Fly ash in cement and
concrete composition
Zbigniew Giergiczny
Silesian University of Technology, Gliwice, Poland
Technological Center Betotech , Ltd.
April, 24–25 2014, Moscow
Subject of presentation
•
•
•
•
•
Definition of fly ash
Classification of fly ash
Fly ash as a cement component
Fly ash as an additive for concrete
Summary
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Fly ash
Fly ash – is one of the residues resulted from hard coal
or brown coal dust combustion in various types of furnaces
in the power or heat and power plants.
FLY ASH
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Classification of fly ash
Fly ash can be classified according to:
• chemical composition,
• amorphous and crystalline phase content,
• fineness (sieve residue),
• unburned carbon content (loss on ignition).
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Classification of fly ash
FLY ASH
SILICEOUS
CALCAREOUS
(siliceous - calcareous)
SILICEOUS - ALUMINOUS
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Fly ash as a cement component
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Fly ash according to cementitious standard EN 197-1
Fly ash is obtained by electrostatic or mechanical
precipitation of dust-like particles from the flue
gases of furnaces fired with pulverised coal. The
ash obtained by other methods should not be used
in the cement according to EN 197-1.
Siliceous fly ash (V) is a fine powder of mostly
spherical particles having pozzolanic properties.
It consists essentially of reactive silicon dioxide
(SiO2) and aluminium oxide (Al2O3). The remainder
contains iron oxide (Fe2O3) and other compounds.
Requirements:
• reactive calcium oxide (CaO) max. 10,0 %
• reactive silicon dioxide content min. 25,0 %
• content of loss on ignition (unburned carbon):
• cat. A ≤ 5,0 %,
• cat. B ≤ 7,0 %,
• cat. C ≤ 9,0 %.
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Siliceous fly ash (V)
• Spherical grains of a high content of the glassy phase
• High fineness (specific surface area from 250.0 to 450.0 m2/kg)
• Pozzolanic properties
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Calcareous fly ash (W)
•
•
•
Very fine powder having pozzolanic properties and/or hydraulic,
It consists of reactive calcium oxide (CaO ≥ 10 %), silicon dioxide
(SiO2) and aluminium oxide (Al2O3). The remainder contains iron
oxide (Fe2O3) and other compounds,
It contains more phases than siliceous fly ash.
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Fly ash with high content of calcium compounds
Time of hydration [days]
POZZOLAN-HYDRAULIC ACTIVITY OF CALCAREOUS FLY ASH
FROM CONVENTIONAL FURNACES
Compressive strength [MPa] after:
Specific surface
of grund fly ash
[m2/kg]
3 days
7 days
28 days
90 days
559
3,4
2,4
5,2
5,2
744
9,3
9,9
11,5
13,8
70 % of siliceous fly ash (specific surface 540[m2/kg]
A1 – unground ash
A2 – ground ash
Compressive strength [MPa]
70 % of calcareous fly ash (specific surface 556[m2/kg]
Temperature [°C]
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Time [days]
Characteristics of fly ash
Morphology of fly ash grains
calcareous
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siliceous
Common cements contain fly ash as a main component
Type of common cement
Portland-fly ash cement
Portland-composite cement1)
Pozzolanic cement2)
Composite cement3)
The content of mineral
constituent, % mass
CEM II/A-V
CEM II/B-V
CEM II/A-W
CEM II/B-W
CEM II/A-M
CEM II/B-M
CEM IV/A
CEM IV/B
CEM V/A
CEM V/B
1)
6-20
21-35
6-20
21-35
6-20
21-35
11-35
36-55
18-30
31-50
Most often this type of cement includes fly ash and blastfurnace slag, but also may include pozzolan, silica fume,
burnt shale and ground limestone.
2)
The cement includes usually a mixture of pozzolans and fly ash or fly ash.
3)
The cement includes pozzolans, blastfurnace slag and siliceous fly ash.
