Fly ash in cement and concrete composition

Fly ash in cement and concrete composition

Zbigniew Giergiczny

Silesian University of Technology, Gliwice, PolandTechnological 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

Z b i g n i e w G i e r g i c z n y. V I n t e r n a t i o n a l C o n f e r e n c e ASHES FROM TPPS

Fly ashFly 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 ASHZ b i g n i e w G i e r g i c z n y. V I n t e r n a t i o n a l C o n f e r e n c e ASHES FROM TPPS

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).


Classification of fly ash

FLY ASH

SILICEOUS

SILICEOUS - ALUMINOUS

CALCAREOUS(siliceous - calcareous)


Fly ash as a cement component


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 %.


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


• 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.

Calcareous fly ash (W)


Fly ash with high content of calcium compoundsPOZZOLAN-HYDRAULIC ACTIVITY OF CALCAREOUS FLY ASH

FROM CONVENTIONAL FURNACES

Temperature [°C]

Tim

e o

f h

yd

rati

on

[d

ay

s]

Specific surface of grund fly ash

[m2/kg]

Compressive strength [MPa] after:

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

A1 – unground ash

A2 – ground ash

Time [days]

Com

pres

sive

str

engt

h [M

Pa]

70 % of siliceous fly ash (specific surface 540[m2/kg]70 % of calcareous fly ash (specific surface 556[m2/kg]


Characteristics of fly ash

Morphology of fly ash grains

calcareous siliceous


Common cements contain fly ash as a main component

1) 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.

Type of common cement The content of mineral constituent, % mass

Portland-fly ash cement

CEM II/A-VCEM II/B-V

6-2021-35

CEM II/A-WCEM II/B-W

6-2021-35

Portland-composite cement1) CEM II/A-MCEM II/B-M

6-2021-35

Pozzolanic cement2) CEM IV/ACEM IV/B

11-3536-55

Composite cement3) CEM V/ACEM V/B

18-3031-50


Properties of cements containing fly ash

0

5

10

15

20

0:002:00

4:006:00

8:0010:00

12:0014:00

16:0018:00

20:0022:00

11:35

9:05

7:05

6:05

4:25

20:05

14:50

12:20

8:14

6:15 Final setting timeInitial setting time

Time, h : min

Tem

pera

ture

, C

Setting time of CEM II/B-V 32,5R depending on ambient temperature


2 dni 7 dni 28 dni 90 dni 180 dni0

10

20

30

40

50

60

70

23.9

37.4

46.7

52.455.5

14.1

25.8

42.3

57.461.3

CEM I 32,5RCEM II/B-V 32,5R

Com

pres

sive

str

engt

h [M

pa]

Increase of compressive strength


Properties of cements containing fly ash

Compressive strength development of cements (standard mortars)

2 7 28 56 900

10

20

30

40

50

60

15.2

26.7

43.8 47

.9 50.1

10.4

25.1

47.5 51

.3

56.7

15.5

27.3

47.2 50

.9 54.9

CEM II/B-M(S-V) 32,5RCEM III/A 32,5N -LHCEM V/A(S-V) 32,5R - LH

Time [days]

Co

mp

res

siv

e s

tre

ng

th [

MP

a]


Pozzolanic activity

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

FLY ASH(reactive SiO2 and Al2O3)

Ca(OH)2

hydrated calcium silicates(C-S-H)

hydrated calcium aluminateshydrated calcium sulfo aluminate

H2O


Amount of Ca(OH)2 in hardened cement paste


CEM I 32,5R CEM III/A 32,5NPermeability of concrete

CEM II/B-S 32,5R CEM II/B-V 32,5R


Chemical composition of calcareous fly ash

Specimen No

Chemical composition [%]

loss on ignition SiO2 Al2O3 Fe2O3 CaO CaOw MgO SO3 K2O 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

P 8 6,11 28,70 9,76 4,00 43,42 5,01 1,74 3,03 0,13 0,22


Phase composition of calcareous fly ash

Mineral constituent Phase composition [%]

PL W1-0' PL W5-0' PL W4-0' ST 2008 P34 P35 P36 P13 P33 P8

Amorphous phase 30,6 64,4 48,6 58,7 20,0 26,5 52,4 3,1 42,0 39,1Quarz SiO2 11,6 6,3 16,8 10,3 24,3 11,3 4,2 11,1 31,9 5,0Mullite Al6Si2O13 2,3 5,6 4,4 2,4 3,8 2,2 1,4 2,3 6,5 2,2Free CaO 5,0 1,2 1,6 1,4 4,5 6,3 3,3 7,2 0,9 6,4Anhydrite CaSO4 5,5 1,8 3,9 4,5 5,0 8,9 10,4 4,0 1,4 3,1Larnite 2CaO · SiO2 12,8 1,9 4,0 4,2 14,4 16,4 11,6 17,8 4,2 21,2Gehlenit Ca2Al2SiO7 10,5 6,8 5,6 5,2 9,4 9,3 5,1 7,8 3,7 6,1Anorthite CaAl2Si2O8 8,9 5,9 11,1 8,4 8,0 6,1 2,0 6,0 6,4 3,4Ca3Al2O6 6,4 1,6 2,4 2,2 6,0 6,9 4,8 8,1 1,5 9,3Hematite α-Fe2O3 1,7 1,2 0,6 0,9 1,4 1,2 0,8 0,5 0,6Brownmillerite Ca2(Al,Fe)2O5

