A comparative study on the pozzolanic activity between nano-SiO₂ and silica fume

Abstract

The pozzolanic activity of nano-SiO₂ and silica fume was comparatively studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and the compressive, bond and bending strengths of hardened paste and concrete were also measured. Results indicate that the compressive strength development of the paste made from Ca (OH)₂ and nano-SiO₂, the reaction rate of Ca (OH)₂ with nano-SiO₂ and the velocity of C−S−H gel formation from Ca(OH)₂ with nano-SiO₂ showed marked increases over those of Ca(OH)₂ with silica fume. Furthermore, the bond strength at the interface between aggregate and hardened cement paste, and the bending strength of concrete incorporated with 3% NS increased more than those with SF, especially at early ages. To sum up, the pozzolanic activity of nano-SiO₂ was much greater than that of silica fume. The results suggest that with a small amount of nano-SiO₂, the Ca(OH)₂ crystal at the interface between hardened cement paste and aggregate at early ages may be effectively absorbed in high performance concrete.

Keywords

Ca(OH)₂ / interaction / nano-SiO₂ / pazzolanic activity / silica fume

References

[1] Wang X, Tan X Y, Yin Y S. Analysis on Toughening Mechanisms of Ceramic Nano-composites[J]. Journal of Chinese Ceramics, 2000, 21: 107-111.

[2] Rong M Z, Zhang M Q, Zheng Y X. Interfacial Effects and Percolation Behavior in Silica Nanoparticles Filled Polypropylene Composites[J]. Acta Material Compositae Sinica, 2002, 19: 1-4.

[3] Dong L J, Xiong C X, Chen J. Dielectric Behavior of BaTiO₃/PVDF NanocompositesIn-situ Synthesized by the Solgel Method[J]. J. Wuhan University of Technology-Mater. Sci. Ed., 2004, 19-1: 9-14.

[4] Huang K Z, Xiong Y, Gong Y. Preparation of SiO₂ Nanoparticles by Ion Exchanging and Study on their Dispersion Stability[J]. J. Wuhan University of Technology-Mater. Sci. Ed., 2004, 19(1): 9-14.

[5] Taylor H F W. Nanostructure of C−S−H: Current Status[J]. Adv. Cem. Bas. Mater., 1993, 1: 38-46.

[6] Richardson I G. The Nature of the Hydration Products in Hardened Cement Paste[J]. Cement & Concrete Composites, 2000, 22: 97-113.

[7] Xiaozhong Zhang, wenyi Chang, Tiejun Zhang, . Nanostructure of Calcium Silicate Hydrate Gels in Cement Paste[J]. J. Am. Ceram. Soc., 2000, 83(10): 2 600-2 604.

[8] Richardson I G, Groves G W. Models for the Composition and Structure of Calcium Silicate Hydrate (C−S−H) Gel in Hardened Tricalcium Silicate Pastes[J]. Cem. Concr. Res., 1992, 22: 1 001-1 006.

[9] Chatterji S. Comment on Mesostructure of Calcium Silicate Hydrate (C−S−H) Gels in Portland Cement Paste: Short-Range Ordering, Nanocrystallinity, and Local Compositional Order[J]. J. Am. Ceram. Soc., 1997, 80: 2 959-2 960.

[10] Mitchell D R G, Hinczak I, Day RA. Interaction of Silica Fume with Calcium Hydroxide Solutions and Hydrated Cement Pastes[J]. Cem. Concr. Res., 1998, 28: 1 571-1 576.

[11] Larbi J J, Fraay A L A, Bijen J M. The Chemistry of the Pore Fluid of Silica Fume-Blended Cement Systems[J]. Cem. Concr. Res., 1990, 20: 506-511.

[12] Papadakis V G. Experimental Investigation and Theoretical Modeling of Silica Fume Activity in Concrete[J]. Cem. Concr. Res., 1999, 29: 79-86.

[13] Li S, Roy D M, Kumar A. Quantitative Determination of Pozzolanas in Hydrated Systems of Cement or Ca(OH)₂ with Fly Ash or Silica Fume[J]. Cem. Concr. Res., 1985, 15: 1 079-1 084.

[14] Taylor H F W. Cement Chemistry[M], 1990 London: Academic Press. 305-307.

[15] Zelic J, Rusic D, Veza D, . The Role of Silica Fume in the Kinetics and Mechanisms during the Early Stage of Cement Hydration[J]. Cem. Concr. Res., 2000, 30: 1 655-1 662.

[16] Taylor H F W. Cement Chemistry[M], 1990 London: Academic Press. 146-148.