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

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, National Cooperation for the Disposal of Radioactive Waste, Switzerland 1 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 2 Materials Science & Technology

Cement-Clay interface Side view Top view ( ) EDZ Cement ESDRED OPC OPA LAC OPA 3 Materials Science & Technology

Cement-Clay interface ( ) EDZ ESDRED OPC LAC OPA 4 Materials Science & Technology

Cement-Clay interface ( ) EDZ ESDRED OPC LAC OPA 5 Materials Science & Technology

OPC: CEM I 42.5 R HS (g/100g) CaO 58.8 alite 31 SiO 2 20.6 belite 36 Al 2 O 3 3.9 aluminate 1.6 Fe 2 O 3 5.2 ferrite 16 MgO 4.6 MgO 4.6 Na 2 O 0.27 CaCO 3 3.1 K 2 O 0.75 CaSO 4 5.1 CO 2 1.4 Na 2 O 0.22 SO 3 3.5 K 2 O 0.27 CaO free 0.71 Na 2 SO 4 0.12 LOI 2.3 K 2 SO 4 0.89 w/c = 0.8 6 Materials Science & Technology

XRD Portlandite (P) Ettringite (E) OPC CaCO 3 (C) P E Monocarbonate (Mc) 12000 E Ht? Hydrotalcite (H) E C-S-H E C E Mc? E P 360 d 10000 210 d 56 8000 28 d counts / - 7 d 6000 2 d 1 d P 4000 4 h 2 h 2000 G 1 h G A C G G G Gypsum (G) unhydrated F A B/A F B/A A 0 Ferrite (F) Alite (A) 5 10 15 20 25 30 35 Belite (B) 2-theta / ° 7 Materials Science & Technology

Composition of the pore solution OPC (CEM I 42.5 R HS) 1 OH - K 0.1 Na 0.01 Al Ca Ca K mol/l Na 0.001 S OH S Si 0.0001 Si Al 0.00001 0.000001 0.01 0.1 1 10 100 1000 Time (days) 8 Materials Science & Technology

Hydration (Lothenbach and Winnefeld, 2006) clinker clinker alite (C 3 S), belite (C 2 S) C-S-H Portlandite Ettringite aluminate(C 3 A), ferrite C 4 AF) 9 Materials Science & Technology

Modeling - Dissolution Empirical Approach: Parrot and Killoh (1984) Cement specific input: 70 surface area, w/c alite: C 3 S ) ( ) ( )( K − = − α − − α 1 N 1 R 1 ln( 1 ) 1 60 t t t N 1 50 ( ) × − α 2 / 3 K 1 = 2 t g/100 g R 40 ( ) t − − α 1 / 3 1 1 t 30 ( ) belite: C 2 S = × − α N R K 1 3 t 3 t 20 ferrite:C 4 AF All parameters (K i , N i ) from 10 Parrot and Killoh (1984) // 0 0 0.1 1 10 100 α : degree of hydration time (days) aluminate:C 3 A 10 Materials Science & Technology

Thermodynamic Modeling Thermodynamic modeling Cements Ca 2+ I clinkers (slowly soluble) CaOH + Speciation in solution CaSO 4 0 K 2 O C 3 S C 2 S Na 2 O C 3 A C 4 AF MgO II soluble solids Portlandite K 2 SO 4 C-S-H Na 2 SO 4 gypsum hemihydrate anhydrite Ettringite CaO calcite AFm III water Hydrotalcites, ... H 2 O 11 Materials Science & Technology

Modeling – Concentrations in solution pH (360 days) 13.3 - OH K 100 Na 10 concentrations (mmol/l) sulfur Ca 1 0.1 Si Al 0.01 1E-3 0.01 0.1 1 10 100 1000 time (days) 12 Materials Science & Technology

Modeling - relative mass of solids (mass refers to total solid, including hydrated) 80 pore solution 75 70 65 60 g/100 g cement hydrated 55 50 45 belite 40 C-S-H 35 alite 30 25 ferrite portlandite 20 gypsum ettringite 15 monocarbonate 10 hydrotalcite 5 0 calcite 0.01 0.1 1 10 100 1000 time (days) unhydrated clinker 13 Materials Science & Technology

Modeling – Volume of solids 60 ettringite 50 monocarbonate calcite 40 3 /100 g cement hydrotalcite gypsum portlandite 30 C 4 AF cm 20 C 2 S C-S-H 10 C 3 S 0 0.01 0.1 1 10 100 1000 time [days] 14 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 15 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 < SiO 2 21.9 93.3 < → 0.16 mmol Al 2 O 3 4.8 0.2 16 Fe 2 O 3 2.5 0.1 < MgO 1.9 0.4 0.7 + CaSO 4 (0.32) + CaO (0.64) Na 2 O 0.25 <0.01 0.2 → C 6 A$ 3 H 32 K 2 O 0.99 0.5 0.5 CO 2 2.0 -- -- SO 3 3.4 0.02 15 → 0.18 mmol LOI 2.3 3.1 dissolved organic carbon 2.5 16 Materials Science & Technology

