crystals
Article
Optimization of Enzyme-Mediated Calcite
Precipitation as a Soil-Improvement Technique:
The Effect of Aragonite and Gypsum on the
Mechanical Properties of Treated Sand
Heriansyah Putra 1,2, *, Hideaki Yasuhara 3 , Naoki Kinoshita 3 and Akira Hirata 4
1
2
3
4
*
Graduate School Science and Engineering, Ehime University, Matsuyama 790-8577, Japan
Faculty of Engineering, Universitas Jambi, Jambi 36361, Indonesia
Department of Civil and Environmental Engineering, Ehime University, Matsuyama 790-8577, Japan;
[email protected] (H.Y.); [email protected] (N.K.)
Department of Applied Chemistry, Ehime University, Matsuyama 790-8577, Japan; [email protected]
Correspondence: [email protected]; Tel.: +81-90-7570-8283
Academic Editor: Helmut Cölfen
Received: 12 December 2016; Accepted: 17 February 2017; Published: 20 February 2017
Abstract: The effectiveness of magnesium as a substitute material in enzyme-mediated calcite
precipitation was evaluated. Magnesium sulfate was added to the injecting solution composed of urea,
urease, and calcium chloride. The effect of the substitution on the amount of precipitated materials
was evaluated through precipitation tests. X-ray powder diffraction and scanning electron microscopy
analyses were conducted to examine the mineralogical morphology of the precipitated minerals and
to determine the effect of magnesium on the composition of the precipitated materials. In addition to
calcite, aragonite and gypsum were formed as the precipitated materials. The effect of the presence
of aragonite and gypsum, in addition to calcite, as a soil-improvement technique was evaluated
through unconfined compressive strength tests. Soil specimens were prepared in polyvinyl chloride
cylinders and treated with concentration-controlled solutions, which produced calcite, aragonite, and
gypsum. The mineralogical analysis revealed that the low and high concentrations of magnesium
sulfate effectively promoted the formation of aragonite and gypsum, respectively. The injecting
solutions which produced aragonite and calcite brought about a significant improvement in soil
strength. The presence of the precipitated materials, comprising 10% of the soil mass within a treated
sand, generated a strength of 0.6 MPa.
Keywords: EMCP technique; calcite; aragonite; gypsum; grouting technique; soil improvement
1. Introduction
The calcite-induced precipitation method (CIPM) has been confirmed as a potential
soil-improvement technique. It can significantly improve the engineering properties of soil, such
as shear strength and stiffness [1–7] and can reduce the permeability [5,8–11]. Many of the studies
have used bacterial cells, e.g., Sporosarcina pasteurii, to dissociate urea into ammonium and carbonate
ions [5,7,12]. The produced carbonate ions are precipitated as calcite crystals in the presence of calcium
ions. The reactions of the urea hydrolysis and the calcite formation are shown in Equations (1)–(3):
CO(NH2 )2 + 2H2 O → 2NH4+ + CO23−
(1)
CaCl2 → Ca2+ + 2Cl−
(2)
Ca2+ + CO23− → CaCO3 ↓ (precipitated)
(3)
Crystals 2017, 7, 59; doi:10.3390/cryst7020059
www.mdpi.com/journal/crystals
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In this technique, the grouting solution, which produces calcium carbonate (i.e., calcite, aragonite,
and/or vaterite), is injected into the sand sample. The mixed solution of reagents composed of urea and
CaCl2 and a bio-catalytic agent (e.g., bacterial cell) is used as the grouting solution. The precipitated
calcium carbonate in sandy soil may provide bridges between the grains of sand, restricting their
movement and, thus, improving the strength and stiffness of the soil. The deposited calcite fills the
voids, thereby reducing the permeability and porosity [8,9]. There are some complexities related to
the use of bacteria in the calcite precipitation technique. For example, the bacterial incubation may be
difficult to control because special treatments are required [13]. In addition, the high concentration
of reagents may have an inhibitory effect on the growth rate of bacteria [14] and, hence, the bacterial
activity may be limited in fine-grained soil [15,16]. An alternative methodology among calcite
precipitation techniques, which is called enzyme-mediated calcite precipitation (EMCP) has been
introduced in our previous works [1,2,4,9,13]. In this technique, the enzyme itself is used to dissociate
urea into ammonium and carbonate ions instead of bacteria. Using an enzyme is more straightforward
than using bacteria because biological treatments do not need to be considered [9]. Enzyme-reagent
mixed solutions, which produce the precipitated calcite, are injected into soil specimens. Thus,
unlike the CIPM procedure, the fixation of the enzyme is not required [9,13]. The efficacy of the
EMCP technique has already been evaluated in previous works [1,4,9,10,13]. Levels of unconfined
compressive strength, ranging from 400 kPa to 1.6 MPa, were achieved, and the permeability of the
improved samples was reduced by more than one order of magnitude [9].
As for the grouting method, calcite precipitation techniques require many injection wells for
treating the large volume [5]. A high amount of calcite is needed to improve the strength of porous
media. Whiffin et al. [7] reported that 60 kg of precipitated materials should be precipitated in 1 m3
of soil in order to obtain a sufficient strength of 300 kPa. This corresponds to precipitated materials
comprising approximately 4% of the soil mass in the treated sand [7]. However, highly concentrated
urea and CaCl2 (>0.5 mol/L) decrease the efficiency of calcite precipitation [10,13,17]. Urea and CaCl2 ,
with concentrations of 0.05–0.50 mol/L, were reported to be the most efficient in the application
of calcite precipitation techniques [13,17,18]. A high amount of precipitated materials has to be
produced by a limited number of injections [5] and, hence, the efficiency of calcite precipitation in high
concentrations of urea and CaCl2 has to be improved.
Putra et al. [4] reported that the substitution of a low concentration of magnesium chloride may be
able to improve the efficiency of the calcite precipitation technique. Precipitated materials comprising
90% of the maximum theoretical mass were obtained by substituting magnesium for 20% of the CaCl2
solutions of 0.5 mol/L. However, as the concentration of magnesium was increased, the amount of
precipitated material gradually decreased. The presence of magnesium in the calcite precipitation
process, which has pH < 11, also has the potential to promote aragonite in addition to calcite [19].
Magnesium ions are found to be the most efficient ions for the aragonite synthesis [20]. Aragonite has
a high mechanical strength and is regarded as a mineral which can improve the bending strength of
rubber and plastics as a filler [20,21]. Despite a metastable relative to calcite, aragonite has higher Mohs
hardness than calcite, namely, 3.25–4.00 and 3.00, respectively [22,23].In addition, the other calcium
carbonate polymorph of vaterite may also be promoted during the precipitation process. Vaterite is an
essential constituent of Portland cement and was found during oil field drilling [24]. As the calcium
carbonate polymorph, aragonite and vaterite have the similar XRD patterns [25–28]. However, studies
on the effects of aragonite on soil-improvement techniques have not been carried out yet.
In this work, magnesium sulfate was added as the substitute material in the enzyme-mediated
calcite precipitation technique (EMCP), and its effects on the amount and the mineralogical substance
of the precipitated materials were evaluated. Magnesium sulfate was added to the injecting solution to
promote the formation of aragonite and gypsum in addition to calcite. The reactions of the gypsum
formation are shown in Equations (4) and (5):
MgSO4 → Mg2+ + SO24−
(4)
substance of the precipitated materials were evaluated. Magnesium sulfate was added to the
injecting solution to promote the formation of aragonite and gypsum in addition to calcite. The
reactions of the gypsum formation are shown in Equations (4) and (5):
MgSO → Mg 2+ + SO 24
4
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(4)
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Ca 2+ + SO2- → CaSO ↓ (precipitated)
(5)
4
4
(5)
Ca2+ + SO24− → CaSO4 ↓ (precipitated)
The microstructures of the precipitated materials were examined by X-ray powder diffraction
The microstructures of the precipitated materials were examined by X-ray powder diffraction
(XRD) and scanning electron microscopy (SEM) to observe the effects of magnesium on the phase
(XRD) and scanning electron microscopy (SEM) to observe the effects of magnesium on the phase
and the substance of the precipitated materials. The effects of the presence of aragonite and gypsum
and the substance of the precipitated materials. The effects of the presence of aragonite and
in EMCP, as a soil-improvement technique, were examined through unconfined compressive
gypsum in EMCP, as a soil-improvement technique, were examined through unconfined compressive
strength (UCS) tests. The selected combinations for the grouting solution were fixed by
strength (UCS) tests. The selected combinations for the grouting solution were fixed by precipitation
precipitation tests and the mineralogical analyses, and then they were utilized to improve the
tests and the mineralogical analyses, and then they were utilized to improve the strength of sand
strength of sand specimens. Soil specimens were prepared in polyvinyl chloride (PVC) cylinders
specimens. Soil specimens were prepared in polyvinyl chloride (PVC) cylinders and treated with
and treated with concentration-controlled solutions composed of urea, urease, calcium chloride, and
concentration-controlled solutions composed of urea, urease, calcium chloride, and magnesium sulfate.
magnesium sulfate. Finally, by comparing the relation between the numbers of injections, the mineral
Finally, by comparing the relation between the numbers of injections, the mineral mass, and the
mass, and the UCS within the treated specimens obtained in this study, with those obtained from the
UCS within the treated specimens obtained in this study, with those obtained from the literature,
literature, the influence of the aragonite and/or the gypsum minerals was explicitly investigated.
the influence of the aragonite and/or the gypsum minerals was explicitly investigated.
