Calcium Aluminate cements - Cours de Génie Civil
Transcript of Calcium Aluminate cements - Cours de Génie Civil
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Calcium Aluminate cements
Chemistry
calciumsilicatesC3S, C2S
SiO2
CaO Al2O3
Portland cements
calciumaluminatecements
slags
calciumaluminates
CA
MagnesiumPotassium
rest
Sodium
CaIron
Aluminium
Silicon
Oxygen
Portland cementsCAC
>4 xcostcost
< 1/1000volumevolume
Special CementsSpecial Cements• do not compete in applications where Portland cement performs well• applications justified by special properties
Calcium Aluminate Cements
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Range of alumina content
~40%0% Al2O3 100%~80%
fusion
sintering
‘standard’grades
40 - 50%examples
Ciment Fondu Lafarge©
Secar© 51
high Al2O3 contentrefractory grades70 - 80%examplesSecar© 71Secar© 80
Flexible – used in two form
CAC
“PURE” form, mortar, concrete
component of a “FORMULATED
BLEND”
« pure form »
• Normal setting
• Rapid hardening
• Resistance to chemical erosion(particularly induced by bacteria)
• Resistance to abrasion(with synthetic aggregate)
DIRECT CONSEQUENCE OF CHANGED MICROSTRUCTURAL FORMATION
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Hydration of CACs
6CA + 6060HH22OO
6CAH10
3C2AH8 + 3AH3 + 2727HH22OO
2C3AH6 + 4AH3 + 3636HH22OO
T < 15°C
T > 70°C
CO
NVER
SION
time and/or tem
perature
AH3 is often present as poorly crystalline gel at lower temps
Limitations due to microstructural developement
0
10
20
30
0 60 120 180 240minutes
mM
ol/l
CaOSiO2 x 1000
HYDRATION
Consequences
• Asymptotic strength gain:
• Difficult to fill in pores - vulnerability to deterioration
• Unhydrated material remains
1 day 3 day 28 day
x2
x2
4
0
10
20
30
0 60 120 180 240minutes
mM
ol/l
CaOAl2O3
Formation of hydrates throughout spaceHYDRATION
7h35 8h45
In situ observation inX-ray microscope, Berkeley
CAC concrete microstructure
7days20°C
7days70°C
W/C = 0.4 W/C = 0.7
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Hydration of CACs
6CA + 6060HH22OO
6CAH10
3C2AH8 + 3AH3 + 2727HH22OO
2C3AH6 + 4AH3 + 3636HH22OO
T < 15°C
T > 70°C
CO
NVER
SION
time and/or tem
perature
AH3 is often present as poorly crystalline gel at lower temps
Hydration at w/c ~ 0.7
cement
water
cementunreactive phases
pores
cementunreactive phases
pores
unconvertedhydrates
converted hydrates
Hydration at w/c ~ 0.4
water
pores
cementunreactive phases
pores
unconvertedhydrates converted
hydrates
cementcement
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Strength Development
PORTLAND w/c~0.4CAC w/c~0.4, ~20°C, no self heating
CAC w/c~0.4, with self heating
CAC, w/c>~0.7,~20°C, no self heating
CAC, w/c>~0.7, with self heating
STR
ENG
TH
TIMEhours days months years
Strength mortars 40 x 40 x 160 mm
0
20
40
60
80
100
120
Com
pres
sive
stren
gth
(MPa
)
7h 31h 31h7h 7h7d 7d35d 35d8d3m 3m 3m40°C
3m20°C
3m8d 24h
S41 at 20°C S41 at 40°C S41 at 70°C
S41ALAG
OPC at 20°C
Source Lamour et al in Calcium Aluminate Cements 2001
Guidlines for good performance
• W/C ~ < 0.4
• Cement content > ~ 400 kg / m3
• Minimum cube strength ~ 40 MPa
• Depends also on aggregate type, grading, etc
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Long term performance
• Porosity ~4%• low penetration of
sulfates and chlorides
Halifax harbour (w/c ~ 0.6)1930
2001
Resistance to corrosion induced by bacteria
Sewage Networks– an aggressive environment
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MANHOLE
SEPTICEFFLUENT
EFFLUENT
- LONG RETENTION TIMES-- HIGH TEMPERATURES- SULFATE RICH EFFLUENT- LOW VENTILATION- TURBULENCE
H2S
H2SH2S
turbulence favours the release of H2Swhich is depositedon the upper surfacesby convection
HH22SS
BACTERIA WHICH REDUCE SUFATES
SO4--
C
H2SHS-
S2-
ACID ACID
CONCRETE WALLSCONCRETE WALLS
HH22SOSO44
Aerobic bacteriaAerobic bacteria((ThiobacilleThiobacille))
OO22
HH22SS
SS0
Generation of sulphuric acid by bacteria
Areas of maximum corrosion
H2S
Bacterialactivity
123456789 pH
T. Thiooxidans
Source: University of Hamburg
Increasingacidity
T. Neopolitanus
T. Tioparus
T. Intermedius
T. Novellus
Process of colonisation:
different types establish activity and reduce pH for succeeding types
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CACmax errosion
< 10 mm
PORTLANDcompletely eroded
> 60 mm
Sewage linings12 year field trial, South Africa
Installed cost 10-20% higher
Corrosion resistance
Corrosion resistancehigh amounts of alumina present
Below pH 4, no more protective layer; but consumption of H+ ions, increase of the neutralisation capacity.
Con
cent
ratio
n m
ol/l
Al(OH)3
Al(OH)4-
Al(H2O)+++
4 8 10 pH
10-3
7 .10-3
Between pH 4 and 10, alumina gel, plays role of a protective layer
pHpH
daysdays
0
1
2
3
4
5
6
100 150 200 250
PortlandPortland
CACsCACs
Alumina suppressesgrowth of bacterialimits pH decrease
Ductile iron pipes lined with CAC are usually steam cured to reduce shrinkage
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Resistance to errosion
Hydraulic structures
Ores passes
Toll lanes
Erosion resistance
CAC with synthetic aggregate
0
1
2
3
4
5
Graniteslab
UsualFondu /ALAG
concrete(69 MPa)
Very highstrengthFondu /ALAG
Concrete(133 MPa)
Glass Very highstrength
OPCconcrete
(135 MPa)
50 MPaOPC +SilicaFume
Concrete
20-30 MPaOPC
Concrete
eros
ion
inde
x (g
lass
= 1
)
Excellent interfacial bondbetween paste and aggregate
CAC – PCconcretes ofcomparable strength
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Formulated Products
CAC PC
C$gypsum
anhydriteplaster ZONE 1
Rapid setting and
hardening
ZONE 2Rapid setting, hardening and
moisture reduction, « drying »
Relative weights
Self levelling floor screeds (zone 2)
Without CAC:Walk - 1 dayCarpet- 28 days +
With CAC:Walk - 4 hrsCarpet- 24 hrs
Formulated Products
CAC PC
C$gypsum
anhydriteplaster ZONE 1
Normal PC products +
extra ettringite
ZONE 2Ettringite
+« alumina gel »
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Changed pattern of strength development
0
20
40
60
0 7 14 21 28 days
Com
pres
sive
Str
engt
h (M
Pa)
All formulations at w/c = 0.35
CAC PC
C$