Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TREATED OIL SAND WASTE FOR USE IN CEMENTITIOUS MATERIALS FOR
GEOTECHNICAL APPLICATIONS
FIELD
The present disclosure relates to cementitious formulations which incorporate
treated oil sand waste (TOSW) which is mostly silicon dioxide. Such
cementitious
formulations include but are not limited to grouts, concrete and controlled
low strength
materials (CLSM) and in these formulations the treated oil sand waste (TOSW)
is used
to replace conventional constituents.
BACKGROUND
There are many cementitious formulations used in geotechnical applications
including, but not limited to, grouts, concrete and controlled low strength
materials
(CLSM). Each of these cementitious formulations, as presently formulated, have
various
drawbacks associated with them. For example, concrete requires a flowability
enhancer
to help wet concrete to flow smoothly while being dispensed through long pipes
such as
is the norm at large constructions sites. Currently a preferred flowability
enhancer used
in concrete mixtures is fly ash, which is a by-product of coal combustion, is
composed of
fine particles which include substantial amounts of amorphous and crystalline
silicon
dioxide (SiO2), calcium oxide (CaO) and aluminum oxide (A1203), and it has
been used
to replace some of the Portland cement in concrete production. However, with
the
shutting down of coal fired plants in the western world, it is becoming
problematic to
predictably source fly ash.
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Controlled low strength materials (CLSM) typically consist of a mixture of
Portland cement, water, aggregate and sometimes fly ash. While ordinary
concrete
typically has strengths exceeding 21 MPa, CLSM formulations have lower
strength
generally less than 8.3 M Pa. Thus, while CLSM formulations are not suitable
for
structural supports, they are typically used as a replacement for compacted
backfill. As
with concrete, the use of fly ash is becoming problematic. CLSM mechanical
properties
have been deliberately kept low so that it can be excavated easily. However,
due to its
pozzolanic nature, the use of fly ash to maintain high flowability will
increase later ages
strength making re-excavation a problem.
Similarly, grout formulations are characterized as being a fluid form of
concrete
used to fill gaps and is typically a mixture of cement, sand and water. In
geotechnical
applications, Portland cement-based grouts are used to stabilize soil,
remediate sinking
structures, underpin existing foundations, construct earth support walls,
construct
groundwater cut-off walls and fill unwanted voids, such as below slabs-on-
grade or
within abandoned pipes and tunnels.
Typical Portland cement formulations use cement with a standard size of around
15 microns. However, in some applications these particles are too large to get
the
degree of compactness that would most beneficial for the application.
Producing grout
formulations with a finer particle sizes let the grout penetrate more deeply
into a fissure.
It would be very advantageous to provide cementitious formulations having
constituents selected to address the above noted limitations, and which
provide the
same or better end product properties of strength, flowability etc. while
still meeting, or
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exceeding the functional requirements of the geotechnical applications for
which the
cementitious formulation is intended for.
SUMMARY
Oil sands drill cuttings waste represents one of the most difficult challenges
for
the oil sands mining sector. Reducing the amount oil sands drill cutting waste
sent to
landfill offers one of the best solutions for waste management. The present
disclosure
provides cementitious formulations comprised of treated oil sand waste for use
in
geotechnical applications. The cementitious formulations include, but are not
limited to,
grouts, concrete and controlled low strength materials (CLSM) and in these
formulations
the treated oil sand waste (TOSW) is used to replace conventional constituents
such as
some of the fly ash in concrete, some of the cement in grout formulations and
some of
the fly ash and cement in the controlled low strength materials. The treated
oil sand
waste is predominantly silicon dioxide (SiO2) which is produced using a
process and
is system which separates water and oil from the solid waste, known as the
thermomechanical cuttings cleaner (TCC).
The present disclosure provides a method of producing cementitious
formulations, comprising:
subjecting oil sands drill cuttings to a process configured for
separating water and hydrocarbons from solid constituents of the oil
sands drill cuttings, and
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producing treated oil sands waste comprising solid S102 particles
having a size distribution in a range from about 0.8 to about 30 microns,
and with about 90% of the sample volume below about 9.9 microns; and
mixing said solid SiO2 particles with constituents used in preselected
cementitious formulations used in a preselected geotechnical application.
