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Jordan Journal of Civil Engineering, Volume 10, No. 4, 2016
- 529 - © 2016 JUST. All Ri
g
hts Reserved.
Efficacy of Cement-Stabilized GBS and GGBS Cushions in Improving the
Performance of Expansive Soils
Sridevi Guda
Professor, B.V. Raju Institute of Technology, India.
E-Mail: gudasridevi@yahoo.co.in
ABSTRACT
Expansive soils undergo alternate swelling and shrinkage with changes in the moisture regime. As a result,
structures founded in these soils undergo distress. Among the several techniques available to mitigate the
problem, CNS layer technique is the one commonly adopted. Since this technique has certain limitations, an
alternative method was tried with stabilized blast furnace slag for better results. Granulated blast furnace slag
is one of the major by-products of steel plant industry. The disposal of it poses a big problem which, if not
solved, causes environmental pollution. Detailed laboratory studies were carried out on this material to
investigate its suitability as a construction material. Experiments were conducted to study the effect of the
cement content as well as the cushion thickness on the heave of the expansive soil bed. Expansive soil for the
study was collected from a depth of 1.5 m in order to see whether it contains no organic matter. The liquid
limit is 73% and the plasticity index is 45%, which are very high and show that the soil has high potential for
undergoing volume changes. A free swell index of 150% shows that the soil has a high degree of
expansiveness. The expansive soil was compacted to its MDD at OMC and above it cement-stabilized blast
furnace slag in the form of a cushion compacted to MDD at OMC was placed and the resulting heave was
measured. Cement content, varying from 2% to 10%, with increments of 2% by weight, was added to GBS in
dry condition and mixed thoroughly. Then, water corresponding to OMC was added and the layer placed
above expansive soil bed and compacted to its MDD. Experiments were conducted for different thickness
ratios of soil (ts) and cement-treated GBS (tc) given by tc/ts = 0.25, 0.5 and 0.75. Studies were also conducted
using cement-stabilized ground granulated blast furnace slag cushion in the same way as mentioned above. It
was found that granulated blast furnace slag cushion, stabilized with cement, was effective in arresting heave
of expansive soils.
KEYWORDS: Expansive soil, Ground granulated blast furnace slag, Cushion, Heave, Swelling
potential, CBR.
INTRODUCTION
In developing countries like India, provision of
complete network of road system with limited finances
by conventional methods and materials is a challenging
task. To meet the growing needs of road traffic, often,
stage-wise construction of low cost roads is preferred.
Local materials, including local soils for the
construction of the lower layers of the pavement-such
as sub-base course and sub-grade soil-are always
preferred. The local soils, such as clays, loess, marine
clays and collapsible soils, exhibit inadequate strength
and stability for supporting the wheel loads. Clays can
Received on 16/7/2015.
Accepted for Publication on 16/4/2016
Efficacy of Cement-Stabilized … Sridevi Guda
- 530 -
be plastic and compressible tending to have low shear
strengths and lose shear strength further upon wetting.
Expansive soils are basically susceptible to detrimental
volume changes with changes in moisture content. In
some clays, these volumetric changes are very high,
leading to failure of the structure. They tend to have
low resilient modulus values. Cyclic expansion-
contraction phenomena are related to seasonal
fluctuations of the soil water content around areas of
the building or pavement (Kassiff et al., 1969; Chen,
1975). It has been established that the stability and
performance of pavement is reflected by soil sub-grade.
Pavements constructed on expansive soils are bound to
fail resulting in poor performance and increased
maintenance cost. The damage caused by expansive
soils amounts to billions of dollars all over the world.
Recent research findings enabled engineers to put forth
several remedial techniques to mitigate these damages
(Nelson and Miller, 1992). Several techniques, such as
belled piers, drilled piers, friction piles and moisture
barriers, were developed to minimize the problems
posed by expansive soils. Stabilizing expansive soils
with admixtures, like lime, cement, chemicals,… etc.,
were tried and found to be effective, but uniform
blending of large quantities of soils with admixtures is
extremely difficult. Among the several methods for
arresting the swelling of expansive soil, providing a
cushion atop is commonly adopted. Various cushion
materials, such as sand, sand and boulders, murrum,…
etc., are used in practice and are found to perform
adequately when the expansive soil shows low to
moderate swelling. Based on experimental studies,
Katti (1978) proposed the CNS cushion technique and
suggested the thickness of cushion, specifications of
the materials and placement conditions to get the best
performance of the cushion. But, later studies by Subba
Rao (1999) showed that the CNS layer becomes
ineffective after the first swell-shrink cycle. Stabilized
fly ash cushion technique developed by Rao et al.
