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CONSOLI ET AL (2022) COMPACTED FILTERED TAILINGS DISPOSAL BY STACKING
* January 2022
* Applied Sciences 12(836)
DOI:10.3390/app12020836
* Project: Brazilian new tailings disposal trend by stacking
Authors:
Nilo Cesar Consoli
* Universidade Federal do Rio Grande do Sul
Jordanna Chamon Vogt
Jordanna Chamon Vogt
* This person is not on ResearchGate, or hasn't claimed this research yet.
João Paulo Sousa Silva
João Paulo Sousa Silva
* This person is not on ResearchGate, or hasn't claimed this research yet.
Helder Mansur Chaves
* Universidade Federal do Rio Grande do Sul
Show all 7 authorsHide
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References (31)
Figures (9)
ABSTRACT AND FIGURES
Failures of tailings dams, primarily due to liquefaction, have occurred in
Brazil in recent years. These events have prompted the Brazilian government to
place restrictions on the construction of new dams, as iron ore tailings
deposited behind upstream dams by spigotting have been shown to have low in situ
densities and strengths and are prone to failure. This work proposes a new trend
for tailings disposal: stacking compacted filtered ore tailings–Portland cement
blends. As part of the proposal, it analyses the behaviour of compacted iron ore
tailings–Portland cement blends, considering the use of small amounts of
Portland cement under distinct compaction degrees. With the intention of
evaluating the stress–strain–strength–durability behaviour of the blends, the
following tests were carried out: unconfined compression tests; pulse velocity
tests; wetting–drying tests; and standard drained triaxial compression tests
with internal measurement of strains. This is the first study performed to
determine the strength and initial shear stiffness evolution of iron ore
tailings–Portland cement blends during their curing time, as well friction angle
and cohesion intercept. This manuscript postulates an analysis of original
experimental results centred on the porosity/cement index (n/Civ). This index
can help select the cement quantity and density for important design parameters
of compacted iron ore tailings–cement blends required in geotechnical
engineering projects such as the proposed compacted filtered iron ore
tailings–cement blends stacking.
Schemes of tailings dam construction methods (a) upstream method (b) dry
stacking method.
…
Location of the Iron Quadrilateral on the map of Brazil and Minas Gerais (MG)
province.
…
Iron ore tailings grain size distribution.
…
Compaction curves of iron ore tailings at standard and modified energies.
…
+4
Cont.
…
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Content may be subject to copyright.
Citation: Consoli, N.C.; Vogt, J.C.;
Silva, J.P.S.; Chaves, H.M.;
Scheuermann Filho, H.C.; Moreira,
E.B.; Lotero, A. Behaviour of
Compacted Filtered Iron Ore
Tailings–Portland Cement Blends:
New Brazilian Trend for Tailings
Disposal by Stacking. Appl. Sci. 2022,
12, 836. https://doi.org/10.3390/
app12020836
Academic Editors: Paulo Joséda
Venda Oliveira and António Alberto
Santos Correia
Received: 29 November 2021
Accepted: 9 January 2022
Published: 14 January 2022
Publisher’s Note: MDPI stays neutral
with regard to jurisdictional claims in
published maps and institutional affil-
iations.
Copyright: © 2022 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
applied
sciences
Article
Behaviour of Compacted Filtered Iron Ore Tailings–Portland
Cement Blends: New Brazilian Trend for Tailings
Disposal by Stacking
Nilo Cesar Consoli 1, * , Jordanna Chamon Vogt 2, João Paulo Sousa Silva 3,
Helder Mansur Chaves 1,
Hugo Carlos Scheuermann Filho 1, Eclesielter Batista Moreira 1and Andres Lotero
1
1Graduate Program in Civil Engineering, Universidade Federal do Rio Grande do
Sul,
Porto Alegre 90035-190, Brazil; heldermansurchaves@hotmail.com (H.M.C.);
hugocsf@gmail.com (H.C.S.F.); eclesielter_ebm@hotmail.com (E.B.M.);
andreslotero@hotmail.com (A.L.)
2Coproducts Business Development, VALE S.A., Nova Lima 34000-000, Brazil;
jordanna.vogt@vale.com
3Exploration and Mineral Projects—Mineral Development Centre, VALE S.A., Santa
Luzia 33040-900, Brazil;
joao.paulo.silva@vale.com
*Correspondence: consoli@ufrgs.br
Abstract:
Failures of tailings dams, primarily due to liquefaction, have occurred in
Brazil in recent
years. These events have prompted the Brazilian government to place restrictions
on the construction
of new dams, as iron ore tailings deposited behind upstream dams by spigotting
have been shown
to have low in situ densities and strengths and are prone to failure. This work
proposes a new
trend for tailings disposal: stacking compacted filtered ore tailings–Portland
cement blends. As part
of the proposal, it analyses the behaviour of compacted iron ore
tailings–Portland cement blends,
considering the use of small amounts of Portland cement under distinct
compaction degrees. With the
intention of evaluating the stress–strain–strength–durability behaviour of the
blends, the following
tests were carried out: unconfined compression tests; pulse velocity tests;
wetting–drying tests; and
standard drained triaxial compression tests with internal measurement of
strains. This is the first
study performed to determine the strength and initial shear stiffness evolution
of iron ore tailings–
Portland cement blends during their curing time, as well friction angle and
cohesion intercept. This
manuscript postulates an analysis of original experimental results centred on
the porosity/cement
index (
η
/Civ). This index can help select the cement quantity and density for important
design
parameters of compacted iron ore tailings–cement blends required in geotechnical
engineering
projects such as the proposed compacted filtered iron ore tailings–cement blends
stacking.
Keywords:
cemented iron ore tailings behaviour; filtered tailings stacking; Portland
cement; compaction
1. Introduction
Tailings are the residues derived from ore extraction and processing and are
mainly
constituted by crushed rock fines, chemicals and water [
1
,
2
]. This combination results in
a material having an aqueous slurry consistency which facilitates the disposal
in large
impoundments designated as tailings dams. In this regard, the upstream method of
con-
struction (Figure 1a) is the cheapest manner to expand the dam once the initial
embankment
has been built. In brief, this methodology consists in founding the raising dam
directly
into the deposited tailings. Nonetheless, as the tailings are customarily found
saturated
at a loose condition, stability issues related to static and/or dynamic
liquefaction may
compromise the security of the dams assembled using the upstream method [3,4].
For this reason, since 2019, building upstream tailings dams has been prohibited
in Brazil due to collapses that released massive mudslides that buried the
surrounding
areas, resulting in destruction, environment pollution and several deaths.
According
to the non-profit organization World Mine Tailings Failures [
5
], 45 tailings dam failures
Appl. Sci. 2022,12, 836. https://doi.org/10.3390/app12020836
https://www.mdpi.com/journal/applsci
Appl. Sci. 2022,12, 836 2 of 18
occurred between 2009 and 2019. A United Nations Environment Programme [
6
] report
documented some of these significant failures, if not in terms of loss of life,
then in terms of
environmental damage. These are some of the incidents which occurred between
2015 and
2020: Fundão, 2015 (Brazil); New Walles, 2016 (USA); Tonglushan, 2017 (China);
Mishor
Rotem, 2017 (Israel); Brumadinho, 2019 (Brazil); and Hpakant, 2020 (Myanmar),
among
others [7,8].
