Development of pore solution chemistry and hydrate assemblages during hydration

of calcium sulfoaluminate cements

Frank Winnefeld, Barbara Lothenbach, Mohsen Ben-Haha

Swiss Federal Laboratories forMaterials Testing and ResearchConcrete/Construction Chemisty LabDübendorf, Switzerland

Materials Science & Technology

Outline

Introduction

Used cements

Hydration of calcium sulfoaluminate cements

- Isothermal heat flow calorimetry- X-ray diffraction analysis- Thermogravimetric analysis- Pore solution chemistry- Microstructure (SEM) - Thermodynamic modelling

Conclusions2

Comparison OPC - CSAOPC CSA

main phases * C3S, C2S, C3A, C4AF C4A3s(= ye‘elimite)

raw materials limestone & clay limestone, bauxite & anhydrite

burning temperature ≈ 1450 °C ≈ 1250 °CCO2-release from raw materials **

C3S:1.80 g / ml C3S

C4A3s:0.56 g/ml C4A3s

grindability medium easygypsum addition ≈ 4-8 wt.-% ≈ 20-25 wt.-%w/c total hydration ≈ 0.4 ≈ 0.8hydration products C-S-H phases,

CH, AFt, …AFt, AFm, Al(OH)3 gel

** Gartner E., Cem. Concr. Res. 34 (2004), 1489.* Cement notation: C = CaO, S = SiO2, A = Al2O3, F = Fe2O3, H = H2O, s = SO3

3

CSA-Cements …

… have attracted new interest during the climate debate as they:need lower burning temperatures,release less CO2 from the raw meal (less limestone),yield a higher volume of hydrate phases (higher water/ cement ratio)

compared to ordinary Portland cement.Besides that, they are of interest concerning waste

encapsulation.But they have some drawbacks:

environment (SO2 release)risk of expansion (ettringite is main hydration product)

4

CSA-cements: risk of expansion

5

United States Patent 4409030, 1983: Material for destroying concrete structures

… comprises a mixture of … coarse-grained quicklime … and … cement. The cement may contain calcium sulfoaluminate ... The material is blended with water and then injected into holes formed in the body to be destroyed, the material expanding as it hydrates to crack and fracture the body.

Basic research is needed to understand the hydration mechanisms of calcium sulfoaluminate based systems !

Hydration of pure ye‘elimite

(1) C4A3s + 18 H C3A·CsH12 + 2 AH3 (monosulfate)

(2) C4A3s + 2 CsH2 + 24 H C3A·3CsH32 + 2 AH3 (ettringite)

(3) C4A3s + 6 CH + 8 CsH2 + 74 H 3 C3A·3CsH32

6

consumption ofcalcium sulfate

reaction (2) reaction (1)

0

40

80

120

160

200

0 2 4 6 8 10 12 14 16 18

heat

flow

/ J/

(g·h

)

time / h

C4A3sC4A3s / CsH2 1:1 (mol)C4A3s / CsH2 1:2 (mol)C4A3s / CsH2 1:3 (mol)C4A3s / CsH2 1:4 (mol)

heat flow calorimetryw/c = 2

0

5

10

15

20

25

30

35

0 8 16 24 32 40 48

heat

flow

/ J/

(g·h

)

time / h

CSA clinkerCSA / gypsum 86/14CSA / gypsum 76/24CSA / gypsum 68/32CSA / gypsum 61/39OPC, w/c = 0.50

Hydration kinetics of CSA cements:influence of calcium sulfate

0

5

10

15

20

25

30

35

0 8 16 24 32 40 48

heat

flow

/ J/

(g·h

)

time / h

CSA clinkerCSA / anhydrite 86/14CSA / anhydrite 76/24CSA / anhydrite 68/32CSA / anhydrite 61/39OPC, w/c = 0.50

dead-burnt anhydrite

w/c 0.70

gypsum *

w/c 0.70

calcium sulfate with poor reactivity:„chaotic“ early hydration

reactive calcium sulfate:enables to control early hydration

* amounts of gypsum given as anhydrous calcium sulfate 7

Strength development of CSA cements

8

0

20

40

60

80

100

120

0.1 1 10 100

com

pres

sive

str

engt

h / M

Pa

time / d

CSA clinkerCSA / gypsum 86/14CSA / gypsum 68/32OPC, w/c = 0.50

w/c = 0.70

EN 196-1 - mortarsvery high strengthdespite high water/cement-ratiogypsum increases early strength

