 2008 Course for Cement Application 2008
Pozzolanic reaction of fly ash (1)
Detrimental Ca(OH)2 is turned into something good
Pozzolanic reaction of fly ash
Fly ash + Ca(OH)2 + Water CSH
Cement hydration
Cement + Water CSH + Ca(OH)2

9. 9
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© Holcim Group Support 2008 Course for Cement Application 2008
Pozzolanic reaction of fly ash (2)
Ca(OH)2
CSH
Water
Alkaline
solution
Cement gel
Alumo-Silica-
Hydrogel
+ 
Dissolved fly ash glas reacts with Ca(OH)2 of OPC to form CSH
Fly ash glas =
Alumo-Silica-
glas

10. 10
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Pore Blocking effect
Cement without
fly ash
Cement with
fly ash
Reduced permeability

11. 11
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Pore size reduction
Pore size distribution in
pure OPCs
Pore size reduction in
fly ash cements
Reduced pore size at same total porosity !
Cl
SO4
Cl
SO4

12. 12
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© Holcim Group Support 2008 Course for Cement Application 2008
 Reduced water demand
 Improved surface finish
 Better fill of precast concrete moulds
Filler effect
Dartsch, Lutze
Betonwerk + Fertigteil-Technik, 58 (1992)
Fly ash
Cement/Aggregates

13. 13
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© Holcim Group Support 2008 Course for Cement Application 2008
Ball bearing effect
 Improved workability
 Better pumpability
Dartsch, Lutze
Betonwerk + Fertigteil-Technik, 58 (1992)
Fly ash
Cement/Aggregates

14. 14
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© Holcim Group Support 2008 Course for Cement Application 2008
First large scale uses of fly ash
Hoover dam spillway
repair works
Hungry Horse dam, 35 % cement
replacement (Total 120’000 t)
1948
1942

15. 15
04.09.2022/SDI
© Holcim Group Support 2008 Course for Cement Application 2008
High durability concrete
Cooling Tower, Germany (2000)
Acid/sulfate resisting concrete B85
Sulfuric acid attack pH 2
no inner plastic coating required
Mix design:
CEM I 42,5 R HS/NA 250 kg
Fly ash 50 kg
Silica fume 20 kg

16. 16
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© Holcim Group Support 2008 Course for Cement Application 2008
High performance concrete
Petronas Towers,
Kuala Lumpur (1999)
 Tallest concrete structure
worldwide
 Supported by 75x75 food
concrete cores in HPC with
138 Mpa
Fly ash used to
Prevent cracking
Reduce heat of hydration
Improve late strength

17. 17
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Evaluation tools
Fly ash

18. 18
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How does an optimum fly ash looks like?
 Fly ash type
 Hard coal fly ash in Europe (EN 450, EN 197-1 Type V)
 Subbituminous fly ash in US (ASTM 618 Class C)
 Key performance indicators
 High fineness (> 3000 cm2/g Blaine/
residue on 45m < 10 %)
 Low LOI (Europe: < 5-7%, US: < 2-6%)
 High reactive silica EN 196-2 (glass content) (> 25 %)
 Low SO3 content (< 3%)
 High total CaO content (> 20%)
 Low CaOfree content (< 1 % or highly reactive)

19. 19
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© Holcim Group Support 2008 Course for Cement Application 2008
What is the impact of KPIs on performance?
 Fineness; sieve residue at 45m
 High fineness (R45<10%) means high
share of spherical particles equivalent to
reactive glass and increase reactivity
 Spherical fly ash particles act as ball
bears between other particles and
reduce water demand
 Increased water demand, reduced
reactivity at R45 > 30%
 Unburnt carbon
 Admixture interaction AEA (>2%)
 Water demand (>7%)
 Black pop-ups (mainly with porous, easy
floating coke!)
 Reactive silica
 Part of total SiO2, acts as pozzolanic
material, >25% improved reactivity
Unburnt carbon
as coke
Unburnt carbon
as coal
Glass spheres

20. 20
04.09.2022/SDI
© Holcim Group Support 2008 Course for Cement Application 2008
What do FA parameters tell about performance?
Chem. Parameter
SiO2
SiO2 reactive
AI2O3
Fe2O3
CaOreact
CaOfree
MgO
Na2Oequ.
SO3
LOI
Fineness
Residue on 45m, %
Blaine, cm2/g
Bulk density, g/cm3
Constituent M.-% Impact on performance
Quartz (inert) > 50% Lower reactivity
Glass > 30% Improved reactivity
Glas component > 15% Pozzolanic reaction partner
Fe-Oxides, Glas > 10% Lower reactivity
Glass constituent > 15% Improved reactivity
Burnt lime > 1% Durability (expansion), standard
Periclase > 1% Durability (expansion)
Alkali salts > 1% Accelerator, ASR sensitive
Gypsum > 3% Set retarder, cem. standard limit
Unburnt carbon > 5-7% Increased water demand/
non-standard compliance
> 30% High water demand/low reactivity
< 2500 High water demand/low reactivity
No proper measure for fly ash
< 1 Increased transport cost
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21. 21
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© Holcim Group Support 2008 Course for Cement Application 2008
Fly ash user manual
 Available on Holcim Portal-Knowledge Management-
CoPMICCem
 Procedure to evaluate suitability of fly ash
 Checklist for power plant visit
 Can be ordered as CD at HGRS-PID

22. 22
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© Holcim Group Support 2008 Course for Cement Application 2008
Workshop task
Fly ash

23. 23
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© Holcim Group Support 2008 Course for Cement Application 2008
Based on a received standard analysis of fly ash:
Which fly ash is performing better and why?
Component
in weight %
SiO2
- SiO2 reactive
AI2O3
Fe2O3
CaO
CaOfree
MgO
Na2Oequ.
SO3
LOI
Fineness
Residue on 45m, %
Blaine, cm2/g
Bulk density, g/cm3
1. Lignite fly ash 2. Hard coal fly ash
56
45
26
7
3.5
0.3
2
0.4
0.8
4
20
3500
0.90
43
20
23
14
11
0.5
4
2.5
1
1
45
2200
1.1
Dry bottom furnace (1050-1300°C)