Development of pore solution chemistry and hydrate assemblages - PowerPoint PPT Presentation

Development of pore solution chemistry and hydrate assemblages during hydration of calcium sulfoaluminate cements Frank Winnefeld, Barbara Lothenbach, Mohsen Ben-Haha Swiss Federal Laboratories for Materials Testing and Research Concrete/Construction Chemisty Lab Dübendorf, Switzerland Materials Science & Technology

Outline � Introduction � Used cements � Hydration of calcium sulfoaluminate cements - Isothermal heat flow calorimetry - X-ray diffraction analysis - Thermogravimetric analysis - Pore solution chemistry - Microstructure (SEM) - Thermodynamic modelling � Conclusions 2

Comparison OPC - CSA OPC CSA main phases * C 3 S, C 2 S, C 3 A, C 4 AF C 4 A 3 s (= ye‘elimite) raw materials limestone & clay limestone, bauxite & anhydrite burning temperature ≈ 1450 °C ≈ 1250 °C CO 2 -release from raw C 3 S: C 4 A 3 s: materials ** 1.80 g / ml C 3 S 0.56 g/ml C 4 A 3 s grindability medium easy gypsum addition ≈ 4-8 wt.-% ≈ 20-25 wt.-% w/c total hydration ≈ 0.4 ≈ 0.8 hydration products C-S-H phases, AFt, AFm, Al(OH) 3 gel CH, AFt, … * Cement notation: C = CaO, S = SiO 2 , A = Al 2 O 3 , F = Fe 2 O 3 , H = H 2 O, s = SO 3 3 ** Gartner E., Cem. Concr. Res. 34 (2004), 1489.

CSA-Cements … … have attracted new interest during the climate debate as they: � need lower burning temperatures, � release less CO 2 from the raw meal (less limestone), � yield a higher volume of hydrate phases (higher water/ cement ratio) compared to ordinary Portland cement. Besides that, they are of interest concerning waste encapsulation. But they have some drawbacks: � environment (SO 2 release) � risk of expansion (ettringite is main hydration product) 4

CSA-cements: risk of expansion United States Patent 4409030, 1983: Material for destroying concrete structures … comprises a mixture of … coarse-grained quicklime … and … cement. The cement may contain calcium sulfoaluminate ... The material is blended with water and then injected into holes formed in the body to be destroyed, the material expanding as it hydrates to crack and fracture the body. Basic research is needed to understand the hydration mechanisms of calcium sulfoaluminate based systems ! 5

Hydration of pure ye‘elimite (1) C 4 A 3 s + 18 H C 3 A·CsH 12 + 2 AH 3 (monosulfate) (2) C 4 A 3 s + 2 CsH 2 + 24 H C 3 A·3CsH 32 + 2 AH 3 (ettringite) (3) C 4 A 3 s + 6 CH + 8 CsH 2 + 74 H 3 C 3 A·3CsH 32 200 consumption of heat flow C4A3s calcium sulfate C4A3s / CsH2 1:1 (mol) calorimetry 160 C4A3s / CsH2 1:2 (mol) heat flow / J/(g·h) w/c = 2 C4A3s / CsH2 1:3 (mol) C4A3s / CsH2 1:4 (mol) 120 80 reaction (2) reaction (1) 40 0 0 2 4 6 8 10 12 14 16 18 time / h 6

Hydration kinetics of CSA cements: influence of calcium sulfate gypsum * dead-burnt anhydrite 35 35 CSA clinker CSA clinker CSA / gypsum 86/14 CSA / anhydrite 86/14 30 w/c 30 w/c CSA / gypsum 76/24 CSA / anhydrite 76/24 0.70 0.70 CSA / gypsum 68/32 heat flow / J/(g·h) heat flow / J/(g·h) CSA / anhydrite 68/32 25 25 CSA / gypsum 61/39 CSA / anhydrite 61/39 OPC, w/c = 0.50 OPC, w/c = 0.50 20 20 15 15 10 10 5 5 0 0 0 8 16 24 32 40 48 0 8 16 24 32 40 48 time / h time / h calcium sulfate with poor reactivity: reactive calcium sulfate: „chaotic“ early hydration enables to control early hydration * amounts of gypsum given as anhydrous calcium sulfate 7

Strength development of CSA cements EN 196-1 - mortars � very high strength 120 despite high CSA clinker w/c = 0.70 CSA / gypsum 86/14 water/cement-ratio compressive strength / MPa 100 CSA / gypsum 68/32 � gypsum increases OPC, w/c = 0.50 early strength 80 60 40 20 0 0.1 1 10 100 time / d 8

