Journal of Rock Mechanics and Geotechnical Engineering 12 (2020) 149e159
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Full Length Article
Behavior of zeolite-cement grouted sand under triaxial compression test
Peyman Jafarpour*, Reza Ziaie Moayed, Afshin Kordnaeij
Department of Civil Engineering, Imam Khomeini International University, Qazvin, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 16 November 2018
Received in revised form
24 May 2019
Accepted 24 June 2019
Available online 11 December 2019
Permeation grouting with cement agent is one of the most widely used methods in various geotechnical
projects, such as increasing bearing capacity, controlling deformation, and reducing permeability of soils.
Due to air pollution induced during cement production as well as its high energy consumption, the use of
supplementary materials to replace in part cement can be attractive. Natural zeolite (NZ), as an environmentally friendly material, is an alternative to reduce cement consumption. In the present study, a
series of consolidated undrained (CU) triaxial tests on loose sandy soil (with relative density Dr ¼ 30%)
grouted with cementitious materials (zeolite and cement) having cement replacement with zeolite
content (Z) of 0%, 10%, 30%, 50%, 70% and 90%, and water to cementitious material ratios (W/CM) of 3, 5
and 7 has been conducted. The results indicated that the peak deviatoric stress (qmax) of the grouted
specimens increased with Z up to 50% (Z50) and then decreased. The strength of the grouted specimens
reduced with increasing W/CM of the grouts from 3 to 7. In addition, by increasing the stress applied on
the grouted specimens from yield stress (qy) to the maximum stress (qmax), due to the bond breakage, the
effect of cohesion (c0 ) on the shear strength reduced gradually, while the effect of friction angle (40 )
increased. Furthermore, in some grouted specimens, high confining pressure caused breakage of the
cemented bonds and reduced their expected strength.
Ó 2019 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by
Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/
licenses/by-nc-nd/4.0/).
Keywords:
Permeation grouting
Sand
Zeolite
Cement
Improvement
1. Introduction
In recent years, due to the development of cities, there is a
growing need for construction of underground structures, highways, and high-rise buildings. Therefore, stabilization of loose
sandy soils is very important when constructing such projects.
Permeation grouting with low pressure is an appropriate method
for improving the loose soil under the foundations of sensitive
structures and bridge footings, due to the merits of no change in soil
structure and no large displacement. In permeation grouting cases,
suspension grout penetrates into the soil pores with low pressure,
creating cohesion between grains and also a denser soil mass.
Adding cement to the soil creates several chemical reactions
that lead to short- and long-term changes in the soil. The main
product of Portland cement hydration is the calcium silicate hydrate (CeSeH) gel that results from the hydration of silica compounds in the cement. Another important product is the calcium
* Corresponding author.
E-mail address: peymanjafarpour@gmail.com (P. Jafarpour).
Peer review under responsibility of Institute of Rock and Soil Mechanics, Chinese Academy of Sciences.
hydroxide (Ca(OH)2). The hydration reactions include the following
two reactions (Rao, 2003):
2C3S þ 6H/CeSeH þ 3Ca(OH)2
(1)
2C2S þ 4H/CeSeH þ Ca(OH)2
(2)
where C, S and H represent CaO, SiO2 and H2O, respectively.
Cement production can cause air pollution, and it consumes
high energy. In addition, cement-based stabilized soils have shown
brittle behavior (Clough et al., 1981; Airey and Fahey, 1991; Coop
and Atkinson, 1993; Lagioia and Nova, 1995; Schnaid et al., 2001;
Collins and Sitar, 2009; Marri et al., 2012; Hamidi and
Hooresfand, 2013; Anagnostopoulos, 2014; de Bono et al., 2014).
The brittle behavior of cemented soil can cause a sudden failure of
its structures. Therefore, the use of cemented soils may not be
applicable in some cases. In order to prevent brittle behavior,
replacing parts of cement with other materials can be very effective
(Lothenbach et al., 2011; Scrivener and Nonat, 2011;
Ramezanianpour et al., 2012).
