IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 1 Potential of calcium...
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Transcript of IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 1 Potential of calcium...
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 1
Potential of calcium sulfoaluminate cements to immobilize ZnCl2-containing wastes
Stéphane BERGER 1, Céline CAU DIT COUMES 1, Patrick LE BESCOP 2, Denis DAMIDOT 3
1 CEA Marcoule, Laboratory for Waste Immobilization2 CEA Saclay, Laboratory for Concrete and Clay Investigation3 Ecole des Mines de Douai, Civil & Environmental Engineering Department
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 2
Overview
• Background
• Research objectives and experimental strategy
• Experimental results
• Conclusion, prospects and work plan
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 3
Cementation is a widely applied process for the conditioning of LLW and ILW radioactive wastes
ProcessProcess
simple inexpensive
Calcium silicate Calcium silicate cementscements
easy supply good mechanical strength compatibility with aqueous wastes good self-shielding high alkalinity precipitation of many radionuclides
Encapsulated ion exchange resins
Cemented waste introducedinto a container
500 µm
BUT…
Some waste components may chemically react with cement phases or mixing water
Possible reduction in the quality of the solidified waste form
1. Background
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 4
Incineration of technological wastesincluding neoprene and P.V.C
Ashes with substantial amounts of soluble ZnCl2
Ex: Zn content = 29.5% by massSoluble Zn concentration in a suspension
(L/S 2.5 mL/g) = 22.4 g/L (0.34 mol/L)
Deleterious effects on Portland cement• setting is strongly delayed and can be inhibited at high zinc chloride loadings (Arliguie 1985)• hydration and hardening are slowed down (Ortego 1989).
0
5
10
15
20
25
30
35
0 20 40 60 80 100 120 140
Time (h)
Te
mp
era
ture
ris
e (
°C)
Fro
m C
au
-dit-
Co
ume
s an
d a
l, IC
CC
20
07> 4 days
Portland Cement with 0,1 mol/L ZnCl2
Portland Cement without ZnCl2
< 24 h
Precipitation of β2-Zn(OH)2 or Zn2Ca(OH)6.2H2O over the cement
grains has been postulated to explain the delay in cement hydration
(Arliguie 1985).
1. Background
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 5
How to deal with adverse cement waste – interactions ?
1. Background
Treatment of the waste in order to convert interfering species into compounds stable in cement
(a) Precipitation as hopeite (Zn3PO4.2H2O) by addition of withocklite
(b) Precipitation as a silicate form (hemimorphite 2ZnO.SiO2.H2O, metasilicate ZnSiO3 or orthosilicate Zn2SiO4) by addition of sodium silicate
(c) Precipitation as calcium hydroxyzincate (CaZn2(OH)6.2H2O) by addition of calcium hydroxide
- (a) and (b) too slow at 25 or 60°C for an industrial application (Drouin, 1994)
- (c) max. (Zn/Cement) ratio : 3.4%- Complexity and cost of the process increased
BUT :
To select a binder which would show an improved compatibility with the waste, such as
a calcium sulfoaluminate cement
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 6
Calcination at 1300-1350°C
clinker cement
Gypsum (from 0 to 30%)
Co-grinding
Manufacturing process of calcium sulfoaluminate cements
Advantages of CSA cements as compared to OPC :
reduced energy consumption during manufacturing
low CO2 emission during manufacturing
high-early strength development
Limestone, claybauxitegypsum
(industrial residues)
1. Background
0.50.52.63.16.61671QuartzCSPericlaseC12A7C3FTC2SC4A3S
Minerals (% weight)
0.50.52.63.16.61671QuartzCSPericlaseC12A7C3FTC2SC4A3S
Minerals (% weight)
Composition of the clinker used in this study :