Numerous other tailings failures have occurred worldwide but were not reported
as
they did not involve any fatalities. These catastrophic incidents may be caused,
in many
cases, by lack of control of the design, but to some extent they reflect a
relatively poor
understanding of the mechanics of tailings. Santamarina et al. [
9
] highlight how knowledge
gaps and management shortcomings contribute to the catastrophic failures that
claim
thousands of lives around the world. Therefore, a deeper knowledge on the
behaviour of
these structures and materials, as well as the search for alternatives focusing
risk mitigation,
is crucial and of great concern to companies, government agencies and society.
Figure 1. Schemes of tailings dam construction methods (a) upstream method (b)
dry stacking method.
Dry stack tailings (Figure 1b) are being adopted in Brazil as a potential
solution for
reducing the risk of catastrophic dam failure and tailings runout. Essentially,
they consist of
the stacking of compacted dry tailings, forming piles of hundreds of meters. In
this regard,
the use of compacted filtered ore tailings–Portland cement blends stacking will
allow
Appl. Sci. 2022,12, 836 3 of 18
tailings disposal sites, which currently do not use binders and thus have
shallow slopes,
to occupy smaller areas by creating steeper, more stable stacks which will
consequently
lead to less environmental and visual impact. The current research is studying
the stress–
strain–strength behaviour of artificially cemented (using Portland cement)
compacted
filtered iron mining tailings for stacking in order to drastically reduce the
possibility
of tailings liquefaction once cementitious bonds (cohesion) are built amongst
tailings
particles. The reason for studying especially iron mine tailings specifically is
that Brazil is
the second largest producer of iron ore (and consequently iron ore tailings) in
the world,
with approximately 388 million metric tons produced in 2020 [10].
Recognizing the topic’s importance and based on concepts of ground improvement,
this research aims to contribute to understanding the mechanical behaviour of
compacted
(considering distinct dry unit weights) iron ore tailings stabilized with early
strength Portland
cement (in distinct amounts), from unconfined compression, initial shear
stiffness, perfor-
mance under wetting–drying cycles and consolidated drained triaxial tests points
of view.
2. Background
The characteristics of ore tailings are highly variable depending on the
composition
of the ores and the extraction processes used. In general, tailings can vary in
size from
colloidal to sand, with the degree of plasticity depending on the surface
activity of the
fines content [
11
]. The most common disposal method for tailings is hydraulic deposition,
followed by sedimentation in an impoundment and consolidation under their own
weight,
which may take many years due to their relatively low hydraulic conductivity
[12,13].
Frequently, the disposal conditions of relatively small size particles result in
a saturated
and low strength environment—often susceptible to liquefaction, caused by either
static or
seismic loading. In general, the large mudflows that follow dam failures imply
the presence
of loose, water-saturated sediments that want to contract upon shear. The water
cannot
drain fast enough, and grains become temporarily suspended, forming a dense fluid
[
9
],
which characterizes the liquefaction phenomenon. Conceptually, Jefferies and
Been [
14
]
define soil liquefaction as a phenomenon in which soil loses much of its strength
or stiffness
for a generally short time but nevertheless long enough to cause failures which
result in
large financial losses, environmental damage and, in the worst cases, loss of
life. This is
particularly important, since there are many incidents on tailings impoundments
that are
claimed to be related to liquefaction.
The stability performance of mine tailings is linked to their dry unit weight (
γd
) and
consequently compaction could reduce liquefaction potential [
15
]. However, the existence
of cementitious bonds amongst tailings particles (due to blends of tailings with
Portland
cement) prevents them of suffering liquefaction and enhances mechanical
behaviour.
3. Experimental Program
3.1. Materials
The iron tailings used in the testing were taken from the Iron Quadrangle
region,
located in the province of Minas Gerais, Brazil (see Figure 2). The grain size
distribution of
the iron mine tailings is given in Figure 3. The iron mine tailings’ physical
properties are
displayed in Table 1, being classified [
16
] as silty sand (SM). Mineralogical characterization
of the iron tailings, acquired using an X-ray diffractometer, detected the
presence of a few
compounds: quartz [SiO
2
], hematite [Fe
2
O
3
], goethite [FeHO
2
], kaolinite [Al
2
H
4
O
9
Si
2
], and
muscovite [Al
3
H
2
KO
12
Si
3
]. Regarding the chemical composition of the studied iron tailings,
the following element concentrations were found after X-ray fluorescence: 69.7%
of SiO
2
,
24.0% of Fe
2
O
3
, 4.8% Al
2
O
3
, 0.40% of MnO, 0.25% of P
2
O
5
, 0.15% of K
2
O, and 0.1% of SO
3
,
amongst others. The results of standard (600 kN.m/m
3
) and modified
(2700 kN.m/m3)
Proctor compaction tests are displayed in Figure 4.
Appl. Sci. 2022,12, 836 4 of 18
Figure 2. Location of the Iron Quadrilateral on the map of Brazil and Minas
Gerais (MG) province.
Figure 3. Iron ore tailings grain size distribution.
Figure 4. Compaction curves of iron ore tailings at standard and modified
energies.
Appl. Sci. 2022,12, 836 5 of 18
Table 1. Physical properties of studied iron ore tailings.
Physical Properties Iron Ore Tailings (IOT)
Specific gravity of solids 2.916
Uniformity coefficient 10.7
Coefficient of curvature 3.9
Mean particle diameter-(mm) 0.085
Liquid limit (%) -
Plastic limit (%) -
Plasticity index (%) Nonplastic
Medium sand (0.425 mm < d< 0.200 mm) (%) 4.0
Fine sand (0.075 mm < d< 0.425 mm) (%) 49.0
Silt (0.002 mm < d< 0.075 mm) (%) 42.0
Clay (d< 0.002 mm) (%) 5.0
USCS Classification (ASTM 2017) SM
Maximum dry unit weight at standard energy compaction (kN/m3)19.2
Optimum moisture content at standard energy compaction (%) 11.6
High early strength (Type III) Portland cement [
17
] was used throughout this investi-
gation. Its rapid strength gain allows blends to achieve important strength
thresholds from
short curing periods. Cement grains’ specific gravity is 3.15.
Distilled water was utilized both for characterization tests and moulding
specimens
for the triaxial tests.
3.2. Methods
3.2.1. Moulding Portland Cement Stabilized Iron Ore Tailings (IOT) Specimens
Cylindrical specimens (50 mm in diameter and 100 mm in height) were moulded for
the unconfined compression and initial shear stiffness tests, as well as for
performance
under wetting–drying and for consolidated isotropically drained triaxial tests
using the
undercompaction method [
18
]. A target dry unit weight (
γd
) for a particular specimen was
then instituted as a result of the dry compacted iron tailings–Portland cement
mix divided
by the total volume of the specimen [
19
]. As exhibited in Equation (1) [
20
], porosity (
η
) is a
function of dry density (
γd
) of the mix and Portland cement content (PC). Each substance
(iron mine tailings and Portland cement) has a unit weight of solids (
γ
s
IOT
and
γ
s
PC
), which
also must be measured for computing porosity.