Used CSA-cements - composition chemical analysis potential phase content wt.-% CSA-1 CSA-2 wt.-% CSA-1 CSA-2 CaO 35.4 41.2 C 4 A 3 s 50 54 SiO 2 3.2 6.9 CA 8 - Al 2 O 3 35.5 26.8 C 2 AS 15 - Fe 2 O 3 0.88 0.88 C 2 S - 17 MgO 0.76 0.75 Cs - 22 Na 2 O 0.05 0.13 CsH 2 22 - K 2 O 0.21 0.40 others * 5 7 TiO 2 1.8 1.2 * mainly titanium containing phases SO 3 16.8 19.5 water/cement ratio L.O.I. 5.1 1.84 � CSA-1: 0.72 � CSA-2: 0.80 9

Isothermal heat flow calorimetry 35 30 CSA-1 heat flow / J/(g·h) 25 CSA-2 20 15 10 5 0 0 8 16 24 32 40 48 time / h 10

Hydration (XRD) of CSA-1 18000 Y - ye'elimite G - gypsum G E C - calcium aluminate E - ettringite Ge - gehlenite M - monosulfate E 15000 EE Ge M G 28 d 12000 7 d intensity / - 2 d M 9000 16 h 8 h 6000 5 h 2 h 3000 E E 1 h G Y G Ge Y G C unhydrated 0 5 10 15 20 25 30 35 40 45 50 55 60 2 Θ / ° 11

Hydration (TGA) of CSA-1 100 100 100 100 100 100 100 100 100 100 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 unhydrated unhydrated unhydrated unhydrated unhydrated unhydrated unhydrated unhydrated unhydrated unhydrated 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 90 90 90 90 90 90 90 90 90 90 1 h 1 h 1 h 1 h 1 h 1 h 1 h 1 h 1 h 2 h 2 h 2 h 2 h 2 h 2 h 2 h 2 h 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 5 h 5 h 5 h 5 h 5 h 5 h 5 h 80 80 80 80 80 80 80 80 80 80 diff. rel. weight / %/K diff. rel. weight / %/K diff. rel. weight / %/K diff. rel. weight / %/K diff. rel. weight / %/K diff. rel. weight / %/K diff. rel. weight / %/K diff. rel. weight / %/K diff. rel. weight / %/K diff. rel. weight / %/K 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 8 h 8 h 8 h 8 h 8 h 8 h rel. weight / % rel. weight / % rel. weight / % rel. weight / % rel. weight / % rel. weight / % rel. weight / % rel. weight / % rel. weight / % rel. weight / % 2 d 2 d 2 d 16 h 16 h 16 h 16 h 16 h 70 70 70 70 70 70 70 70 70 70 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 28 d 7 d 7 d 60 60 60 60 60 60 60 60 60 60 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 -0.1 -0.1 -0.1 -0.1 -0.1 -0.1 -0.1 -0.1 -0.1 -0.1 50 50 50 50 50 50 50 50 50 50 Al(OH) 3 - gel Al(OH) 3 - gel Al(OH) 3 - gel Al(OH) 3 - gel Al(OH) 3 - gel Al(OH) 3 - gel Al(OH) 3 - gel Al(OH) 3 - gel Al(OH) 3 - gel -0.2 -0.2 -0.2 -0.2 -0.2 -0.2 -0.2 -0.2 -0.2 -0.2 gypsum gypsum gypsum gypsum gypsum gypsum gypsum gypsum 40 40 40 40 40 40 40 40 40 40 monosulfate monosulfate monosulfate monosulfate monosulfate -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 -0.3 30 30 30 30 30 30 30 30 30 30 -0.4 -0.4 -0.4 -0.4 -0.4 -0.4 -0.4 -0.4 -0.4 -0.4 ettringite ettringite ettringite ettringite ettringite ettringite ettringite ettringite ettringite 20 20 20 20 20 20 20 20 20 20 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 0 0 0 0 0 0 0 0 0 0 100 100 100 100 100 100 100 100 100 100 200 200 200 200 200 200 200 200 200 200 300 300 300 300 300 300 300 300 300 300 400 400 400 400 400 400 400 400 400 400 500 500 500 500 500 500 500 500 500 500 600 600 600 600 600 600 600 600 600 600 700 700 700 700 700 700 700 700 700 700 800 800 800 800 800 800 800 800 800 800 900 900 900 900 900 900 900 900 900 900 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 temperature / °C temperature / °C temperature / °C temperature / °C temperature / °C temperature / °C temperature / °C temperature / °C temperature / °C temperature / °C 12

Pore solution composition of CSA-1 pH 10.7 12.7 consumption K 100 of gypsum concentration / mmol/l 10 Na Al S 1 Ca 0.1 OH 0.01 Si Fe 0.001 0.0001 1 10 100 1000 time / h 13

Hydration (XRD) of CSA-2 18000 Y - ye‘elimite E - ettringite B - belite M - monosulfate E A - anhydrite S - strätlingite E (C 2 ASH 8 ) 15000 E S S E M Y 28 d 12000 7 d M intensity / - 2 d 9000 16 h 6 h 6000 4 h 2 h 3000 E E 1 h A Y Y Y Y B unhydrated 0 5 10 15 20 25 30 35 40 45 50 55 60 2 Θ / ° 14