A pozzolan is a siliceous or siliceous-aluminous material. It
possesses slight or no cementing property but will, in the presence
of moisture and in a finely divided form, react with Ca(OH)2 at
https://doi.org/10.1016/j.jrmge.2019.06.010
1674-7755 Ó 2019 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BYNC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
150
P. Jafarpour et al. / Journal of Rock Mechanics and Geotechnical Engineering 12 (2020) 149e159
ordinary temperatures to form compounds possessing cementitious properties (ASTM C125-07, 2007). The pozzolanic reactions
are as follows (Muhunthan and Sariosseiri, 2008):
Ca(OH)2 þ SiO2/CeSeH
(3)
Ca(OH)2 þ Al2O3/CeAeH
(4)
The natural zeolite (NZ), a new environmentally friendly
pozzolanic material, is an appropriate alternative for these purposes. Zeolite contains a large amount of SiO2 and Al2O3 compounds, which are combined with Ca(OH)2 produced in cement
hydration process, resulting in production of CeAeH and CeSeH
gels, which improve the microstructure of the cemented sand. Due
to its advantages such as high cation exchange capacity and high
specific surface area, zeolite has been used in various geotechnical
studies (Kaya and Durukan, 2004; Ahmadi and Shekarchi, 2010;
Hong et al., 2011; Ören et al., 2011; Ling et al., 2013, 2015;
Narasimhulu et al., 2013; Turkoz and Vural, 2013; Shang, 2015;
Mola-Abasi and Shooshpasha, 2016; Savaş, 2016). In recent years,
zeolite has been used as a cement additive to stabilize soils by
mixing method (Shi, 2013; Mola-Abasi et al., 2016, 2018a, b). The
results of unconfined compression tests conducted by Shi (2013) on
clayey silt and gravel sand using cement-zeolite (with a zeolite to
cement ratio of 1:9) by mixing method for stabilization demonstrated that the maximum unconfined compression strength (UCS)
was obtained for 10% binder compared to 2.5% and 5% contents.
Mola-Abasi et al. (2016) investigated the zeolite influence on the
UCS of mix-cemented sandy soil. The results demonstrated that the
UCS value of the cemented sand increases with zeolite content (Z)
increasing up to 30% (Z30) and decreases beyond Z30.
The amounts of SiO2 and Al2O3 in reaction with CaO in cement
hydration and pozzolanic reactions have a significant influence on
the strength of zeolite-cement grouted sand specimens. Under
sufficient CaO compound, increasing SiO2 and Al2O3 compounds
can result in more cementitious products and consequently increase its strength (Kordnaeij et al., 2019a). To consider the effect of
active compounds (CaO, SiO2 and Al2O3) on the strength of grouted
specimens, Mola-Abasi et al. (2018b) introduced a parameter called
active particles (compounds). By defining the parameter active
compounds (AC), the influence of zeolite and cement compounds
on the cementation of the cemented specimens is considered.
Mola-Abasi et al. (2018a) conducted unconfined compression tests
on zeolite-cement-sand and showed that by replacement of
cement with 30% zeolite, the amounts of SiO2 and Al2O3 compounds are close to that of CaO compound. Accordingly, they
concluded that 30% is the optimum value of zeolite content corresponding to the maximum UCS.
The cemented sands, due to consolidation before shear loading,
show a more complex behavior in the triaxial test than that in the
unconfined compression test. Saxena and Lastrico (1978) reported
that the cohesion caused by the cementation between particles
plays a significant role in the strength of the specimen at axial
strain (ε) smaller than 1%. When ε > 1%, the effect of internal friction angle dominates the shear strength of the cemented soils. They
also found that high confining pressure could break the bonds of
the sand particles. Coop and Atkinson (1993) proposed three
stressestrain behavior states of the cemented soils as indicated in
Fig. 1. In the first state, the isotropic consolidation pressure is larger
than the bonding strength of the specimen and the cementation
bonds are destroyed under isotropic consolidation pressure prior to
the shear loading. Therefore, like uncemented sand specimens, the
shear strength of the specimen is governed by frictional behavior.
In the second state, the isotropic consolidation pressure is lower
than the bonding strength of the specimen, which does not lead to
Fig. 1. Stressestrain curves of cemented specimens having different cementation
levels. q - deviatoric stress; p0 - mean stress; εa - axial strain (Coop and Atkinson, 1993).
the destruction of the cementation bonds. In this case, the
cementation bonds will be destroyed during axial loading. Afterwards, the strength will be affected by friction and specimen will
behave like uncemented specimen. In this state, a limited peak in
stressestrain curve is usually seen after an elastic response. The
third behavior state occurs at the specimens under low isotropic
consolidation pressure and the cementation bonds of the specimen
prior to shear loading are intact. In this state, the stressestrain
curve has a considerable peak corresponding to the peak strength
of the cemented samples.
The specimen shape of failure from brittle to ductile is affected
by cement amount, soil density, and confining pressure. Increasing
the density of cement-stabilized soil leads to increased stiffness
and brittle behavior (Huang and Airey, 1998). The ductility of the
stabilized soils increases with decreasing cement content (Consoli
et al., 2007). High confining pressure destroys the bonds between
stabilized soil particles and causes a ductile failure, while the
cemented soil under low confining pressure shows a brittle failure
(Clough et al., 1981; Airey and Fahey, 1991; Coop and Atkinson,
1993; Lagioia and Nova, 1995; Cuccovillo and Coop, 1999; Schnaid
et al., 2001; Collins and Sitar, 2009; Hamidi and Hooresfand,
2013; Anagnostopoulos, 2014).
