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

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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

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

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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$