Hydration of low pH cements Barbara Lothenbach 1 , Erich Wieland 2 , - - PowerPoint PPT Presentation

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Hydration of low pH cements Barbara Lothenbach 1 , Erich Wieland 2 , - - PowerPoint PPT Presentation

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Hydration of low pH cements Barbara Lothenbach 1 , Erich Wieland 2 , B. Schwyn 3 , R. Figi 1 ,D. Rentsch 1 1 Empa, Laboratory for Concrete & Construction Chemistry, Switzerland 2 PSI, Laboratory for Waste Management, Switzerland 3 Nagra,

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Materials 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

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Materials Science & Technology

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
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Materials Science & Technology

Cement-Clay interface

( ) EDZ OPA

LAC ESDRED OPC Side view Top view Cement OPA

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Materials Science & Technology

Cement-Clay interface

( ) EDZ OPA

LAC ESDRED OPC

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5

Materials Science & Technology

Cement-Clay interface

( ) EDZ OPA

LAC ESDRED OPC

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Materials Science & Technology

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

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Materials Science & Technology

OPC

2000 4000 6000 8000 10000 12000 5 10 15 20 25 30 35 2-theta / ° counts / -

360 d 210 d 56 28 d 7 d 2 d 1 d 4 h 2 h 1 h unhydrated E P E E A F G A E E C E A B/A B/A G G C F G G P P Ht? Mc?

Ettringite (E) Gypsum (G) Ferrite (F)

XRD

Portlandite (P) Alite (A) Belite (B)

Monocarbonate (Mc) Hydrotalcite (H)

C-S-H

CaCO3 (C)

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Materials Science & Technology

OPC (CEM I 42.5 R HS)

0.000001 0.00001 0.0001 0.001 0.01 0.1 1 0.01 0.1 1 10 100 1000 Time (days) mol/l Al Ca K Na OH S Si

K Na S OH- Ca Si Al

Composition of the pore solution

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Materials Science & Technology

clinker

Hydration

(Lothenbach and Winnefeld, 2006)

clinker Ettringite Portlandite C-S-H alite (C3S), belite (C2S) aluminate(C3A), ferrite C4AF)

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Materials Science & Technology

All parameters (Ki, Ni) from Parrot and Killoh (1984)

Modeling - Dissolution

( )( )(

)

( ) ( ) ( )

3 1

1 1 1 1 ) 1 ln( 1

3 3 / 1 3 / 2 2 1 1 1 N t t t t t N t t t

K R K R N K R α α α α α − × = − − − × = − − − =

−

Empirical Approach: Parrot and Killoh (1984)

g/100 g 10 20 30 40 50 60 70 0.1 1 10 100 time (days)

//

alite: C3S ferrite:C4AF belite: C2S aluminate:C3A Cement specific input: surface area, w/c

α: degree of hydration

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Materials Science & Technology

K2SO4 Na2SO4 hemihydrate CaO

Thermodynamic Modeling

C3S C2S C3A C4AF Cements

I clinkers (slowly soluble) II soluble solids

gypsum anhydrite calcite

K2O Na2O MgO III water

H2O Ettringite Portlandite C-S-H AFm Hydrotalcites, ...

Ca2+ CaOH+ Speciation in solution CaSO4

Thermodynamic modeling

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Materials Science & Technology

Modeling – Concentrations in solution

0.01 0.1 1 10 100 1000 1E-3 0.01 0.1 1 10 100

Al OH

  • Na

sulfur Ca Si K concentrations (mmol/l) time (days)

pH (360 days) 13.3

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Materials Science & Technology

Modeling - relative mass of solids

(mass refers to total solid, including hydrated)

0.01 0.1 1 10 100 1000 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80

gypsum ferrite alite pore solution belite calcite hydrotalcite ettringite monocarbonate portlandite C-S-H

unhydrated clinker g/100 g cement hydrated

time (days)

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Materials Science & Technology

Modeling – Volume of solids

0.01 0.1 1 10 100 1000 10 20 30 40 50 60

C2S C4AF gypsum

hydrotalcite calcite

ettringite monocarbonate portlandite C-S-H C3S

cm

3/100 g cement

time [days]

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Materials Science & Technology

Summary - OPC

Comparable to other OPC systems investigated Main hydration products

C-S-H, portlandite, ettringite hydrotalcite, monocarbonate, calcite

pH increases with time Solution dominated by OH, K, Na

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Materials Science & Technology

ESDRED: 60% CEM I + 40% silica fume 5% 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

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Materials Science & Technology

