Hydration of low ph cements

Transcription

1 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

2 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

3 Cement-Clay interface Side view Borehole 1 (350 mm) Top view EDZ ESDRED Cement OPC OPA LAC OPA 3

4 OPC: CEM I 42.5 R HS (g/100g) CaO 58.8 alite 31 SiO belite 36 Al 2 O aluminate 1.6 Fe 2 O ferrite 16 MgO 4.6 MgO 4.6 Na 2 O 0.27 CaCO K 2 O 0.75 CaSO CO Na 2 O 0.22 SO K 2 O 0.27 CaO free 0.71 Na 2 SO LOI 2.3 K 2 SO w/c = 0.8 4

5 Hydration (Lothenbach and Winnefeld, 2006) clinker clinker alite (C 3 S), belite (C 2 S) aluminate(c 3 A), ferrite C 4 AF) C-S-H Portlandite Ettringite 5

6 Modeling - Dissolution Empirical Approach: Parrot and Killoh (1984) R R R t t t = = = K N K K ( )( ) ( 1 N ) 1 1 α ln(1 α ) 2 / ( 1 αt ) 1/ 3 ( 1 αt ) N ( 1 α ) 3 All parameters (K i, N i ) from Parrot and Killoh (1984) α: degree of hydration t t 3 t g/100 g // alite: C 3 S belite: C 2 S ferrite:c 4 AF time (days) aluminate:c 3 A Cement specific input: surface area, w/c 6

7 Cements Thermodynamic Modeling Thermodynamic modeling I clinkers (slowly soluble) C 3 S C 2 S C 3 A C 4 AF II soluble solids K 2 SO 4 Na 2 SO 4 hemihydrate CaO III water H 2 O K 2 O Na 2 O MgO gypsum anhydrite calcite Ca 2+ CaOH + Speciation in solution CaSO 4 0 Portlandite C-S-H Ettringite AFm Hydrotalcites,... 7

8 Modeling Volume of solids ettringite monocarbonate cm 3 /100 g cement gypsum C 4 AF portlandite calcite hydrotalcite 10 C 2 S C-S-H C 3 S time [days] 8

9 ESDRED: 60% CEM I + 40% silica fume 5% alkali free accelerator CEM I 42.5 N silica fume alkali-free (g/100g) accelerator CaO < SiO < Al 2 O Fe 2 O < MgO Na 2 O 0.25 < K 2 O CO SO LOI dissolved organic carbon mmol + CaSO 4 (0.32) + CaO (0.64) C 6 A$ 3 H mmol 9

10 counts / days 56 days 7 days 1 day 1 h unhydrated Ettringite G F A A + $ + 2C$ + 4C -> C 6 A$ 3 H 32 XRD belite 35 2-theta / E E Anhydrite Hemicarbonate 1-56 days Portlandite Monocarbonate 1-7 days E E E Hemicarbonate C-S-H Alite Alite/ C 3 A 10

11 relative weight (%) gypsum ettringite 1 h C-S-H 360 days 210 days 7 days unhydrated hemicarbonate 1-56 days max. 4 days 360 days TGA ESDRED 7days temperature ( C) 2 days 1 day 4 days portlandite 1-14 days max. 4 days 14 days unhydrated 1 h CaCO 3 unhydrated 1 hour hours 4 hours 6 hours 1 day days 4 days 7 days days 28 days 56 days days 360 days Diff. relative weight (%/K) 11

12 Silica fume Q 4 Reactivity of SiO 2 anhydrous cement Q 0 Si-NMR Q 1 Q 2 12

13 dissolution of silica fume 50% Si NMR 45% 40% initial amount of silica fume silica fume [g/100 g] 35% 30% 25% 20% 15% 10% 5% 0% time [days] 13

14 dissolution of silica fume 50% Si NMR 45% 40% initial amount of silica fume silica fume [g/100 g] 35% 30% 25% 20% 15% 10% 5% SiO 2 [%]= e -0.05t 0% time [days] 14

15 Composition of the pore solution 1.E+00 1.E-01 K OH - DOC 1.E-02 Na mol/l 1.E-03 S Ca 1.E-04 Si 1.E-05 Al 1.E Time (days)

16 Composition of the pore solution ESDRED (CEM I 42.5 N + SF + Sigunit) 0.25 K, Na => in C-S-H Low C/S => more K, Na in C-S-H 0.2 K 0.15 mol/l 0.1 OH - Na ph (360 days) 11.3 Al Ca K Na OH S Si Al S Ca Time (days) Si 16

17 alkali uptake 50% % 350 silica fume [g/100 g] 40% 35% 30% 25% 20% 15% 10% silicafume Na + K initial amount of silica fume Na + K [mm] 5% 50 0%

18 dissolution of silica fume 50% % 40% initial amount of silica fume 13.0 silica fume [g/100 g] 35% 30% 25% 20% 15% silicafume ph 10% ph % 0%