(2007) has yielded very promising results in arresting
heave. It is observed that stabilizing agents, like lime or
cement, react with reactive silica present in the fly ash
to produce cementitious bonds that help in arresting
heave. In developing countries, industrial wastes are no
longer considered as wastes and studies have been
carried out to explore the possibility of using them in
geotechnical applications. Mathur et al. (1997) reported
the suitability of slag obtained from steel industry as an
aggregate in pavements.
Granulated blast furnace slag is a by-product
obtained in the manufacture of pig iron in the blast
furnace and is formed by the combination of iron ore
with lime stone flux. The molten slag is cooled and
solidified by rapid water quenching to glassy state,
which results in the formation of sand size fragments.
The gradation and physical structure of the blast furnace
slag depend on the chemical composition of the slag, its
temperature at the time of water quenching and method
of production (Lee, 1974). Blast furnace slag has a
glassy, disordered, crystalline structure which can be
seen by microscopic examination which is responsible
for producing a cementing effect. GGBS is cementitious
on its own. It is a hydraulic material and therefore
requires no additives for hydration and hardening to take
place other than water if hydrated at an elevated
temperature and for a long time (Song et al., 2000). The
main constituents of the slag are lime, alumina, silica
and magnesia. Higgins (1998) observed that GGBS on
its own has only mild cementitious properties and in
conventional concrete it is used in combination with
Portland cement whose alkalinity provides the catalyst to
activate the cementitious properties of the GGBS. He
also reported that lime (calcium hydroxide) could
provide the necessary alkali for activation. However, BS
6699, British Standard specification for GGBS for use
with Portland cement (1986), specifies a requirement
that (CaO+ MgO+ A12O3)/ SiO2 should be greater than
1. In addition, as the CaO/ SiO2 ratio increases, the rate
of reactivity of the GGBS also increases up to a limiting
point at which increasing the CaO content makes
granulation to glass difficult. For optimum hydraulicity,
the CaO/ SiO2 ratio would need to be around 1.5. In
most applications, activation of GGBS is required which
can be achieved by blending calcium hydroxide, calcium
Jordan Journal of Civil Engineering, Volume 10, No. 4, 2016
- 531 -
sulphate, ordinary Portland cement, sodium hydroxide,
sodium carbonate and sodium sulphate (Gjorv, 1989).
Calcium sulphate is a successful activator apart from
performing an important role as a reactant (Taylor, 1986;
Daimon, 1980). A reactant participates significantly in
the reaction process, while an activator creates an
appropriate environment for the reaction process without
necessarily participating in the reaction.
In India, about 15 million tons of slag are produced
annually from steel plants (Singh et al., 2008).
Environmentally safe disposal of large quantities of
slag is not only expensive, but also poses problems in
the form of land use and health hazards. With the rise
in carbon emissions resulting in global warming and
climate change, innovative methods are vital. Studies
are conducted using GGBS with small amounts of
cement (Cockka, 2009). The production of GGBS
involves a carbon dioxide emission of only 30%
compared to cement production. Numerous additives,
such as cement kiln dust, rice husk ash, marble powder,
fly ash and GGBS, have been tried over the past
decades and their usefulness and efficiency in terms of
improvement in geotechnical properties are well
established by several researchers (Kolawole Juwunlo
Osinubi, 2006; Indraratna, 2005; Tasong et al., 1999;
Wilkinson et al., 2010). In some sulphate bearing clays,
excessive swelling was observed when the soil was
stabilized with lime. Following this, research was
carried out with ground granulated blast furnace slag
(GGBS). It was found that GGBS can reduce the
expansive tendencies of lime-stabilized sulfate bearing
clays (Wild et al., 1998). Blending cement with GGBS
produces well-established sulphate-resisting properties
in concretes. Studies were conducted with GGBS-
stabilized expansive soil with and without lime as a
cushioning material on the expansive soil sub-grade
and considerable reduction was found in the swelling
of the expansive sub-grade soil. Moreover, disposal of
these materials is not only cost intensive, but also
requires valuable land. As such, efforts are made in this
direction exploring the possibility of using these
materials alone or in combination with other additives.