XRD

500 1000 1500 2000 2500 3000 3500 4000 5 10 15 20 25 30 35 2-theta / ° counts / -

360 days 56 days 7 days 1 day 1 h unhydrated

Ettringite E E Alite/ belite

F G A

E E C

Anhydrite

E

C 3 A

Hemicarbonate 1-56 days Portlandite 1-7 days Mono- carbonate Hemi- carbonate Alite

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Materials Science & Technology

TGA

50 55 60 65 70 75 80 85 90 95 100 100 200 300 400 500 600 700 800 temperature (°C) relative weight (%)

  • 0.15
  • 0.10
  • 0.05

0.00 0.05 0.10 0.15

  • Diff. relative weight (%/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 days 1 h unhydrated 360 days 360 days 210 days 14 days 4 days 2 days 1 day portlandite 1-14 days

  • max. 4 days

gypsum

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Materials Science & Technology

10 20 30 40 50 60 0.01 0.1 1 10 100 1000 time (days) g/100 g pore solution ettringite calcite portlandite // //

TGA – Quantification of solution and solids

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Materials Science & Technology

5 10 15 20 25 0.01 0.1 1 10 100 1000 time (days) % portlandite // // For comparison: OPC 5 10 15 20 25 0.01 0.1 1 10 100 1000 time (days) % portlandite // //

ESDRED - Portlandite

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Materials Science & Technology

Reactivity of SiO2

Si-NMR

Silica fume Q4 anhydrous cement Q0 Q1 Q2

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Materials Science & Technology

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] silica fume [g/100 g] initial amount of silica fume

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Materials Science & Technology

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] silica fume [g/100 g] initial amount of silica fume

SiO2 = 0.17 + 0.23e-0.05t

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Materials Science & Technology

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 1000 Time (days) mol/l

K Na S OH- Ca Si Al DOC

Composition of the pore solution

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Materials Science & Technology

ESDRED (CEM I 42.5 N + SF + Sigunit)

0.05 0.1 0.15 0.2 0.25 0.01 0.1 1 10 100 1000 Time (days) mol/l Al Ca K Na OH S Si

K Na S OH- Ca Si Al pH (360 days) 11.3

Composition of the pore solution

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

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Materials Science & Technology

Modeling ESDRED hydration

Portland cement hydration

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

(Paglia et al., 2004)

  • silica fume dissolution according to NMR data

Problems

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

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Materials Science & Technology

1E-3 0.01 0.1 1 10 100 1000 5 10 15 20 25 30 35 40 45 50

stratlingite silica fume aluminate ferrite alite pore solution belite calcite hydrotalcite ettringite monocarbonate portlandite C-S-H

unhydrated clinker g/100 g cement hydrated

time (days)

Experimental: Portlandite 1-7 days Hemi-/Monocarbonate: 1-28 day Stratlingite difficult to detect by XRD

Modeling - relative mass of solids

(mass refers to total solid, including hydrated)

pH > 13 pH ≤ 12.5 pH 11.3

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Materials Science & Technology

0.01 0.1 1 10 100 1000 5 10 15 20 25 30 35 40 45 50 55

silica fume

stratlingite

C3A C2S C4AF

hydrotalcite calcite

ettringite

monocarbonate

portlandite C-S-H C3S

cm

3/100 g cement

time [days]

Modeling – Volume of solids

C-S-H C/S ~0.9 C-S-H C/S ~ 1.5

11 11.5 12 12.5 13 13.5 pH

pH measured No Al in C-S-H

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Materials Science & Technology

Tobermorite structure

Interlayer Interlayer

Richardson, 1999 Al-substitution CaO layers alkalis SiO2 - Dreierketten Al-substitution increase at low C/S ratios Al-substitution increases uptake of alkalis

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Materials Science & Technology

Modeling – Volume of solids

0.01 0.1 1 10 100 1000 5 10 15 20 25 30 35 40 45 50 55

silica fume

stratlingite

C3A C2S C4AF

hydrotalcite calcite

ettringite

monocarbonate

portlandite C-S-H C3S

cm

3/100 g cement

time [days]

C-S-H C/S ~0.9 C-S-H C/S ~ 1.5 Al/Si = 0.08 C-(Al)-S-H portlandite

hydrotalcite calcite

ettringite

11 11.5 12 12.5 13 13.5 pH

pH measured

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Materials Science & Technology

Strong dependency on silica fume dissolution

Modeling – Volume of solids

0.01 0.1 1 10 100 1000 5 10 15 20 25 30 35 40 45 50 55 Al(OH)3 gypsum

silica fume

stratlingite

C3A C2S C4AF

hydrotalcite calcite

ettringite

monocarbonate

portlandite C-S-H C3S

cm

3/100 g cement

time [days]