η=100 −100(" γd
1+PC
100 #" 1
γsIOT
+
PC
100
γsPC #) (1)
After the weighing of the dry materials (i.e., iron mine tailings and cement),
these were
manually mixed with a spoon until a powder having a visual uniformity was
obtained.
Next, the correct amount of distilled water was supplemented to reach moisture
content of
11.6% (optimum moisture content for standard Proctor compaction effort—see Table
1) for
the iron tailings—Portland cement blend, and the mixture continued up to the
formation of
a homogeneous paste. Following, the specimen was statically compacted inside a
cylin-
drical split mould to its target dry unit weight. Three layers were used in the
compaction
process, with the top of the first and second layers being slightly scarified in
order to
guarantee the adherence of the subsequent layer. Once the moulding was finished,
the
specimen was retrieved from the mould, measured, weighed and sealed inside a
plastic bag
(to maintain water content) and sent to be cured in a humid room at 23
±
2
◦
C with relative
moisture of about 95%. As acceptance criteria, the obtained dry unit weight (
γd
) should
range within
±
1% of the target value, whereas the moisture content (w) should be around 0.5%
of the previously assigned value. Within each tested dosage, the cement content
was calculated
over the mass of dry iron mine tailings and the dry unit weight (
γd
) was determined as the ratio
between the mass of dry solids and the total volume of the test specimen.
Appl. Sci. 2022,12, 836 6 of 18
3.2.2. Program of Unconfined Compression Tests
The unconfined compression tests followed the ASTM C39 standard [21]. Specimens
were moulded with 11.6% of moisture content (optimum moisture content for
standard
Proctor compaction effort), dry densities of 17 kN/m
3
, 18 kN/m
3
and 19 kN/m
3
(corre-
sponding to 89%, 94% and 99% of degree of compaction of standard Proctor
compaction
effort, respectively), Portland cement contents of 1%, 2%, 3%, 4% and 5%
(determined
following international [
22
] and Brazilian [
23
,
24
] experience with soil–cement). Specimens
were cured for 2, 4, 7, 28 and 90 days. One day prior to the test, the specimens
were sub-
merged in a water container for 24 h in order to reduce possible suction effects
[
20
,
23
]. The
temperature of the water tank was controlled according to the adopted curing
temperature
(i.e., 23
◦
C). Next, the unconfined compression test was performed using an automatic
loading press with maximum capacity of 50 kN at a displacement rate of 1.14
mm/min;
the maximum load measured using a load cell. A full factorial design setting was
used to
define the mix designs for the tests. For this reason, all possible combinations
of amounts
of cement and dry unit weight values were tested considering each curing period.
Thus,
15 dosages were intended to be tested within each curing time; in triplicate
moulded for
each dosage.
3.2.3. Program of Pulse Velocity Tests and Ultrasonic Elastic Constants
Initial Shear Modulus (G
0
) of artificially cemented soils can be determined using
ultrasonic pulse velocity tests performed in accordance with ASTM D2845 [
25
]. For homo-
geneous and elastic media, G
0
may be calculated through the product between the bulk
density and the square of the velocity of a shear wave passing through it [
26
]. Therefore,
as this test is non-destructive, pulse velocity tests were performed on the same
specimens
moulded for an unconfined compression test, immediately before taking specimens
to
failure, using special transducers coupled on top and underneath the samples
using a
special coupler gel. An ultrasonic pulse device was used to emit compression (54
kHz)
and shear waves (250 kHz) that are emitted and cross the cylindrical specimens,
with the
propagation times measured. Therefore, the shear modulus at very small
deformations (G
0
)
can be obtained.
3.2.4. Program of Durability of Specimens Submitted to Wetting–drying Cycles
Durability tests consisting of wetting–drying cycles were carried out in
accordance
with ASTM D559 [
27
], but without brushing. Specimens were moulded with 11.6% of
moisture content, dry densities of 17 kN/m
3
, 18 kN/m
3
and 19 kN/m
3
, and Portland
cement contents of 1%, 2%, 3%, 4% and 5%. The same experimental design setting
previ-
ously described for the strength tests was used herein, with the difference that
only one
specimen for each dosage was tested. This test method aims to simulate harsh
on-field
conditions over 12 cycles of such procedures [
28
]. After 2, 4, and 7-days of curing were
completed, each specimen cycle started by immersing it in water for 5 h at 23
◦
C. Then,
specimens were submitted to a drying process in an oven during 42h at 71
◦
C. Twelve
cycles of these procedures are required to simulate harsh on-field conditions.
After each
one of the 12 cycles, the initial shear modulus (G
0
) was measured in accordance with ASTM
D2845 [
25
]. After the 12th cycle, specimens were taken to failure through unconfined
compression tests in accordance with the ASTM C39 standard [21].
3.2.5. Program of Consolidated Isotropically Drained (CID) Triaxial Tests
A series of consolidated isotropically drained (CID) triaxial compression tests
was
conducted on artificially cemented compacted filtered iron mining tailings, with
the aim of
evaluating the deviatoric stress–axial strain–volumetric strain behaviour of the
materials.
The general procedures described by BS 1377 were followed [
29
]. In this regard, two
representative dosages were chosen and tested under three effective confining
pressures
(
σ
’
3
= 50, 100 and 200 kPa). The first dosage contained 3% of cement and was moulded
at a dry unit weight of 17 kN/m
3
, and the second had the same amount of cement but
Appl. Sci. 2022,12, 836 7 of 18
was compacted to a dry density of 19 kN/m
3
. The pressures throughout the tests were
electronically monitored by pressure transducers, whereas the vertical load was
assessed
using a 20 kN high-resolution load cell. The axial displacements were globally
measured
using a linear variable differential transformer (LVDT) and locally assessed by
Hall effect
sensors positioned directly in contact with the test specimen [
30
]. The volumetric strain
was measured by an Imperial College volume gauge [
31
] connected to the drainage outlet.
To ensure the saturation of tailings specimens, a back pressure of approximately
500 kPa
was applied to produce Bparameters higher than 95%. All reported test specimens
were
isotropically consolidated to their desired consolidation pressure before
shearing. Finally,
shearing of specimens in triaxial tests occurred at a rate of 1 mm/h. For the
calculation of
the applied stresses, the area corrections proposed by La Rochelle et al. [
32
] were adopted.
4. Results and Analysis
4.1. Unconfined Compressive Strength (qu)
Figure 5a portrays q
u
as a function of porosity/cement index (
η
/C
iv
) (stated as porosity
(
η
) divided by the volumetric cement content (C
iv
), the latter expressed as a percentage
of cement volume to the total volume of the iron tailings–Portland cement mixes
[
33
]) for
the curing periods studied (2, 4, 7, 28 and 90 days). Diambra et al. [
34
] carried out the
theoretical approach validating the shape of the equation. Figure 5a indicates
that the
η
/C
iv
index is useful in normalizing strength results for iron ore tailings–Portland
cement blends.