2.
2. Materials
Materials and
and Methods
Methods
2.1.
2.1. Materials
Materials
The
of of
urea
(CO(NH
2)2), )calcium
chloride (CaCl2), and
The mixed
mixed solution
solutionofofreagents
reagentscomposed
composed
urea
(CO(NH
2 2 ), calcium chloride (CaCl2 ),
magnesium
sulfate
(MgSO
4
)
and
purified
urease
were
used
as
the
grouting
material
and magnesium sulfate (MgSO4 ) and purified urease were used as the grouting materialininthis
thisstudy.
study.
The
high-purity
reagents
of
urea,
CaCl
2
,
and
MgSO
4
were
obtained
from
Kanto
Chemicals
The high-purity reagents of urea, CaCl2 , and MgSO4 were obtained from Kanto ChemicalsCo.,
Co.,Inc.,
Inc.,
Tokyo,
Tokyo, Japan.
Japan. The
The urease
urease enzyme
enzyme (020-83242),
(020-83242), purified
purified from
from jack
jack bean
bean meal
meal and
and with
with the
the activity
activity of
of
2950
U/g,
was
used
as
the
biocatalytic
dissociation
of
urea.
Silica
sand
#6
with
e
max
,
e
min
,
coefficient
2950 U/g, was used as the biocatalytic dissociation of urea. Silica sand #6 with emax , emin , coefficient of
of
uniformity
(CU),
specific
gravities
(Gs)
of 0.899,
0.549, and
1.550,
andrespectively,
2.653, respectively,
was
uniformity
(CU),
andand
specific
gravities
(Gs) of
0.899,
0.549, 1.550,
2.653,
was prepared
prepared
to
evaluate
the
effects
of
precipitated
materials
on
the
mechanical
properties.
It
was
to evaluate the effects of precipitated materials on the mechanical properties. It was classified
as
classified
as
poorly-graded
sand
(SP)
based
on
the
unified
soil
classification
system
(USCS)
[29].
poorly-graded sand (SP) based on the unified soil classification system (USCS) [29]. The grain size
The
grain size
distribution
ofissilica
sand
is shown
in Figure 1 [4,30].
distribution
curve
of silica curve
sand #6
shown
in #6
Figure
1 [4,30].
Percent finer [%]
100
80
60
40
20
0
0.01
0.10
1.00
10.00
Grain size [mm]
Figure
Figure 1.
1. Particle
Particlesize
sizedistribution
distribution of
of silica
silica sand
sand #6
#6 used
used in
in this
this work
work [4,30].
[4,30].
2.2.
2.2. Precipitation
Precipitation Tests
Tests
Precipitation
test
tubes
to to
evaluate
thethe
amount
of
Precipitation tests
testswere
wereperformed
performeddirectly
directlyinintransparent
transparent
test
tubes
evaluate
amount
precipitated
materials.
TheThe
experimental
procedures
developed
bybyNeupane
of precipitated
materials.
experimental
procedures
developed
Neupaneetetal.
al. [13]
[13] and
and
Putra
et
al.
[4]
were
adopted
in
this
work.
Urease
with
concentrations
of
1.0,
2.0,
3.0,
4.0,
and
5.0 g/L
g/L
Putra et al. [4] were adopted in this work. Urease with concentrations of 1.0, 2.0, 3.0, 4.0, and 5.0
and
and distilled
distilled water
water were
were mixed
mixed separately.
separately. The
The mixed
mixed solutions
solutions were
were stirred
stirred for
for 22 min
min and
and then
then
filtered through filter paper (pore size (PS) of 11 µm) to remove the undissolved particles. The particles
retained on the filter paper were dried at 60 ◦ C for 24 h, and then the amount of solved particles was
evaluated. The solved particles were shown as a percentage, namely, the ratio of the solved mass to
the mixed mass of urease. The urea and CaCl2 , with a concentration of 1.0 mol/L, were mixed with
distilled water. The filtered urease and urea-CaCl2 solutions were mixed thoroughly in a transparent
Crystals 2017, 7, 59
4 of 15
test tube, to obtain a total volume of 30 mL, and then allowed to react for an entire three-day curing
period. Samples were kept in a box without shaking at a room temperature of 20 ◦ C. After the curing
time, the grouting solution was filtered through filter paper (PS of 11 µm). The particles retained on
the filter paper and the particles remaining in the tubes were dried at 60 ◦ C for 24 h, and then the total
mass of the precipitated minerals was evaluated by combining the precipitated minerals deposited in
the test tubes with the materials remaining on the filter paper. Two identical tests were conducted for
each condition to check the reproducibility. The mass of the precipitated minerals was shown as the
precipitation ratio, namely, the ratio of the actual mass of the precipitated minerals to the theoretical
mass of the maximum precipitation of CaCO3 (Equations (6) and (7)):
actual mass of precipitated minerals mp
Precipitaion ratio (%) =
theoretical mass of CaCO3 (mt )
mt = C × V × M
(6)
(7)
where:
mp : mass of the precipitated materials evaluated from the tests (g)
mt : theoretical mass of CaCO3 (g)
C: concentration of the solution (mol/L)
V: volume of the solution (L)
M: molar mass of CaCO3 (100.087 g/mol)
The relation among the urease concentrations, the mass of solved particles, and the precipitation
ratio was assessed to determine the optimum urease concentration.
Magnesium sulfate was newly-added to the grouting solution. The concentrations of magnesium
sulfate, varying from 0.02 to 0.10 mol/L, were substituted to obtain a total concentration of
CaCl2 –MgSO4 of 1.0 mol/L. The selected concentration of urease was utilized to dissociate
the 1.0 mol/L of urea. The effects of magnesium sulfate on the amount and the mineralogical substance
of the precipitated materials were evaluated. The experimental conditions for the test tube experiments
are listed in Table 1. The total amount of precipitated materials was examined thoroughly by the tests.
The morphologies of the dried precipitated materials were characterized by XRD, and the evolutions
of the shapes of the particles were observed by SEM.
Table 1. Experimental conditions for test tube experiments to evaluate the effect of magnesium.
Case
A0
A1
A2
A3
A4
A5
Conc. of Urea
Conc. of CaCl2
Conc. of MgSO4
(mol/L)
(mol/L)
(mol/L)
1.00
1.00
1.00
1.00
1.00
1.00
1.00
0.98
0.96
0.94
0.92
0.90
0.00
0.02
0.04
0.06
0.08
0.10
2.3. Mineralogical Analysis
XRD patterns were recorded on a Rigaku RINT2200, Tokyo, Japan using a scanning 2θ
range from 2◦ –50◦ . The dried precipitated materials were observed to evaluate the effect of the
substitution of magnesium sulfate on the mineralogical substance of precipitated materials. An XRD
quantitative analysis was used to obtain the mineral composition of the precipitated materials [31–33].
The procedure was as follows: The mineral types of the precipitated materials were obtained from
the XRD analysis. The pure minerals for each mineral of the precipitated materials and internal
Crystals 2017, 7, 59
5 of 15
quantitative analysis was used to obtain the mineral composition of the precipitated materials [31–33].
The procedure
Crystals
2017, 7, 59 was as follows: The mineral types of the precipitated materials were obtained 5from
of 15
the XRD analysis. The pure minerals for each mineral of the precipitated materials and internal
standard material were prepared to develop the calibration curve. They can be determined after the
standard
material
werehave
prepared
develop the
curve. They
be determined
after the
precipitated
materials
beentoidentified
by calibration
the XRD analysis.
The can
internal
standard materials
precipitated
materials
have
been
identified
by
the
XRD
analysis.
The
internal
standard
materials
should
should have a simple pattern and peaks that do not overlap with the peaks of the targeted materials
have
a simple
patterncurve
and peaks
that do not
the peaks
of internal
the targeted
materials
[33].
