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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
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