The process configured for separating water and hydrocarbons from solid
constituents of the oil sands drill cuttings is carried out in a
thermomechanical cuttings
cleaner.
The solid SiO2 particles have a mean size of about 2.7 microns.
A further understanding of the functional and advantageous aspects of the
present disclosure can be realized by reference to the following detailed
description and
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments disclosed herein will be more fully understood from the following
detailed description thereof taken in connection with the accompanying
drawings, which
form a part of this application, and in which:
Figure la shows a scanning electron micrograph (SEM) image of a particle of
the treated oil sand waste (TOSW) produced using the thermomechanical cuttings
cleaner (TCC) technology disclosed in (Ormeloh, 2014);
Figure lb shows an energy dispersive X-ray analysis (EDX) for the TOSW
particle of Figure la;
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Figure 2 shows the particle size distribution using Laser diffraction for
ordinary
Portland cement (OPC) and TOSW;
Figure 3 shows the effect of TOSW replacement rate on cement paste water of
consistency;
Figure 4 shows the effect of TOSW replacement rate on cement paste heat flow;
Figure 5 shows heat of hydration with adapted reference curves for cement
pastes incorporating different percentage of TOSW;
Figure 6 shows DTG curves for cement pastes incorporating different
percentages of TOSW;
Figure 7 shows compressive strength results for mixtures incorporating
different
percentages of TOSW at different ages;
Figure 8 shows reduction in compressive strength due to TOSW incorporation at
different ages;
Figure 9 shows results for measured shrinkage for mixtures incorporating
different percentages of TOSW;
Figure 10 shows results for measured mass loss for mixtures incorporating
different percentages of TOSW;
Figure 11 shows pore size distribution for mixtures incorporating different
percentages of TOSW;
Figure 12 shows a followability and water/powder ratio chart for CLSM
formulations;
Figure 13 shows bleeding results as percentage of volume for the CLSM
formulations;
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Figure 14 shows drying shrinkage for G260 (Group 2 with cement content of 60
kg/m3) and G290 (Group 2 with cement content of 90 kg/m3) mixtures;
Figure 15 shows the results of ICP-MS analysis showing effect of curing days
on
Group 2 leachates samples;
Figure 16 shows the results of an ICP-MS analysis showing results of 28 days
of
curing on Group 2 and Group 3 mixtures;
Figure 17 shows the development of compressive strength with age of Group 2
and Group 3 selected mixtures;
Figure 18 shows the linear relationship between split tensile strength and
compressive strength;
Figure 19 is a photograph of cementitious grout incorporating TOSW;
Figure 20 shows a plot of slump variation for all tested concrete specimens
over
the investigated time period;
Figure 21 shows a plot of compressive strength development for all tested
concrete mixtures over the investigated time period;
Figure 22 shows a plot of splitting tensile strength development for all
tested
concrete mixtures over the investigated time period;
Figure 23 is a plot showing correlation between the experimental data and
predicted values for the splitting tensile strength;
Figure 24 is a plot of flexural strength development for all tested concrete
mixtures over the investigated time period;
Figure 25 is a plot showing the correlation between the experimental data and
predicted values for the flexural strength;
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Figure 26 is a plot showing modulus of elasticity development for all tested
concrete mixtures over the investigated time period;
Figure 27 is a plot showing the correlation between the experimental data and
predicted values for the modulus of elasticity;
Figure 28 is a plot showing pull-out strength development for all tested
concrete
mixtures over the investigated time period;
Figure 29 is a bar graph showing compressive strength and pull-out strength of
the tested concrete mixtures at age 28 days as percentage of the control
mixture;
Figure 30 is a bar graph showing durability factor for different concrete
mixtures;
and
Figure 31 is a plot showing corrosion current through the test time for
different
formulations.
DETAILED DESCRIPTION
Various embodiments and aspects of the disclosure will be described with
reference to details discussed below. The following description and drawings
are
illustrative of the disclosure and are not to be construed as limiting the
disclosure. The
drawings are not to scale. Numerous specific details are described to provide
a
thorough understanding of various embodiments of the present disclosure.
However, in
certain instances, well-known or conventional details are not described in
order to
provide a concise discussion of embodiments of the present disclosure.
