hydration of “low ph” cements - ttu cae network blogs

1Materials Science & Technology

Barbara Lothenbach1, Erich Wieland2, B. Schwyn3,

R. Figi1, D. Rentsch1

1 Empa, Laboratory for Concrete & Construction Chemistry, Switzerland 2 PSI, Laboratory for Waste Management, Switzerland

3 Nagra, National Cooperation for the Disposal of Radioactive Waste, Switzerland

Hydration of “low pH” cements


Objectives

�Hydration of

� OPC: CEM I 42.5 HS

� ESDRED:

CEM I 42.5 N + 40% silica fume + accelerator

� LAC: CEM III/B 42.5 L + 10% nanosilica

Cementitious materials used in field experiments

- composition of the pore solution- mineral composition of the cement matrix

- comparison


Cement-Clay interface

Borehole 1 (350 mm)

EDZ

OPA

LAC

ESDRED

OPC

Side view Top view

Cement

OPA


OPC: CEM I 42.5 R HS(g/100g)

CaO 58.8 alite 31

SiO2 20.6 belite 36

Al2O3 3.9 aluminate 1.6

Fe2O3 5.2 ferrite 16

MgO 4.6 MgO 4.6

Na2O 0.27 CaCO3 3.1

K2O 0.75 CaSO4 5.1

CO2 1.4 Na2O 0.22

SO3 3.5 K2O 0.27

CaOfree 0.71 Na2SO4 0.12

LOI 2.3 K2SO4 0.89

w/c = 0.8


clinker

Hydration (Lothenbach and Winnefeld, 2006)

clinker

EttringitePortlanditeC-S-Halite (C3S), belite (C2S)

aluminate(C3A), ferrite C4AF)


All parameters (Ki, Ni) from

Parrot and Killoh (1984)

Modeling - Dissolution

( )( )( )

( )( )

( ) 3

1

1

11

1

)1ln(1

3

3/1

3/22

1

1

1

Ntt

t

tt

Nttt

KR

KR

N

KR

α

α

α

αα

−×=

−−

−×=

−−−= −

Empirical Approach: Parrot and Killoh (1984)

g/1

00 g

0

10

20

30

40

50

60

70

0 0.1 1 10 100time (days)

//

alite: C3S

ferrite:C4AF

belite: C2S

aluminate:C3A

Cement specific input: surface area, w/c

α: degree of hydration


K2SO4

Na2SO4

hemihydrateCaO

Thermodynamic Modeling

C3S C2S C3A C4AF

Cements

I clinkers (slowly soluble)

II soluble solids

gypsumanhydrite

calcite

K2ONa2OMgO

III water

H2O

Ettringite

Portlandite

C-S-H

AFm

Hydrotalcites, ...

Ca2+

CaOH+ Speciation in solutionCaSO4

0

Thermodynamic modeling


Modeling – Volume of solids

0.01 0.1 1 10 100 1000

0

10

20

30

40

50

60

C2S

C4AF

gypsum

hydrotalcitecalcite

ettringite

monocarbonate

portlandite

C-S-H

C3S

cm

3/1

00 g

cem

ent

time [days]


ESDRED: 60% CEM I + 40% silica fume5% alkali free accelerator

CEM I 42.5 N silica fume alkali-free(g/100g) accelerator

CaO 61.6 2.1 <

SiO2 21.9 93.3 <

Al2O3 4.8 0.2 16

Fe2O3 2.5 0.1 <

MgO 1.9 0.4 0.7

Na2O 0.25 <0.01 0.2

K2O 0.99 0.5 0.5

CO2 2.0 -- --

SO3 3.4 0.02 15

LOI 2.3 3.1

dissolved organic carbon 2.5

→ 0.16 mmol

→ 0.18 mmol

+ CaSO4 (0.32)+ CaO (0.64)→ C6A$3H32


0

500

1000

1500

2000

2500

3000

3500

4000

5 10 15 20 25 30 35

2-theta / °

co

un

ts /

-

360 days

56 days

7 days

1 day

1 h

unhydrated

Ettringite

E E

Alite/

belite

FG A

EE

Anhydrite

E

C 3 A

Hemicarbonate

1-56 days Portlandite

1-7 daysMono-

carbonate

Hemi-

carbonate

Alite

C-S-H

XRDA + $ + 2C$ + 4C -> C6A$3H32


TGA

50

55

60

65

70

75

80

85

90

95

100

0 100 200 300 400 500 600 700 800

temperature (°C)

rela

tiv

e w

eig

ht

(%)