19 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 19

20 Modeling - relative mass of solids (mass refers to total solid, including hydrated) ph > 13 ph pore solution C-S-H ph 11.3 g/100 g cement hydrated silica fume belite alite Experimental: Portlandite 1-7 days Hemi-/Monocarbonate: 1-28 days 10 calcite 5 aluminate ferrite monocarbonate ettringite 0 1E time (days) portlandite hydrotalcite 20

21 ph 12 Modeling Volume of solids ph measured monocarbonate calcite hydrotalcite hydrotalcite cm 3 /100 g cement C 3 A C 4 AF C 2 S C 3 S ettringite silica fume portlandite C-(Al)-S-H C-A-S-H time [days] Al/Si =

22 ph 12 Modeling Volume of solids ph measured strätlingite calcite monocarbonate thaumasite thaumasite hydrotalcite cm 3 /100 g cement ettringite C 3 A C 4 AF C 2 S C 3 S silica fume portlandite C-(Al)-S-H C-A-S-H time [days] Al/Si =

23 Thaumasite formation possible 1 eff saturation index 1 IAP = log n K S0 n = number of ions effective saturation index portlandite thaumasite ettringite time (days) 23

24 ph Strong dependency on silica fume dissolution Al(OH) Modeling Volume of solids monocarbonate ESDRED ESDRED silica fume reacted Calcite calcite gypsum gypsum hydrotalcite hydrotalcite 40 cm 3 /100 g cement C 3 A C 4 AF C 2 S C 3 S ettringite silica fume portlandite C-(A)-S-H C-S-H time [days] Al/Si =

25 Summary - ESDRED Mix of OPC with SiO days: similar to OPC >2 days: SiO 2 : no (temporary small amount) portlandite low ph buffering capacity ph decreases, no further SiO 2 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 25

26 (contains ~74% slag) LAC: 90% CEM III/B + 10% Nanosilica Portland cement slag Nanosilica (g/100g) CaO SiO >99.8 Al 2 O Fe 2 O MgO 5 7 Na 2 O K 2 O CO SO (as S(-II)) LOI 0.7 w/b =

27 days 56 days 7 days Ettringite Hemicarbonate > 1 day Monocarbonate XRD E E E E C E C-S-H counts / day 1 h unhydrated gypsum belite 35 2-theta / Alite C 3 A Alite/ 27

28 relative weight [%] h C-S-H Ettringite ettringite gypsum 1 day AFm hemicarbonate 210 days 1 h LAC unhydrated TGA temperature [ C] 6 h 360 days 1 day 2 days 7days No portlandite unhydrated CaCO 3 unhydrated 1 hour hours 6 hours 1 day 2 days days 28 days days 210 days 360 days Diff. relative weight [%/K] 28

29 dissolution of nanosilica 25% Si NMR 20% nanosilica [g/100] 15% 10% NS = 0.1* *t initial amount of nanosilica 5% 0% time [days] 29

30 dissolution of slag 100% Selective dissolution with EDTA 90% slag [g/100 g unhydrated LAC] 80% 70% 60% 50% 40% 30% 20% slag [%]= 51-8*log(time) initial slag content of LAC 10% 0% time [days] 30

31 1 0.1 LAC: CEM III/B 42.5 L + Nanosilica Composition of the pore solution OPC K OH - slag nano silica Na 0.01 HS- SO 4 mol/l Ca Si Al Time (days) 31

32 Sulfur speciation LAC: CEM III/B 42.5 L + Nanosilica 0.1 S tot 0.01 SO 4 HS - mol/l SO 3 S 2 SO 2 O detection limit Time (days) 32

33 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? 33

34 LAC modelled calcite ettringite 45 hydrotalcite 40 gypsum stratlingite 35 cm 3 /100 g cement nanosilica unhydrated clinker C-A-S-H Al/Si = slag time [days] 34

35 effective saturation index 1 Effective SI strätlingite effective saturation index OPC LAC ESDRED portlandite thaumasite ettringite time (days) time (days) 35

36 Summary - LAC Slag with OPC and SiO days: similar to OPC, >1 days: slag + SiO 2 : 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

37 Comparison: hydrates after 1 year LAC Ettringite C-S-H portlandite counts / ESDRED OPC monocarbonate ferrite E E E portlandite E C E portlandite theta / alite alite/ belite 37

38 Comparison: different pore solutions ph values 13.5 OPC CEM I HS 13 ph LAC 90% CEM III/B 10% nanosilica 11.5 ESDRED: 60% CEM I 40% silica fume accelerator time (days) 38

39 Comparison: main phases OPC ESDRED LAC ESDRED 39

40 ph OPC LAC ESDRED 40

41 Conclusions OPC - hydration consistent with previous hydration studies - ph = 13.3 after 12 months ESDRED (CEM I + 40 % SiO 2 ) - 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% SiO 2 ) - Initially similar to OPC - HS - increases with time reducing conditions - ph = 12.3 after 12 months 41

42 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 42