Numerous studies are reported on injection of cement-based
grout for stabilization of soils (Mollamahmutoglu and Yilmaz,
2011; Pantazopoulos and Atmatzidis, 2012; Pantazopoulos et al.,
2012; Markou and Droudakis, 2013; Abraham et al., 2014;
Mollamahmutoglu and Avci, 2015a, b; Yildiz and Soganci, 2015;
lu, 2016), only a few studies have been
Avci and Mollamahmutog
carried out on the addition of zeolite to cement for soil stabilization
using mixing method (Shi, 2013; Mola-Abasi et al., 2016, 2018a, b).
Therefore, the study on loose sandy soil injected with zeolitecement grout can be of great importance. Accordingly, in the present study, the influence of zeolite content, water to cementitious
material ratio (W/CM) and confining pressure (CP) on the strength
and behavior of zeolite-cement grouted sands under consolidated
undrained (CU) triaxial tests is investigated.
2. Material and methods
2.1. Materials
Firoozkooh uniform silica sand (D11) was utilized in this
investigation. The characteristics of D11 and its grain-size distribution curve are presented in Table 1 and Fig. 2, respectively.
Portland cement of Abyek (Type II) and clinoptilolite type NZ from
the quarries in the north of Semnan, Iran were used. Table 2 presents the chemical compositions of the cementitious materials
P. Jafarpour et al. / Journal of Rock Mechanics and Geotechnical Engineering 12 (2020) 149e159
Table 1
Characteristics of the sand used.
151
Table 2
Chemical compositions (%) of the cementitious materials used.
Characteristic
Value
Standard
Material
CaO
SiO2
MgO
K2O
Na2O
Al2O3
Fe2O3
SO3
Specific gravity, Gs
Minimum void ratio, emin
Maximum void ratio, emax
Coefficient of uniformity, Cu
Coefficient of curvature, Cc
D10 (mm)
D30 (mm)
D60 (mm)
Soil classification
2.63
0.52
0.89
3.87
1.13
0.29
0.55
1.03
SP
ASTM
ASTM
ASTM
ASTM
ASTM
ASTM
ASTM
ASTM
ASTM
Cement
Zeolite
61.9
4.2
20.3
69.12
3
0.65
0.68
1.09
0.2
0.84
5.4
10.79
3.94
0.73
1.97
0.04
D854-14, 2014
D4253-00(2006), 2006
D4254-00(2006), 2014
D2487-11, 2011
D2487-11, 2011
D2487-11, 2011
D2487-11, 2011
D2487-11, 2011
D2487-11, 2011
Note: D60, D30 and D10 are the particle sizes corresponding to 60%, 30% and 10% finer
on the cumulative particle-size distribution curve, respectively.
utilized in this study (ASTM C114-11, 2011). The specific gravity (Gs)
values of zeolite and cement are 2.2 and 3.1, respectively. In order to
reduce the viscosity of the grouts, which results in better permeation in the soil, a superplasticizer from Namikaran company of Iran
was utilized, which amounts to 1% of cementitious material mass
(according to the manufacturer’s suggestion, within 0.5%e1.5%).
2.2. Sample preparation
Specimens with the relative density (Dr) of about 30%, indicating
a loose condition, were prepared. The weight of each specimen was
determined from the specific gravity (Gs) of soil and the soil void
ratio (e) obtained from the following equation:
emax e
Dr ¼
emax emin
(5)
The calculated amount of soil was poured in the split, cylindrical
and acrylic mold of 50 mm in diameter and 100 mm in height. A
thin talc was placed inside the mold so that the specimen can be
easily removed from the mold when opening. All the sand specimens were prepared using dry pouring method by a funnel. Two
PVC-type caps containing a valve for entering and exiting suspension were put on each side of the molds. For dispersing the grout
across the specimen surface, a layer of coarse sand with a thickness
of about 1.7 cm was placed at the bottom of the caps (ASTM D432002, 2002). At the end, the caps were clamped using tie rods.
2.3. Grouting procedure
The grouting suspensions were prepared with the weight ratio
of W/CM equal to 3, 5 and 7. At first, the cement and zeolite mix was
poured into the mixer container in the required amounts. Subsequently, water and superplasticizer were added to them and mixed
for 5 min at 1000 rounds per minute (rpm). The measured apparent
viscosities of grouts with and without superplasticizer for a 60 rpm
rotation speed and at 0 min (Pantazopoulos and Atmatzidis, 2012)
are reported in Table 3. From Table 3, it can be found that:
(1) The superplasticizer has an important effect on the viscosity
of grout.
(2) The suspension viscosity has been increased with increasing
zeolite. This could be due to high cation exchange capacity
and high specific surface area, and thus high water absorption of zeolite.
(3) The suspension viscosity has been decreased with increasing
W/CM ratio. In fact, with increasing W/CM ratio, the suspension viscosity is close to that of water (1 mPa s).
As can be seen in Table 3, the viscosities of suspensions containing the superplasticizer are less than 1.88 mPa s, which are
appropriate for grouting; while most of the suspensions’ viscosities
without superplasticizer are too high to permeate in the soil.
Therefore, the superplasticizer was used for preparing all suspensions to improve their rheological properties.