-0.15

-0.10

-0.05

0.00

0.05

0.10

0.15

Dif

f. r

ela

tiv

e w

eig

ht

(%/K

)

unhydrated

1 hour

2 hours

4 hours

6 hours

1 day

2 days

4 days

7 days

14 days

28 days

56 days

210 days

360 days

ESDRED

C-S-H

CaCO3

ettringite

hemicarbonate

1-56 days

max. 4 days

unhydrated

1 h

7days

7 days1 h

unhydrated

360 days

360 days

210 days

14 days

4 days2 days

1 day

portlandite

1-14 days

max. 4 days

gypsum


Reactivity of SiO2

� Si-NMR

Silica fume Q4

anhydrouscement Q0

Q1Q2


Si NMR

dissolution of silica fume

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

0.01 0.1 1 10 100 1000

time [days]

sil

ica f

um

e [

g/1

00 g

]

initial amount of silica fume


Si NMR


0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

0.01 0.1 1 10 100 1000

time [days]

sil

ica f

um

e [

g/1

00 g

]


SiO2 [%]= 17 + 23e-0.05t


1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

0.01 0.1 1 10 100 1000Time (days)

mo

l/l

K

Na

S

OH-

Ca

Si

Al

DOC

Composition of the pore solution


ESDRED (CEM I 42.5 N + SF + Sigunit)

0

0.05

0.1

0.15

0.2

0.25

0.01 0.1 1 10 100 1000Time (days)

mo

l/l

Al

Ca

K

Na

OH

S

Si

K

Na

S

OH-

Ca

SiAl

pH (360 days)11.3


K, Na => in C-S-HLow C/S => more K, Na in C-S-H


alkali uptake

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

0.01 0.1 1 10 100 1000

sil

ica f

um

e [

g/1

00 g

]

0

50

100

150

200

250

300

350

400

Na +

K [

mM

]

silicafume

Na + K




0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

0.01 0.1 1 10 100 1000

time [days]

sil

ica f

um

e [

g/1

00 g

]

11.0

11.5

12.0

12.5

13.0

13.5

pH

silicafume

pH



Modeling ESDRED hydration

Portland cement hydration

• similar to OPC system• 1st hour increased dissolution of clinker

(Paglia et al., 2004; XRD)• silica fume dissolution according to NMR data

decreases at low pH values

Problems

� Alkali (K) and Al-uptake in C-S-H not well known� strätlingite or Al-in C-S-H?

EDS: 0.08 Al/Si in C-S-H


Experimental:

Portlandite 1-7 days

Hemi-/Monocarbonate: 1-28 days

Modeling - relative mass of solids(mass refers to total solid, including hydrated)

pH > 13 pH ≤ 12.5

pH 11.3

1E-3 0.01 0.1 1 10 100 1000

0

5

10

15

20

25

30

35

40

45

50

silica fume

aluminateferrite

alite

pore solution

belite

calcite hydrotalcite

ettringite

monocarbonate

portlandite

C-S-H

unhydrated clinker

g/1

00 g

cem

ent hydra

ted

time (days)


0.01 0.1 1 10 100 1000

0

5

10

15

20

25

30

35

40

45

50

55

silica fume

C3A

C2S

C4AF

hydrotalcite

calcite

ettringite

monocarbonate

portlandite

C-A-S-H

C3S

cm

3/1

00 g

cem

ent

time [days]