The results indicate that the behaviour of the studied blends presents the same
trend, thus
generating a single equation (Equation (2)).
qu(kPa)=A×104×η
Civ −D
(2)
Scalar “D” has been found to be a constant (D= 1.3) to all curing times studied
(from
2 to 90 days),
while scalar “A” increases with curing time, as shown in Table 2. “A” changes
from 1.63 (for 2 days of curing) to 4.89 (for 90 days of curing) and the
coefficient of determination
(R
2
) varies in the range 0.92 to 0.97. From 2 days of curing to 4, 7, 28 and 90
days of curing, the
strength increase percentages were of 63.2%, 82.8%, 147.9% and 200.0%,
respectively.
Table 2. “A” and “C” scalars for Equations (2) and (3), respectively.
Curing Period
Strength Data—quStiffness Data—G0
“A” Coefficient of
Determination (R2)“C” Coefficient of
Determination (R2)
2 days 1.63 0.92 1.46 0.86
4 days 2.66 0.96 2.98 0.92
7 days 2.98 0.97 4.11 0.97
28 days 4.04 0.94 4.53 0.96
90 days 4.89 0.96 6.04 0.96
Appl. Sci. 2022,12, 836 8 of 18
Figure 5.
Compacted (
γd
= 17 kN/m
3
,
γd
= 18 kN/m
3
,
γd
= 19 kN/m
3
) filtered iron mining tailings
treated with early strength Portland cement (from 1% to 5%): (
a
) unconfined compressive strength
(q
u
) versus porosity/cement index (
η
/C
iv
) considering distinct curing time periods and (
b
) initial
shear stiffness (G
0
) versus
η
/C
iv
taking under consideration different curing time periods (2, 4, 7, 28
and 90 days of curing).
Appl. Sci. 2022,12, 836 9 of 18
4.2. Initial Shear Modulus
Similarly, as presented for the unconfined compressive strength test results, the
poros-
ity/cement index was used for the initial shear modulus (G
0
) results for the curing periods
studied (2, 4, 7, 28 and 90 days), as presented in Figure 5b. Therefore, an
adequate associa-
tion between G
0
and the
η
/C
iv
index (considering the same power shape as for strength)
could be obtained as the coefficient of determination (R
2
) varies in the range 0.86 to 0.97 for
the studied curing times, in the format of a specific equation (Equation (3)).
G0(MPa)=C×104×η
Civ −E
(3)
Scalar “E” has been found to be a constant (E= 1.3) for all curing times studied
(from
2 to 90 days), while scalar “C” increases with curing time, as shown in Table 2.
“C” changes
from 1.46 (for 2 days of curing) to 6.04 (for 90 days of curing). From 2 days of
curing to
4, 7, 28 and 90 days of curing, the initial shear modulus (G
0
) increase percentage were of
104.1%, 181.5%, 210.3% and 313.7%, respectively. It is interesting to observe
that the rate of
increase of q
u
and G
0
was not the same with curing time. The rate of increase of G
0
was
higher up to 28 days of curing and the rate of increase of q
u
was higher from 28 days to
90 days of curing.
4.3. Durability under Wetting–Drying Cycles
Figure 6presents G
0
variation of iron ore tailings compacted at
γd
of 17, 18 and
19 kN/m3
and treated with 1 to 5% of early strength Portland cement. Wetting–drying
cycles were performed after 2, 4 and 7 days of curing. Such performance mimics
the
behaviour of the studied blends after being submitted to harsh on-field
conditions over
12 cycles of such procedures. It is well established that increasing both the
quantity of
cement and
γd
improves the stiffness of the compacted iron ore tailings–Portland cement
mixes considering wetting–drying cycles. Disregarding the initial curing time
(2, 4 or
7 days), Figure 6shows a comparable qualitative response regarding the impact of
wetting–
drying cycles: G
0
increased from zero to three wetting–drying cycles and then oscillated
about an average, distinctive for each
γd
and quantity of cement employed, for additional
cycles. The oven drying for 42 h at 71
±
2
◦
C, during the drying part of the wetting–drying
cycles, triggered the catalysis of the chemical reactions of the Portland
cement, bringing
about the increase of G
0
of iron tailings–Portland cement mixes in the initial cycles. Distinct
results were achieved by Consoli et al. [
28
], who assessed the effect of wetting–drying
cycles on G
0
of a nonplastic silt. Test results by Consoli et al. [
28
] indicated that G
0
of
nonplastic silt–Portland cement (also early strength) blends mostly reduced with
more
wetting–drying cycles, reaching a steadiness at about six wetting–drying cycles.
Figure 7presents the correlation of q
u
and G
0
as a function of
η
/C
iv
index after
12 wetting–drying cycles. Looking at q
u
results Figure 7a, it can be noticed that after
12 wetting–drying cycles, q
u
is related to
η
/C
iv
index through Equation (4). This equation
has the same form as Equation (2) and the scalar of present equation is found
above results
of 90 days of curing at 23
◦
C. The q
u
, after 12 wetting–drying cycles, being above the results
of 90 days of curing at 23
◦
C is an example of enhancement triggered by the catalysis of the
chemical reactions of the Portland cement, due to oven drying for 42 h at 71
±2◦C.
Appl. Sci. 2022,12, 836 10 of 18
Figure 6. Cont.
Appl. Sci. 2022,12, 836 11 of 18
Figure 6.
Performance (initial shear stiffness (G
0
) variation) of compacted iron ore tailings treated
early strength Portland cement after wet–dry cycles after: (
a
) curing for 2 days, (
b
) curing for 4 days
and (c) curing for 7 days.
Appl. Sci. 2022, 12, x FOR PEER REVIEW 13 of 20
(a) (b)
Figure 7. Compacted filtered iron mining tailings treated with early strength
Portland cement and
cured for 2, 4 and 7 days: (a) qu versus η/Civ after 12 wet-dry cycles and (b)
G0 versus η/Civ after 12
wetting–drying cycles.
On the other hand, focusing on the G0 results in Figure 7b, it can be noted that
after
12 wetting–drying cycles, G0 is related to η/Civ index through Equation (5).
Such an equa-
tion has the same form as Equation (3), and the scalar of present equation is
higher than
the results of 90 days of curing at 23 °C. However, for qu and G0, results after
12 wetting–
drying cycles are of the same order of magnitude as the results after 90 days of
curing at
23 °C.
𝑞𝑘𝑃𝑎=6.45×10×𝜂
𝐶. (4)
𝐺𝑀𝑃𝑎=8.59×10×𝜂
𝐶. (5)
4.4. Triaxial
Figure 8 presents the stress–axial strain–volumetric strain curves of the
standard con-
solidated drained triaxial tests of artificially cemented specimens of iron ore
tailings
moulded with γd of 17 kN/m3 and 19 kN/m3. All specimens have shown a quite stiff
re-
sponse at small axial strains (connected to the contraction of the material),
followed by
quite brittle behaviour (strong strain-softening response), and the tendency to
dilation of
the material. The brittleness and dilation tendency are gradually suppressed due
to the
increase of confining pressures.
