The nanostructure of Calcium-Silicate-Hydrate: The role of interlayer water

1. ACI Spring 2008 ConventionSub-Committee 236D meeting The nanostructure of Calcium-Silicate-Hydrate: The role of interlayer water Rouhollah Alizadeh, James J. Beaudoin, Laila Raki Institute for Research in Construction, National Research Council Canada

2. Outline • Introduction • Calcium-Silicate-Hydrate (C-S-H) Models • Experiments and Results • Sample PreparationHelium InflowX-Ray Diffraction29Si NMRAnalogies with hydrated cement • Concluding Remarks

3. Calcium Hydroxide Ettringite Calcium-Silicate-Hydrate (C-S-H), 60% of the paste C-S-Hin Cement Paste

4. Feldman-Sereda model, 1968 Powers-Brunauer model, 1946 Dreierkette-based models, T/J model by Taylor 1986 Jennings CM-II model, 2008 C-S-HStructural Models

5. Experiments Synthesis of Phase Pure C-S-H 1.2 CaO + SiO2 + H2O  C-S-H The C-S-H samples were conditioned at 11%RH Samples were dried by applying vacuum and heat

6. Experiments Helium Inflow He, 2 atm Helium Pycnometer

7. Experiments Helium Inflow Weight Loss from 11%RH (%) Helium inflow versus time at each weight loss for C-S-H

8. Experiments Helium Inflow Total helium inflow versus weight loss for C-S-H Increase in the helium inflow for up to about 5% weight loss Decrease in the helium inflow when more water is removed

9. ExperimentsX-Ray Diffraction 1.18 nm Weight Loss, % 1.07 nm 0 % 5 % 0.96 nm 10 % X-ray diffraction patterns for C-S-H showing changes in 002 basal spacing

10. ExperimentsX-Ray Diffraction Change in the basal spacing versus weight loss Sudden decrease in the basal spacing between 4 and 6 % weight loss Total decrease of 0.22 nm in basal spacing which is close to the diameter of a water molecule (0.28 nm)

11. X X X X X X X X ExperimentsHelium Inflow and XRD X X X X X X X X X

12. Experiments29Si NMR Q2 Q1 Weight Loss from 11%RH (%) 11.6 6.3 3.7 0.0 Q1 Q2 Chemical Shift (from TMOS), ppm Change in the polymerization of C-S-H on drying

13. Experiments29Si NMR X X X X X Schematic nanostructural model of C-S-H

14. Experiments29Si NMR Condensation of silicate chains in the interlayer Increased shielding of Q1 sites Formation of new Q2 silicon sites No sign of Q3 was observed in the spectrum

15. ExperimentsAnalogies with hydrated cement paste Cement Paste (W/C: 0.4) Q1 Q2 C-S-H (C/S: 1.2) Total helium inflow versus weight loss for hydrated Portland cement Feldman, 1970s Polymerization of C-S-H and hydrated b-C2S, effect of heat treatmentCong & Kirkpatrick, 1995

16. Conclusions Synthetic C-S-H can be used as a viable prototype for C-S-H present in hydrated Portland cement. Significant decrease in the interlayer spacing occurs at about 4-6% weight loss which corresponds well with the decrease in the helium inflow and increase in the silicate polymerization. Helium inflow in hydrated cement paste follows a similar pattern to that of synthetic C-S-H. Increased silicate polymerization of hydrated cement paste has been observed on drying.

17. Reference • Alizadeh R., Beaudoin J. J., and Raki L. “C–S–H (I)—A Nanostructural Model for the Removal of Water from Hydrated Cement Paste?” J. Am. Ceram. Soc. 90 (2) 670-672 (2007) The new results will be published soon.

18. Acknowledgments • NRC-IRC • Dr. Steven Lang • Dr. Tai Sato • Mr. Gordon Chan • Mr. Jim Margeson Thank you