Al/Si = 0.08C-(Al)-S-H

hydrotalcite

calcite

11

11.5

12

12.5

13

13.5

pH

pH measured


0.01 0.1 1 10 100 1000

0

5

10

15

20

25

30

35

40

45

50

55 strätlingite

silica fume

thaumasite

C3A

C2S

C4AF

hydrotalcitecalcite

ettringite

monocarbonate

portlanditeC-A-S-H

C3S

cm

3/1

00 g

cem

ent

time [days]


Al/Si = 0.08C-(Al)-S-H

11

11.5

12

12.5

13

13.5

pH

pH measured

thaumasite


-1

-0.5

0

0.5

1

0.01 0.1 1 10 100 1000time (days)

effe

ctive

sa

tura

tio

n in

de

x

portlandite

ettringite

-1

-0.5

0

0.5

1

0.01 0.1 1 10 100 1000time (days)

effe

ctive

sa

tura

tio

n in

de

x

portlandite

ettringite

thaumasite

ionsofnumbern

K

IAP log

n

1

index saturation eff

S0

=

=

Thaumasite formation possible


0.01 0.1 1 10 100 1000

0

5

10

15

20

25

30

35

40

45

50

55 Al(OH)3

silica fume

gypsum

C3A

C2S

C4AF

hydrotalcite

calcite

ettringite

monocarbonate

portlandite

C-S-H

C3S

cm

3/1

00 g

cem

ent

time [days]

Strong dependency on silica fume dissolutionModeling – Volume of solids

10

10.5

11

11.5

12

12.5

13

13.5

pH

ESDRED

ESDRED

silica fume reacted

Al/Si = 0.08C-(A)-S-Hportlandite

Calcite

gypsum

hydrotalcite


� Mix of OPC with SiO2

� 0-2 days: similar to OPC

� >2 days: SiO2:

� no (temporary small amount) portlandite – low pH buffering capacity

� pH decreases, no further SiO2 reaction

� Hydration products

� C-S-H (low C/S), ettringite

� hydrotalcite, calcite, hemi-/monocarbonate

� pH decreases with time (11.3 after 1 year)

� Solution dominated by Ca, K, Na, OH, DOC

� Longterm unclear (ettringite <-> thaumasite ?)

� potential for stratlingite, Si-hydrogarnet or thaumasite

Summary - ESDRED


Portland cement slag Nanosilica

(g/100g)

CaO 66 41

SiO2 17 36 >99.8

Al2O3 4 12

Fe2O3 3 0.3

MgO 5 7

Na2O 0.1 0.3

K2O 1 0.3

CO2 1.7 0.01

SO3 3.2 0.8 (as S(-II))

LOI 0.7

w/b = 1.1

LAC: 90% CEM III/B + 10% Nanosilica

(contains ~74% slag)


XRD

0

500

1000

1500

2000

2500

3000

3500

4000

5 10 15 20 25 30 35

2-theta / °

co

un

ts /

-

Hemicarbonate

> 1 dayC-S-H

1 h

1 day

7 days

56 days

360 days

unhydrated

Ettringite

E E

Alite/

belite

EE

C

gypsum

E

C 3 A

Mono-

carbonate

Alite


40

50

60

70

80

90

100

0 100 200 300 400 500 600 700 800

temperature [°C]

rela

tiv

e w

eig

ht

[%]

-0.18

-0.12

-0.06

0.00

0.06

0.12

0.18

Dif

f. r

ela

tive

we

igh

t [%

/K]

unhydrated

1 hour

2 hours

6 hours

1 day

2 days

7 days

28 days

56 days

210 days

360 days

LAC

C-S-H

CaCO3

ettringite

hemicarbonate

unhydrated

6 h

7days

1 day

1 h

unhydrated

360 days

210 days

2 days

1 day

1 h

gypsum

Ettringite

TGA

No portlanditeAFm


Si NMR

dissolution of nanosilica

0%

5%

10%

15%

20%

25%

0.01 0.1 1 10 100 1000

time [days]

nan

osil

ica [

g/1

00]

initial amount of nanosilica

NS = 0.1*10-0.25*t


Selective dissolution with EDTA

dissolution of slag

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0.01 0.1 1 10 100 1000

time [days]

sla

g [

g/1

00 g

un

hyd

rate

d L

AC

]

initial slag content of LAC

slag [%]= 51 - 8*log(time)