However, the performance and efficiency of these
additives are influenced by several parameters, like
chemical and mineralogical composition of the soil, as
well as geotechnical properties of the additives.
So, in the present work, the industrial waste blast
furnace slag that contains substantial amounts of silica
and alumina, is used with cement as stabilizing agent to
form a cushion on the top of the expansive clay bed.
Blast furnace slag was used in two forms: the nodule
form and the ground form.
Hydration Mechanism of Portland Cement-GGBS
Mixture
Upon addition of water to a GGBS cement mixture,
hydration takes place and water begins to combine with
Portland cement to form calcium silicate hydrate. The
other reaction products of Portland cement are calcium
hydroxide and later sodium and potassium hydroxides.
These alkalis activate the GGBS which reacts with
water to produce hydrates similar to those produced by
Portland cement hydration. The GGBS, due to its high
alumina and silica content, produces somewhat more
complex hydrates than ordinary Portland cement
(OPC). Precipitates of calcium silicate hydrates and
calcium aluminate hydrates resulting from the
hydration reaction cause the excess silicates and
aluminates from the GGBS hydration to combine with
calcium hydroxide in a pozzolanic reaction. The above
reactions take place in sequential order. The first stage
starts immediately and stage four takes much longer
time to finish. Therefore, the strength development of
Portland cement/ GGBS is slower than Portland cement
alone (Wild et al., 1998).
OBJECTIVES OF THE STUDY
a. To study the swelling behaviour of expansive soil
when cement-stabilized granulated blast furnace
slag cushion and cement-stabilized ground
granulated blast furnace slag cushion with varying
cement contents were placed over it.
b. To compare the performances of granulated blast
Efficacy of Cement-Stabilized … Sridevi Guda
- 532 -
furnace slag (GBS) and ground granulated blast
furnace slag (GGBS) cushions.
c. To study the effect of cushion thickness on the
swelling behaviour of expansive soil.
d. To evaluate the soaked CBR of cement-stabilized
GBS-soil system and cement-stabilized GGBS-soil
system.
MATERIALS
Soil: The soil used in the study was collected from
Chuttugunta, Guntur Dist., in Andhra Pradesh, India.
While collecting the soil, it was ensured that the
material did not contain any organic matter. The
properties of the soil are presented in Table 1. The
liquid limit is 73% and the plasticity index is 45%,
which are very high and show that the soil has high
potential for undergoing volume changes. A free swell
index of 150% shows that the soil has a high degree of
expansiveness.
Granulated Blast Furnace Slag (GBS) and Ground
Granulated Blast Furnace Slag (GGBS): The material
was procured from the Visakhapatnam Steel Plant,
Visakhapatnam. The geotechnical and the chemical
properties of granulated blast furnace slag are given in
Table 2 and Table 3. The geotechnical properties of
GGBS are given in Table 4.
Cement: Cement used in the study was 53-grade
ordinary Portland cement.