Laboratory equipment prepared according to ASTM D4320-02
(2002) was used for grouting to produce small-size grouted sand
specimens (Kordnaeij et al., 2019b). Initially, water (with volume
three times the void volume in the specimens) was pumped from
the bottom to the top of the specimen at a pressure of 10 kPa to
enhance saturation. Water flow continued until no air bubbles
appeared from the top of the specimen (Kordnaeij et al., 2019a). The
injection of grout was conducted under injection pressure of less
than 50 kPa. The grouts were passed through the specimens up to
twice the specimen’s void volume (Dupla et al., 2004;
Pantazopoulos and Atmatzidis, 2012; Kordnaeij et al., 2019a, b, c).
The grouted sands were removed from the molds after 48e72 h and
wrapped in a plastic sheet while the talc sheet is around them
(Fig. 3) and then placed in double plastic bags to prevent changes in
water content of the specimens for 28 d curing at the temperature
of approximately 23 C.
Table 3
Apparent viscosity of grouts.
Grout
W/CM
Apparent viscosity (mPa s)
Z0
Z10
Z30
Z50
Z70
Z90
Without superplasticizer
3
5
7
3
5
7
1.7
1.39
1.36
1.34
1.29
1.21
2.18
1.61
1.45
1.45
1.33
1.22
2.71
1.74
1.59
1.57
1.36
1.24
5.91
2.11
1.65
1.65
1.43
1.26
6.12
2.65
2.13
1.77
1.55
1.31
6.24
3
2.61
1.88
1.65
1.36
With superplasticizer
Fig. 2. Grain-size distribution curve of the used sand.
Note: Zi represents the cement replacement with zeolite content equal to i (%).
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P. Jafarpour et al. / Journal of Rock Mechanics and Geotechnical Engineering 12 (2020) 149e159
2.4. Triaxial tests
The triaxial tests were conducted in strain control mode at strain
ratio of 0.5%/min with a constant confining pressure during the test.
Parameters of mechanical behaviors of grouted sand were obtained
by measuring changes in stress, strain and excess pore pressure in
the CU triaxial tests according to ASTM D4767-95 (1995). The tests
were conducted with a computer-controlled triaxial device, as
shown in Fig. 4. In order to accelerate the saturation of the specimens, before allowing deaired water to infiltrate into the specimens, they were percolated by CO2 to expel the air in the specimen
pores and were saturated under a back pressure of 300 kPa to
ensure B values (ratio of pore water pressure increment to corresponding cell pressure increment) equal to or greater than 95%. The
specimens were then isotropically consolidated at the desired
effective consolidation stresses (100 kPa, 300 kPa and 500 kPa). In
the grouted sand specimens, consolidation was continued until full
dissipation of excess pore water pressure was expected.
Fig. 3. Grouted sand specimen.
Fig. 4. Computer-controlled triaxial device.
Fifty four CU tests were carried out to investigate the effects of Z,
W/CM and CP on the resistance and failure behavior of the grouted
sand specimens. In the present study, a wide range of zeolite contents (0%, 10%, 30%, 50%, 70% and 90%) and three W/CM ratios (3, 5
and 7) as well as three CP values (100 kPa, 300 kPa and 500 kPa)
were investigated. Table 4 summarizes the CU tests conducted in
the present study.
2.5. Scanning electron microscope (SEM) analysis
Microscopic investigation would help to distinguish the grouted
sand microstructure, and the cementitious bonds formed between
Table 4
Specimen characteristics for CU triaxial tests.
Test No.
a
1
2a
3a
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
a
Z (%)
W/CM
CP (kPa)
e
e
e
0
0
0
0
0
0
0
0
0
10
10
10
10
10
10
10
10
10
30
30
30
30
30
30
30
30
30
50
50
50
50
50
50
50
50
50
70
70
70
70
70
70
70
70
70
90
90
90
90
90
90
90
90
90
e
e
e
3
3
3
5
5
5
7
7
7
3
3
3
5
5
5
7
7
7
3
3
3
5
5
5
7
7
7
3
3
3
5
5
5
7
7
7
3
3
3
5
5
5
7
7
7
3
3
3
5
5
5
7
7
7
100
300
500
100
300
500
100
300
500
100
300
500
100
300
500
100
300
500
100
300
500
100
300
500
100
300
500
100
300
500
100
300
500
100
300
500
100
300
500
100
300
500
100
300
500
100
300
500
100
300
500
100
300
500
100
300
500
Uncemented specimen.
P. Jafarpour et al. / Journal of Rock Mechanics and Geotechnical Engineering 12 (2020) 149e159
the sand particles due to chemical reactions. To this end, SEM images were taken from the center of the grouted sand specimen
columns at the SEM laboratory (VEGA-TESCAN model), Razi
Metallurgical Research Center, Tehran, Iran. The SEM analyses were
performed on injected specimens with grouts containing W/CM ¼ 3
and Z ¼ 0%, 50% and 90%. Also, the SEM analyses were carried out
on grouted specimens with Z ¼ 50% and W/CM ¼ 3, 5 and 7.
