Abstract
At present there is a pressing need to find an environmentally friendly grouting material for the construction of tunnels. Silica nanoparticles hold great potential of replacing the organic molecule based grouting materials currently used for this purpose. Chemically, silica nanoparticles are similar to natural silicates which are essential components of rocks and soil. Moreover, suspensions of silica nanoparticles of different sizes and desired reactivity are commercially available. However, the use of silica nanoparticles as grouting material is at an early stage of its technological development. There are some critical parameters such as long term stability and functionality of grouted silica that need to be investigated in detail before silica nanoparticles can be considered as a reliable grouting material. In this review article we present the state of the art regarding the chemical properties of silica nanoparticles commercially available, as well as experience gained from the use of silica as grouting material. We give a detailed description of the mechanisms underlying the gelling of silica by different salt solutions such as NaCl and KCl and how factors such as particle size, pH, and temperature affect the gelling and gel strength development. Our focus in this review is on linking the chemical properties of silica nanoparticles to the mechanical properties to better understand their functionality and stability as grouting material. Along the way we point out areas which need further research.
Highlights
1 Introduction Silica sols have increasingly been used in diverse applications in several different areas, one of which is the field of grouting
5 Conclusions Silica gels created from silica nanoparticles is a complex interdisciplinary subject
We have methodically worked our way through the different factors that may affect the silica gels, from the availability of different silica sols to the impact of environmental factors
Summary
Silica sols have increasingly been used in diverse applications in several different areas, one of which is the field of grouting. There is lot of experience in controlling the viscosity, achieving the desired penetration length, desired gel time and good sealing of the small cracks or pores by using organic molecules based grouts, the big issue is their toxicity, As shown by Svedrup et al there was considerable leaching from the acrylamide based grout used in a tunnel in Norway [7]. The induction of gelling is controllable and the gelling can be set to occur instantly or up to several hours which is often required for applications under specific conditions Other salts such as KCl and CaCl2 have been used as accelerators but not to the same extent as NaCl. Field experience in using silica sols as grouting material in Scandinavia is limited to the use of NaCl or CaCl2 as accelerators [13, 14]. We shall try to correlate these factors with the knowledge about the workability of grouted silica gels wherever it is possible
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