Seville 97

LAFARGE

Seville 97 

D. Sorrentino - P. Barriac

SO3 in cement

- P. D. Sorrentino Barriac

Aluminates Alumino-ferrites

Alite

10 

Belite

Free lime

Alite

10 µm

Alkali Sulfates

Aluminates

Hydrates formed after 30 seconds on :

C3A

C3S

What happened ???

CA 3

+

C

+

H

=

C4AHn

Aluminate “FLASH” set, + disturbed C3S set + decreased strength CA 3

C3S

The need to Neutralize C3A by coating of Ettringite C3A 3CaSO4 32H2O

To be supplied C3A + 3 C + 3 S + 32 H

instantaneously

rapid solubility, proximity, pH

in a watertight shell

Reactive C3A

C3S

Watertight Ettringite shell

3 C

C3S

H2O

C3A

pH

3 S Free CaO

In general, C3A and calcium sulfate are reactive...

but their “reactivity” can vary

Their reactivity depends on : Aluminates and alumino-ferrites Crystalline impurities Cristallinity Fineness Percentage Surface reactivity

Their reactivity depends on : Aluminates and alumino-ferrites Crystalline impurities Cristallinity Fineness Percentage Surface reactivity

Their reactivity depends on : Aluminates and alumino-ferrites

Calcium sulfates

Crystalline impurities

Crystalline impurities

Cristallinity

Anhydrite 2,8g/l Gypsum 2 g/l Hemihydrate8 g/l

Fineness

Fineness

Percentage

Percentage

Surface reactivity

Surface reactivity

Aluminates and alumino-ferrites Reactive

Calcium sulfates

+ + + +

Non Reactive

Non Reactive Reactive

Non Reactive Non Reactive

Reactive

Why?

Reactive

BAD

BAD

GOOD

GOOD

Aluminates and alumino-ferrites Reactive

Calcium sulfates

+ + + +

Non Reactive

Non Reactive Reactive

Non Reactive Non Reactive

Reactive

Why?

Reactive

BAD

BAD

GOOD

GOOD

Aluminate “flash” set Stiffening due to Ettringite needles

Plaster set Stiffening due to Ettringite needles Stiffening due to Syngenite needles

Aluminates and alumino-ferrites Reactive

Calcium sulfates

+ + + +

Non Reactive

Non Reactive Reactive

Non Reactive Non Reactive

Reactive

Why?

Reactive

BAD

BAD

Aluminate “flash” set Stiffening due to Ettringite needles

Plaster set Stiffening due to Ettringite needles Stiffening due to Syngenite needles

GOOD

Weak level of Ettringite and micro-needles

GOOD

Formation of watertight Ettringite shell

Ettringite needles

Syngenite CaSO4, K2SO4, H2O

Gypsum

C3A reactivity

Flash set Stiffening of ettringite needles

Formation of blocking ettringite coating

C3A

ettringite needles

C3 A

C4AHn

Small amount of ettringite micro needles produced

ettringite coating Plaster set Stiffening of ettringite needles Syngenite stiffening

C3 A

C3 A

micro crystalline ettringite

syngenite

ettringite needles

gypsum

Calcium sulfate reactivity

C3S

Watertight Ettringite shell

3 C

C3S

H2O

C3A

pH

3 S Free CaO

Alkaline S CaSO4 0.5H2O CaSO4 2H2O CaSO4

C3S

Watertight Ettringite shell

3 C

C3S

H2O

C3A

pH

3 S Free CaO

CaSO4 0.5H2O

Alkaline S

2CaSO4, K2SO4

CaSO4 0.5H2O

CaSO4 2H2O

CaSO4 2H2O

CaSO4 and C3S

CaSO4

C3S

Watertight Ettringite shell

3 C

C3S

H2O

C3A

sol. alum. Na K

pH

3 S Free CaO

CaSO4 0.5H2O

Na K

2CaSO4, K2SO4

sol. Ca++

Alkaline S CaSO4 0.5H2O

CaSO4 2H2O

CaSO4 2H2O

CaSO4 and C3S

CaSO4

To get a WATERTIGHT ETTRINGITE SHELL :

High pH respect the balance of:

}

aluminates sulfates calcium

quantity reactivity

This will allow you to better control :

workability setting strengths

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