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 7
Two main features of CSA cement hydration
1. Background
Hydrates repartition depends on the amount of gypsum
mixed with the clinker
0102030405060708090
100
% gypsum
% h
ydra
tes
Mo
difi
ed
fro
m G
lass
er
and
al,
CC
R 2
00
1
AH3
Ettringite
Calcium monosulfoaluminatehydrate
CSHGypsum
Rapid heat production
20
3040
50
6070
80
0 10 20 30 40Time (h)
Tem
pera
ture
(°C
)
Portland cement
CSA cement
semi-adiabatic Langavant calorimetry
Both influences of temperature and gypsum content have to be studied
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 8
Overview
• Background
• Research objectives and experimental strategy
• Experimental results
• Conclusion
• Prospects and work plan
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 9
2. Research objectives and experimental strategy
Objectives : - to assess the potential of CSA cement to immobilize ZnCl2-containing wastes- to progress in the understanding of CSA cement hydration
Investigation of the influence of three parameters
the gypsum content of the cement
the thermal evolution of the solidified waste form
the ZnCl2 concentration of the mixing solution
on the rate of hydration and products formed
the properties of the solidified waste forms (porosity, mechanical strength, dimensional variations, evolution under leaching)
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 10
2. Research objectives and experimental strategy
Cement prepared by mixing clinker with variable gypsum contents (from 0 to 35 %)
Mixing solution
demineralized water + possible dissolution of a ZnII salt ([Zn2+]max = 0.5 mol/L)
2 kinds of materials
Mortars (W/C = 0.55, S/C = 3)
29-0285 (I) - Strat lingite, syn - Ca2Al2SiO7·8H2O - Y: 32.73 % - d x by: 1. - W L: 1.5406 - Hexagonal (Rh) -
46-1045 (*) - Quartz, syn - SiO2 - Y: 49.88 % - d x by: 1. - W L: 1.5406 - Hexagonal - a 4.91344 - b 4.91344
05-0586 (*) - Calcite, syn - CaCO3 - Y: 43.64 % - d x by: 1. - WL: 1.5406 - Hexagonal (Rh) - a 4.98900 - b 4Operations: Y Scale Add 20 | Smooth 0.105 | Strip kAlpha2 0.500 | Import
c:\michel\bpHT1p.RAW - File: bpHT1p.RAW - Type: 2Th/Th locked - Start: 10.000 ° - End: 60.000 ° - Step:
Operations: Y Scale Add 20 | Y Scale Mul 0.333 | Smooth 0.105 | Strip kAlpha2 0.500 | Import
Cendres Volantes - File: Cv.raw - Type: 2Th/Th locked - Start: 10.000 ° - End: 60.000 ° - Step: 0.020 ° - Ste
Operations: Y Scale Mul 0.333 | Smooth 0.105 | Strip kAlpha2 0.500 | Import
métakaolin - File: mk.RAW - Type: 2Th/Th locked - Start: 10.000 ° - End: 60.000 ° - Step: 0.020 ° - Step tim
Lin
(Cou
nts)
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
160
2-Theta - Scale
11 20 30 40 50 60
XRD DSC / TGA SEM
Langavant calorimetry Dimensional stability Mechanical strength
Pastes (W/C = 0.55)
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 11
2. Research objectives and experimental strategy
20
40
60
80
0 2 4 6 8 10 12 14 16 18 20Time (h)
Te
mp
era
ture
(°C
)
20°C curing
semi-adiabatic curing
After elaboration, the samples were either cured in a sealed plastic bag at 20°Cor submitted to a thermal cycle in an oven.
Thermal cycles: temperature profiles defined from the temperature evolution of mortars under semi-adiabatic conditions and applied on investigated samples to reproduce the temperature rise and decrease which may occur in a massive structure during cement hydration
20
40
60
80
0 1 2 3 4 5Time (h)
Te
mp
era
ture
(°C
)
temperature profile applied to the paste
Temp. in paste
Temp. in mortar
20% gypsum, 0.5 mol/L ZnCl2
Temperature profiles were defined by interpolating in 20-40 segments the curves recorded on mortars.
Some corrections were required to keep the inner temperature of the
paste near that of the mortar under semi-adiabatic curing.