[33]. The
calibration
was developed
byoverlap
mixing with
the pure
and the
standard
materials
The
was developed
mixing the
pure and70%–30%,
the internal
standard and
materials
with
withcalibration
ratios of curve
0%–100%,
10%–90%,by
30%–70%,
50%–50%,
90%–10%,
100%–0%,
ratios
of 0%–100%,
10%–90%,
50%–50%,was
70%–30%,
and
100%–0%,
respectively.
respectively.
The fixed
mass of30%–70%,
the pure minerals
taken in90%–10%,
a porcelain
basin
and mixed
with the
The
fixedstandard
mass of materials.
the pure minerals
was
taken in
a porcelain
andmixed
mixedmaterials,
with the internal
internal
The XRD
analysis
was
conductedbasin
on the
and the
standard
materials.
The
XRD
analysis
was
conducted
on
the
mixed
materials,
and
the
intensity
of the
intensity of the main peak of the pure materials was examined. The same procedure was adopted
main
peak
of the pure
materialsofwas
examined.
The same
procedure
was adopted
for the different
for the
different
proportions
pure
and internal
standard
materials
and, consequently,
the
proportions
of pure
andbe
internal
calibration curve
could
drawn.standard materials and, consequently, the calibration curve could
be drawn.
In order to eliminate any errors during the sample preparation, validation data were also
In order
to eliminate
anyoferrors
the sample
preparation,
validation
data
were also
provided.
The
fixed mass
pureduring
materials
was mixed
at different
ratios,
without
theprovided.
internal
The
fixed mass
of pure
materials
was mixed
at different
ratios,with
without
internal
standard
standard
materials,
and
was prepared
for the
XRD analysis
the the
same
procedure.
Thematerials,
intensity
and
was
prepared
forthe
thematerials
XRD analysis
with theon
same
procedure. curve,
The intensity
the main
peak
of the
of the
main
peak of
was plotted
the calibration
and theofmass
of the
materials
materials
was plotted
on the
calibration
curve,
and the mass
of the
materials
was examined.
The error
was examined.
The error
was
shown as
a percentage
error,
namely,
the ratio
of the difference
in
was
shown
as
a
percentage
error,
namely,
the
ratio
of
the
difference
in
mass
between
the
mass
of
the
mass between the mass of the mixed materials and the obtained mass from the calibration curve to
mixed
materials
and the
obtained mass from the calibration curve to the mass of the mixed materials.
the mass
of the mixed
materials.
2.4.
2.4. Unconfined
Unconfined Compressive
Compressive Strength
Strength Tests
Tests
Unconfined
Unconfined compressive
compressive strength
strength (UCS)
(UCS) tests
tests were
were conducted
conducted to
to evaluate
evaluate the
the improvement
improvement in
in
mechanical
properties
of
the
treated
sand
specimens.
Polyvinyl
chloride
(PVC)
cylinders,
5
cm
in
mechanical properties of the treated sand specimens. Polyvinyl chloride (PVC) cylinders, 5 cm in
diameter
to prepare
The fixed
diameter and
and 10
10 cm
cm in
in height,
height, were
were used
used to
prepare the
the sand
sand specimens.
specimens. The
fixed volume
volume of
of the
the
grouting
solution
was
injected
into
the
prepared
sand
specimens.
The
injected
volume
was
controlled
grouting solution was injected into the prepared sand specimens. The injected volume was
by
the number
of number
pore volumes
one PV
being
mL. Firstly,
dry
silicadry
sand
with
a relative
controlled
by the
of pore(PV),
volumes
(PV),
one ~75
PV being
~75 mL.
Firstly,
silica
sand
with a
density
of
50%
was
prepared
in
the
PVC
cylinders.
Secondly,
one
PV
of
the
grout
solution
was
poured
relative density of 50% was prepared in the PVC cylinders. Secondly, one PV of the grout solution
into
PVC into
cylinders
fromcylinders
the top. The
bywere
1–3 PV
with aby
three-day
was the
poured
the PVC
fromsand
the samples
top. Thewere
sandtreated
samples
treated
1–3 PV curing
with a
time.
After
the
curing
time,
the
treated
sand
was
removed
from
the
PVC
cylinders.
The
surface
of the
three-day curing time. After the curing time, the treated sand was removed from the PVC cylinders.
samples
was
flattened
before
the
UCS
tests
were
performed.
The
procedure
of
sample
preparation
The surface of the samples was flattened before the UCS tests were performed. The procedurefor
of
UCS
tests
is
shown
in
Figure
2.
Two
tests
were
carried
out
for
each
condition
to
check
the
reproducibility.
sample preparation for UCS tests is shown in Figure 2. Two tests were carried out for each
The
UCS tests
were performed
under wet The
conditions
to avoid
unexpected
precipitation
that may
condition
to check
the reproducibility.
UCS tests
wereany
performed
under
wet conditions
to
occur
when
specimens
are
intentionally
dried
out.
avoid any unexpected precipitation that may occur when specimens are intentionally dried out.
Figure 2.
2. Procedure
Procedure of
of sample
sample preparation
preparation for
for UCS
UCS test.
test.
Figure
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6 of 15
Crystals 2017, 7, 59
6 of 15
3. Results and Discussion
Crystals
2017,and
7, 59 Discussion
3. Results
6 of 15
The efficiency of varying the concentrations of urease on the calcite precipitation technique was
The efficiency
of varying the concentrations of urease on the calcite precipitation technique
3. Results
and Discussion
evaluated.
Figure
3 shows
the relation among the urease concentration, the solved mass of urease,
was evaluated. Figure 3 shows the relation among the urease concentration, the solved mass of
and the precipitation
ratio
of thethe
calcite.
It should
noticed
that
the reproducibility
of the two
Theand
efficiency
of varying
concentrations
of be
urease
the
calcite
precipitation
technique
urease,
the precipitation
ratio of
the calcite. It should
be on
noticed
that the
reproducibility
of the
identical
tests
under
each
experimental
condition
was
confirmed.
As
is
apparent,
the
precipitated
was
evaluated.
Figure
3
shows
the
relation
among
the
urease
concentration,
the
solved
mass
of
two identical tests under each experimental condition was confirmed. As is apparent, the
and
the
precipitation
ratio
of
the
calcite.
It
should
be
noticed
that
the
reproducibility
of
the
ratio urease,
increased
significantly
when
2.0
g/L
of
urease
was
added.
The
increase
in
the
precipitated
precipitated ratio increased significantly when 2.0 g/L of urease was added. The increase in the
identical
tests
under
each
experimental
condition
was confirmed.
As grouting
issolution.
apparent,
the
masstwo
occurred
due
tooccurred
the
increase
the
solvedinmass
of urease
in urease
the grouting
However,
precipitated
mass
due
tointhe
increase
the solved
mass
of
in the
solution.
precipitated
ratio
increased
significantly
when
2.0
g/L
of
urease
was
added.
The
increase
in
thethere
the increasing
concentration
had no significant
on impact
the solved
mass
and,
hence,
However, urease
the increasing
urease concentration
had no impact
significant
on the
solved
mass
and,
precipitated
mass
occurred
due
to
the
increase
in
the
solved
mass
of
urease
in
the
grouting
solution.
hence,
there was
no significant
in themass
precipitated
mass as the concentration
wasthan
greater
was no
significant
increase
in the increase
precipitated
as the concentration
was greater
2.0 g/L.
However,
the In
increasing
urease
concentration
had
no significant
impactwas
on the
solved mass
and,
than
2.0
g/L.
the
filtered
process,
when
the
mixed
solution
which
composed
of
a
high
In the filtered process, when the mixed solution which was composed of a high concentration of urease
hence,
there was
no significant
increase
in the
precipitated
mass as the
concentration
wasthe
greater
concentration
ofamount
urease
was
filtered,
a high
amount
of undissolved
urease
remained
on
filter
was filtered,
ag/L.
highIn
of undissolved
urease
remained
on thewhich
filter
paper
and, hence,
the
filtered
than
2.0
the
filtered
process,
when
the
mixed
solution
was
composed
of
high
paper and, hence, the filtered process was inefficient. The results indicated that the aurease
process
was inefficient.
Thewas
results
indicated
the urease
concentration
the filtered
process was
concentration
filtered,
highthat
amount
of undissolved
urease in
remained
on the
concentration of
in urease
the filtered
processa was
limited.
Urease
with a concentration
of 2.0
g/L filter
was
limited.
Urease
with
a concentration
of 2.0 g/L
was
selected
as results
the optimum
concentration
with the
paper
and,
hence,
the
filtered
process
was
inefficient.
The
indicated
that
the
urease
selected as the optimum concentration with the average consumed urease of 74% and precipitation
concentration
in
the
filtered
process
was
limited.