As used herein, the terms "comprises" and "comprising" are to be construed as
being inclusive and open ended, and not exclusive. Specifically, when used in
the
specification and claims, the terms "comprises" and "comprising" and
variations thereof
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mean the specified features, steps or components are included. These terms are
not to
be interpreted to exclude the presence of other features, steps or components.
As used herein, the term "exemplary" means "serving as an example, instance,
or illustration," and should not be construed as preferred or advantageous
over other
configurations disclosed herein.
As used herein, the terms "about" and "approximately" are meant to cover
variations that may exist in the upper and lower limits of the ranges of
values, such as
variations in properties, parameters, and dimensions.
As used herein, the term "grout" refers to a composition which generally
includes
the following constituents Portland cement, water, fine aggregate and
sometimes
chemical admixtures, pozzolanic additive and filler materials.
Grouts are used in geotechnical applications including stabilizing soil,
rennediating sinking structures, underpinning existing foundations,
constructing earth
support walls, constructing groundwater cut-off walls and filling unwanted
voids, such as
below slabs-on-grade or within abandoned pipes and tunnels.
As used herein, the term "concrete" refers to a composition which generally
includes the following constituents Portland cement, water, fine and course
aggregate
and sometimes chemical admixtures, pozzolanic additive and filler materials.
As used herein, the phrase "controlled low strength materials (CLSM)" refers
to a
composition which generally includes Portland cement, water, aggregate and
sometimes fly ash.
Oil sands industry is a major driver for economic activity in Canada.
Concurrently, solid waste generated by oil sands mining sector has serious
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environmental and ecological impacts. Oil sand drill cuttings solid waste
represents one
of the main challenges for the oil sand mining sector. Reducing the amount of
oil sand
drill cutting solid waste sent to landfill sites offers an efficient solution
for waste
management. Many technologies have been developed to treat these cuttings and
s reduce the amount of waste to be landfilled. One of the recent
technologies is
Thermomechanical Cuttings Cleaner (TCC), which separates water and oil from
the
solid waste as disclosed in Ormeloh, 2014. In this pre-treatment technique,
drill cuttings
solid waste is thermally treated to recover hydrocarbons. The TCC system
operates by
converting kinetic energy to thermal energy in a thermal desorption process
thereby
transforming drilling waste into re-usable products. A significant advantage
of using
kinetic energy rather than indirect heating allows for short retention times
with the result
being the quality of the separated components is unaffected by the treatment.
The by-
product of the TCC process (i.e. the remaining solids) is very fine quartzes
powder, is
referred herein as Treated Oil Sand Waste (TOSW),
U.S. Patent No. 8,607,894 discloses a TCC system.
The TOSW particles used in the formulations disclosed herein, once obtained
were subject to characterization studies. Figure la shows a scanning electron
micrograph (SEM) image of a particle of the treated oil sand waste (TOSW)
produced
using the thermomechanical cuttings cleaner (TCC) technology disclosed in
Ormeloh
and Figure lb shows an energy dispersive X-ray analysis (EDX) for the TOSW
particle
of Figure la from which it can be seen the TOSW particles are predominantly
SiO2.
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Figure 2 shows the particle size distribution using Laser diffraction for
ordinary Portland
cement (OPC) (broken line) and TOSW (solid line) and as can be seen the TOSW
SiO2
particles have a size distribution between about 0.8 to about 30 microns, and
with a
about 90% of the sample volume below 9.9 microns. The mean size of TOSW SiO2
particles is about 2.7 microns.
The various cementitious formulations produced according to the present
disclosure using SiO2 particles isolated from oils sands residue using the
TOSW
process will now be illustrated for grout formulations, concrete and
controlled low
strength materials, but it will be understood these are exemplary and not
meant to be
interpreted as limiting.
GROUT FORMULATIONS
Chemical compositions for OPC and TOSW used in the present grout
formulations were obtained through X-ray diffraction and are provided in Table
1. The
grain size distribution curves for OPC and TOSW are shown in Figure 2 as noted
.. above.
Types OPC TOSW
Chemical analysis
Si02 21.60 61.24
A1203 6.00 8.73
Fe2O3 3.10 3.00
CaO 61.41 5.55
MgO 3.40 0.92
K20 0.83 1.60
Na2O 0.20 0.85
P20, 0.11 0.15
SO3 1.76 3.00
T102 0.46
Loss on Ignition 0.81 12.60
Table 1: Chemical composition and physical properties of cementitious
materials.