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 12
Overview
• Background
• Research objectives and experimental strategy
• Experimental results
• Conclusion
• Prospects and work plan
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 13
3. Experimental results
3.1 Hydration of reference materials : influence of the gypsum content
0
50
100
150
200
250
300
350
400
450
500
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Time (h)
Cu
mu
late
d h
eat
(J/
g o
f ce
me
nt)
0%2% 1%3%
5%7%
10%
MortarsNo ZnCl2 additionGypsum: 0-10%
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 14
3. Experimental results
3.1 Hydration of reference materials : influence of the gypsum content
0
50
100
150
200
250
300
350
400
450
500
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Time (h)
Cu
mu
late
d h
eat
(J/
g o
f ce
me
nt)
0%2% 1%3%
5%7%
10%
MortarsNo ZnCl2 additionGypsum: 0-10%
Two effects were observed when the gypsum content increased from 0 to 10%:• the induction period decreased strongly, especially at low gypsum contents,
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 15
3. Experimental results
3.1 Hydration of reference materials : influence of the gypsum content
0
50
100
150
200
250
300
350
400
450
500
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Time (h)
Cu
mu
late
d h
eat
(J/
g o
f ce
me
nt)
0%2% 1%3%
5%7%
10%
MortarsNo ZnCl2 additionGypsum: 0-10%
Two effects were observed when the gypsum content increased from 0 to 10%:• the induction period decreased strongly, especially at low gypsum contents,• the cumulated heat output was reduced when the gypsum content exceeded 5%.
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 16
3. Experimental results
0
50
100
150
200
250
300
350
400
450
500
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Time (h)
Cu
mu
late
d h
eat
(J/
g o
f ce
me
nt)
0%
10%
20%
35%
Beyond a gypsum content of 10%, heat output and induction period did not vary anymore.
MortarsNo ZnCl2 additionGypsum: 10-35%
3.1 Hydration of reference materials : influence of the gypsum content
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 17
3. Experimental results
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 5 10 15 20 25
Time (h)
Re
ac
ted
ye
elim
ite
/ 5
min
(%
)
0% gypsum
10% gypsum
20% gypsum
35% gypsum
Without gypsum:
• yeelimite started to react much later, in agreement with the long induction period previously observed.
• Yeelimite was almost totally depleted at 24 h while with gypsum, 10 to 20% were still unreacted.
(based on XRD relative peak areas)
3.1 Hydration of reference materials : influence of the gypsum content
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 20
3. Experimental results
3.1 Hydration of reference materials : products formed
What about the influence of the thermal cycle ?
- Precipitation of calcium monosulfoaluminate hydrate promoted by a low gypsum content and by the thermal cycle.- CAH10 destabilized by an increase in the gypsum content and/or temperature.
2-Theta - Scale
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
E
E
E
M
M
EE A
A
CA
H 10
CA
H 10
2 Theta scale2-Theta - Scale
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
E
E
E
M
M
EE A
A
CA
H 10
CA
H 10
2 Theta scale
Gypsum = 0%
- Curing at 20°C- Thermal cycle
2-Theta - Scale
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
E
E
M +
E
E
E
MA
A
2 Theta scale2-Theta - Scale
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
E
E
M +
E
E
E
MA
A
2 Theta scale
Gypsum = 10%
- Curing at 20°C- Thermal cycle
Time = 24 hCement pastesNo ZnCl2 addition
E: C3A.3CS.H32M: C3A.CS.H12Y: C4A3SA: AH3
E: C3A.3CS.H32M: C3A.CS.H12Y: C4A3SA: AH3
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 21
3. Experimental results
3.1 Hydration of reference materials : products formed
What about the influence of the thermal cycle ?
2-Theta - Scale
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
E
EE
E
EG
M +
E
E
GE
E
2-Theta - Scale
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
E
EE
E
EG
M +
E
E
GE
E
2 Theta scale
With a gypsum content > 20%, the thermal cycle had no significant effect on the mineralogy: gypsum stabilized ettringite in spite of the temperature increase.
Gypsum = 20%
- Curing at 20°C- Thermal cycle
Time = 24 hCement pastesNo ZnCl2 addition
2 Theta scale2-Theta - Scale
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Gypsum = 35%
- Curing at 20°C- Thermal cycle
E: C3A.3CS.H32M: C3A.CS.H12G: CSH2Y: C4A3SA: AH3
E: C3A.3CS.H32M: C3A.CS.H12G: CSH2Y: C4A3SA: AH3
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 22
3. Experimental results
3.2 Hydration of ZnCl2-containing materials
• A retardation was observed, especially with a gyspum-free cement, but its magnitude was much smaller than that recorded with OPC.