LAC: CEM III/B 42.5 L + Nanosilica

0.000001

0.00001

0.0001

0.001

0.01

0.1

1

0.01 0.1 1 10 100

Time (days)

mo

l/l

SO4

HS-

KNa

OH-

Ca

SiAl


OPC slagnano silica


LAC: CEM III/B 42.5 L + Nanosilica

0.0001

0.001

0.01

0.1

0.01 0.1 1 10 100 1000

Time (days)

mo

l/l

SO4

Stot

HS-

S2O3

SO3

S2O3

detection limit

SO4

SO3

Sulfur speciation


Modeling LAC hydration

Portland cement hydration

• according to OPC system• nanosilica dissolution according to NMR data

• slag dissolution according to selective dissolution

Problems� Alkali (K) and Al-uptake in C-S-H not well known

� strätlingite or Al-in C-S-H?


LAC modelled

Al/Si = 0.08

0.01 0.1 1 10 100 1000

0

5

10

15

20

25

30

35

40

45

50

55

C-A-S-H

stratlingite

nanosilica

unhydrated clinker

hydrotalcite

calcite

ettringite

gypsum

slag

cm

3/1

00 g

cem

ent

time [days]


Effective SI

-1

-0.5

0

0.5

1

0.01 0.1 1 10 100 1000time (days)

effectiv

e s

atu

ratio

n in

dex

portlandite

ettringite

thaumasite

strätlingite

-1

-0.5

0

0.5

1

0.01 0.1 1 10 100 1000time (days)

effe

ctive

sa

tura

tio

n in

de

xOPC

LAC

ESDRED


� Slag with OPC and SiO2

� 0-1 days: similar to OPC,

� >1 days: slag + SiO2: � Reducing conditions (HS-)

� no portlandite

� pH decreases

� Main hydration products� C-S-H (low C/S), ettringite -> strätlingite?

� pH decreases with time (12.3 after 1 year)

� Solution dominated by Ca, K, Na,OH and HS--

Summary - LAC


Comparison: hydrates after 1 year

0

500

1000

1500

2000

2500

3000

3500

4000

5 10 15 20 25 30 35

2-theta / °

co

un

ts /

-

C-S-H

ESDRED

LAC

OPC

Ettringite

EE

alite/

belite

E

E

CE

portlandite

portlandite

alite

portlanditemonocarbonate

ferrite


Comparison: different pore solutions

pH values

11

11.5

12

12.5

13

13.5

0.01 0.1 1 10 100 1000

time (days)

pH

OPC

CEM I HS

ESDRED:

60% CEM I

40% silica fume

accelerator

LAC

90% CEM III/B

10% nanosilica


Comparison: main phases

OPC LAC ESDREDESDRED


pH

OPC LAC ESDRED


Conclusions

� OPC- hydration consistent with previous hydration studies - pH = 13.3 after 12 months

� ESDRED (CEM I + 40 % SiO2)- Initially similar to OPC - Silica fume dissolution proceeds slowly

- C-S-H: Initially C/S ~ 1.5, after 10 days ↓ (final C/S ~ 0.9)- Portlandite consumed after 10 days

- Alkali and pH ↓ (after 12 months: pH = 11.3)

� LAC (CEM III/B + 10% SiO2)- Initially similar to OPC - HS- increases with time – reducing conditions- pH = 12.3 after 12 months


Conlcusion 2: SCM

� Reactivity of slag, silica fume

-> depends on hydrate assemblage

� Al and alkali uptake in C-S-H !

� No portlandite, strätlingite formation

� Thaumasite formation possible

� Thermodynamic models for

Al-alkali-C-S-H missing

hydration of “low ph” cements - ttu cae network blogs

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