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A total of five (5) mixtures were tested to assess the effect of TOSW addition
on
the cementitious materials performance. The different mixtures were achieved
by
varying TOSW contents in the tested mixtures from 0%, 10%, 20%, 30% to 50% as
a
partially replacement of cement (i.e. by volume as TOSW is typically less
dense than
cement). Table 2 provides a summary for tested mixtures composition.
TOSW %
Materials 0% 10% 20% 30% 50%
Cement 400 g 360 g 320 g 280 g 200 g
TOSW 28 g 57 g 85 g 142 g
Water 168g 167.81 g 168.21 g 168.03g 168.24g
Table 2: Composition for tested mixtures.
TESTS AND SPECIMENS PREPARATION
All tested cement paste mixtures were prepared according to ASTM 0305
(Standard Practice for Mechanical Mixing of Hydraulic Cement Pastes and
Mortars of
Plastic Consistency). For each cement paste mixture, specimens for different
tests were
prepared from the same batch. After casting, specimens were maintained at
ambient
temperature (i.e. 23 1 C) and covered with polyethylene sheets until
demolding to
avoid any moisture loss. Immediately after demolding, specimens were moved to
a
moist curing room (Temperature = 23 1 C and relative humidity = 98 %) until
the
testing age.
The effect of TOSW addition on water demand for normal consistency was
evaluated according to ASTM C187 (Standard Test Method for Amount of Water
Required for Normal Consistency of Hydraulic Cement Paste). In addition, the
effect of
TOSW addition on cement reactivity was monitored through measuring the heat of
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hydration for each cement paste mixture and setting time according to ASTM
C191
(Standard Test Methods for Time of Setting of Hydraulic Cement by Vicat
Needle).
Cubic specimens (50 x 50 x 50 mm) were used to determine the compressive
strength
at ages 7, 28 and 90 days according to ASTM C109 (Standard Test Method for
Compressive Strength of Hydraulic Cement Mortars [Using 2-in. or (50-mm) Cube
Specimens)]. Prismatic specimens (25 x 25 x 280 mm) were used for evaluating
drying
shrinkage following ASTM Method C490 (Standard Practice for Use of Apparatus
for the
Determination of Length Change of Hardened Cement Paste, Mortar, and
Concrete).
Identical size specimens were used to measure the mass loss in order to dispel
the
effect of the specimen size on the results.
Thermo-gravimetric analysis was also conducted on selected cement paste
samples to assess the development of their microstructure. Cubic specimens of
size 50
x 50 x 50 mm were prepared for leaching test. Collected leachate samples were
analyzed every 3 days up to 18 days using inductively coupled plasma mass
.. spectrometry (ICP-MS). Cement paste fragments were taken from tested
specimens
and immediately plunged in an isopropanol solvent to stop hydration and
subsequently
dried inside a desiccator until a constant mass was achieved. The pore size
distribution
for each specimen was determined automatically using a Micromeritics AutoPore
IV
9500 Series porosimeter.
zo RESULTS AND DISCUSSION
Water of Consistency
Figure 3 shows the water of consistency, which represents the amount of water
required to achieve a normal consistency for all tested cement paste mixtures
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incorporating different percentages of TOSW. Results reveal that the water of
consistency for tested cement paste mixtures slightly decreases as the
percentage of
TOSW increases. However, increasing the TOSW dosage higher than 20% results in
a
lower reduction in the water of consistency. For instance, paste mixtures
incorporating
20% and 30% of TOSW had exhibited a reduction in the water demand for normal
consistency with about 6.7% and 4.3% than that of the pure OPC paste mixture.
This
can be attributed to two compensating effects induced by TOSW: TOSW is a very
fine
material, hence, addition of such fine particles will increase the specific
surface area of
the powder, leading to a higher water demand to achieve a given consistency.
Simultaneously, TOSW small particles size enhances the packing density of
powder and reduce the interstitial void, thus decreasing entrapped water
between
cement particles and making it available leading to a lower flow resistance.