10 10.5 11 11.5 12 12.5 13 13.5 pH

ESDRED ESDRED silica fume reacted

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

Calcite

ettringite

gypsum

hydrotalcite

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Materials Science & Technology

Strong dependency on silica fume dissolution

Modeling – Volume of solids

0.01 0.1 1 10 100 1000 5 10 15 20 25 30 35 40 45 50 55 Al(OH)3 gypsum

silica fume

stratlingite

C3A C2S C4AF

hydrotalcite calcite

ettringite

monocarbonate

portlandite C-S-H C3S

cm

3/100 g cement

time [days]

10 10.5 11 11.5 12 12.5 13 13.5 pH

ESDRED ESDRED silica fume reacted

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

Calcite

ettringite

thaumasite

hydrotalcite

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Materials Science & Technology

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

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

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Materials Science & Technology

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)

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Materials Science & Technology

XRD

500 1000 1500 2000 2500 3000 3500 4000 5 10 15 20 25 30 35 2-theta / ° counts / -

Hemicarbonate > 1 day C-S-H

1 h 1 day 7 days 56 days 360 days unhydrated

Ettringite E E Alite/ belite E E C

gypsum

E

C 3 A

Mono- carbonate Alite

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Materials Science & Technology

40 50 60 70 80 90 100 100 200 300 400 500 600 700 800 temperature [°C] relative weight [%]

  • 0.18
  • 0.12
  • 0.06

0.00 0.06 0.12 0.18

  • Diff. relative weight [%/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 Gypsum

TGA

No portlandite AFm

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Materials Science & Technology

20 40 60 80 100 120 0.01 0.1 1 10 100 1000 time (days) g/100 g pore solution ettringite calcite portlandite // //

TGA – Quantification of solution and solids

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Materials Science & Technology

dissolution of nanosilica

0% 5% 10% 15% 20% 25% 0.01 0.1 1 10 100 1000 time [days] nanosilica [g/100g unhydrated LAC] initial amount of nanosilica

SiO2 = 0.10 e-0.45*t

Si NMR

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Materials Science & Technology

dissolution of slag

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 50 100 150 200 250 300 350 400 time [days] slag [g/100 g unhydrated LAC] slag content LAC

slag =0.35+ 0.32 e-0.4*t

Selective dissolution with EDTA

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Materials Science & Technology

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) mol/l

SO4 HS- K Na OH- Ca Si Al

Composition of the pore solution

OPC slag nano silica

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Materials Science & Technology

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) mol/l

SO4 Stot HS- S2O3 SO3 S2O3 detection limit SO4 SO3

Sulfur speciation

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Materials Science & Technology

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?

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Materials Science & Technology

LAC modelled

0.01 0.1 1 10 100 1000 5 10 15 20 25 30 35 40 45 50 55

stratlingite

nanosilica unhydrated clinker

hydrotalcite calcite

ettringite

gypsum

C-S-H slag

cm

3/100 g cement

time [days]

No Al in C-S-H

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Materials Science & Technology

LAC modelled

0.01 0.1 1 10 100 1000 5 10 15 20 25 30 35 40 45 50 55

stratlingite

nanosilica unhydrated clinker

hydrotalcite calcite

ettringite

gypsum

C-S-H slag

cm

3/100 g cement

time [days]

Al/Si = 0.1 C-(A)-S-H

calcite

ettringite

hydrotalcite

nano silica

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Materials Science & Technology

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

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Materials Science & Technology

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

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Materials Science & Technology

Comparison

0.001 0.01 0.1 1 10 10.5 11 11.5 12 12.5 13 13.5 14

pH Ca [mM]

OPC CEM I HS ESDRED: 60% CEM I 40% silica fume accelerator LAC 90% CEM III/B 10% nanosilica

  • versaturated with respect

to portlandite

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Materials Science & Technology

Comparison: oversaturation

ettringite

  • 4
  • 2

2 4 6 8 10 12 0.01 0.1 1 10 100 1000 time (days) saturation index OPC ESDRED LAC

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Materials Science & Technology

strätlingite

  • 5
  • 4
  • 3
  • 2
  • 1

1 2 3 4 5 0.01 0.1 1 10 100 1000 time (days) saturation index OPC ESDRED LAC

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Materials Science & Technology

Comparison: main phases

OPC LAC ESDRED ESDRED

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Materials Science & Technology

pH

OPC LAC ESDRED

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Materials Science & Technology

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