Figure 7.
Compacted filtered iron mining tailings treated with early strength Portland
cement and
cured for 2, 4 and 7 days: (
a
)q
u
versus
η
/C
iv
after 12 wet-dry cycles and (
b
)G
0
versus
η
/C
iv
after
12 wetting–drying cycles.
Appl. Sci. 2022,12, 836 12 of 18
On the other hand, focusing on the G
0
results in Figure 7b, it can be noted that after
12 wetting–drying cycles, G
0
is related to
η
/C
iv
index through Equation (5). Such an equation
has the same form as Equation (3), and the scalar of present equation is higher
than the
results of 90 days of curing at 23
◦
C. However, for q
u
and G
0
, results after 12 wetting–drying
cycles are of the same order of magnitude as the results after 90 days of curing
at 23 ◦C.
qu(kPa)=6.45 ×104×η
Civ −1.30
(4)
G0(MPa)=8.59 ×104×η
Civ −1.30
(5)
4.4. Triaxial
Figure 8presents the stress–axial strain–volumetric strain curves of the
standard
consolidated drained triaxial tests of artificially cemented specimens of iron
ore tailings
moulded with
γd
of 17 kN/m
3
and 19 kN/m
3
. All specimens have shown a quite stiff
response at small axial strains (connected to the contraction of the material),
followed by
quite brittle behaviour (strong strain-softening response), and the tendency to
dilation of
the material. The brittleness and dilation tendency are gradually suppressed due
to the
increase of confining pressures.
The peak failure envelope leads to a peak angle of shearing resistance (
ϕ0
peak
) of about
34.1
◦
for both dry unit weights and a peak cohesion intercept of (c
0
peak
) of 80.9 kPa for (
γd
)
of 17 kN/m
3
and 157.2 kPa for (
γd
) of 19 kN/m
3
. The increase of the degree of compaction
at standard Proctor energy from 89% to 99% did not cause any change in
ϕ0
peak
but almost
double c
0
peak
. On the other side, the critical state line reaches an angle of shearing
resistance
at a critical state (ϕ0cs ) of 36.3◦.
Values of secant deformation modulus (E
sec
), obtained at axial strains of 0.1%, 0.5%
and 1.0% and for confining stresses ranging from 50 to 200 kPa, are presented in
Table 3.
Regarding the specimens prepared with
γd
= 17 kN/m
2
, it can be seen in Table 3that the
higher modulus is E
sec
= 816.1 MPa (for
εa
= 0.1% and confining pressure of 200 kPa), while
for specimens prepared with
γd
= 19 kN/m
3
, the higher modulus is
Esec = 2599.9 MPa;
the latter (
γd
= 19 kN/m
2
) being more than three times the secant modulus value at
γd= 17 kN/m3.
Table 3.
Secant modulus (E
sec
) of cement treated iron ore tailings (at distinct axial strains) considering
dry unit weights of (a) γd= 17 kN/m3and (b) γd= 19 kN/m3.
γd= 17 kN/m3& 3% PC III γd= 19 kN/m3& 3% PC III
Esec (MPa) Esec (MPa)
Confining Pressure
εa(%) = 0.1 εa(%) = 0.5 εa(%) = 1.0
Confining Pressure
εa(%) = 0.1 εa(%) = 0.5 εa(%) = 1.0
50 kPa 714.7 441.6 355.1 50 kPa 1888.9 1412.8 378.6
100 kPa 740.2 605.3 524.2 100 kPa 2042.7 1652.9 812.5
200 kPa 816.1 500.1 526.6 200 kPa 2599.9 1808.6 965.3
(a) (b)
Appl. Sci. 2022,12, 836 13 of 18
Figure 8.
Stress–axial strain–volumetric strain curves for the consolidated drained
triaxial tests of
specimens moulded with (
a
)
γd
of 17 kN/m
3
and 3% of early strength Portland cement blended with
iron tailings under confining pressures of 50, 100 and 200 kN/m
3
and (
b
)
γd
of 19 kN/m
3
and 3% of
early strength Portland cement blended with iron tailings under confining
pressures of 50, 100 and
200 kN/m3.
5. Discussion
An original study with the objective of contributing to the understanding of the
geomechanical behaviour of a new form of iron ore tailings disposal (stacking of
compacted
filtered ore tailings–Portland cement blends) was presented as an alternative
method to
the conventional tailings dam disposal. Adequate correlations between the
η
/C
iv
index
with q
u
and G
0
through power functions were obtained (Figure 5). In artificially cemented
soils the
η
/C
iv
ratio is usually adjusted by a power (
ξ
) applied to the variable C
iv
(defined
by curve fitting) to make the rates of variation of
η
and 1/C
iv
compatible [
20
]. The value
of
ξ
determines the greater or lesser contribution of porosity or cement content in
the
mechanical response. According to Diambra et al. [
34
], its magnitude is directly associated
with the properties of the soil matrix and usually approximates the inverse of
the exponent
of the power function (
ξ≈
1/D or 1/Ein Equations (2) and (3), respectively). In the present
study, an assumed value of
ξ
=1 allowed the best fit (R
2
> 0.92) for correlating the
η
/C
iv
index with qu,G0and durability.
Rios et al. [
35
], working with a residual soil of very low (or no) plasticity corresponding
to a well graded silty sand and with three different grain size fractions of
this same soil
determined that, under conditions of similar mineralogy, the particle size
distribution is
the most relevant factor in the definition of the magnitude of
ξ
. The research concludes
that soils with higher fines (silt) content, fine sand fraction, and better
graded, with broader
grain size distribution curves, reported lower power values (
ξ≈
0.21) compared to poorly
Appl. Sci. 2022,12, 836 14 of 18
graded and fine to coarse sandy soil fractions (
ξ≈
1). However, mineralogical composition
(related to particle shape) is reported as the most decisive factor in the
magnitude of
ξ
,
reporting adjusted values of
ξ
=1 and
ξ
=0.1 when comparing two uniform sands (with
similar particle size distribution) characterized by having majority quartz and
mica phases,
respectively. The preponderant contents of quartz and iron minerals (hematite
and goethite)
in the filtered iron ore tailings determine the value of the fitting power (
ξ
=1). Values of
ξ=1
have been widely reported in the literature for the definition of dosage
equations in
soils of granular or frictional nature treated with Portland cement [
36
]. This value, equal to
unity, determines an equivalent influence between porosity and cement volumetric
content
on qu,G0and durability.
Adding cement is considered an effective procedure to prevent liquefaction of
soils.