1,3 2,0 0,1 3,1 3,7 2,2 3,2 0,6 3,0


Pozzolanic activity of mineral additives

2 7 28 90 180 3600

20

40

60

80

100

70% W

70% W+

70% V

70% S+

70% V+

Time [days]

Act

ivity

ind

ex

[%]

+ - ground components


2 7 28 90 180 3600

20

40

60

80

CEM II/B-W+

CEM II/B-M (V-W+)

CEM II/B-M (LL-W+)

CEM II/B-M (S-W+)

CEM II/B-S 32,5R*

CEM II/B-M (V-LL) 32,5R*

Time [days]

Co

mp

ress

ive

str

en

gth

[MP

a]

Compressive strength of Portland – composite cement

- cements industrially produced


Production scheme of CEM II/B-M (V-W) 32,5R


2 7 28 90 1800

10

20

30

40

50

60

70

80

CEM II/B-M (V-W) 32,5R

CEM I 42,5R

CEM II/B-S 32,5R

Time [days]

Co

mp

ress

ive

str

en

gth

[MP

a]

Compressive strength of CEM II/B-M(V-W) 32,5R


Results of conducted research


SILICEOUS FLY ASH AS A CONCRETE

COMPONENT

Chemical composition of fly ash according to EN 450-1

ComponentAllowed content

Fly ash received from coal combustion only

Fly ash received from co-combustion only

Loss on Ignition category A category B category C

5,0 %≤ 7,0 %≤ 9,0 %

Chlorides 0,10 %SO3 3,0 %

CaO free 1,5 %1)

CaO reactive 10,0 %SiO2 reactive

Determination ofthe content is not

necessary

It is assumed that the requirement has been met

≥ 25,0 %

Sum of oxides: SiO2, Al2O3, Fe2O3 70,0 %

Content of MgO 4,0 %Sum of alkalis expressed in Na2Oeq 5,0 %

Content of soluble phosphate compounds expressed in P2O5

100mg/kg

1) Fly 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


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

40 % 12 %

Pozzolanic activity index: after 28 daysafter 90 days

75 % 85 %

The soundness(test necessary when content of CaOfree

below 1,5 %

max. 10 mm

Consistent densityMaximum 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)

95% of water demand of Portland cement CEM I used in tests


PropertyASTM C618 CAN/CSA –A23.5-98

Class F Class C Class F Class CI Class CH

Total content of CaO ≤ 10% ≥ 10% ≤ 8% 8 – 20% ≥ 20%

Loss on ignition, maximum, % 6* 12 6

Fineness (sieve residue 45 μm), maximum, %

34

Water demand, maximum, % 105% –

SO3 content, maximum, % 5

Oxides sum content(SiO2, Al2O3, Fe2O3)

> 70% > 50% - - -

Activity index after 7 and 28 days 75%** 68%**

Autoclave soundness, % 0,8*- 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

Requirements set against fly ash in the standards ASTM and CAN-CSA


Fly ash Fly ash Loss on ignotion – 1,79 % - category A Loss on ignotion – 8,48 % - category C Fineness – 1,0 % - category S Fineness – 27,5 % - category N

Microscope image of fly ash


10.5 30.660

65

70

75

80

85

90

95

100

105

110

Fineness [%]

Wa

ter

de

ma

nd

[%

]

Correlation of water demand and fineness of fly ashwith similar loss on ignition (4,78% and 4,99%)


4.99 9.5660

70

80

90

100

110

120

Loss on ignition [%]

Wa

ter

de

ma

nd

[%

]

Correlation of water demand and loss on ignitionof fly ash with similar fineness (30,6% and 29,8%)


Fly ash with different contents of loss on ignition (unburned carbon)

Type of fly ash Slump test [cm]Amount of

superplasticizer [% mass of cement]

Air content [%]

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

Fly ash – loss on ignition 2,2% Fly ash – loss on ignition 17,9%


Effect of fly ash particle size on the amountin concrete mixing water at constant consistence [acc. Lindon K.A. Sear]



Concrete with the addition of fly ash

Lower total porosity

Lower share of the capillary pores

Larger share of the gel pores

Microstructure


The diffusion coefficient of chloride ions in the concrete with fly ash and slag cements


relative to the witnesses relative to the strength af-ter 28 days

0

20

40

60

80

68.6

61.2

26.9

16.2

non-air-entrained concrete

air-entrained concrete

The

decr

ease

in s

tren

gth

[%]

20 % - limit strength loss rela-tive to witnesses

28 days


0

20

40

60

80

49,0

43.6

17.8 5.1

Th

e d

ecr

ea

se in

str

en

gth

[%

]

56 days

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


0

20

40

60

80

18.8

10.74.2 3,0

The

dec

reas

e in

str

engt

h [

%]

90 days


The change in temperature inside of the concrete block (volume 15 m3)


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, specifications

and conformity criteria for common cements”

– PN-EN 450 „Fly ash for concrete — Part 1: Definition, specificationsand 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

Documents

Fly ash in cement and concrete composition