• Setting inhibition was never observed: setting occurred in less than 2h with gypsum, and in less than 24h without it.
0
50
100
150
200
250
300
350
400
450
500
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
Time (h)
Cu
mu
late
d h
eat
(J/g
of
cem
ent) 0.5 mol/l
With gypsum Without gypsum
0 mol/l
0 mol/l
0.5 mol/l
0
50
100
150
200
250
300
350
400
450
500
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
Time (h)
Cu
mu
late
d h
eat
(J/g
of
cem
ent) 0.5 mol/l
With gypsum Without gypsum
0 mol/l
0 mol/l
0.5 mol/l
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 23
3. Experimental results
3.2 Hydration of ZnCl2-containing materials
0
50
100
150
200
250
300
350
400
450
500
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
Time (h)
Cu
mu
late
d h
ea
t (J
/g o
f c
em
en
t)
0
50
100
150
200
250
300
350
400
450
500
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
Time (h)
Cu
mu
late
d h
ea
t (J
/g o
f c
em
en
t)
0
50
100
150
200
250
300
350
400
450
500
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
Time (h)
Cu
mu
late
d h
ea
t (J
/g o
f c
em
en
t)
CaCl2
ZnCl2
Zn(NO3)2
Ca(NO3)2
CaSO4ZnSO4
acceleration Zn2+ > Ca2+ delay
Salt concentration : 0.5 mol/l
0% gypsumH2O
Temperature of the mixing solution: 20°C
What about the influence of the zinc cation ?
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 24
3. Experimental results
3.2 Hydration of ZnCl2-containing materials
What about the influence of the Zinc counter-ion ?
0
50
100
150
200
250
300
350
400
450
500
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
Time (h)C
um
ula
ted
he
at
(J/g
of
ce
me
nt)
0
50
100
150
200
250
300
350
400
450
500
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
Time (h)
Cu
mu
late
d h
ea
t (J
/g o
f c
em
en
t)
CaCl2
Zn(NO3)2
CaSO4
acceleration SO42- >> 2 NO3
- > 2 Cl- delaySalt concentration : 0.5 mol/l
Chloride anions strongly slowed down hydration but zinc cations accelerated it!
Temperature of the mixing solution: 20°C
ZnSO4
Ca(NO3)2
ZnCl2
0% gypsumH2O
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 25
3. Experimental results
3.2 Hydration of ZnCl2-containing materials
0
50
100
150
200
250
300
350
400
450
500
0 2 4 6 8 10 12 14 16
Time (h)
Cu
mu
late
d h
eat
(J/g
of
cem
ent)
H2O ZnCl2
CaCl2
0
50
100
150
200
250
300
350
400
450
500
0 2 4 6 8 10 12 14 16
Time (h)
Cu
mu
late
d h
eat
(J/g
of
cem
ent)
H2O ZnCl2
CaCl2
20% gypsum
With gypsum in the binder, similar rates of hydration with CaCl2 and ZnCl2 solutions.
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 26
3. Experimental results
AFm phases
Calcium monosulfoaluminate hydrate : C3A.CaSO4.12H2O
Friedel’s salt : C3A.CaCl2.12H2O
Kuzel’s salt : C3A.1/2CaSO4.1/2CaCl2.12H2O
3.2 Hydration of ZnCl2-containing materials : products formed at early age
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 27
3. Experimental results
3.2 Hydration of ZnCl2-containing materials : products formed at early age
Hydrates formed (7 d)
0% gypsum
Curing at 20°C
CAH10 (+) Calcium monosulfoaluminate hydrate (++)
Ettringite (+) Gibbsite (tr)
Thermal cycle Calcium monosulfoaluminate hydrate (+++)
Gibbsite (+)
Without ZnClWithout ZnCl22
- Destabilization of CAH10
- Precipitation of calcium monosulfoaluminate hydrate favoured instead of ettringite
Hydrates formed (7 d)
0% gypsum
Curing at 20°C
CAH10 (tr)
Calcium monosulfoaluminate hydrate (+) Friedel’s salt (+) Kuzel’s salt (++)
Ettringite (++) Gibbsite (tr)
Thermal cycle
Calcium monosulfoaluminate hydrate (++) Friedel’s salt (+) Kuzel’s salt (++)
Ettringite (+) Gibbsite (+)
With ZnClWith ZnCl22
- Destabilization of CAH10
- Precipitation of calcium monosulfoaluminate hydrate favoured instead of ettringite- No influence on the Friedel’s and Kuzel’s salts