3. Results and discussion
The CU tests with three CPs of 100 kPa, 300 kPa and 500 kPa
were carried out on clean sand and grouted sand specimens with
different water to cementitious materials (zeolite þ cement) ratios
(W/CM ¼ 3, 5 and 7) and cement replacement with zeolite contents
(Z ¼ 0%, 10%, 30%, 50%, 70% and 90%) at 28 d curing period. In the
following sections, the effects of each of these parameters on the
mechanical behaviors of the grouted sand specimens are discussed.
3.1. Effect of cement grouting
Fig. 5 shows the results of triaxial tests on the clean (uncemented) sand and the grouted sand specimens with cement alone
(Z0) and W/CM of 3. The stressestrain and pore pressure behavior of
uncemented loose sand specimens are typical behavior of ductile
material. This is also reflected in the bulging of specimens at failure.
As shown in Fig. 5a, the deviatoric stress (q) increases with increase
in confining pressure (CP). Fig. 5 shows that grouting has a
noticeable effect on the specimen’s strength at all of the CP values.
The peak deviatoric stress (qmax) increases significantly due to
cement grouting. The effect of cementitious bonds is considerable
up to the yield stress (qy). The yield stress is the threshold of the
Fig. 5. Shear behavior of clean sand and sand specimens grouted with cement containing W/CM ¼ 3. CS: clean sand; GS: grouted sand.
153
major plastic strains, indicating the beginning of the progressive
debonding (Trhlíková, 2013). Beyond qy, the bond’s effect dissipates
gradually (Fig. 5a). For cement grouted specimens, qy associated
with the beginning of cementitious bond breakage increases with
CP increasing from 100 kPa to 500 kPa. At the beginning of loading,
the positive pore pressure occurs, followed by significant negative
pore pressure at the final state. While uncemented sand specimens
show ductile behavior, cement content leads to more brittle
behavior. The general behavioral pattern in this case (cement
grouted) begins with linearly elastic behavior due to cementitious
bonds to reach a yield stress at a low axial strain, followed by a
gentle stress increase at high strain to reach qmax and finally, more
gentle strain-softening behavior after qmax. This is consistent with
previous research conducted on cement grouted sand specimens
(Dano and Hicher, 2003).
3.2. Effect of zeolite content
Fig. 6 demonstrates the shear behavior of the grouted sand
specimens with zeolite contents of Z ¼ 0%, 50% and 90% and W/CM
of 3 under CP ¼ 100 kPa. All of the specimens grouted with zeolitecement suspensions show a contractive-like response with positive
pore water pressure, followed by negative pore water pressure at
the final state. The negative pore water pressure near failure causes
the specimens to resist more stresses due to suction creation in
pores.
Fig. 6. Shear behavior of grouted sand specimens with different zeolite contents and
W/CM ¼ 3 under CP ¼ 100 kPa.
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The qmax values of the grouted sand specimens with respect to
the zeolite content for different values of W/CM (3, 5 and 7) and CP
(100, 300 and 500 kPa) are shown in Fig. 7. As it can be seen, at all of
the CP values, with increasing zeolite content up to Z ¼ 50% (Z50),
qmax of the grouted sand specimens increases. Beyond Z50, qmax
Fig. 7. Peak strength (qmax) of the grouted sand specimens against zeolite content: (a)
W/CM ¼ 3; (b) W/CM ¼ 5; and (c) W/CM ¼ 7.
reduces with increasing zeolite content. Such variations in qmax
versus changes in zeolite content are influenced by two factors of
the cementitious bonds formed by grouting into the sand specimens and decreasing soil porosity by partial filling of the soil pores.
Kordnaeij et al. (2019a) stated that by increasing the zeolite
content up to 30% (Z30), the bonds formed between grouted sand
particles become stronger than the bonds of specimens grouted
with cement alone. The addition of zeolite to cement grouting
suspension, due to its high pozzolanic reaction, improves the
strength of the grouted sand specimens. This is due to the high
amounts of Al2O3 and SiO2 in zeolite, which react with Ca(OH)2
from cement hydration, resulting in production of additional C-A-H
and CeSeH gels in the stabilized sand specimens. With increasing
zeolite content, the cement amount in the grouted specimen reduces. This means that as zeolite content increases, whereas the
amount of CaO reduces, the amounts of SiO2 and Al2O3 compounds
increase (Table 2). If the amounts of Al2O3 and SiO2 compounds in
the grouted sand specimens are greater than that of CaO compound, due to the lack of sufficient CaO, the pozzolanic reactions
are reduced. The pozzolanic reactions continue as long as sufficient
CaO compound is present (Mola-Abasi et al., 2018b). According to
the quantities of zeolite and cement in each injection grout, as well
as the amounts of Al2O3, SiO2 and CaO in zeolite and cement, active
compounds (AC, minimum weight percentage between
SiO2 þ Al2O3 and CaO in the grouted specimens) parameter is
measured. The parameter AC is determined as follows (Kordnaeij
et al., 2019a):
If CaO SiO2 þ Al2 O3 /AC ¼ CaO amount
(6)
If CaO > SiO2 þ Al2 O3 /AC ¼ SiO2 þ Al2 O3 amount
(7)
Table 5 shows an example of determining the parameter AC for
sand specimen injected with grout having Z30 and W/CM ¼ 3. The
quantities of Al2O3, SiO2 and CaO given in Table 2 are used to
determine AC.