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Properties of cements containing fly ash
20
Temperature, C
15
10
5
0
Final setting time
6:15
Initial setting time
4:25
8:14
6:05
12:20
7:05
14:50
9:05
20:05
11:35
Setting time of CEM II/B-V 32,5R depending on ambient temperature
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Properties of cements containing fly ash
70
Compressive strength [Mpa]
60
CEM I 32,5R
CEM II/B-V 32,5R
61.3
57.4
50
52.4
55.5
46.7
40
42.3
37.4
30
20
10
25.8
23.9
14.1
0
2 dni
7 dni
28 dni
Increase of compressive strength
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90 dni
180 dni
56.7
50.1
50.9
51.3
47.9
47.2
40
47.5
43.8
50
27.3
10.4
10
15.5
20
25.1
26.7
30
15.2
Compressive strength [MPa]
60
CEM II/B-M(S-V) 32,5R
CEM III/A 32,5N -LH
CEM V/A(S-V) 32,5R - LH
0
2
7
28
Time [days]
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56
90
54.9
Compressive strength development of cements
(standard mortars)
Pozzolanic activity
FLY ASH
(reactive SiO2 and Al2O3)
Ca(OH)2
H2O
Pozzolanic reaction rate depends on:
•
•
•
•
•
•
•
chemical and mineral composition of fly ash,
temperature and time of reaction,
pressure,
amount of water,
fly ash / Ca(OH)2 ratio,
fly ash specific surface,
presence of chemical admixtures
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hydrated calcium silicates
(C-S-H)
hydrated calcium aluminates
hydrated calcium sulfo aluminate
Amount of Ca(OH)2 in hardened cement paste
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Permeability of concrete
CEM I 32,5R
CEM II/B-S 32,5R
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CEM III/A 32,5N
CEM II/B-V 32,5R
Chemical composition of calcareous fly ash
Chemical composition [%]
Specimen No
loss on
ignition
SiO2
Al2O3
Fe2O3
CaO
CaOw
MgO
SO3
K2 O
Na2O
PL W1-0’
2,56
33,62
19,27
5,39
31,32
2,87
1,85
4,50
0,11
0,31
PL W4-0’
2,67
45,17
20,79
4,58
20,60
1,18
1,49
2,96
0,19
0,23
PL W5-0’
3,58
38,63
27,92
6,62
19,01
0,76
1,90
1,57
0,16
0,14
ST 2008
2,91
42,94
17,24
4,31
25,89
1,40
2,04
3,47
0,26
0,13
P 34
2,01
41,27
16,54
4,59
28,47
3,00
1,45
3,40
0,25
0,23
P 35
1,63
34,38
15,85
4,74
33,55
2,53
1,61
5,84
0,27
0,29
P 36
1,59
28,71
14,72
4,65
36,35
1,20
1,72
9,68
0,28
0,45
P 13
3,87
34,35
13,14
3,78
37,14
5,16
1,76
3,38
0,19
0,33
P 33
3,60
56,90
18,20
3,17
14,11
0,95
0,94
1,60
0,14
0,11
P8
6,11
28,70
9,76
4,00
43,42
5,01
1,74
3,03
0,13
0,22
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Phase composition of calcareous fly ash
Phase composition [%]
Mineral constituent
PL W1-0' PL W5-0' PL W4-0' ST 2008
Amorphous phase
Quarz SiO2
Mullite Al6Si2O13
Free CaO
Anhydrite CaSO4
Larnite 2CaO · SiO2
Gehlenit Ca2Al2SiO7
Anorthite CaAl2Si2O8
Ca3Al2O6
Hematite α-Fe2O3
Brownmillerite
Ca2(Al,Fe)2O5
30,6
11,6
2,3
5,0
5,5
12,8
10,5
8,9
6,4
1,7
64,4
6,3
5,6
1,2
1,8
1,9
6,8
5,9
1,6
1,2
1,3
2,0
48,6
16,8
4,4
1,6
3,9
4,0
5,6
11,1
2,4
P34
P35
P36
P13
P33
P8
58,7
10,3
2,4
1,4
4,5
4,2
5,2
8,4
2,2
0,6
20,0
24,3
3,8
4,5
5,0
14,4
9,4
8,0
6,0
0,9
26,5
11,3
2,2
6,3
8,9
16,4
9,3
6,1
6,9
1,4
52,4
4,2
1,4
3,3
10,4
11,6
5,1
2,0
4,8
1,2
3,1
11,1
2,3
7,2
4,0
17,8
7,8
6,0
8,1
0,8
42,0
31,9
6,5
0,9
1,4
4,2
3,7
6,4
1,5
0,5
39,1
5,0
2,2
6,4
3,1
21,2
6,1
3,4
9,3
0,6
0,1
3,1
3,7
2,2
3,2
0,6
3,0
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Pozzolanic activity of mineral additives
100
70% W
Activity index [%]
80
70% W+
60
70% V
70% S+
40
70% V+
20
0
2
7
28
90
180
Time [days]
+ - ground components
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360
Compressive strength of Portland – composite cement
80
Compressive strength [MPa]
CEM II/B-W+
60
CEM II/B-M (V-W+)
CEM II/B-M (LL-W+)
40
CEM II/B-M (S-W+)
CEM II/B-S 32,5R*
20
CEM II/B-M (V-LL) 32,5R*
0
2
7
28
90
Time [days]
180
- cements industrially produced
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360
Production scheme of CEM II/B-M (V-W) 32,5R
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Compressive strength of CEM II/B-M(V-W) 32,5R
Compressive strength [MPa]
80
70
60
CEM II/B-M (V-W) 32,5R
50
CEM I 42,5R
40
30
CEM II/B-S 32,5R
20
10
0
2
7
28
Time [days]
90
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180
Results of conducted research
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SILICEOUS FLY ASH
AS A CONCRETE
COMPONENT
Chemical composition of fly ash according to EN 450-1
Component
Allowed content
Fly ash received from
Fly ash received from
coal combustion only
co-combustion only
Loss on Ignition
 category A
 category B
 category C
Chlorides
SO3
CaO free
CaO reactive
SiO2 reactive
 5,0 %
≤ 7,0 %
≤ 9,0 %
 0,10 %
 3,0 %
 1,5 %1)
 10,0 %
Sum of oxides: SiO2, Al2O3, Fe2O3
Content of MgO
Sum of alkalis expressed in Na2Oeq
Content of soluble phosphate
compounds expressed in P2O5
Determination of
the content is not
necessary
It is assumed that the
requirement has been met