Used CSA-cements - composition

9

wt.-% CSA-1 CSA-2CaO 35.4 41.2SiO2 3.2 6.9Al2O3 35.5 26.8Fe2O3 0.88 0.88MgO 0.76 0.75Na2O 0.05 0.13K2O 0.21 0.40TiO2 1.8 1.2SO3 16.8 19.5L.O.I. 5.1 1.84

chemical analysiswt.-% CSA-1 CSA-2C4A3s 50 54CA 8 -C2AS 15 -C2S - 17Cs - 22CsH2 22 -others * 5 7

potential phase content

* mainly titanium containing phases

water/cement ratioCSA-1: 0.72CSA-2: 0.80

Isothermal heat flow calorimetry

10

0

5

10

15

20

25

30

35

0 8 16 24 32 40 48

heat

flow

/ J/

(g·h

)

time / h

CSA-1

CSA-2

Hydration (XRD) of CSA-1

11

10 15 20 25 30 35 40 45 50 55 602Θ / °

0

3000

6000

9000

12000

15000

18000

5

inte

nsity

/ -

unhydrated

2 h

5 h

8 h

2 d

7 d

G

G G GY YGe

Y - ye'elimiteC - calcium aluminateGe - gehlenite

C

G - gypsum

16 hM

M - monosulfate

28 d

E

E

EE

GeGM

1 h

E - ettringite

E E

Hydration (TGA) of CSA-1

12

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500 600 700 800 900 1000

diff.

rel.

wei

ght /

%/K

rel.

wei

ght /

%

temperature / °C

unhydrated

gypsum

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500 600 700 800 900 1000

diff.

rel.

wei

ght /

%/K

rel.

wei

ght /

%

temperature / °C

unhydrated

1 h

gypsum

ettringite

Al(OH)3 - gel

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500 600 700 800 900 1000

diff.

rel.

wei

ght /

%/K

rel.

wei

ght /

%

temperature / °C

unhydrated

1 h2 h

gypsum

ettringite

Al(OH)3 - gel

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500 600 700 800 900 1000

diff.

rel.

wei

ght /

%/K

rel.

wei

ght /

%

temperature / °C

unhydrated

1 h2 h5 h

gypsum

ettringite

Al(OH)3 - gel

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500 600 700 800 900 1000

diff.

rel.

wei

ght /

%/K

rel.

wei

ght /

%

temperature / °C

unhydrated

1 h2 h5 h8 h

gypsum

ettringite

Al(OH)3 - gel

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500 600 700 800 900 1000

diff.

rel.

wei

ght /

%/K

rel.

wei

ght /

%

temperature / °C

unhydrated

1 h2 h5 h8 h

16 h

ettringite

Al(OH)3 - gel

monosulfate

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500 600 700 800 900 1000

diff.

rel.

wei

ght /

%/K

rel.

wei

ght /

%

temperature / °C

unhydrated

1 h2 h5 h8 h

16 h

ettringite

Al(OH)3 - gel

monosulfate

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500 600 700 800 900 1000

diff.

rel.

wei

ght /

%/K

rel.

wei

ght /

%

temperature / °C

unhydrated

1 h2 h5 h8 h

16 h2 d

gypsum

ettringite

Al(OH)3 - gel

monosulfate

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500 600 700 800 900 1000

diff.

rel.

wei

ght /

%/K

rel.

wei

ght /

%

temperature / °C

unhydrated

1 h2 h5 h8 h

16 h2 d

7 d

gypsum

ettringite

Al(OH)3 - gel

monosulfate

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500 600 700 800 900 1000

diff.

rel.

wei

ght /

%/K

rel.

wei

ght /

%

temperature / °C

unhydrated

1 h2 h5 h8 h

16 h2 d

7 d28 d

gypsum

ettringite

Al(OH)3 - gel

monosulfate

Pore solution composition of CSA-1

0.0001

0.001

0.01

0.1

1

10

100

1 10 100 1000

conc

entr

atio

n / m

mol

/l

time / h

FeSi

OH

NaS

Ca

K

Al

13

10.7 12.7pH

consumptionof gypsum

Hydration (XRD) of CSA-2

14

5 10 15 20 25 30 35 40 45 50 55 602Θ / °

0

3000

6000

9000

12000

15000

18000

inte

nsity

/ -

2 h

4 h

6 h

16 h

7 d

unhydratedY Y Y YA B

Y - ye‘elimiteB - beliteA - anhydrite S - strätlingite

(C2ASH8)

28 d

E

E

EES SM Y

M - monosulfate

2 dM

E - ettringite

1 hE E

Hydration (TGA) of CSA-2

15

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500 600 700 800 900 1000

diff.

rel.

wei

ght /

%/K

rel.

wei

ght /

%

temperature / °C

unhydrated

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500 600 700 800 900 1000

diff.

rel.

wei

ght /

%/K

rel.

wei

ght /

%

temperature / °C

unhydrated

1 h

ettringite

Al(OH)3 - gel

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500 600 700 800 900 1000

diff.

rel.

wei

ght /

%/K

rel.