Urease
with
a
concentration
of
2.0
g/L
was
average
consumed
urease
of
74%
and
precipitation
ratio
of
57%.
ratio of 57%.
selected as the optimum concentration with the average consumed urease of 74% and precipitation
Urease concentration (1st test)
ratio of 57%.
2.5
3.0
2.0
2.5
Urease concentration (2nd test)
Precipitation ratio [%]
CO(NH2) 2 : 1.0 mol/L
concentration (1st test)
: 1.0 mol/L
CaCl2Urease
Urease concentration (2nd test)
Precipitation ratio [%]
47%
51%
74%
1.5
2.0
42%
47%
1.0
1.5
87%
0.5
1.0
87%
0.0
0.5
1.0
0.0
42%
CO(NH2) 2 : 1.0 mol/L
CaCl2 : 1.0 mol/L
74%
51%
2.0
3.0
4.0
5.0
Initial concentration of urease [g/L]
1.0
2.0
3.0
4.0
5.0
70
60
70
50
60
40
50
30
40
20
30
10
20
0
10
Precipitation
ratio [%]
Precipitation
ratio [%]
ActualActual
concentration
of
concentration
of
ureaseurease
[g/L] [g/L]
3.0
0
Initial concentration
of its
urease
[g/L]
Figure
3. Evaluation
consumed
urease and
onon
the
precipitated
ratio.
Figure
3. Evaluation
ofofconsumed
urease
and
itseffect
effect
the
precipitated
ratio.
Figure
3. Evaluation
of magnesium
consumed urease
and in
its the
effect
on the
precipitated ratio.
The effects
of the
substituted
sulfate
CaCl
2–urea solutions were evaluated.
The
effects
of the
substituted
magnesium
sulfate
in thewith
CaClvarious
solutions were
evaluated.
2 –ureacombinations
2–
Filtered
urease,
with
a concentration
of 2.0 g/L,
was mixed
of CaCl
The
effects
of
the
substituted
magnesium
sulfate
in
the
CaCl
2–urea
solutions
were
evaluated.
Filtered
urease,
with
a
concentration
of
2.0
g/L,
was
mixed
with
various
combinations
of
CaCl
4
MgSO4 and 1.0 mol/L of urea. The evolutions of the precipitated mass, as the effect of2 –MgSO
the
2–
Filtered
urease,
with
a
concentration
of
2.0
g/L,
was
mixed
with
various
combinations
of
CaCl
and 1.0
mol/L
of
urea.
The
evolutions
of
the
precipitated
mass,
as
the
effect
of
the
substitution
of
substitution of magnesium sulfate, are depicted in Figure 4. As is apparent, the precipitated amount
MgSO
4 and 1.0 mol/L of urea. The evolutions of the precipitated mass, as the effect of the
magnesium
sulfate,
areasdepicted
in Figureof4.MgSO
As is4 was
apparent,
the Aprecipitated
gradually
increased
the concentration
increased.
precipitationamount
ratio of gradually
more
substitution
of magnesium
sulfate,
depicted
in Figure
4. As isThe
apparent,
the
precipitated
amount
than 100%
obtained when
0.10are
mol/L
of
MgSO
4 wasA
added.
results
indicated
that
minerals
increased
as thewas
concentration
of MgSO
was
increased.
precipitation
ratio
of
more
than
100%
was
4
gradually
as formed
the concentration
of MgSO4 was
increased.
A precipitation
ratio of
more
otherwhen
than increased
calcite
were
during
the
precipitation
process.
Therefore,
aminerals
mineralogical
analysis
obtained
0.10 mol/L
of MgSO
was
added.
The
results
indicated
that
other
than
calcite
4 mol/L of MgSO4 was added. The results indicated that minerals
than
100% was
obtained when
0.10
was
needed
to determine
the type
and the composition
of theaprecipitated
materials.
were other
formed
during
the
precipitation
Therefore,
mineralogical
analysis was
needed to
than calcite were formed duringprocess.
the precipitation
process.
Therefore, a mineralogical
analysis
determine
the
type
and
the
composition
of
the
precipitated
materials.
was needed to determine the type and the composition of the precipitated materials.
Concentration of CaCl [mol/L]
2
Precipitation
ratio [%]
Precipitation
ratio [%]
120
1.00
0.98
0.96
0.94
0.92
0.90
0.94
0.92
0.90
0.06
0.08
0.10
Concentration of CaCl [mol/L]
CO(NH2)2: 1.00 mol/L
Urease : 2.00
0.96
0.98 g/L
100 1.00
120
CO(NH2)2: 1.00 mol/L
Urease : 2.00 g/L
80
100
2
60
80
40
60
20
40
0
20
0.00
0.02
0.04
Concentration of MgSO [mol/L]
0
0.00
0.02
0.04
0.06
4
0.08
0.10
Figure 4. PrecipitatedConcentration
mass in variousofconcentrations
MgSO [mol/L]of MgSO4-CaCl2.
4
Figure 4. Precipitated mass in various concentrations of MgSO4-CaCl2.
Figure 4. Precipitated mass in various concentrations of MgSO4 -CaCl2 .
Crystals 2017, 7, 59
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Crystals 2017, 7, 59
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XRD and SEM analyses were conducted to evaluate the effect of magnesium on the mineralogy
and morphology
of precipitated
materials.
Theto
XRD
results
ineffect
Figure
show the impact
magnesium
XRD and SEM
analyses were
conducted
evaluate
the
of5magnesium
on the of
mineralogy
onand
the crystalline
material.
In A0, without
magnesium,
the results
main material
was5calcite
low peaks
morphology
of precipitated
materials.
The XRD
in Figure
showand
thethe
impact
of
of magnesium
aragonite (i.e.,
= 3.392,
3.182,material.
and 2.705)
also found.
In addition,
the other
calcium
on dthe
crystalline
In were
A0, without
magnesium,
the main
material
wascarbonate
calcite
and the low
peaks ofmay
aragonite
(i.e.,
d = 3.392,
3.182, the
andprecipitation
2.705) were also
found.
addition, the
polymorph
of vaterite
also be
generated
during
process.
AsInaforementioned,
polymorph
of vaterite
maysimilar,
also beand
generated
during overlap.
the precipitation
theother
XRDcalcium
patternscarbonate
of aragonite
and vaterite
are very
may partially
Therefore,
Asof
aforementioned,
XRD patterns
of aragonite
and vaterite
are very
may
theprocess.
presence
vaterite cannotthe
completely
be excluded
because
of the variety
of similar,
vateriteand
structures.
partially
overlap.
Therefore,
the
presence
of
vaterite
cannot
completely
be
excluded
because
of
the
However, vaterite may not be able to exist as a distinct structure [34] and, thus, the distinct peaks
variety
of
vaterite
structures.
However,
vaterite
may
not
be
able
to
exist
as
a
distinct
structure
[34]
obtained from the analyses (Figure 5) are most likely to be aragonite. In A1, when 0.02 mol/L of
and, thus, sulfate
the distinct
from thesolution,
analyses (Figure
5)of
arearagonite
most likely
to be aragonite.
In
magnesium
waspeaks
addedobtained
to the grouting
the peak
significantly
increased
A1, when 0.02 mol/L of magnesium sulfate was added to the grouting solution, the peak of
and,
in contrast, the peak of calcite decreased. The peaks of gypsum (i.e., d = 7.63 and 4.283)
aragonite significantly increased and, in contrast, the peak of calcite decreased. The peaks of
were also found in addition to that of calcite and aragonite. The peaks of calcite were found to
gypsum (i.e., d = 7.63 and 4.283) were also found in addition to that of calcite and aragonite. The
be approximately constant when the range in substituted magnesium sulfate was 0.04–0.10 mol/L.
peaks of calcite were found to be approximately constant when the range in substituted magnesium
As the concentration of magnesium sulfate was increased, the peaks of gypsum gradually increased.
sulfate was 0.04–0.10 mol/L. As the concentration of magnesium sulfate was increased, the peaks of
The results of mineralogical analysis revealed that the precipitated materials were composed of calcite,
gypsum gradually increased. The results of mineralogical analysis revealed that the precipitated
aragonite,
gypsum.
materialsand
were
composed of calcite, aragonite, and gypsum.
