calcium aluminate cements - cours de génie civil

1

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

2

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

3

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

5

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

6

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

8

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

9

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

10

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

11

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$