Table 1. Geotechnical properties of expansive soil
Grain-Size Distribution
Sand
(
%
)
27.2
Silt and Cla
y
(
%
)
72.8
Li
q
uid Limit
(
%
)
73
Plastic Limit
(
%
)
28
Plasticit
y
Index
(
%
)
45
Shrinka
g
e Limit
(
%
)
14
IS Classification CH
S
p
ecific Gravit
y
2.68
OMC
(
%
)
25
Maximum Dr
y
Densit
y
(
M
g
/cum
)
1.56
Free Swell Index
(
%
)
150
CBR
(
%
)
(
Soaked
)
0.99
Table 2. Geotechnical properties of granulated blast furnace slag
Specific gravity 2.2
Grain-size distribution:
Fine sand size (0.425 to 0.075 mm) (%)
Silt and clay sizes (%)
98.5
1.5
Maximum dry density (Mg/m3) 1.50
Optimum moisture content (%) 24.4
c, Cohesion (kPa) (undrained) 20
, Angle of internal friction (degrees) 15
Soaked CBR (%) 4.3
Jordan Journal of Civil Engineering, Volume 10, No. 4, 2016
- 533 -
Table 3. Chemical composition of granulated blast furnace slag
Name of chemical Symbol % by weight
Silica SiO2 27 -38
Alumina Al2O3 7 – 15
Ferric Oxide Fe2O3 0.2 – 1.6
Manganese Oxide MnO 0.15 – 0.76
Calcium Oxide CaO 34 – 43
Sulphur Trioxide SO3 up to 0.07
Potassium Oxide K2O 0.08 - 1.83
Sodium Oxide Na2O 0.20 - 0.48
Loss on Ignition 0.20 - 0.85
* Data Source: National Slag Association.
Table 4. Geotechnical properties of ground granulated blast furnace slag
Specific gravity 2.85
Grain-size distribution:
Fine sand size (0.425 to 0.075 mm)(%)
Silt and clay sizes (%)
73
27
Maximum dry density (Mg/m3) 1.80
Optimum moisture content (%) 15.0
Plasticity Index (%) NP
Free Swell Index (%) 0
Soaked CBR (%) 6.2
HEAVE STUDIES
A schematic diagram of the experimental set up for
heave studies is shown in Figure (1). The experimental
study was carried out in galvanized iron (G.I.)
cylindrical test moulds, 280 mm in diameter and 600
mm in height. A 10 mm thick sand layer, compacted to
its maximum dry density and OMC, was laid at the
bottom of the mould. A cylindrical casing made of G.I.,
190 mm in diameter and 300 mm in height, was placed
centrally in the test tank. The gap between the casing
and the test mould was filled with coarse sand
compacted to its maximum dry density and OMC in
order to serve as draining face while saturating the
sample. The expansive soil was compacted to its MDD
and OMC in 4 layers, each 50 mm thick. A hollow
PVC pipe was placed on the top of the soil layer before
the GBS layer was compacted. Cement content,
varying from 2% to 10%, with increments of 2% by
weight, was added to GBS in dry condition and mixed
thoroughly. Then, water corresponding to OMC was
added and the layer placed above the expansive soil
Efficacy of Cement-Stabilized … Sridevi Guda
- 534 -
bed and compacted to its maximum dry density. After
the cement-stabilized GBS layer was compacted, heave
stake was placed through PVC pipe on the top of the
clay bed. A dial gauge was mounted on the top of the
heave stake. After noting the initial reading on the dial
gauge, water was admitted into the test tank in order to
saturate the sample and the heave of the soil recorded.
The process was continued till there was no change in
the dial gauge reading. After the soil specimen has
completely swollen, the moisture content was found to
ensure whether the sample was fully saturated or not.
Experiments were conducted for different thickness
ratios of soil (ts) and cement-treated GBS (tc) given by
tc/ts = 0.25, 0.5 and 0.75. Studies were also conducted
using cement-stabilized ground granulated blast
furnace slag cushion in the same way as explained
above.