1) Fly
≥ 25,0 %
 70,0 %
 4,0 %
 5,0 %
 100mg/kg
ash, in which the free CaO content is higher than 1.5% by mass may be accepted provided the
soundness - Le Chatelier's test at ≤ 10 mm
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Phisical properties of fly ash according to EN 450-1
Property
Requirement
Fineness, sieve residue with 0,045 mm of mesh
sieve acc.to PN-EN 451-2
 category N
 category S
after 28 days
Pozzolanic activity index:
after 90 days
The soundness
(test necessary when content of CaOfree
below 1,5 %
 40 %
 12 %
 75 %
 85 %
max. 10 mm
Consistent density
Maximum difference
 200 kg/m3 compared to the one
declared by the producer
Initial setting time of paste containing 25% of fly
ash and 75% of Portland cement CEM I
Not longer that 120 minutes compared
to the setting time of applied Portland
cement CEM I
Water demand (determined for fly ash of S
category)
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 95% of water demand of Portland
cement CEM I used in tests
Requirements set against fly ash in the standards ASTM
and CAN-CSA
Property
Total content of CaO
Loss on ignition, maximum, %
Fineness (sieve residue 45 μm),
maximum, %
Water demand, maximum, %
ASTM C618
Class F
≤ 10%
Class C
≥ 10%
6*
Class F
≤ 8%
12
Class CI Class CH
≥ 20%
8 – 20%
6
34
–
105%
SO3 content, maximum, %
Oxides sum content
(SiO2, Al2O3, Fe2O3)
Activity index after 7 and 28 days
Autoclave soundness, %
CAN/CSA –A23.5-98
5
> 70%
> 50%
-
75%**
*- it is allowed till 12% under the condition of suitability verification
** - can not be compared because of the different compositions of mortars
fineness and density of fly ash can vary by up to 5% of the declared value
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68%**
0,8
-
Microscope image of fly ash
Fly ash
Loss on ignotion – 1,79 % - category A
Fineness – 1,0 % - category S
Fly ash
Loss on ignotion – 8,48 % - category C
Fineness – 27,5 % - category N
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Correlation of water demand and fineness of fly ash
with similar loss on ignition (4,78% and 4,99%)
110
105
Water demand [%]
100
95
90
85
80
75
70
65
60
10.5
30.6
Fineness [%]
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Correlation of water demand and loss on ignition
of fly ash with similar fineness (30,6% and 29,8%)
120
Water demand [%]
110
100
90
80
70
60
4.99
9.56
Loss on ignition [%]
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Fly ash with different contents of loss on ignition
(unburned carbon)
Fly ash – loss on ignition 17,9%
Fly ash – loss on ignition 2,2%
Type of fly ash
Slump test [cm]
Amount of
superplasticizer
[% mass of cement]
Fly ash I
(2,2% loss on ignition)
18 cm
0,87
1,7
Fly ash II
(17,9% loss on ignition)
18 cm
2,1
1,7
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Air content [%]
Effect of fly ash particle size on the amount
in concrete mixing water at constant consistence
[acc. Lindon K.A. Sear]
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Microstructure
Lower total
porosity
Concrete with
the addition
of fly ash
Lower share of the
capillary pores
Larger share
of the gel pores
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The diffusion coefficient of chloride ions in the concrete
with fly ash and slag cements
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Frost resistance of concrete (F150); start test after 28, 56 and 90 days
Cement
(30% of fly ash); 350 kg/m3; w/c = 0.5
80
The decrease in strength [%]
28 days
60
68.6
61.2
non-air-entrained concrete
40
air-entrained concrete
20
20 % - limit strength loss relative
to witnesses
26.9
16.2
0
relative to the witnesses
The decrease in strength [%]
56 days
relative to the strength after
28 days
The decrease in strength [%]
80
60
40
49,0
43.6
20
17.8
80
90 days
60
40
20
5.1
0
relative to the strength after
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18.8
4.2
10.7
3,0
0
relative to the witnesses
relative to the witnesses
relative to the strength after
28 days
The change in temperature inside of the concrete block
(volume 15 m3)
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Conclusions
1. Fly ash, as a by-product of coal combustion, is an interesting
mineral additive which should be widely applied in industrial
practice, specially, in the production of cement and concrete
2. Used in the production of cement and concrete shall comply
with the following standards:
– PN-EN 197-1 „Cement — Part 1: Composition,
and conformity criteria for common cements”
specifications
– PN-EN 450 „Fly ash for concrete — Part 1: Definition, specifications
and conformity criteria”
3. Fly ash applied in the above technologies should be
characterized by: homogeneity, stability of physical
characteristics, appropriate activity and spherical shape of the
grains
Thank you for your attention