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 28
3. Experimental results
3.2 Hydration of ZnCl2-containing materials : products formed
Hydrates formed
0% gypsum 20% gypsum
Curing at 20°C
CAH10 (+) Calcium monosulfoaluminate hydrate (++)
Ettringite (+) Gibbsite (tr)
Calcium monosulfoaluminate hydrate (tr) Ettringite (+++)
Gibbsite (tr)
Thermal cycle Calcium monosulfoaluminate hydrate (+++)
Gibbsite (+)
Calcium monosulfoaluminate hydrate (tr) Ettringite (+++)
Gibbsite (+)
Without ZnClWithout ZnCl22
Almost no influence on the stability of ettringite
Hydrates formed 0% gypsum 20% gypsum
Curing at 20°C
CAH10 (tr) Friedel’s salt (+) Kuzel’s salt (++) Ettringite (++) Gibbsite (tr)
Calcium monosulfoaluminate hydrate (tr) Ettringite (+++)
Gibbsite (tr)
Thermal cycle
Calcium monosulfoaluminate hydrate (++) Friedel’s salt (+) Kuzel’s salt (++)
Ettringite (+) Gibbsite (+)
Calcium monosulfoaluminate hydrate (tr) Ettringite (+++)
Friedel’s salt (++) Gibbsite (+)
With ZnClWith ZnCl22
Precipitation of Friedel’s salt
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 29
3. Experimental results
3.2 Hydration of ZnCl2-containing materials : products formed
Where are the zinc cations?
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 30
3. Experimental results
Experimental device
constant temperature (20°C) and pH stirring and injection of N2 into the cells to avoid carbonation samples protected from lateral attack by polymer coating renewal of the solution at regular intervals, in connection with the quantity of added HNO3
N2 gas
pH regulator
pH meterAutomatic supplying
pump
Thermoregulated water
Nitric acid0.5 M
Reactor
Leaching by pure water at fixed pH (7) and temperature (20°C)
4 months of leaching – 22 renewals : [Zn] in the leachates below 0.1 mg/L (detection limit of the ICP method)
Zinc is well insolubilized
3.2 Hydration of ZnCl2-containing materials : products formed
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 31
3. Experimental results
3.2 Hydration of ZnCl2-containing materials : products formed
Investigation of simplified systems
Ettringite + ZnCl2 solution
Partial conversion of ettringite into CaZn2(OH)6.2H2O
No clear evidence of Zn insertion into ettringite
Calcium monosulfoaluminate hydrate + ZnCl2 solution
Total conversion into ettringite + Friedel’s salt + CaZn2(OH)6.2H2O + Zn4Al2(OH)12CO3.xH2O
No clear evidence of Zn insertion into ettringite or Friedel’s salt
Friedel’s salt
Complementary work is needed
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 32
3. Experimental results
3.3 Properties of hardened mortars : porosity
0
5
10
15
20
25
0% 10% 20%Gypsum content
To
tal
po
rosi
ty(
%)
Curing at 20°C, [ZnCl2] = 0M
0
5
10
15
20
25
0% 10% 20%Gypsum content
To
tal
po
rosi
ty (
%)
28 days 90 days
Total porosity increased with the gypsum content.
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 33
3. Experimental results
3.3 Properties of hardened mortars : porosity
28 days 90 days
Curing at 20°C, [ZnCl2] = 0M Thermal cycle, [ZnCl2] = 0M
0
5
10
15
20
25
0% 10% 20%Gypsum content
To
tal
po
rosi
ty(
%)
0
5
10
15
20
25
0% 10% 20%Gypsum content
To
tal
po
rosi
ty (
%)
No significant influence of the thermal cycle on the total porosity
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 34
3. Experimental results
3.3 Properties of hardened mortars : porosity
Curing at 20°C, [ZnCl2] = 0M Thermal cycle, [ZnCl2] = 0M Thermal cycle, [ZnCl2] = 0.5M
0
5
10
15
20
25
0% 10% 20%Gypsum content
To
tal
po
rosi
ty(
%)
0
5
10
15
20
25
0% 10% 20%Gypsum content
To
tal
po
rosi
ty (
%)
28 days 90 days
Adding ZnCl2 slightly decreased the porosity of gypsum-free mortars.