In general, the behaviour pattern of filtered iron ore tailings–Portland cement
blends is
determined by brittle and strain softening behaviour at low confining stresses
(mainly
due to cementing agent bonds), which evolves to more gentle strain softening
with peak
strength occurring at higher axial strains as confining stress levels increase
(Figure 8). This
behaviour is analogous to that reported for a wide range of cemented sands
tested at low
confining stresses [
37
,
38
]. The larger the
γd
of the compacted specimens (lower
η
), the
larger the peak deviator stress reached, the stiffer and more dilative the
material, and the
greater the post-peak drop in the deviator stress. On the other hand, volumetric
strains are
strongly dilatant at low stress levels. Some authors (e.g., Airey [
39
], Coop and Willson [
40
],
Consoli et al. [
38
]), from the study of different artificially and naturally cemented sands,
agree that at high confining stresses (higher than those investigated here)
volumetric strains
tend towards compression. Additionally, a cohesive behaviour (dominated by
cement) at
low confining stresses and/or high cement contents tends to evolve to a
frictional behaviour
(dominated by the sand matrix) at high confining stresses and/or low cement
contents.
Figure 9shows the deviatoric stress—axial strain—volumetric strain curves (for
con-
solidated drained triaxial tests) of the uncemented filtered iron ore tailings
and 3% early
strength Portland cement mixed with the iron ore tailings, both compacted to a
γd
of
17 kN/m3
and submitted to confining stresses of 200 kPa. The uncemented filtered iron ore
tailings show strong contractive behaviour, confirming the relevance of
compressibility of
the filtered iron ore tailings and the possibility of uncontrolled positive
pore-pressure gen-
eration if under undrained shear conditions, which would lead to loss of
effective stresses
and increased liquefaction potential of the tailings at relatively low confining
stresses. In
contrast, the occurrence of volumetric dilatational strains (generation of
negative pore-
pressures if under undrained shear conditions), at low stress levels, and high
peak cohesion
intercepts (c
0
peak
) reported in tailings treated with the addition of 3% cement would reduce
the liquefaction potential of compacted filtered iron ore tailings piles.
Appl. Sci. 2022,12, 836 15 of 18
Figure 9.
Stress–axial strain–volumetric strain curves for the consolidated drained
triaxial tests of
specimens moulded with filtered iron ore tailings and 3% early strength Portland
cement mixed with
iron ore tailings at a dry unit weight (γd) of 17 kN/m3under confining pressures
of 200 kN/m3.
6. Conclusions
An extensive laboratory testing program was carried out to investigate the
effec-
tiveness of using Portland cement and compaction energies to evaluate the
engineering
behaviour of filtered iron ore tailings. The observations and conclusions can be
summarized
as follows:
The employment of the porosity/cement index (
η
/C
iv
) with the purpose of expressing
the performance of iron ore tailings combined with the incorporation of Portland
cement
and densification through compaction, with curing periods varying from 2 to 90
days, can
be considered successful. High coefficients of determination were obtained when q
u
and G
0
results were correlated with this parameter. Based on the dosage equations
established in
present research for the studied iron ore tailings–Portland cement blends, there
are several
technical ways of reaching a q
u
or a G
0
target value for a given project and the best solution
Appl. Sci. 2022,12, 836 16 of 18
might change from situation to situation depending on the time period available
for curing,
accessibility to equipment to reach a given porosity and cost of Portland
cement.
The stress–strain response showed a strength peak for all the samples and a
softening
following a peak. Also, the increase in effective stress causes an expansive
response in
volumetric strain. The peak failure envelope leads to a peak angle of shearing
resistance
(
ϕ0
peak
) of about 34.1
◦
for both dry unit weights and a peak cohesion intercept of (c
0
peak
)
of 80.9-kPa for (
γd
) of 17-kN/m
3
and 157.2-kPa for (
γd
) of 19-kN/m
3
. The increase of
the degree of compaction at standard Proctor energy from 89% to 99% did not
cause any
change in
ϕ0
peak
but almost double c
0
peak
. On the other side, the critical state line reaches an
angle of shearing resistance at critical state (
ϕ0cs
) of 36.3
◦
. The use of 3% of Portland cement
for triaxial testing represents an intermediate amount of cement studied in this
research.
The present work has been envisaged as a contribution to the behaviour of
compacted
iron ore tailings–Portland cement blends to be disposed by stacking. The
influence of
degree of compaction as well as the amount of Portland cement on strength and
stiffness
properties was evaluated. The blends studied herein were compacted at optimum
moisture
content. It might not be possible to do so in the field, especially during rainy
seasons.
Therefore, the influence of compaction moisture content in the mechanical
behaviour
requires further study. Another point requiring future research is the
development of
alternative sustainable binders for stabilization of stacking filtered tailings
in order to
have a less costly, greener engineering solution. It is also necessary to
emphasize that the
present study was constrained to the range of low to medium confining pressures,
making
it attractive to tailings disposal by stacking up to heights of 10–12 m. Other
studies are
necessary to evaluate changes in the behaviour of the material under higher
stackings,
when the confining pressure will be greater than the studied range. At last, the
addition
of a binder to the compacted filtered tailings reduces the volume of
hydraulically carried
out sediments, thus allowing smaller sedimentation structures downstream of the
disposal
structure (e.g., ponds and sedimentation dikes).
Author Contributions:
Conceptualization, N.C.C.; methodology, N.C.C. and A.L.; validation, N.C.C.,
H.M.C. and E.B.M.; formal analysis, N.C.C. and H.C.S.F.; investigation, A.L.,
H.M.C. and E.B.M.;
resources, N.C.C.; data curation, N.C.C., H.C.S.F. and E.B.M.; writing—original
draft preparation,
N.C.C.; writing—review and editing, N.C.C., J.C.V., J.P.S.S. and A.L.;
supervision, N.C.C.; project
administration, N.C.C.; funding acquisition, N.C.C. All authors have read and
agreed to the published
version of the manuscript.
Funding:
The authors wish to make explicit their appreciation to VALE S.A. (IAP-001247
and
IAP-001466) and CNPq (Brazilian Research Council) for the support to the
research group.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement:
Some or all data, or models, used during the study are available from
the corresponding author upon reasonable request.
Conflicts of Interest:
The authors declare no conflict of interest. The funders had no role in the
design
of the study; in the collection, analyses, or interpretation of data; or in the
decision to publish the
results.
Abbreviations
A,C,D,Escalars
BSkempton’s parameter
c0
peak peak cohesion at effective stresses
Civ volumetric cement content
dparticle diameter
Esec secant modulus
G0initial shear modulus
Appl. Sci. 2022,12, 836 17 of 18
IOT iron ore tailings
PC Portland cement
quunconfined compressive strength
ξpower function parameter
εaaxial strain
εvvolumetric strain
γddry unit weight
γsunit weight of solids
ϕ0cs angle of shearing resistance at critical state
ϕ0
peak peak angle of shearing resistance at effective stresses
ηporosity
η/Civ porosity/cement index
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CITATIONS (0)
REFERENCES (31)
ResearchGate has not been able to resolve any citations for this publication.
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through techniques that combine modification of grain size through the insertion
of sand, incorporation of Portland cement and densification through compaction
is seen as an alternative. In this context, a dosage method to use a local
lateritic soil as construction material in a most rational way reducing the
economic and environmental impacts related to this activity is still missing.