Variables Studied
Cement content added
to the GBS/GGBS 2.0, 4.0, 6.0, 8.0 and 10.0
cushion (%)
Ratio of thickness of 0.25, 0.5 and 0.75
cushion to the expansive
soil bed tc/ts
RESULTS AND DISCUSSION
Effect of Cement Content
The effect of cement content used for stabilizing
blast furnace slag is shown in Figure (2). Figure (2)
shows the variation of swelling potential with the
cement content for different ratios of the thickness of
the stabilized blast furnace slag cushion (tc) to the soil
bed thickness (ts). The ratio of heave of expansive soil
bed to its initial thickness, expressed as a percentage, is
called the swelling potential of the soil. From Figure
(2), it can be seen that the swell potential the decreases
with the increase in cement content. However, for low
percentages of cement content, the reduction in swell
potential is very small, but beyond 4% cement content,
there is a substantial decrease in swell potential. The
Dial gauge
Heave stake
Hollow PVC pipe
Test tank
GBS/GGBS layer
200 mm thick soil bed
Sand drain all around and at the bottom
Figure (1): Experimental set-up for swelling studies
Jordan Journal of Civil Engineering, Volume 10, No. 4, 2016
- 535 -
silicates present in granulated blast furnace slag react
with calcium ions present in the cement in the presence
of moisture to form water insoluble calcium -
aluminosilicates which are in the form of a gel. The
pozollanic reactivity depends on parameters like
reactive silica, free lime and their specific surface. At
low cement contents, the free lime available in cement
is not sufficient for the pozzolanic reaction; hence there
is only a small reduction in swell potential. As the
cement content is increased, greater quantity is
available to penetrate into the pores of GBS for the
pozzolanic reaction with reactive silica present in the
slag, which results in considerable reduction of the
swell potential. The reduction in swell potential beyond
8% cement content is not appreciable, because the free
lime present in the cement reacts with the available
reactive silica present in the slag and further addition of
cement will be of no use, because there is no reactive
silica present in the slag. However, free lime content
can be supplemented by an external source, whereas
the reactive silica cannot be supplemented.
Figure (2): Variation of swelling potential with % of cement in GBS
Figure (3): Variation of swelling potential with % of cement in GGBS
0
2
4
6
8
10
12
0 2 4 6 8 101214
Swelling Potential (%)
% Cement in GBS
tc/ts=0.25
tc/ts=0.5
tc/ts=0.75
0
1
2
3
4
5
6
0 2 4 6 8 10 12 14
Swelling Potential (%)
% Cement in GGBS
tc/ts=0.25
tc/ts=0.5
tc/ts=0.75
Efficacy of Cement-Stabilized … Sridevi Guda
- 536 -
Effect of Cushion Thickness
Effect of thickness of cement-stabilized blast
furnace slag layer on swell potential can also be seen in
Figure (2). It can be seen that swelling potential
decreases with the increase in the thickness of the GBS
layer. The swell potential of clayey bed without any
cushion was found to be 19% and there is a marked
decrease in swell potential when stabilized blast
furnace slag cushion was placed over the clay bed. For
a cement content of 10%, the swell potential of
expansive clay was reduced to 3.57% because of the
development of cementitous bonds. The swell potential
may further come down if the super structure is built
because of increase in physical overburden on the
expansive clay bed. Hence, stabilizing expansive soils
using blast furnace slag cushion could be a better
alternative for reducing heave in the areas nearby steel
plants, as this proves to be economical apart from
solving the disposal problem.
Effect of Cement Content and Cushion Thickness of
Ground Granulated Blast Furnace Slag Cushion
Figure 3 shows the variation of swelling potential
with cement content for different ratios of cement-
stabilized ground granulated blast furnace slag cushion
to the thickness of expansive clay bed. It can be seen
that swelling potential decreases with the increase in
cement content for all the different cushions provided.
A considerable reduction in swell potential is observed
even for a small amount of cement content. For tc/ts =
0.25 and a cement content of 2%, the reduction in swell
potential of expansive clay was observed to be 73%
with respect to uncushioned clay bed. Since ground
granulated blast furnace slag is in the form of fine
powder, more surface area is available for the reaction
between lime present in cement and silica and alumina
present in GGBS. As a result, cementitious bonds
develop more freely, which are responsible for
arresting the heave of the expansive clay bed.
However, upon increasing the cement content, there is
negligible reduction in the swell potential. From the
figure, it can also be seen that the swelling potential
decreases considerably when the thickness of the
cement-stabilized GGBS cushion is increased. For tc/ts
= 0.75 and a cement content of 10%, the reduction in
swell potential of expansive clay was observed to be
82% with respect to uncushioned clay bed. Ground
granulated blast furnace slag cushion is more
efficacious in reducing the heave of expansive soils.
The relative performance of different cushions in the
reduction of heave is presented in Table 5.