7000
A0 (Ca 1.00; Mg 0.00)
7000
Cal
Cal: Calcite
Arg: Aragonite
A1 (Ca 0.98; Mg 0.02)
5000
4000
3000
2000
1000
0
Cal
0
10
Arg Cal
Arg
20
30
Cal Cal
Cal
5000
4000
3000
2000
Gp
1000
Gp
40
0
50
Ο
0
10
Cal: Calcite
Arg: Aragonite
Gp: Gypsum
30
40
5000
4000
3000
Cal
2000
Gp
1000
0
Arg
Arg
Gp
10
Arg
20
Gp
Cal Cal Cal
30
50
5000
4000
Gp
3000
Cal
2000
0
50
Ο
Gp
0
10
Cal: Calcite
Arg: Aragonite
Gp: Gypsum
6000
30
Cal
40
4000
3000
Cal
2000
Gp
Cal
Arg
Arg
20
Gp
Cal Cal Cal
30
40
Ο
Deviation angle, 2 θ [ ]
A5 (Ca 0.90; Mg 0.10)
6000
Intensity [cps]
Gp
10
Cal Cal Cal
50
7000
A4 (Ca 0.92; Mg 0.08)
0
20
Gp
Deviation angle, 2 θ [ ]
7000
1000
Arg
Cal Arg
Ο
Deviation angle, 2 θ [ ]
5000
Cal: Calcite
Arg: Aragonite
Gp: Gypsum
1000
Cal
40
A3 (Ca 0.94; Mg 0.06)
6000
Intensity [cps]
Intensity [cps]
Cal
7000
A2 (Ca 0.96; Mg 0.04)
6000
Intensity [cps]
20
Arg
Deviation angle, 2 θ [ ]
7000
0
Arg
Arg Cal
Ο
Deviation angle, 2 θ [ ]
0
Cal: Calcite
Arg: Aragonite
Gp: Gypsum
6000
Intensity [cps]
Intensity [cps]
6000
Gp
5000
4000
3000
Cal
2000
Arg
Gp Cal
Arg
1000
Cal
50
Cal: Calcite
Arg: Aragonite
Gp: Gypsum
0
0
10
20
Gp
Cal Cal Cal
30
40
Cal
50
Ο
Deviation angle, 2 θ [ ]
Figure 5. X-ray diffraction results of precipitated materials.
Figure 5. X-ray diffraction results of precipitated materials.
The XRD quantitative analysis was used to determine the composition of the precipitated
The XRD
quantitative
analysis
was
used
to determine
thea composition
of the
precipitated
materials
[31–33].
The calibration
curve
was
developed
by mixing
pure and internal
material
with
materials
[31–33].
The calibration
curve
was developed
mixing a 90%–10%,
pure and and
internal
material
the ratios
of 0%–100%,
10%–90%,
30%–70%,
50%–50%,by70%–30%,
100%–0%,
respectively. Validation data were also produced to eliminate any errors that might occur due to the
Crystals 2017, 7, 59
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with the ratios of 0%–100%, 10%–90%, 30%–70%, 50%–50%, 70%–30%, 90%–10%, and 100%–0%,
Crystals 2017, 7, 59
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respectively. Validation data were also produced to eliminate any errors that might occur due to the
process,
e.g.,
sample
preparation.
which has
hasclearly
clearlydifferent
differentpeaks
peaksfrom
from
those
process,
e.g.,
sample
preparation.Quartz
Quartz (SiO
(SiO22)) which
those
of of
thethe
precipitated
materials,
was
selected
as
the
internal
standard
material
in
this
work.
Calcite
and
gypsum,
precipitated materials, was selected as the internal standard material in this work. Calcite and
with
claimed
purity
levels
greater
than
95.0%than
from
the Kanto
Chemicals
Co., Inc., Co.,
Tokyo,
and
gypsum,
with
claimed
purity
levels
greater
95.0%
from the
Kanto Chemicals
Inc.,Japan
Tokyo,
aragonite
redaragonite
C, from Sefrou,
Marocco,
were
used as
theused
pureasmaterials.
The XRD The
results
for
quartz,
Japan and
red C, from
Sefrou,
Marocco,
were
the pure materials.
XRD
results
calcite,
aragonite,
and
gypsum
are
shown
in
Figure
6.
for quartz, calcite, aragonite, and gypsum are shown in Figure 6.
15000
8000
Calcite
Quartz
Intensity [cps]
Intensity [cps]
12000
9000
6000
3000
0
0
10
20
30
40
6000
4000
2000
0
50
Ο
0
10
Aragonite
40
50
40
50
Gypsum
Intensity [cps]
2000
Intensity [cps]
30
Deviation angle, 2 θ [ ]
40000
2500
1500
1000
500
0
20
Ο
Deviation angle, 2 θ [ ]
0
10
20
30
40
50
30000
20000
10000
0
0
10
20
30
Deviation angle, 2 θ [Ο]
Ο
Deviation angle, 2 θ [ ]
Figure
standardand
andpure
pureminerals.
minerals.
Figure6.6.X-ray
X-raydiffraction
diffractionresults
results of
of internal
internal standard
Variouscombinations
combinations of
of masses
(Cal)–SiO
2, aragonite (Arg)–SiO2, and gypsum (Gp)–
Various
massesofofcalcite
calcite
(Cal)–SiO
2 , aragonite (Arg)–SiO2 , and gypsum
SiO2 were evaluated under the same terms. Two sets of combinations of Cal–Arg–Gp were also
(Gp)–SiO2 were evaluated under the same terms. Two sets of combinations of Cal–Arg–Gp were
assessed to validate the results of the quantitative analysis. The experimental conditions for the
also assessed to validate the results of the quantitative analysis. The experimental conditions for the
quantitative analysis are shown in Table 2.
quantitative analysis are shown in Table 2.
Table 2. Experimental conditions for calibration curve of quantitative analysis.
Table 2. Experimental conditions for calibration curve of quantitative analysis.
Case
1
2
3
4
5
6
7
Val 1
Val 2
Material Mass (%) *
Mass
(%) * Material
Case Pure Material Material
Internal
Standard
Cal
Arg
Gp
SiO
2
Pure Material
Internal
Standard Material
1 Cal 0
0
0
100
Arg
Gp
SiO2
2
10
10
10
90
0
0
0
100
3
30
30
30
70
10
10
10
90
4 30 50
50
50
30 50
30
70
5 50 70
70
30
50 70
50
50
6 70 90
90
10
70 90
70
30
90 100 90
10
7 90 100 100
0
100
100
100
0
Val 1 40
40
20
40
40
20
Val 2 30
30
40
30
30
40
* In a total mass of 0.10 g.
-
* In a total mass of 0.10 g.
The relation between the intensity and the percentage mass of the pure materials is shown in
Figure 7. In two experiments (i.e., Val 1 and Val 2), the data were examined to validate the
calibration curve. The maximum percentage error was found to be 4%.
Crystals 2017, 7, 59
9 of 15
The relation between the intensity and the percentage mass of the pure materials is shown in
Figure 7. In two experiments (i.e., Val 1 and Val 2), the data were examined to validate the calibration
curve.
percentage error was found to be 4%.
Crystals The
2017,maximum
7, 59
9 of 15
6000
(a)
Intensity [cps]
5000
y = 55.786x
R2 = 0.99
Err= 3.38%
4000
3000
Val 1;
Err: 3.47%
2000
Val 2;
Err: 2.33%
1000
0
Calibration curve
Validation data
0
20
40
60
80
100
Mass of calcite [%]
2000
(b)
Intensity [cps]
1600
y = 17.705x
R2 = 0.99
Err= 2.74%
1200
Val 1;
Err: 4.39%
800
Val 2;
Err: 1.82%
400
0
0
20
40
Calibration curve
Validation data
60
80
100
Mass of aragonite [%]
30000
(c)
Intensity [cps]
25000
y = 240.39x
2
R = 0.99
Err= 3.63%
20000
15000
Val 2;
Err: 1.50%
10000
5000
0
Val 1;
Err: 4.25%
0
20
Calibration curve
Validation data
40
60
80
100
Mass of gypsum [%]
Figure
Figure 7.
7. Calibration
Calibration curve
curve for
for XRD
XRD quantitative
quantitative analysis:
analysis: (a)
(a) calcite;
calcite; (b)
(b) aragonite;
aragonite; and
and (c)
(c) gypsum.
gypsum.