Fig. 8 shows the variations of AC against zeolite content for
suspensions with all W/CM ratios. In this figure, the maximum
amounts of AC are related to Z ¼ 30%. Thus, it is expected that with
an increase in zeolite content by more than 30%, qmax of the
grouted sand specimen will be reduced. However, in Fig. 7, the
highest values of qmax were obtained in specimens grouted with
suspensions having Z50 instead of Z30. This is because the increase
in qmax, in addition to its dependence on cementitious bonds, is
affected by the grouted sand specimen’s porosity (n). In addition,
grouting reduces n value of specimens compared to that of clean
sand. Fig. 9 indicates the variation of the porosity due to grouting
against zeolite content of grouted sand specimens with different
W/CM ratios. By increasing the amount of zeolite in the grout, due
to the lower Gs of zeolite (2.2) compared to that of cement (3.1), a
greater reduction is obtained in the n value of the grouted sand
specimens. Therefore, although the optimum zeolite content for
the stronger cementitious bonds is 30%, increasing zeolite content
always increases the grouted specimen’s porosity. By conducting a
series of unconfined compression tests, Kordnaeij et al. (2019a)
stated that the optimum amount of zeolite content (30%) corresponding to the UCS is affected by the cementitious bonds alone.
Under unconfined compression test, due to the lack of confining
pressure, the decreasing effect of porosity on UCS is not considered. However, in the present study, due to the fact that the
specimens are subjected to confining pressure, both cementitious
bonds and porosity affect the strength of the grouted sand specimens. Accordingly, for all W/CM and CP values, the highest
deviatoric stress is obtained at zeolite content of 50%. But, beyond
Z50, any increase in zeolite content tends to decrease qmax.
P. Jafarpour et al. / Journal of Rock Mechanics and Geotechnical Engineering 12 (2020) 149e159
155
Table 5
An example of determining AC for the grouted specimens with Z30 and W/CM ¼ 3.
W/CM
3
CM (%)
11
Z (%)
30
C (%)
70
Amount of SiO2þAl2O3 (%)
In cement (¼(20.3 þ 5.4) 104CM$C)
In zeolite (¼(69.12 þ 10.79) 104CM$Z)
Total
1.98
2.64
4.62
Amount of CaO
(¼(61.9CM$Cþ4.2CM$Z) 104) (%)
AC (%)
4.9
4.62
Note: C: cement content; AC: minimum of amount of SiO2þAl2O3 or CaO.
Fig. 8. Variations of AC against zeolite content for different W/CM values.
Fig. 9. Variations of porosity (n) due to grouting versus zeolite content for different W/
CM values.
In Fig. 10, the SEM images of specimens injected with W/CM ¼ 3
and Z0, Z50 and Z90 are presented. The microstructure difference is
shown with different zeolite contents. According to Fig. 10a,
Ca(OH)2 sheets are observed in the grouted specimen with cement
alone (Z0). In the specimen grouted with Z50 (Fig. 10b), the amount
of Ca(OH)2 is reduced, while the cementitious gels are clearly
visible. As the Ca(OH)2 compound from the hydration reactions is
consumed by pozzolanic reaction with Al2O3 and SiO2 compounds
in zeolite, additional gels are produced. To confirm Ca(OH)2 and gel
in Fig. 10, energy dispersive spectroscopy (EDS) spectra are used.
Fig. 11 shows the average element composition of the grouted
specimens (taken from the selected target in Fig. 10) as a spectral
diagram. As seen in Fig. 11a, high-intensity peaks for Ca (51.08%)
and O (25.98%) indicate the major elements that compose Ca(OH)2.
Fig. 11b shows strong peaks for O (23.08%), Si (22.28%), Ca (15.91%),
and a weaker peak for Al (3.04%), indicating the elements that
compose high CeSeH gels and low C-A-H gels. The Au peak in
Fig. 11 is a result of the gold coating used in specimen preparation
for SEM tests.
Although the porosity of sand specimen grouted with Z90 decreases, Ca(OH)2 and gels are not observed (Fig. 10c). Due to the low
cement content, the hydration reaction and subsequently the
amount of Ca(OH)2 are reduced, and eventually the pozzolanic
reaction to form gels decreases.