Table 5. Relative performance of different cushions
Type of cushion Swelling
potential (%) % Reduction with respect
to uncushioned soil bed
No cushion 19
Cement-stabilized GBS cushion 4.17 78
Cement-stabilized GGBS cushion 3.35 82
CBR Studies
California Bearing Ratio (CBR) tests were
performed on the soil samples as per the Bureau of
Indian Standard specifications (IS:2720-part: 16,
1979), in soaked condition. In the experimental study,
CBR samples were prepared for different thickness
ratios of the stabilized GBS/GGBS cushion (tc) and the
expansive soil bed (ts). Both the soil bed and lime-
Jordan Journal of Civil Engineering, Volume 10, No. 4, 2016
- 537 -
treated GBS/GGBS were compacted to their respective
MDD and OMC values in the same manner as in the
case of heave studies. Lime content of the cushioning
material was varied from 2% to 10%, with increments
of 2%. After compaction, a surcharge weight of 5 kg,
sufficient to produce intensity equal to the weight of
the base material and the pavement, was placed during
soaking and penetration. A metal penetration plunger
of a diameter of 50 mm was used to penetrate into the
samples at a rate of 1.25 mm/min. Three CBR tests
were conducted on each specimen and the average of
the three was reported. Both heave and CBR studies
were conducted for different thickness ratios of the soil
(ts) and the lime-treated cushion (tc), given by
tc/ts=0.25,0.5 and 0.75 corresponding to the different
lime contents used in the cushion.
Effect of Cement- Stabilized GBS Cushion and
Cement-Stabilized GGBS Cushion on Soaked CBR
of Expansive Soils
The soaked CBR of blast furnace slag in nodule
form (GBS) was found to be 4.3% and that in ground
form was 6.2%. With the addition of an activator, a
considerable increase in soaked CBR was observed.
Fig.4 shows the variation of the soaked CBR with the
different thickness ratios of cement-stabilized GBS
cushion and the expansive clay bed. From Fig.4, it is
evident that the soaked CBR increases with an increase
in the thickness of the cushion. It can also be seen that
as the cement content increases, an increase in the
soaked CBR occurs, which is due to the pozzolanic
reaction between the lime present in the cement and the
silica present in the GBS. GBS has both cementitious
and pozzolanic properties. Fig.5 shows the variation of
the soaked CBR with the different thickness ratios of
cement – stabilized GGBS cushion and the expansive
clay bed. When mixed with water, GGBS develops its
hydraulic reaction (Feng, 2004). However, at room
temperature, GGBS is normally not a hydraulic
material. Activators are required to initiate hydration. If
GGBS is placed in water alone, it dissolves to a small
extent, but a protective film deficient in Ca2+ is quickly
formed, which inhibits further reaction. During initial
hydration, the reaction of GGBS produces
aluminosilicate and coats on the surface of GGBS
grains within a few minutes of exposure to water and
these layers are impermeable to water, inhibiting
further hydration, the reactions (Daimon, 1980; Caijun
et al., 1993). Richardson et al. (1994) found only a
small amount of C-S-H which formed after 150 days of
moist curing. Therefore, GGBS used on its own shows
little hydration. Reaction continues if the pH is kept
sufficiently high. The pore solution of a lime, which is
essentially an alkali hydroxide, is a suitable medium.
The presence of solid Ca(OH)2 ensures that the supply
of OH- is maintained (Taylor, 1997). The final products
of the GGBS reaction are similar to the products of
cement hydration, but the rate and intensity of reaction
differ. Slag also exhibits pozzolanic reactivity in the
presence of calcium hydroxide (Mindess, 2003). The
pozzolanic reaction takes place in which calcium
hydroxide is consumed to form secondary calcium
silicate hydrates. The primary factors of slag which
influence hydration are: chemical composition of the
GGBS, alkali concentration of the reacting system,
glass content of the GGBS, fineness of the GGBS and
temperature during the early phases of the hydration
process. Upon soaking, the lime present in the cement
reacts with the reactive silica present in the GGBS,
which is responsible for the formation of cementitious
bonds. Further, internal friction between the particles
of GBS either in granular form or ground form also
contributes to the increase in the value of CBR. The
hydration products of GGBS are found to be more
crystalline than the hydration products of Portland
cement and so add density to the cement paste (Taylor,
1990; Smolczyk, 1980). Erdal Cokca (2008) studied
the effect of ground granulated blast furnace slag
(GGBS) and GBS-cement with a view to decrease the
construction cost. It was found that there was a
decrement of 62% in the swelling potential with
GGBS-treated soil compared to virgin soil.