The compositions of the precipitated materials were examined by plotting the intensity of the
The compositions of the precipitated materials were examined by plotting the intensity of the
main peaks of calcite, aragonite, and gypsum on the calibration curves, and the mass percentage
main peaks of calcite, aragonite, and gypsum on the calibration curves, and the mass percentage was
was obtained. Table 3 shows the mineral compositions of the precipitated materials and its
obtained. Table 3 shows the mineral compositions of the precipitated materials and its summaries
summaries are depicted in Figure 8. The total amount of precipitated materials is seen to gradually
are depicted in Figure 8. The total amount of precipitated materials is seen to gradually increase
increase after the substitution of magnesium sulfate. In the case of A0, which is without magnesium,
after the substitution of magnesium sulfate. In the case of A0, which is without magnesium, mostly
mostly calcite (i.e., 96.4%) was found as the precipitated material. In the case of A1, when 0.02
mol/L of magnesium was added, a significant amount of aragonite was formed; a mass percentage
of aragonite of 66.75% was obtained in addition to that of calcite of 26.15%. Moreover, a mass
percentage of gypsum of 7.10% was also formed. Furthermore, the mass percentage of gypsum
increased as the concentration of magnesium sulfate was further increased. The results indicated
Crystals 2017, 7, 59
10 of 15
calcite (i.e., 96.4%) was found as the precipitated material. In the case of A1, when 0.02 mol/L of
magnesium was added, a significant amount of aragonite was formed; a mass percentage of aragonite
of 66.75% was obtained in addition to that of calcite of 26.15%. Moreover, a mass percentage of
gypsum of 7.10% was also formed. Furthermore, the mass percentage of gypsum increased as the
concentration of magnesium sulfate was further increased. The results indicated that the substitution
Crystals
7, 59
10 of
15
of
low 2017,
concentrations
of magnesium sulfate (i.e., 0.02 and 0.04 mol/L) significantly promoted
the
formation of aragonite in the precipitation process. The presence of a low concentration of magnesium
significantly
formationion
of to
aragonite
in the
precipitation
sulfate
mightpromoted
allow thethe
magnesium
delay the
reaction
rate and process.
promoteThe
the presence
formationofofa
low
concentration
of
magnesium
sulfate
might
allow
the
magnesium
ion
to
delay
the
aragonite. In contrast, the substitutions of 0.06–0.10 mol/L magnesium sulfate might reaction
enhance rate
the
and promote
formation
of aragonite.
In contrast, the substitutions of 0.06–0.10 mol/L
reaction
rate andthe
promote
the formation
of gypsum.
magnesium sulfate might enhance the reaction rate and promote the formation of gypsum.
Table 3. Amount and composition of precipitated materials.
Table 3. Amount and composition of precipitated materials.
Concentration
Concentration of
Case
of CaCl2 (molŁ)
Case
CaCl2 (mol\L)
Concentration of
Concentration
of
MgSO4 (molŁ)
MgSO4 (mol\L)
A0 A0
1.001.00
0.00
0.00
A1 A1
0.980.98
0.02
0.02
A2 A2
0.960.96
0.04
0.04
A3
A4
A5
A3
A4
A5
0.94
0.06
0.94
0.06
0.92
0.08
0.92
0.08
0.90
0.10
0.90
0.10
Mineral Composition
Total
Total
Precipitated
Precipitated
Mass (g) *
Mineral Composition
Aragonite
Gypsum
Calcite
Aragonite
Gypsum
(g)
(%)
(g)
(%)
(g)
(g)
(%)
(g)
(%)
(g)(%) (%)
1.65
96.67
0.06
3.33
0.00
1.65 96.67 0.06 3.33 0.000.00 0.00
1.65
1.65 96.13
96.13 0.07
0.07 3.873.870.000.000.00 0.00
0.48
26.58
1.19
0.48 26.58 1.19 65.30
65.300.150.158.12 8.12
0.46
25.72 1.22
68.21 0.11 6.07
0.46 25.72 1.22 68.21 0.11 6.07
1.39
1.39 70.38
70.38 0.48
0.48 24.46
24.460.100.105.14 5.14
1.41
71.00 0.47
23.64 0.11 5.32
1.41 71.00 0.47 23.64 0.11 5.32
1.41
19.67
1.41 60.36
60.36 0.46
0.46 19.72
19.720.460.46
19.67
1.47
65.30 0.45
20.15 0.33 14.55
1.47 65.30 0.45 20.15 0.33 14.55
1.31
51.29 0.49
19.21 0.75 29.50
1.31 51.29 0.49 19.21 0.75 29.50
1.26
48.61 0.59
22.64 0.75 28.75
1.26 48.61 0.59 22.64 0.75 28.75
1.91
58.13 0.30
9.19
1.07 32.68
1.91 56.57
58.13 0.28
0.30 8.089.191.251.07
1.99
35.3532.68
1.99 56.57 0.28 8.08 1.25 35.35
Calcite
Mass (g) *
1.71
1.71
1.72
1.72
1.82
1.82
1.79
1.79
1.98
1.98
1.98
1.98
2.33
2.33
2.25
2.25
2.55
2.55
2.60
2.60
3.28
3.28
3.51
3.51
* In 30 mL of grout solution.
* In 30 mL of grout solution.
Concentration of CaCl [mol/L]
Precipitated composition [%]
2
100
1.00
0.98
0.96
0.94
0.92
0.90
0.02
0.04
0.06
0.08
0.1
80
60
40
20
0
0
Concentration of MgSO [mol/L]
4
Gypsum
Aragonite
Calcite
Figure 8.
8. Composition
Composition of
of precipitated
precipitated materials.
materials.
Figure
The evolutions of the crystal phase observed by SEM are shown in Figure 9. In A0, which is the
The evolutions of the crystal phase observed by SEM are shown in Figure 9. In A0, which is the
crystal structure image of the precipitated materials without the substitution of magnesium sulfate,
crystal structure image of the precipitated materials without the substitution of magnesium sulfate,
rhombohedral calcite was formed. As the magnesium sulfate was substituted, the structure phase
rhombohedral calcite was formed. As the magnesium sulfate was substituted, the structure phase
changed, and new crystals of aragonite and gypsum were also formed. The phase of aragonite
clearly appeared in A1 and A2, when 0.02–0.04 mol/L of magnesium was added, respectively.
Gypsum clearly formed when magnesium with concentrations of >0.06 mol/L (i.e., A3, A4, and A5)
were added. The agglomeration phase of the precipitated materials was also formed by the
substitution of magnesium. The SEM results confirmed that magnesium sulfate could be utilized to
promote the formation of aragonite and gypsum in addition to calcite.
Crystals 2017, 7, 59
11 of 15
changed, and new crystals of aragonite and gypsum were also formed. The phase of aragonite clearly
appeared in A1 and A2, when 0.02–0.04 mol/L of magnesium was added, respectively. Gypsum
clearly formed when magnesium with concentrations of >0.06 mol/L (i.e., A3, A4, and A5) were
added. The agglomeration phase of the precipitated materials was also formed by the substitution
of magnesium. The SEM results confirmed that magnesium sulfate could be utilized to promote the
formation
and gypsum in addition to calcite.
Crystals 2017,of
7, aragonite
59
11 of 15
Aragonite
Calcite
Calcite
A0
A1
Calcite
Aragonite
Gypsum
A2
A3
Calcite
Gypsum
Calcite
Gypsum
A4
A5
Figure 9.
9. Scanning
microscopy of
of precipitated
precipitated minerals.
minerals.
Figure
Scanning electron
electron microscopy
In order to evaluate the effect of the presence of aragonite and gypsum, as the precipitated
materials on the mechanical properties of treated sand, A0, A1, A2, and A5 were selected as the
grouting solutions. A0, which may produce mostly calcite, A1 and A2, which may produce mostly
aragonite-calcite, and A5, which may produce mostly calcite-gypsum, were injected into the sand
samples. Then, the effects of the presence of aragonite and gypsum in the EMCP technique were
examined through UCS tests. By comparing all of the cases with those obtained from the literature,
Crystals 2017, 7, 59
12 of 15
In order to evaluate the effect of the presence of aragonite and gypsum, as the precipitated
materials on the mechanical properties of treated sand, A0, A1, A2, and A5 were selected as the
grouting solutions. A0, which may produce mostly calcite, A1 and A2, which may produce mostly
aragonite-calcite, and A5, which may produce mostly calcite-gypsum, were injected into the sand
samples. Then, the effects of the presence of aragonite and gypsum in the EMCP technique were
examined through UCS tests. By comparing all of the cases with those obtained from the literature,
the effectiveness of aragonite and gypsum in the EMCP technique was evaluated. The experimental
conditions for the PVC cylinder tests are listed in Table 4.
Table 4. Experimental conditions for PVC cylinder tests.