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 35
3. Experimental results
3.3 Properties of hardened mortars : compressive strength
0
10
20
30
40
50
60
0 20 40 60 80 100 120 140 160 180
Time (days)
Rc
(MP
a)
Gypsum : 0% 10% 20%
Mixing solution = waterNo thermal cycle
gypsum addition (10, 20%) decrease in the
compressive strength
0
10
20
30
40
50
60
0 40 80 120 160 200 240 280 320 360
Time (days)
Rc
(MP
a)
Gypsum : 0% 10% 20%
Mixing solution = waterThermal cycle
Thermal cycle strength loss without gypsum only
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 36
3. Experimental results
3.3 Properties of hardened mortars : compressive strength
0
10
20
30
40
50
60
0 40 80 120 160 200 240 280 320 360
Time (days)
Rc
(MP
a)
20% gypsum – ZnCl2
0% gypsum – ZnCl2
20% gypsum – H2O
0% gypsum – H2O
Mixing solution = water or ZnCl2 0.5 MThermal cycle
ZnCl2 addition strength increase, especially with gypsum (20%)
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 37
0
500
1000
1500
2000
2500
3000
3500
0 20 40 60 80 100 120Time (days)
Len
gth
ch
ang
e (µ
m/m
)
0% gypsum
0% gypsum - thermal cycle
10% gypsum
10% gypsum - thermal cycle
20% gypsum
20% gypsum - thermal cycle
3. Experimental results
3.3 Properties of hardened mortars : length change under wet curing
Swelling was increased by the thermal cycle for a gypsum-free cement only
Mixing solution = water
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 38
3. Experimental results
3.3 Properties of hardened mortars : length change under wet curing
0
500
1000
1500
2000
2500
3000
3500
0 20 40 60 80 100 120Time (days)
Leng
th c
hang
e (µ
m/m
)
0% gypsum - H2O
0% Gypsum - ZnCl2
20% gypsum - H2O
20% Gypsum - ZnCl2
Swelling was increased by ZnCl2 for a gypsum-free cement only
Mixing solution = water or ZnCl2 0.5 MThermal cycle
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 39
Overview
• Background
• Research objectives and experimental strategy
• Experimental results
• Conclusion
• Prospects and work plan
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 40
4. Conclusions
CSA cements showed a much better compatibility with zinc chloride than OPC: hydration was slightly slowed down but setting inhibition was never observed, even at high Zn concentrations (0.5 mol/L).
Adding a 20% gypsum content to cement was beneficial in the presence of ZnII ions increase in the compressive strength decrease in expansion under wet-curing stabilization of ettringite, even at high temperature (80°C)
Chloride anions induced a strong retardation of a gypsum-free cement, but this effect was balanced by the accelerating effect of zinc cations and sulfate anions.
In the presence of zinc chloride, the mineralogy observations revealed the precipitation of chloro-AFm phases such as Kuzel’s and Friedel’s salts.
The thermal history of the samples proved to be a key parameter since a temperature rise accelerated the rate of hydration and modified the nature of the hydrates, particularly with a low gypsum content.
IAEA CRP meeting, Romania, 24-28 November 2008 – C. CAU DIT COUMES 41
5. Prospects and work plan
Task Year 1 Year 2 Year 3 Investigation of CSA hydration by : ZnCl2-containing solutions B(OH)4
- -containing solutions Investigation of Zn-containing hydrates: AFt and AFm phases Hydrotalcite-like phases
Investigation of the durability of solidified waste forms (leaching by pure water)
CSA cements+ ZnCl2
Characterization of: - the mineralogy of older samples- the microstructure of hardened cement pastes as a function of various parameters (hydration degree, compositions of cement and mixing solution, temperature)
Investigation of leaching by pure water (experiments under way):- analysis of the degraded solid and leachates- modelling of leaching using a reactive transport model
CSA cements+ B(OH)4
-Investigation of the influence of B(OH)4
- ions on the hydration process of CSA cements