Sharma and Shivapullaiah (2012) studied the
compaction behavior and effect of unconfined strength
Efficacy of Cement-Stabilized … Sridevi Guda
- 538 -
of soil stabilized with fly ash and GGBS. They found
that the addition of GGBS with and without fly ash and lime has significant influence on the geotechnical
characteristics of the soil.
Hence, it can be inferred that cement-stabilized
GBS as well as GGBS cushion are effective in
improving the soaked CBR of the cushion-expansive
soil system.
The changes of microstructural development of
GGBS due to the addition of lime and cement play a
0
5
10
15
20
25
30
35
40
024681012
Soaked CBR, (%)
Cement, content %
Figure (4): Variation of soaked CBR for different cement
contents in GBS
tc/ts=0.25
tc/ts=0.5
tc/ts=0.75
0
20
40
60
80
100
120
140
0 5 10 15
Soaked CBR (%)
Cement content (%)
Figure (5): Variation of soaked CBR for different
cement contents in GGBS
tc/ts=0.25
tc/ts=0.5
tc/ts=0.75
Jordan Journal of Civil Engineering, Volume 10, No. 4, 2016
- 539 -
significant role in altering the geotechnical properties
and the mechanical behavior of the stabilized mixes.
The microstructures of the three materials viz. GGBS
and cement-stabilized GGBS are presented in Fig.6,
Fig.7 and Fig. 8. Fig.6 is a scanning electron
micrograph showing the characteristic morphology of
the GGBS. This material consists of particles of
different sizes and shapes and there is no evidence of
hydration of the GGBS. GGBS is a latent hydraulic
material and alkali should be added to initiate the
pozzolanic reaction. Fig. 7 and Fig. 8 show the SEM of
GGBS stabilized with 2% cement and 4% cement,
respectively. As could be seen from the figures, the
matrix becomes more impervious upon increasing the
cement content. Cement- stabilized GGBS appears like
a continuous phase as separation of particles is not
observed.
Figure (6): Scanning electron micrograph of GGBS
Figure (7): Scanning electron micrograph of GGBS stabilized with 2% cement
Efficacy of Cement-Stabilized … Sridevi Guda
- 540 -
Figure (8): Scanning electron micrograph of GGBS stabilized with 4% cement
CONCLUSIONS
Blast furnace slag and ground granulated blast
furnace slag cushions, stabilized with cement, are
effective in minimizing the swell of expansive soils.
For GGBS cushion, there is a significant reduction of
heave at low cement contents.
However, in the case of GBS cushion, as the cement
content is increased, the swell potential decreases steeply.
6%-8% cement content has been found to be optimum.
With the increase in the thickness of the cushion, there is a
corresponding decrease in the swell potential.
Soaked CBR was found to increase in both cement-
stabilized GBS-clay system as well as cement-
stabilized GGBS-clay system. As the cement content is
increased, the soaked CBR increased continuously and
as the thickness of the cushion material is increased,
there is an increase in the soaked CBR. At room
temperature, activators are required to initiate
hydration of GGBS. In the absence of activators, when
GGBS is placed in water alone, it dissolves to a certain
extent, but a protective film deficient in Ca2+ forms
which inhibits further reaction. GGBS with 2% of
cement as activator can be used as cushioning material
to minimize the heave of expansive soil and this
cement-stabilized expansive soil cushion system has
increased soaked CBR which improves the
performance of pavements.
Abbreviations
GBS: Granulated Blast Furnace Slag. GGBS: Ground Granulated Blast Furnace Slag.
CNS: Cohesive Non-Swelling. MDD: Maximum Dry Density.
OMC: Optimum Moisture Content. CBR: California Bearing Ratio.
Jordan Journal of Civil Engineering, Volume 10, No. 4, 2016
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