Case
U1
U2
U3
U4
Grouting
Solution
A0
A1
A2
A5
Conc. of
Urease (g/L)
2.00
2.00
2.00
2.00
Reagent Compositions
Conc. of Urea
Conc. of CaCl2
Conc. of MgSO4
(molŁ)
(molŁ)
(molŁ)
1.00
1.00
1.00
1.00
1.00
0.98
0.96
0.90
0.00
0.02
0.04
0.10
In order to evaluate the amount of precipitated material within the sand sample, the acid leaching
method with a percentage error of 1.8% was conducted [4]. In this process, the treated sample was
washed with distilled water to dissolve the salt materials and then dried at a temperature of 100 ◦ C
for 24 h. The dried samples were weighed and washed with 0.1 mol/L of HCl several times until air
bubbles no longer appeared. Filter paper (PS of 11 µm) was utilized to minimize the lost mass of sand
during the washing process. The sample was dried again, and the final weight was taken. The dry
weight lost during the acid leaching was examined and assumed to be the weight of the precipitated
materials [4,9,13]. The reactions taking place are expressed by Equations (8) and (9):
CaCO3 + 2HCl → CaCl2 + CO2 + H2 O
(8)
CaSO4 + 2HCl → CaCl2 + H2 SO4
(9)
The results of the PVC cylinder tests are depicted in Figure 10. The mass of the precipitated
materials, varying in the range of 4%–10% of the soil mass, was obtained by 1–3 PV injections
(Figure 10a). The precipitated mass within the treated sand increased as the number of injections was
further increased. When one pore volume (PV) of grouting solution was injected, a lower precipitated
mass was obtained for U1 than for U2 , U3 , and U4 . The precipitated mass increased as the number
of injections was increased. However, the obtained mineral mass in the case of U4 was found lower
than the other cases (Figure 10a). The maximum strength of 0.6 MPa was achieved in the presence a
10% mineral precipitation in U2 and U3 . The UCS of the treated sand improved 2.5-fold compared
to that without magnesium (i.e., U1 ). In the case of U4 , a lower mass of precipitated materials was
formed with the same number of injections. The presence of a high concentration of magnesium
sulfate might promote the formation of gypsum and enhance the reaction rate. The precipitate was
formed before all of the grouting solution flowed through the sample and, hence, a higher amount of
precipitated minerals was formed close to the surface. The maximum precipitated mass of 8%, which
corresponds to the strength of 0.2 MPa (Figure 10b), was obtained. The presence of a high concentration
of magnesium sulfate in the grouting solution enhanced the reaction rate. The precipitation process
occurred quickly after mixing, and the precipitated materials might have formed before all of the
solution had been passed through the sand samples. The precipitated materials were concentrated in
the upper side of the sand samples. This may have hampered the permeation of the injecting solution
between the soil particles and, hence, the number of injections was limited. However, the mineralogical
analyses of the treated sand were not conducted, so the exact composition of the precipitated materials
Crystals 2017, 7, 59
13 of 15
cannot be identified. In comparison to the previous study, in which the calcite precipitation technique
was performed without magnesium [7], the maximum strength obtained in this study was roughly
40% higher for the same mineral mass. The combination of calcite-aragonite (i.e., U2 and U3 ) as
the precipitated minerals brought about a significant improvement in the strength of the treated
sand. The results indicated that the substitution of a low concentration of magnesium sulfate into the
Crystals 2017,
7, 59
of 15
injecting
solution
in the EMCP technique has the potential to improve the strength of the treated13sand.
1.0
(a)
(b)
10
8
UCS [MPa]
Mineral mass [%]
12
6
4
U1 (Ca 1.00; Mg 0.00)
U2 (Ca 0.98; Mg 0.02)
U3 (Ca 0.96; Mg 0.04)
U4 (Ca 0.90; Mg 0.10)
2
0
0
1
2
3
4
0.1
0.0
Number of injections [PV]
U1 (Ca 1.00; Mg 0.00)
U2 (Ca 0.98; Mg 0.02)
U3 (Ca 0.96; Mg 0.04)
U4 (Ca 0.90; Mg 0.10)
Whiffin et al. (2007)
0
2
4
6
8
10
12
Mineral mass [%]
Figure
Results of
of PVC
PVC cylinder
tests: (a)
(a) mineral
mineral mass
mass in
in various
various number
number of
of injections;
injections; and
and (b)
(b)
Figure 10.
10. Results
cylinder tests:
relation
relation between
between mineral
mineral mass
mass and
and UCS.
UCS.
4. Conclusions
The applicability of magnesium sulfate as the
the substituted
substituted material
material in
in enzyme-mediated
enzyme-mediated calcite
precipitation
been
evaluated
for itsfor
possible
application
as a soil-improvement
technique.
precipitation (EMCP)
(EMCP)has
has
been
evaluated
its possible
application
as a soil-improvement
The
effects of
theeffects
addition
of magnesium
on the amount
andthe
theamount
mineralogical
substance
of the
technique.
The
of the
addition ofsulfate
magnesium
sulfate on
and the
mineralogical
precipitated
have been materials
assessed. The
of the mechanical
properties
of treated
sand
substance ofmaterials
the precipitated
haveevolution
been assessed.
The evolution
of the
mechanical
was
also evaluated
through
unconfined
compressive
strength
(UCS)compressive
tests. The precipitated
mass tests.
was
properties
of treated
sand was
also evaluated
through
unconfined
strength (UCS)
seen
increase as mass
the concentration
of magnesium
was increased.
mineralogical
analysis
The to
precipitated
was seen to
increase as sulfate
the concentration
ofThe
magnesium
sulfate
was
revealed
that
themineralogical
substitution ofanalysis
magnesium
sulfate
into
thesubstitution
injecting solution
composedsulfate
of urea,into
urease,
increased.
The
revealed
that
the
of magnesium
the
and
CaCl2solution
was a potential
method
for urease,
promoting
formation
aragonite
and gypsum.
Especially,
injecting
composed
of urea,
andthe
CaCl
2 was a of
potential
method
for promoting
the
the
low concentrations
magnesium
sulfate (i.e.,the
0.02
and
0.04 mol/L) significantly
promoted
the
formation
of aragonite of
and
gypsum. Especially,
low
concentrations
of magnesium
sulfate (i.e.,
formation
of mol/L)
aragonite.
Furthermore,
a large
of gypsum
was Furthermore,
formed whena0.10
mol/L
of
0.02 and 0.04
significantly
promoted
theamount
formation
of aragonite.
large
amount
magnesium
sulfate
was when
substituted.
of gypsum was
formed
0.10 mol/L of magnesium sulfate was substituted.
showed that besides
besides calcite, the presence of aragonite as a precipitated
precipitated
The UCS test results showed
mineral resulted in greater improvement in the strength of the treated sand than the sand treated
by calcite.
calcite. A maximum strength of 0.6 MPa was obtained from the treated samples in the
purely by
mineral mass
mass of
of 10%.
10%. In comparison to the previous
previous studies,
studies, which
which addressed
addressed calcite
calcite
presence of a mineral
only, the
the obtained
obtained strength in this study was higher for the same precipitated mass.
precipitation only,
mass.
results of
of this
this study
study have
have elucidated
elucidated that
that the
the application
application of
of magnesium
magnesium sulfate
sulfate to the EMCP
The results
alternative soil-improvement
soil-improvement method.
method.
technique may be an alternative
Acknowledgments:
hashas
beenbeen
partlypartly
supported
by a research
from grant
the Penta-Ocean
Acknowledgments: This
Thiswork
work
supported
by a grant
research
from the Constructions
Penta-Ocean
Co.,
Ltd.
and
BU
Kemendikbud,
Ministry
of
Education
and
Culture
of
Indonesia.
Their
support
is
Constructions Co., Ltd. and BU Kemendikbud, Ministry of Education and Culture of Indonesia.
Their
support
gratefully acknowledged.
is gratefully acknowledged.
Author Contributions: Heriansyah Putra has performed all the experiments and analyzed the data;
Author Contributions:
has performed
all the experiments
and analyzed
the data;the
Hideaki
Hideaki
Yasuhara has Heriansyah
supervised Putra
this work,
partly conducted
the experiments
and analyzed
data;
Naoki
Kinoshita
has suggested
how topartly
proceed
this work
and
partly conducted
the experiments;
has
Yasuhara
has supervised
this work,
conducted
the
experiments
and analyzed
the data; Akira
NaokiHirata
Kinoshita
suggested
how how
to conduct
the experiments
and partly
analysed
the data.the experiments; Akira Hirata has suggested
has suggested
to proceed
this work and
conducted
how to conduct
the experiments
analysed
the data.
Conflicts
of Interest:
The authorsand
declare
no conflict
of interest.
Conflicts of Interest: The authors declare no conflict of interest.
References
1.
2.
Neupane, D.; Yasuhara, H.; Kinoshita, N. Evaluation of enzyme mediated calcite grouting as a possible
soil improvement technique. In Computer Method and Recent Advances in Geomechanics; Oka, F., Murakami,
A., Uzuoka, R., Kimoto, S., Eds.; CRC Press: Boca Raton, FL, USA, 2015; pp. 1169–1172.
