Mechanical tests on a new non-cementitious grout, silica sol:
A laboratory study of the material characteristics
Division of GeoEngineering, Department of Civil and Environmental Engineering, Chalmers University of Technology, SE-412 96 Go
Received 1 March 2005; received in revised form 10 September 2005; accepted 13 September 2005
Available online 2 November 2005
This introductory study on mechanical properties aims to characterize silica sol and to improve knowledge of the suitability of silica
sol as grout. Silica sol is a non-cementitious grout that consists of spherical particles of amorphous silica, with a diameter of 5–100 nm.
For a testing period of six months, specimens of silica sol were kept at 8 °C with three relative humidities: 75%, 95% and 100%. During
the test period measurements of the drying shrinkage, compressive strength, modulus of elasticity (YoungÕs modulus), shear strength and
ﬂexural strength were made. The results show that the strength of silica sol continues to increase for a long time and during the test
period of six months the strength kept increasing. The increase of strength depends on the humidity to which silica sol is exposed but
the humidity also aﬀects the drying shrinkage. A lower humidity results in a faster increase in strength but also a larger shrinkage.
Ó 2005 Elsevier Ltd. All rights reserved.
Keywords: Grout; Silica sol; Colloidal silica; Mechanical tests; Durability
Cement is the dominant type of grout used for perme-
ation grouting in hard rock today. In most applications ce-
ment is the most suitable grout. However, the limitation in
penetrability for cement-based grouts makes them less suit-
able in low permeable rock. In situations where large
reduction of the water leakage is required, cement cannot
always seal eﬃciently enough to meet the requirements.
The minimum fracture aperture that cement can penetrate
is around 50–100 lm(Kutzner, 1996; Emmelin et al., 2004)
and to seal fractures of this aperture is not always suﬃ-
cient. Especially for urban environments with sensitive sur-
roundings, there are often strict regulations and fractures
narrower than 50–100 lm must be sealed. Cement also
has a high pH value, which can be a problem when a con-
trolled and stable environment is wanted, for example in a
nuclear waste repository.
Silica sol, a new non-cementitious grout for permeation
grouting in hard rock, has been studied by Axelsson and
Nilsson (2002), Funehag and Gustafson (2004) and Fune-
hag (2005). These studies show that silica sol can penetrate
fractures with an aperture of at least 10 lm. Studies by
Yonekura (1997), Persoﬀ et al. (1999) and Gallagher and
Koch (2003) investigated the mechanical properties of sil-
ica sol grouted sands. To characterize the mechanical prop-
erties of silica sol itself, this introductory study is made.
Silica sol consists of very small, spherical particles made
of amorphous silica, SiO
, suspended in water (Iler, 1979).
The particle size ranges from 5 to 100 nm; the pH value of
silica sol is around 10, which means that silica sol has a
lower pH than cement. To use silica sol as a grout, the par-
ticles have to aggregate and form a gel within predictable
time. This is done with diﬀerent kinds of saline solutions;
the most common are NaCl and CaCl
. Adding more salt
causes a quicker gelling. When silica sol starts to aggregate,
a network made up of the silica particles forms and the
water that is present in the sol becomes trapped inside
the network. Depending on the environment (temperature,
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Tunnelling and Underground Space Technology 21 (2006) 554–560