Therefore, the current research aims to evaluate the performance of a lateritic
soil via modification of grain size through the insertion of sand, incorporation
of Portland cement and densification through compaction. For this, unconfined
compression, and durability (wetting and drying) tests were carried out on
specimens of compacted clayey gravel lateritic soil, whose granulometry was
modified by the insertion of distinct amounts (from zero to 45%) of weathered
sand, treated with distinct Portland cement contents (from 4 to 10%), molded at
different dry unit weights (from 16.8 to 20.1 kN/m3) and cured for 7 and 28
days. Results of the mechanical tests have shown the significant influence
exerted by cement content and dry unit weight of the blend, followed by curing
time and finally sand insertion. Satisfactory correlations between the response
variables (qu and ALM) and the adjusted porosity/cement index (η/Cv) were
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breakages in developed countries occurred decades ago. In recent years, the
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strength contributions of the sand and cement phases. The sand matrix obeys the
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analytical solutions are compared against the results of tests on three
different types of cemented clean sand cured for different time periods. While
the analytical relation fits the experimental data well, it also provides a
theoretical basis for the explanation of some features related to the
experimentally derived strength relationships for cemented clean sand. The value
of the power relationship between the strength and the porosity/cement ratio
index seems to be governed by the soil matrix properties, while the
interdependency of the strength and the curing time can also be captured. For a
given cemented sand, the model equally confirms the existence of a unique
tensile/compressive strength ratio (qt/qu), independent of the curing time and
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Commission on Large Dams and World Information Service on Energy and analyzed
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perspective. In addition, we prepared a tailings dam spatial database. The
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Impact of Severe Climate Conditions on Loss of Mass, Strength, and Stiffness of
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* May 2018
* J MATER CIVIL ENG
* Nilo Cesar Consoli
* Alejandro Quiñonez Samaniego
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* Eduardo Bittar
The influence of wet-dry cycles on the enduring performance (loss of mass,
strength, and stiffness) of compacted fine-grained soils-portland cement blends
might be important information for designing earthworks that could be subjected
to severe climate conditions. This study assesses possible variations of
cement-treated fine-grained soils' accumulated loss of mass (ALM), unconfined
compressive strength (qu) and maximum shear stiffness (Gli ) when subjected to
wetting-drying cycles (mimicking severe climate conditions). Brushing of
specimens (to check loss of mass), ultrasonic pulse velocity tests, and
unconfined compression tests are performed after wetting-drying cycles for this
study. Results show that, for each specimen tested, ALM changes at a constant
rate with the number of cycles (NC). In addition, qu increases from zero to
three wetting-drying cycles and fluctuates around an average for further cycles,
whereas G0 decreases from zero to three wetting-drying cycles and then
fluctuates around an average (distinct for each dry unit weight and amount of
cement used) for further cycles. The possible cause of such contradictory
results is the effect of oven drying for 42 h at 71 ± 2°C (during the drying
part of the wet-dry cycles), which might provoke the catalysis of the chemical
reactions of the portland cement, as well as the retraction (and consequent
fissuring) of the specimens of silt-portland cement blends in the initial
cycles. Finally, the porosity/cement index is found to be a predictor of the
ALM, ALM/NC, qu, and G0 fine-grained soil-cement blends studied after a series
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* ENG GEOL
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* M.R. Coop
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* Fernando Schnaid
Tailing dam failures result in irreversible environmental impacts and cause
fatalities. In recent years the mechanical behaviour of tailing geo-materials
has received more attention by the geomechanics and engineering geology
communities in an attempt to understand better their behaviour in the light of
designing safer tailing dams. In this study, the mechanical behaviour of a gold
tailing from Brazil is thoroughly investigated by conducting a series of
compression and shearing tests as well as dynamic element tests. Fabric effects
from the sample preparation method, the susceptibility to liquefaction and the
possibility of any transitional behaviour are presented and discussed within a
soil mechanics framework. Comparisons are made between the present gold tailing
and previously published data on other tailings, giving a general view of the
mechanics of tailings and the effects of grading. The results show that for this
tailing the rate of convergence for different initial densities to the normal
compression line is slow, and so the depositional density would affect the
volume to far higher stresses than the material would be expected to experience
in-situ. For this tailing any fabric effects from the sample preparation method
were found to be very small to negligible with respect to small-strain behaviour
and critical state behaviour. For different tailings, even if the particle sizes
may cover a wide range, the susceptibility to static liquefaction, as determined
by the location of the horizontal asymptote of the critical state line in the
specific volume-log stress plane, shows no consistent variation. So it can be
concluded that neither the pond nor the upper beach tailings are more
susceptible.
View
Show abstract
Theoretical Derivation of Artificially Cemented Granular Soil Strength
Article
* Jan 2017
* J GEOTECH GEOENVIRON
* Andrea Diambra
* Erdin Ibraim
* Anderson Peccin Da Silva
* Lucas Festugato
This paper provides a theoretical derivation for the unconfined compression
strength of artificially cemented granular soils. The proposed developments are
based on the concept of superposition of failure strength contributions of the
soil and cement phases. The granular matrix obeys the critical state soil
mechanics concept, whereas the strength of the cemented phase can be described
using the Drucker-Prager failure criterion. In the process, the analytical
relation is suitably adjusted to parallel a recently proposed empirical
relationship that links unconfined compression strength of artificially cemented
granular soils to an adjusted porosity/cement ratio parameter. Although the
proposed analytical relation fits the experimental data for different granular
soils and cement curing time well, further parametric analysis offers the
possibility of exploring the effect of some material parameters on the
unconfined compression strength of artificially cemented granular soils.
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Show abstract
A Unique Relationship Determining Strength of Silty/Clayey Soils - Portland
Cement Mixes
Article
* Dec 2016
* SOILS FOUND
* Nilo Cesar Consoli
* Pedro Miguel Vaz Ferreira
* Chao-Sheng Tang
* Marina Bellaver Corte
This technical note advances the understanding of the key parameters controlling
the unconfined compressive strength (qu) of artificially cemented silty/clayey
soils by considering distinct moisture contents, distinct specimen porosities
(η), different Portland cement contents and various curing time periods. The qu
values of the specimens moulded for each curing period were normalized (i.e.
divided) by the qu attained by a specimen with a specific porosity/cement index.
A unique relationship was found, establishing the relationship between strength
for artificially cemented silty/clayey soils considering all porosities,
Portland cement amounts, moisture contents and curing periods studied. From a
practical viewpoint, this means that, at limit, carrying out only one unconfined
compression test with a silty/clayey soil specimen, moulded with a specific
Portland cement amount, a specific porosity and moisture content and cured for a
given time period, allows the determination of a general relationship equation
that controls the strength for an entire range of porosities and cement
contents, reducing considerably the amount of moulded specimens and reducing
projects development cost and time.
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KEY PARAMETERS ON MECHANICAL BEHAVIOR OF FULL DEPTH RECLAMATION (FDR-C) USING
CEMENT
* Francisco Dalla Rosa
* Matheus de Conto Ferreira
* Antônio Thomé
* [...]
* Lélio Antônio Teixeira Brito
This project aim to identify the key parameters on mechanical properties of Cold
In-Place Recycling pavements using cements.
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Project
BRAZILIAN NEW TAILINGS DISPOSAL TREND BY STACKING
* Nilo Cesar Consoli
* Lucas Festugato
* Hugo Carlos Scheuermann Filho
* [...]