wei

ght /

%

temperature / °C

unhydrated

1 h2 h

ettringite

Al(OH)3 - gel

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500 600 700 800 900 1000

diff.

rel.

wei

ght /

%/K

rel.

wei

ght /

%

temperature / °C

unhydrated

1 h2 h

4 h

ettringite

Al(OH)3 - gel

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500 600 700 800 900 1000

diff.

rel.

wei

ght /

%/K

rel.

wei

ght /

%

temperature / °C

unhydrated

1 h2 h

4 h6 h

ettringite

Al(OH)3 - gel

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500 600 700 800 900 1000

diff.

rel.

wei

ght /

%/K

rel.

wei

ght /

%

temperature / °C

unhydrated

1 h2 h

4 h6 h

16 h

ettringite

Al(OH)3 - gel

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500 600 700 800 900 1000

diff.

rel.

wei

ght /

%/K

rel.

wei

ght /

%

temperature / °C

unhydrated

1 h2 h

4 h6 h

16 h

2 d

ettringite

Al(OH)3 - gel

monosulfate

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500 600 700 800 900 1000

diff.

rel.

wei

ght /

%/K

rel.

wei

ght /

%

temperature / °C

unhydrated

1 h2 h

4 h6 h

16 h

2 d7 d

ettringite

Al(OH)3 - gel

monosulfate

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500 600 700 800 900 1000

diff.

rel.

wei

ght /

%/K

rel.

wei

ght /

%

temperature / °C

unhydrated

1 h2 h

4 h6 h

16 h

2 d7 d

28 d

ettringite

Al(OH)3 - gel

strätlingite

monosulfate

Pore solution composition of CSA-2

0.0001

0.001

0.01

0.1

1

10

100

1 10 100 1000

conc

entr

atio

n / m

mol

/l

time / h

Fe

Si

OH

NaS

Ca

K

Al

16

10.9 12.9pH

consumptionof anhydrite

Microstructure of CSA-1 and CSA-2

16 h 28 d

20 µmCSA-1, 28 d20 µmCSA-1, 16 h

G

C

EGel

CSA-1

E = ettringiteC = clinkerG = gypsumGel = gel-like

phases

CSA-2

20 µmCSA-2, 16 h

CGel

ES = strätlingite

171720 µmCSA-2, 28 d

S

S

S

S

Thermodynamic modelling

C4A3s, CA, C2S=> Dissolution kinetics

(XRD)

Composition of cement

I Slowly soluble solids

K2ONa2OMgO

18

K2SO4Na2SO4

CaO

II Rapid soluble solids

gypsumanhydrite

III Water

H2Owww.empa.ch/cemdataLothenbach B., Winnefeld F., Cem. Concr. Res. 36 (2006), 209.

thermodynamic modelling GEMS-PSI

ettringite

C-S-H

monosulfateAl(OH)3 gel

Ca2+

CaOH+ speciationCaSO4

0

strätlingite, …

Modelling: solid phases of CSA-1

19

0

10

20

30

40

50

60

70

80

0 1 10 100 1000

amou

nt /

g/10

0 g

cem

ent

time / h

pore solution

C4A3s

CA

inert phases (C2AS, CT)

gypsum

ettringite

monosulfate Al(OH)3 gel

lines: modellingdata points: XRD (C4A3s, CA)

TGA (pore solution)

Modelling: liquid phases of CSA-1

20

0.01

0.1

1

10

100

1 10 100 1000

concentration mmol/l

time / h

Ca

Na S

OH

K Al

lines: modellingdata points: experimental

Modelling: solid and liquid phase of CSA-2

Up to now, the hydration has been modelled only with insufficient accuracy (poor correlation with experimental data, especially with pore solution composition),

mainly due to:

some uncertain thermodynamic data (e. g. CAH10)kinetic restraints (slow dissolution of anhydrite)

=> work in progress

21

Conclusion – hydration of CSA cements (I)

Solid phases:ettringite formation until CaSO4 is (almost) used, then monosulfate occursAl(OH)3 gel forming by-product of hydrationwith C2S als minor phase (CSA-2) strätlingite forms after 28 ddissolution of calcium sulfates hindered

Pore solution:first hours: dominated by alkalis, calcium and sulfatepH 10.5 - 10.8when CaSO4 (almost) used: mainly alkalis, OH and AluminumpH 12.5 - 12.8 after 28 d

22

Conclusion – hydration of CSA cements (II)

Microstructure:CSA-1: quite dense already after 18 hours,very dense after 28 days despite high w/c of 0.72CSA-2: dense, but inhomogeneouslarge strätlingite crystals after 28 days

Application:binder for various applications (e. g. „plaster“boards)acceleration of OPC or slag hydration in ternary blends also incorporatng gypsum or anhydriteshrinkage reducing / expansive agentwaste encapsulation

23