XRD Ettringite Hemicarbonate Hemi- Portlandite 1-56 days 360 days carbonate 4000 1-7 days Mono- carbonate 56 days E 3500 E E E E C 7 days 3000 2500 counts / - 1 day 2000 1 h 1500 unhydrated 1000 C 3 A 500 G F A Anhydrite Alite 0 Alite/ belite 5 10 15 20 25 30 35 2-theta / ° 17 Materials Science & Technology

TGA unhydrated ESDRED 1 hour unhydrated 2 hours 100 0.15 relative weight (%) 4 hours 6 hours 95 1 h 1 day 0.10 1 day 90 2 days 2 days 7days 4 days 4 days 85 7 days 0.05 360 days 14 days 80 28 days gypsum unhydrated CaCO 3 56 days 75 0.00 Diff. relative weight (%/K) 210 days 360 days 14 days 70 C-S-H portlandite 1 h -0.05 7 days 1-14 days 65 hemicarbonate max. 4 days 1-56 days 60 max. 4 days -0.10 360 days 55 ettringite 210 days 50 -0.15 0 100 200 300 400 500 600 700 800 temperature (°C) 18 Materials Science & Technology

TGA – Quantification of solution and solids 60 // pore solution ettringite 50 calcite portlandite 40 g/100 g 30 20 10 // 0 0 0.01 0.1 1 10 100 1000 time (days) 19 Materials Science & Technology

ESDRED - Portlandite 25 25 // // 20 20 % portlandite % portlandite For comparison: OPC 15 15 10 10 5 5 // // 0 0 0 0 0.01 0.01 0.1 0.1 1 1 10 10 100 100 1000 1000 time (days) time (days) 20 Materials Science & Technology

Silica fume Q 4 Reactivity of SiO 2 anhydrous cement Q 0 � Si-NMR Q 1 Q 2 21 Materials Science & Technology

dissolution of silica fume Si NMR 50% 45% initial amount of silica fume 40% silica fume [g/100 g] 35% 30% 25% 20% 15% 10% 5% 0% 0.01 0.1 1 10 100 1000 time [days] 22 Materials Science & Technology

dissolution of silica fume Si NMR 50% 45% initial amount of silica fume 40% silica fume [g/100 g] 35% 30% 25% SiO 2 = 0.17 + 0.23e -0.05t 20% 15% 10% 5% 0% 0.01 0.1 1 10 100 1000 time [days] 23 Materials Science & Technology

Composition of the pore solution 1.E+00 K OH - DOC 1.E-01 Na 1.E-02 Ca S mol/l 1.E-03 Si 1.E-04 Al 1.E-05 1.E-06 Time (days) 0.01 0.1 1 10 100 1000 24 Materials Science & Technology

Composition of the pore solution ESDRED (CEM I 42.5 N + SF + Sigunit) K, Na => in C-S-H 0.25 Low C/S => more K, Na in C-S-H K 0.2 pH (360 days) Al 11.3 Ca OH - K 0.15 Na OH mol/l S Si 0.1 Na 0.05 S Ca 0 Al Time (days) 0.01 0.1 1 10 100 1000 Si 25 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? 26 Materials Science & Technology

Modeling - relative mass of solids (mass refers to total solid, including hydrated) pH > 13 pH ≤ 12.5 pH 11.3 50 pore solution 45 C-S-H Experimental: 40 Portlandite 1-7 days silica fume Hemi-/Monocarbonate: 1-28 day 35 g/100 g cement hydrated Stratlingite difficult 30 to detect by XRD 25 belite 20 15 ettringite alite 10 aluminate monocarbonate stratlingite ferrite 5 calcite hydrotalcite 0 1E-3 0.01 0.1 1 10 100 1000 portlandite time (days) 27 Materials Science & Technology unhydrated clinker

13.5 Modeling – Volume of solids pH measured 13 12.5 C-S-H C/S ~ 1.5 pH 12 C-S-H C/S ~0.9 11.5 11 stratlingite 55 50 calcite monocarbonate 45 hydrotalcite 40 35 ettringite 3 /100 g cement 30 portlandite C-S-H 25 No Al in C-S-H 20 silica fume cm 15 C 4 AF C 3 A 10 C 2 S 5 C 3 S 0 0.01 0.1 1 10 100 1000 time [days] 28 Materials Science & Technology

Tobermorite structure SiO 2 - Dreierketten Al-substitution increase at low C/S ratios CaO layers Al-substitution increases uptake of alkalis alkalis Interlayer Interlayer Al-substitution Richardson, 1999 29 Materials Science & Technology

13.5 Modeling – Volume of solids pH measured 13 12.5 C-S-H C/S ~ 1.5 pH 12 C-S-H C/S ~0.9 11.5 11 stratlingite 55 calcite 50 ettringite calcite monocarbonate 45 hydrotalcite hydrotalcite 40 35 ettringite 3 /100 g cement 30 portlandite portlandite C-S-H C-(Al)-S-H Al/Si = 0.08 25 20 silica fume cm 15 C 4 AF C 3 A 10 C 2 S 5 C 3 S 0 0.01 0.1 1 10 100 1000 time [days] 30 Materials Science & Technology