High-temperature phase transition and the activity of tobermorite

Abstract

The high-temperature phase transition of tobermorite was investigated by TGA/DSC, X-ray diffraction and Infrared spectroscopy (IR), respectively. The experimental results showed that Si-OH bonds were cleaved at 724 °C and dehydroxylation occured at the same time, implying that the crystal structure of tobermorite was broken. As a result, the dehydroxylation tobermorite was metastable state, exhibiting obviously hydrolysis activity. The suspension was alkaline and Ca²⁺ ions content reached a maximum value 4.76% after heat treatment at 724 °C. The dehydroxylation tobermorite had potential reactive activity due to the strong hydrolysis activity. The disordered structure recombined to wollastonite, and the crystal structure became ordering and stable at 861 °C Finally, 2M-wollastonite structure can be found in the sample as the temperature reached up to 1 000 °C.

Keywords

reaction / tobermorite / crystal structure / hydrolysis

References

[1] Alexanderson J Relations between Structure and Mechanical Properties of Autoclaved Aerated Concrete[J]. Cement and Concrete Research, 1979, 9(4): 507-514.

[2] Mostafa NY Influence of Air-cooled Slag on Physicochemical Properties of Aautoclaved Aerated Concrete[J]. Cement and Concrete Research, 2005, 35(7): 1 349-1 357.

[3] Isu N, Ishida H, Mitsuda T Influence of Quartz Particle Size on the Chemical and Mechanical Properties of Autoclaved Aerated Concrete (I) Tobermorite Formation[J]. Cement and Concrete Research, 1995, 25(2): 243-248.

[4] Narayanan N, Ramamurthy K Structure and Properties of Aerated Concrete: A Review[J]. Cement and Concrete Composites, 2000, 22(5): 321-329.

[5] Hülya K Thomas Carlsson. Microstructural Investigations of Naturally and Artificially Weathered Autoclaved Aerated Concrete[J]. Cement and Concrete Research, 2003, 33(9): 1 423-1 432.

[6] Shaw S, Clark SM, Henderson CMB Hydrothermal Formation of the Calcium Silicate Hydrates, Tobermorite (Ca₅Si₆O₁₆(OH)₂·4H₂O) and Xonotlite (Ca₆Si₆O₁₇(OH)₂): An in situ Synchrotron Study[J]. Chemical Geology, 2000, 167(1–2): 129-140.

[7] Richardson IG The Calcium Silicate Hydrates[J]. Cement and Concrete Research, 2008, 38(2): 137-158.

[8] Eℓ-Hemaly SAS, Mitsuda T HFW Taylor. Synthesis of Normal and Anomalous Tobermorites[J]. Cement and Concrete Research, 1977, 7(4): 429-438.

[9] Shaw S, Henderson CMB, Komanschek BU Dehydration/Recrystallization Mechanisms, Energetics, and Kinetics of Hydrated Calcium Silicate Minerals: An in situ TGA/DSC and Synchrotron Radiation SAXS/WAXS Study[J]. Chemical Geology., 2000, 167(1–2): 141-159.

[10] García L, Macphee DE, Palomo A, Fernández-Jiméneza A Effect of Alkalis on fresh C-S-H Gels FTIR Analysis[J]. Cement and Concrete Research, 2009, 9(3): 147-153.

[11] Labgairi K, Jourani A, Kaddami M 2 An Isothermal (30 °C) Study of Heterogeneous Equilibria in the Sucrose (C₁₂H₂₂O₁₁)-Calcium Hydroxide (Ca(OH)₂)-Water System[J]. Fluid Phase Equilibria, 2011, 307(115): 100-103.