Neupane, D.; Yasuhara, H.; Kinoshita, N.; Putra, H. Distribution of grout material within 1-m sand column
Crystals 2017, 7, 59
14 of 15
References
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
Neupane, D.; Yasuhara, H.; Kinoshita, N. Evaluation of enzyme mediated calcite grouting as a possible soil
improvement technique. In Computer Method and Recent Advances in Geomechanics; Oka, F., Murakami, A.,
Uzuoka, R., Kimoto, S., Eds.; CRC Press: Boca Raton, FL, USA, 2015; pp. 1169–1172.
Neupane, D.; Yasuhara, H.; Kinoshita, N.; Putra, H. Distribution of grout material within 1-m sand column
in insitu calcite precipitation technique. Soil Found. 2015, 55, 1512–1518. [CrossRef]
Neupane, D.; Yasuhara, H.; Kinoshita, N.; Ando, Y. Distribution of mineralized carbonate and its quanti fi
cation method in enzyme mediated calcite precipitation technique. Soil Found. 2015, 55, 447–457. [CrossRef]
Putra, H.; Yasuhara, H.; Kinoshita, N.; Neupane, D.; Lu, C.-W. Effect of Magnesium as Substitute Material in
Enzyme-Mediated Calcite Precipitation for Soil-Improvement Technique. Front. Bioeng. Biotechnol. 2016, 4,
37. [CrossRef] [PubMed]
Van Paassen, L.A.; Daza, C.M.; Staal, M.; Sorokin, D.Y.; van der Zon, W.; van Loosdrecht, M.C.M. Potential
soil reinforcement by biological denitrification. Ecol. Eng. 2010, 36, 168–175. [CrossRef]
Cheng, L.; Cord-Ruwisch, R.; Shahin, M.A. Cementation of sand soil by microbially induced calcite
precipitation at various degrees of saturation. Can. Geotech. J. 2013, 50, 81–90. [CrossRef]
Whiffin, V.S.; van Paassen, L.A.; Harkes, M.P. Microbial Carbonate Precipitation as a Soil Improvement
Technique. Geomicrobiol. J. 2007, 24, 417–423. [CrossRef]
Harkes, M.P.; van Paassen, L.A.; Booster, J.L.; Whiffin, V.S.; van Loosdrecht, M.C.M. Fixation and distribution
of bacterial activity in sand to induce carbonate precipitation for ground reinforcement. Ecol. Eng. 2010, 36,
112–117. [CrossRef]
Yasuhara, H.; Neupane, D.; Hayashi, K.; Okamura, M. Experiments and predictions of physical properties of
sand cemented by enzymatically-induced carbonate precipitation. Soil Found. 2012, 52, 539–549. [CrossRef]
Putra, H.; Yasuhara, H.; Kinoshita, N.; Neupane, D. Optimization of Calcite Precipitation as a Soil
Improvement Technique. In Proceedings of the 2nd Makassar International Conference on Civil Engineering,
Makassar, Indonesia, 11–12 August 2015; pp. 9–14.
Martinez, B.C.; DeJong, J.T.; Ginn, T.R.; Montoya, B.M.; Barkouki, T.H.; Hunt, C.; Tanyu, B.; Major, D.
Experimental Optimization of Microbial-Induced Carbonate Precipitation for Soil Improvement. J. Geotech.
Geoenviron. Eng. 2013, 139, 587–598. [CrossRef]
DeJong, J.T.; Fritzges, M.B.; Nüsslein, K. Microbially Induced Cementation to Control Sand Response to
Undrained Shear. J. Geotech. Geoenviron. Eng. 2006, 132, 1381–1392. [CrossRef]
Neupane, D.; Yasuhara, H.; Kinoshita, N.; Unno, T. Applicability of Enzymatic Calcium Carbonate
Precipitation as a Soil-Strengthening Technique. J. Geotech. Geoenviron. Eng. 2013, 139, 2201–2211. [CrossRef]
Nemati, M.; Greene, E.A.; Voordouw, G. Permeability profile modification using bacterially formed calcium
carbonate: Comparison with enzymic option. Process Biochem. 2005, 40, 925–933. [CrossRef]
Yasuhara, H.; Hayashi, K.; Okamura, M. Evolution in Mechanical and Hydraulic Properties of
Calcite-Cemented Sand Mediated by Biocatalyst. In Geo-Frontiers 2011: Advances in Geotechnical Engineering;
ASCE: Reston, VA, USA, 2011; pp. 3984–3992.
Van Paassen, L.A.; Ghose, R.; van der Linden, T.J.M.; van der Star, W.R.L.; van Loosdrecht, M.C.M.
Quantifying Biomediated Ground Improvement by Ureolysis: Large-Scale Biogrout Experiment. J. Geotech.
Geoenviron. Eng. 2010, 136, 1721–1728. [CrossRef]
De Muynck, W.; de Belie, N.; Verstraete, W. Microbial carbonate precipitation in construction materials:
A review. Ecol. Eng. 2010, 36, 118–136. [CrossRef]
Okwadha, G.D.O.; Li, J. Optimum conditions for microbial carbonate precipitation. Chemosphere 2010, 81,
1143–1148. [CrossRef] [PubMed]
Boyd, V.H. The Effect of Calcium and Magnesium on Carbonate Mineral Precipitation during Reactive
Transport in a Model Subsurface Pore Structure. Ph.D. Thesis, University of Illinois, Champaign, IL,
USA, 2012.
Park, W.K.; Ko, S.-J.; Lee, S.W.; Cho, K.-H.; Ahn, J.-W.; Han, C. Effects of magnesium chloride and organic
addictives on synthesis of aragonite precipitated calcium carbonate. J. Cryst. Growth 2008, 310, 2593–2601.
[CrossRef]
Litvin, A.L.; Valiyaveettil, S.; Kaplan, D.L.; Mann, S. Template-Directed Synthesis of Aragonite Under
Supramolecular Hydrogen-Bonded Langmuir Monolayers. Adv. Mater. 1997, 9, 124–127. [CrossRef]
Crystals 2017, 7, 59
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
15 of 15
“Aragonite.” A Dictionary of Earth Sciences. Encyclopedia.com. Available online: http://www.
encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/aragonite (accessed on
1 November 2016).
“Calcite.” A Dictionary of Earth Sciences. Encyclopedia.com. Available online: http://www.encyclopedia.
com/science/dictionaries-thesauruses-pictures-and-press-releases/calcite (accessed on 1 November 2016).
Friedman, G.; Schultz, D. Precipitation of vaterite (CaCO3 ) during oil field drilling. Mineral. Mag. 1994, 58,
401–408. [CrossRef]
Kahmi, S.R. On the structure of vaterite, CaCO3 . Acta Crystallogr. 1963, 16, 770–772.
Wang, J.; Becker, U. Structure and carbonate orientation of vaterite (CaCO3 ). Am. Mineral. 2009, 94, 380–386.
[CrossRef]
De Villiers, J.P.R. Crystal structures of aragonite, strontianite, and witherite. Am. Mineral. 1971, 56, 758–767.
Dal Negro, A.; Ungaretti, L. Refinement of the Crystal Structure of Aragonite. Am. Mineral. 1971, 56, 768–772.
ASTM International. International, Standard Practice for Classification of Soils for Engineering Purposes (Unified
Soil Classification System); ASTM Standard Guide. D5521-5; ASTM: West Conshohocken, PA, USA, 2000.
Yasuhara, H.; Neupane, D.; Kinosita, N.; Hayashi, K.; Unno, T. Solidification of sand soils induced by calcium
carbonate precipitation utilizing biocatalyst. J. Jpn. Soc. Civ. Eng. Ser. C Geosph. Eng. 2014, 70, 290–300.
[CrossRef]
Chung, F.H. Quantitative interpretation of X-ray diffraction patterns of mixtures. III. Simultaneous
determination of a set of reference intensities. J. Appl. Crystallogr. 1975, 8, 17–19. [CrossRef]
Chipera, S.J.; Bish, D.L. Fitting Full X-Ray Diffraction Patterns for Quantitative Analysis: A Method for
Readily Quantifying Crystalline and Disordered Phases. Adv. Mater. Phys. Chem. 2013, 3, 47–53. [CrossRef]
Connolly, J.R. Introduction Quantitative X-ray Diffraction Methods. Fundamentals of X-ray Powder Diffraction;
Nuevo Mexico University: Albuquerque, NM, USA, 2012.
Demichelis, R.; Raiteri, P.; Gale, J.D.; Dovesi, R. The multiple structures of vaterite. Cryst. Growth Des. 2013,
13, 2247–2251. [CrossRef]
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