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Geotechnical News • December 2017
THE GROUT LINE
Paolo Gazzarrini
Overture
49th episode of the Grout Line and for
this issue an article related to research
on sodium silicates. The article is
related to the application of a new
type of sodium silicate for grouting
(or for “squeezing” – which grouting
is affectionately referred to as in this
particular industry) mainly in the Oil
Industry.
Authors of the research and article are
Michael McDonald, Xianglian Li &
Timothy Evans, Julie Qiulin Shang,
Yu Guo & Bingfeng Xue.
Chemical grouting using a newly developed form of
sodium silicate
Michael McDonald, Xianglian Li, Timothy Evans, Julie Qiulin Shang, Yu Guo, Bingfeng Xue
Introduction
Sodium silicate has been a major
class of chemical grouts over several
decades for soil stabilization and water
control. Over this span, a wide variety
of sodium silicate-based formulations
have been developed to best meet
geotechnical conditions and end-use
requirements. Properties of silicate-
based grouts have been adjusted by
selection of setting agent and/or the
use of additives. With few excep-
tions, the choice of sodium silicate
has been confined to one particular
grade. Conventional manufactur-
ing of sodium silicate has restricted
the choice of products. Recently, a
novel and cost effective process was
developed to produce a lower alkalin-
ity with larger, more reactive silicate
molecules. Compared to conventional
sodium silicate, the proposed silicate
has a much higher ratio of silica to
alkali and will be described as a “high
ratio silicate” and more specifically, a
4.5 ratio sodium silicate.
To investigate the suitability of high
ratio silicate for chemical grouting of
geomaterials an in-depth study was
performed at the University of West-
ern Ontario Geotechnical Research
Centre (GRC). The study modelled
the reaction kinetics of the high
ratio sodium silicate with two differ-
ent setting agents. i.e. triacetin and
citric acid. These setting agents were
chosen because they have a success-
ful track record as well as excellent
HS&E characteristics. The researchers
at the Geotechnical Research Centre
evaluated grouts formulated with high
ratio sodium silicate in terms of the
strength gain, durability, permeability
reduction. The results were bench-
marked against conventional sodium
silicate. The premise that a lower
alkalinity would have better durability
was confirmed in the lab studies. Test-
ing also indicated other performance
enhancements such as higher compres-
sive strength.
The early adopters for evaluation of
high ratio sodium silicate have been
the petroleum industry. The industry
commonly uses sodium silicate to
modify the reservoir permeability,
block fractures, shutoff water and gas
migrating to the surface of the well. At
the time of this article, over 20 wells
have used sodium silicate to remediate
cement and block gas migration. Field
results show a high success rate at
blocking gas on the first treatment and
providing substantial cost savings.
Brief description of the
chemistry
The manufacturing of sodium silicate
provides a starting point to under-
standing the chemistry as well as the
limitations in types of sodium silicate.
The “Ratio” is the critical parameter
that governs sodium silicate chemistry
and refers to the proportion of sand
to alkali or more precisely the weight
ratio SiO2:Na2O. The vast major-
ity of grout treatments have used a
3.2 ratio sodium silicate. Compared
to lower ratio sodium silicates, the
3.2 ratio sodium silicates system is
easier to polymerize and set. Upon
setting and forming a silica gel,
