Adsorption and Desorption Characteristics of Alkali Ions in Hydrated C₃S-nano SiO₂ Pastes

Abstract

C3S pastes containing 0%, 5%, 10%, and 15% nano-SiO2 mixed with de-ionized water and alkali solutions were prepared. When C3S was completely hydrated, the pastes were ground into powders with a particle size less than 80 μm. Adsorption and desorption characteristics of alkali ions adsorbed by C₃S-nano SiO₂ pastes mixed with de-ionized water immersed in alkali solutions and those in C₃S-nano SiO₂ pastes mixed with alkali solutions, were investigated. Meawhile, the adsorption mechanisms of alkali ions were discussed. Results showed that the contents of alkali ions adsorbed by C₃S-nano SiO₂ pastes mixed with de-ionized water increased with increasing substitution levels of nano-SiO₂ and/or the initial alkali concentrations. In C₃S-nano SiO₂ pastes mixed with de-ionized water, each paste was characterized by having a fixed alkali-adsorption capacity that was essentially independent of alkali concentration. No obvious difference between the adsorption capacity of a given paste for K⁺ and Na⁺ was observed. Adsorption of alkali ions in the pastes is considered to be caused by surface force which is related to the BET specific surface area of the paste, and charge compensation of C-S-H gel, mainly by electrostatic interactions. In C₃S-nano SiO₂ pastes mixed with alkali solutions, alkali ions may enter the structure of C-S-H gel to replace a part of Ca²⁺ in the interlayer. This assumption is supported by the structural characterization of C-S-H gel using ²⁹Si MAS NMR.

Keywords

C₃S pastes / nano-SiO₂ / adsorption / desorption / alkali ions

References

[1] Rajabipour F, Giannini E, Dunant C, et al. Alkali-silica Reaction: Current Understanding of the Reaction Mechanisms and the Knowledge Gaps[J]. Cement and Concrete Research, 2015, 76: 130-146.

[2] Fournier B, Bérubé M. Alkali-aggregate Reaction in Concrete: A Review of Basic Concepts and Engineering Implications[J]. Canadian Journal of Civil Engineering, 2000, 27: 167-191.

[3] Shehata M H, Thomas M D A. Alkali Release Characteristics of Blended Cements[J]. Cement and Concrete Research, 2006, 36(6): 1166-1175.

[4] Kandasamy S, Shehata M H. The Capacity of Ternary Blends Containing Slag and High-calcium Fly Ash to Mitigate Alkali Silica Reaction[J]. Cement and Concrete Composites, 2014, 49: 92-99.

[5] Duchesne J, Bérubé M A. The Effectiveness of Supplementary Cementing Materials in Suppressing Expansion Due to ASR: Another Look at the Reaction Mechanisms. Part 2: Pore Solution Chemistry[J]. Cement and Concrete Research, 1994, 24(2): 221-230.

[6] Ochs M, Pointeau I, Giffaut E. Caesium Sorption by Hydrated Cement as a Function of Degradation State: Experiments and Modelling[J]. Waste Management, 2006, 26: 725-732.

[7] Shayan A, Diggins R, Ivanusec I. Effectiveness of Fly Ash in Preventing Deleterious Expansion Due to Alkali-aggregate Reaction in Normal and Steam-cured Concrete[J]. Cement and Concrete Research, 1996, 26: 153-164.

[8] Duchesne J, Bérubé M A. Long-term Effectiveness of Supplementary Cementing Materials against Alkali-silica Reaction[J]. Cement and Concrete Research, 2001, 31(7): 1057-1063.

[9] Hong S Y, Glasser F P. Alkali Binding in Cement Pastes. Part I. The C-S-H Phase[J]. Cement and Concrete Research, 1999, 29: 1893-1903.

[10] Stade H. On Reaction of C-S-H (di, poly) with Alkali Hydroxides[J]. Cement and Concrete Research, 1989, 19: 802-810.

[11] Bach T T H, Chabas E, et al. Retention of Alkali Ions by Hydrated Low-pH Cements: Mechanism and Na+/K+ Selectivity[J]. Cement and Concrete Research, 2013, 51(0): 14-21.

[12] Lothenbach B, Rentsch D, Wieland E. Hydration of a Silica Fume Blended Shotcrete Cement[J]. Journal of Physics and Chemistry of Earth, 2014, 70-71: 3-16.

[13] Chen W, Brouwers H J H. Alkali Binding in Hydrated Portland Cement Paste[J]. Cement and Concrete Research, 2010, 40: 716-722.

[14] Taylor H F W. A Method for Predicting Alkali Ion Concentrations in Cement Pore Solutions[J]. Advances in Cement Research, 1987, 1(1): 5-17.

[15] Richardson I G. The Nature of C-S-H in Hardened Cements[J]. Cement and Concrete Research, 1999, 29(8): 1131-1147.

[16] Jakobsen A, Anderson S, Jakobsen H J. Characterization of White Portland Cement Hydration and the C-S-H Structure in the Presence of Sodium Aluminate by 27Al and 29Si MAS NMR Spectroscopy[J]. Cement and Concrete Research, 2004, 34(5): 857-868.

[17] Viallis-Terrisse H, Nonat A, Petit J C. Zeta-Potential Study of Calcium Silicate Hydrates Interacting with Alkaline Cations[J]. Journal of Colloid and Interface Science, 2001, 244: 58-65.

[18] Rejmak P, Dolado J S, Stott M J, et al. 29Si Chemical Shift Anisotropies in Hydrated Calcium Silicates: a Computational Study[J]. The Journal of Physical Chemistry C, 2013, 117(16): 8374-8380.

[19] Magi M, Lippmaa E, Samoson A, et al. Solid-state High-resolution Silicon-29 Chemical Shifts in Silicates[J]. The Journal of Physical Chemistry, 1984, 88(8): 1518-1522.