* Cesar Alberto Ruver
Failures of tailings dams, primarily due to liquefaction, have occurred in
Brazil in the last years. Iron ore tailings deposited behind upstream dams are
materials of low in situ densities and stre ngths. Building new tailings dams to
dispose tailings through spigotting behind such dams is nowadays restricted in
Brazil. Brazilian new disposal trend is by stacking of compacted filtered ore
tailings-Portland cement blends. Present research aims to analyse the behaviour
of compacted ore tailings-Portland cement blends, considering the use of small
amounts of Portland cement under distinct compaction degrees. ... [more]
View project
Article
Full-text available
POROSITY/CEMENT INDEX CONTROLLING FLEXURAL TENSILE STRENGTH OF ARTIFICIALLY
CEMENTED SOILS IN BRAZIL
January 2020 · Geotechnical and Geological Engineering
* Nilo Cesar Consoli
* Andressa Silva
* Alice Müller Barcelos
* [...]
* Filipe Favretto
When the soil does not attain a target mechanical behaviour, modifying the
project, removing and replacing the material or improving the soil is necessary.
Adding Portland cement to soils and performing densification through compaction
are effective approaches for ground improvement. Tensile strength is a
mechanical property employed to evaluate the performance of cemented materials,
and it can ... [Show full abstract] be assessed by flexural tensile strength
tests and splitting tensile strength tests. The porosity/cement index has been
shown to govern the splitting tensile strength of artificially cemented sands,
but no attempt was made to find a relation between this ratio and flexural
tensile strength. Hence, this study aims to quantify the influence of porosity,
Portland cement content and the porosity/cement index on the flexural strength
of three artificially cemented soils (sand, silt and silty sand). An
experimental program of flexural and splitting tensile strength tests, as well
as unconfined compression tests, was carried out to assess that influence on
specimens with different porosities and cement contents. Results demonstrate
that the porosity/cement index is an appropriate parameter to assess the
flexural strength of the artificially cemented silty and sandy soils. The ratio
between flexural tensile strength and splitting tensile strength was found to be
3.31, 4.59 and 5.19 for artificially cemented sand, silt and silty sand,
respectively, being independent of porosity, cement content and porosity/cement
index.
View full-text
Article
BEHAVIOUR OF SILTY SANDS STABILISED WITH CEMENT SUBJECTED TO HARD ENVIRONMENTAL
CONDITIONS
May 2019 · ICE Proceedings Geotechnical Engineering
* Nilo Cesar Consoli
* Helena Batista Leon
* Mariana da Silva Carretta
* [...]
* J. Antonio H. Carraro
The present study evaluates the effect of three distinct amounts of fines,
Portland cement and dry unit weights on the accumulated loss of mass (ALM),
maximum shear modulus at small strains (G0) and tensile strength (qt) of
stabilised sands subjected to wet-dry cycles. Tensile strength test results
showed that addition of fines to a sand stabilised with cement increased its
tensile strength, ... [Show full abstract] irrespective of the dry unit weight
(d) and cement amount present in the mixture. Increasing the amounts of fines
of compacted cement-stabilised silty sand specimens subjected to wetting-drying
cycles reduces ALM and increases G0 and qt of the mixtures. This may be due to
the fact that specimens with larger amounts of fines have more contact points
amongst particles, which provides better opportunities for the cement to develop
more efficient bonds within the soil fabric, improving its mechanical
performance. The increase in cement content and in d of compacted
cement-stabilized silty sand specimens reduced their ALM and increased G0 after
each one of the twelve wet-dry cycles. The G0 and qt of cement-stabilized silty
sand specimens with fines increases up to the sixth cycle, remaining practically
constant after that, when these specimens are subjected to wetting-drying
cycles.
Read more
Article
COPPER SLAG-HYDRATED LIME-PORTLAND CEMENT STABILIZED MARINE DEPOSITED CLAY
September 2019 · Proceedings of the Institution of Civil Engineers Ground
Improvement
* Nilo Cesar Consoli
* Abdullah Ekinci
* Hugo Carlos Scheuermann Filho
Marine clay is commonly found worldwide and is challenging to work with in the
geotechnical and geoenvironmental perspective. This is due to its diverse
characteristics, such as high compressibility and sensitivity. Hence, there is a
need to seek effective treatment solutions that are less environmentally harmful
than the traditional methods. Thus, the present research intends to assess the
... [Show full abstract] performance of marine clay treated with a binder that
incorporates Portland cement, hydrated lime and copper slag. For this,
unconfined compression and split tensile tests were carried out in order to
assess the distinct binder content effects and to correlate those responses to
the porosity/binder index. Moreover, SEM tests were conducted with the aim to
study the microstructure of the mixes containing copper slag. The results
indicate that the employment of lime, the dry unit weight and the curing period
are the most influential factors regarding the strength of the mixtures, in that
order. In addition, good correlations were obtained between the strength and the
adjusted porosity/binder index for all mixtures.
Read more
Article
Full-text available
THE EFFECTS OF CURING TIME AND TEMPERATURE ON STIFFNESS, STRENGTH AND DURABILITY
OF SAND-ENVIRONMENT...
August 2019 · Soils and Foundations -Tokyo-
* Nilo Cesar Consoli
* Helena Batista Leon
* Mariana da Silva Carretta
* [...]
* David Eduardo Lourenço
Agricultural-industrial wastes, like rice-husk ash (RHA) and carbide lime (CL),
have great potential applications in such earthworks as the stabilization of
slopes and pavement layers and the spread footings and bed of pipelines,
particularly in the regions near where the waste is produced. Present research
evaluates the potential use of RHA mixed with CL as a binder, improving
strength, ... [Show full abstract] stiffness and durability properties of a
uniform sand. Two different curing temperatures, 23 °C and 40 °C, and curing
periods, 7 and 28 days, of compacted sand-RHA-CL blends (distinct dry unit
weights and contents of RHA and CL) were evaluated to determine the importance
of these changes on the reactions between the materials. The experimental
program aims to assess the following parameters: initial shear modulus (G0),
unconfined compressive strength (qu), and accumulated loss of mass (ALM).
Studies have been carried out to quantify these parameters as a function of a
novel index called porosity/volumetric binder content (η/Biv). The results
showed higher values of G0 and qu, as well as a small rate of ALM with reduction
of porosity and with rise of the environment friendly binder content. The latter
is achieved either by increasing eith the RHA or the CL content. The curing
temperature acts as a catalyser, accelerating the pozzolanic reactions between
RHA and CL. Longer curing periods also benefit reactions between materials by
enhancing their geotechnical properties. An analysis of variance (ANOVA) was
carried and the results showed the dry unit weight, RHA content and curing type
are significantly effect the strength results. It was also possible to verify
that curing for 28 days at 23 °C and for 7 days at 40 °C are statistically
equivalent in terms of strength. The G0 results after weathering cycles tended
to decrease in specimens at a 40 °C curing temperature and increase in specimens
at a 23 °C curing temperature.
View full-text
Last Updated: 22 Jan 2022
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