The shear strength of the grouted sand specimens includes two
components of cohesion due to cementitious bonds (c0 ) and internal friction angle (40 ). Fig. 12 shows the variations of the drained
shear strength parameters corresponding to qy for the sand specimens grouted with different Z and W/CM values. As seen in Fig. 12a,
all grouted specimens have cohesion at the yield point (c0y ). With
increasing zeolite content up to Z30, c0y in the grouted sand specimens increases. After Z30, any increase in Z leads to a decrease in c0y .
This is because the cohesion is related to the cementitious bonds
formed in the grouted sand specimens. Kordnaeij et al. (2019a)
showed that the most bonds are formed in the grouted specimens with Z30. Therefore, for all W/CM values, Z30 corresponds to
the maximum c0y . The effective internal friction angles at the yield
point (40y ) for grouted specimens with different W/CM and Z values
are shown in Fig. 12b. As it can be seen, grouting with cement alone
has an increasing effect on 40y of the grouted specimen. This is due
to the fact that, as previously mentioned, the porosity of the
specimens decreases with increasing zeolite in the grouted specimens (Fig. 9).
Fig. 13 shows the variations of c0 and 40 corresponding to failure
(qmax) towards Z for the grouted sand specimens. As illustrated in
Fig. 13a, in most grouted sand specimens, the cohesion corresponding to failure (c0p ) is zero or negligible. This is because the
beginning of cementitious bond breakage occurs after qy. Thus,
before qy, the strength of the cemented specimens is substantially
affected by their c0 values. By increasing stress applied on the
grouted specimens from qy to qmax, due to the bond breakage, the
influence of c0 on the shear strength reduces gradually, while the
influence of 40 increases. In other words, after qy, with the continuation of the loading and reaching qmax, a large number of
cementitious bonds are broken and the strength of the grouted
sand is mainly affected by 40. However, some of the specimens at
failure still have (though small) c0 value.
Fig. 13a shows that specimens grouted with cement alone
(Z ¼ 0%) do not show any c0 in the failure area. Because by
increasing stress from qy to qmax, the brittle failure and loss of c0
occur across the shear plane in the middle of the specimen, while
destruction elsewhere in the specimen may not occur and they
have c0 value. As seen in Fig. 13a, with increasing Z up to 30% (Z30),
c0p increases, but beyond Z30, any increase in zeolite content tends to
reduce c0p value. The values of c0p in specimens grouted with 70% and
90% zeolite are negligible or zero. According to Fig. 13a, for all
zeolite contents, with increasing W/CM or reducing cementitious
materials, c0p values increase. The values of c0p for specimens grouted
with Z30 and W/CM of 3, 5 and 7 are 58 kPa, 35 kPa and 13 kPa,
156
P. Jafarpour et al. / Journal of Rock Mechanics and Geotechnical Engineering 12 (2020) 149e159
Fig. 10. SEM analysis images of sand specimens grouted with (a) Z0, (b) Z50, and (c) Z90.
Fig. 11. EDS spectra of the selected target taken from the SEM images in Fig. 10: (a) Z0 and (b) Z50.
respectively. The effective peak friction angle (40p ) for clean
(ungrouted) sand is 32.29 . The 40p values for grouted sand specimens with different W/CM and Z values are presented in Fig. 13b. As
show in this figure, grouting with cement has an incremental effect
on 40p at the failure of the grouted sand specimen, due to the
occupation of soil pores by cement and thus the increase in soil
density. According to Fig. 13b, for all W/CM ratios, increasing the
zeolite content increases 40p of the grouted specimens as the
specimens injected with grout having higher zeolite content have
lower pores and porosity (Fig. 9) and, as a result, higher 40p.
P. Jafarpour et al. / Journal of Rock Mechanics and Geotechnical Engineering 12 (2020) 149e159
157
Fig. 12. Variations of shear strength parameters at yield point versus zeolite content for the grouted specimens.
Fig. 13. Variations of shear strength parameters at failure versus zeolite content for the grouted specimens.
Fig. 15. Effects of W/CM on qmax of the grouted specimens.
Fig. 14. Stressestrain curves of grouted specimens with Z ¼ 50% and different W/CM
ratios under CP ¼ 100 kPa.
3.3. Effect of W/CM
The stressestrain curves of the grouted sand specimens with Z50
(Zopt) and different W/CM ratios under CP ¼ 100 kPa are presented
in Fig. 14. The qy and qmax values of the grouted specimens decrease
with increasing W/CM of the grouts from 3 to 7. As seen in Fig. 14,
with increasing W/CM, the behavior of the grouted sand specimens
changes to a ductile state. Fig. 15 shows the effect of W/CM on qmax
of the grouted sand specimens with Z0, Z50 and Z90 under CP of
100 kPa, 300 kPa and 500 kPa. The highest qmax and qy values are
obtained for the grouted sand specimens with W/CM ¼ 3. In
particular, qmax values of the grouted sand specimens with W/
CM ¼ 3 and Zopt for CP values of 100 kPa, 300 kPa and 500 kPa are
1406 kPa, 1725 kPa and 2110 kPa, respectively. Also, qy values in this
case for CP values of 100 kPa, 300 kPa and 500 kPa are 297 kPa,
557 kPa and 867 kPa, respectively. The reason for the decrease of
soil resistance by increasing W/CM of grout from 3 to 7 is the
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Fig. 16. SEM analysis images of sand specimens grouted with (a) W/CM ¼ 3, (b) W/CM ¼ 5, and (c) W/CM ¼ 7.
reduction of cementitious materials, which subsequently reduces
the amount of bonding gels (C-A-H and CeSeH gels) as well as
density of the grouted sand specimens. Increasing qy of the grouted
specimens by reducing W/CM is due to the formation of stronger
bonds.
Fig. 16 shows the SEM images of the specimens grouted with Z50.
The microstructure difference is shown with different W/CM ratios.
Although grouting with a high W/CM ratio results in a more uniform injection, reducing W/CM or increasing the grout concentration, due to more cementitious materials, leads to occupation of
more volume of sand specimen pores by cementitious material
particles. Therefore, it can be conclusive that by increasing the W/
CM ratio, the amount of small gels increases (Fig. 16).
(4)
(5)
(6)
4. Conclusions
Due to the high contribution of cement production to environmental pollution, as well as its high energy consumption and cost,
the use of alternative materials such as zeolite, which are more
environmentally friendly and cheaper than cement, can be attractive. In the present study, 57 CU triaxial tests were conducted on
clean and sand specimens grouted with zeolite and cement. Tests
were performed on injected specimens with grouts having Z ¼ 0%,
10%, 30%, 50%, 70% and 90%, and W/CM ¼ 3, 5 and 7, under
CP ¼ 100 kPa, 300 kPa and 500 kPa. The main results are drawn as
follows:
(1) The peak deviatoric stress (qmax) increased significantly due
to cement grouting. The effect of cementitious bonds is
considerable up to the yield stress (qy) and beyond that, the
bond’s effect dissipates gradually. While uncemented sand
specimens show ductile behavior, cement grouting leads to
more brittle behavior.
(2) All of the specimens grouted with zeolite-cement suspensions show a contractive-like response with positive pore
water pressure, followed by negative pore water pressure at
the failure state. After qmax, the behavior of the specimens is
ductile or brittle, depending on the Z, CP and W/CM values.
(3) Under all of the CP values, with increasing Z up to 50% (Z50),
qmax of the grouted sand specimens increases. Beyond Z50, by
increasing zeolite content, qmax reduces. Such variations in
qmax versus changes in zeolite content are influenced by
cementitious bonds formed by grouting into the sand
(7)
specimens and increasing soil density by partial filling of the
soil pores.
The qmax and qy values of the grouted sand specimens
decrease with increasing W/CM of the grouts from 3 to 7.
With increasing W/CM, under constant CP and Z values, the
behavior of the grouted sand specimens changes to a more
ductile state. Increasing qy of the grouted sand specimens by
reducing W/CM is due to the formation of stronger bonds.
With increase in CP, qmax of the grouted specimen increases.
Also, qy due to cementitious bonds increases with increasing
CP. In all W/CM and Z values, with increase in CP, the behavior
of the grouted specimens tends to become more ductile.
The shear strength of the grouted sand specimens includes
two components of internal friction angle and cementitious
bonds. Specimens grouted with cement alone (Z ¼ 0%) do not
show any c0 in the failure area. With increasing Z up to 30%
(Z30), c0 value at failure increases, but beyond Z30, any increase in Z tends to reduce c0 value. The values of c0 at the
failure point in specimens grouted with 70% and 90% zeolite
are negligible or zero. For all Z values, with increasing W/CM
or reducing cementitious materials, the c0 values increase.
Grouting with cement has an incremental effect on the peak
friction angle (40 ) of the grouted specimen. Increasing the
zeolite content increases the 40 values of the grouted sand
specimens. In general, it can been stated that by increasing
stress applied on the grouted specimens from qy to qmax, due
to the bond breakage, the influence of bonds on the strength
reduces gradually, while the influence of 40 increases.
It should also be noted that the present study has been conducted on a specific type of soil (SP) with a low relative density
(Dr ¼ 30%). Therefore, to consider the effect of zeolite-cement
grouting on the behavior of different groutable soils, further experiments are required. In addition, researches on the effect of
initial relative density on the groutability and behavior of soils
injected with zeolite-cement grout are proposed.
Declaration of Competing Interest
We wish to confirm that there are no known conflicts of interest
associated with this publication and there has been no significant
financial support for this work that could have influenced its
outcome.
P. Jafarpour et al. / Journal of Rock Mechanics and Geotechnical Engineering 12 (2020) 149e159
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Peyman Jafarpour obtained his BSc degree in Civil Engineering from Malayer University, Iran, in 2016, and his
MSc degree in Geotechnical Engineering from Imam
Khomeini International University, Iran, in 2018. His main
research interest includes improvement and stabilization
of problematic soils with new environmentally friendly
methods and materials.