Therefore,
the controlling factor for which one of the compensating effects will dominate
the
behaviour mainly depends on the particle size of the used fine material. In
this study,
.. the addition of 20% TOSW can be considered as the threshold value and is
highly
dependent on its particle size. At TOSW addition rate below 20%, the increase
in water
demand is compensated by the reduction in flow resistance leading to a lower
water of
consistency. Conversely, as the TOSW addition rate exceeds 20%, the increase
in
water demand dominates the behaviour leading to a higher water of consistency.
Also,
higher free water is expected in mixtures incorporating TOSW, as TOSW addition
was
found to enhance formation of nnonocarboaluminate hydrate that needs less
water than
that of ettringite as will be discussed later.
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Heat of Hydration
Figure 4 illustrates the effect of TOSW addition of cement hydration through
monitoring the heat liberation for pure cement paste and paste mixtures
incorporating
different percentages of TOSW as a partial replacement of cement. It is clear
that
adding TOSW as a partial replacement of cement reduces the hydration heat. The
higher the replacement rate of cement by TOSW, the greater the reduction in
the main
hydration peak. This can be attributed to the dilution effect. Generally, once
water and
cement come in contact, cement wetting and hydration of free lime cause
initial rapid
heat liberation, resulting in a peak within the first 1-2 min. The second peak
of hydration
curve, the so-called "silicate peak" is related to the rapid hydration of
tricalcium silicate
(C3S) and the precipitation of portlandite (CH). A third hydration peak can
occur as a
result of calcium carboalunninates formation from the reaction between
limestone and
aluminates from C3A existing in the OPC.
In order to characterise the differences between the control paste mixture and
other pastes, an adapted reference curve was plotted. This curve is obtained
by
multiplying the curve values of the control paste by 100% minus the respective
incorporation rate of TOSW of the composition under consideration. Hence, the
effect of
cement substitution with an inert material (i.e. TOSW) is simulated.
Theoretically, the
substitution of cement with an inert material decreases the hydration heat
since it is
normalised with respect to the mass of binder. This actually results in a
lower heat flow
per gram of binder.
Figure 5 represents the adapted reference curves and the curves with actual
substitutions of mineral additions. The magnitude of the main peak of the
cement pastes
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with TOSW is slightly greater than the peaks of the adapted reference curves.
For
instance, cement paste mixture incorporating 20% TOSW exhibited a 7.60% higher
heat
flow peak than that of the adapted curve based on 20% substitution percentage
(i.e.
Ref. 20%). However, a chemically inert behaviour does not mean that the
hydration
kinetics cannot be influenced and only retarded due to the dilution effect.
The
chemically inert mineral additions in mortars can alter the degree of
hydration. This can
explain the increase in the slopes of hydration curve during the acceleration
periods (i.e.
slopes of heat flow curves up to the second peak), which can be regarded as
indicators
of nucleation effect (Table 3). These results were confirmed by setting time
results
lc which showed a slight variation in the measured setting time. For
instance, the initial
setting time setting time for all tested cement paste mixtures ranged between
2.68 hrs
and 2.93 hrs. Moreover, changes in the value and location of the third peak
are more
pronounced as TOSW addition rate increases.
Curves 10% Ref-
20% Ref- 30% Ref - 50% __ Ref -
______________ TOSW 10% TOSW 1 20% TOSW 50% " TOSW 50%
Slope 0.51 0.48 0.49 ¨1 0.43 0.42 0.37 1 0.30
0.27
Increase (%) 6% 14% 14.'1/0 11%
Table 3. Slopes of heat flow curves during the acceleration periods for tested
mixtures
Figure 4 shows that as the percentage of TOSW increases the third peak starts
to decrease at its original location along with the occurrence of a shoulder
after the third
heat peak. Moreover, at high percentage of TOSW, the third peak is noticeable
at
around 18 hrs which is correlated with the hydration of C3A. This can be
explained as
follows: TOSW addition enhances and accelerates the ettringite formation by
offering
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nucleation sites. Hence, higher amount of C3A is consumed leading to depletes
of
alunninates. Simultaneously, TOSW represents another source for aluminates,
which
will react with limestone to form calcium carboaluminates. This was confirmed
by
thermogravimetric analyze for selected cement paste samples.
In thermogravimetric analyzer, the change in mass of a sample placed in a
controlled atmosphere is continuously recorded. Thus, decomposition and water
loss
from hydration products are observed and quantified. The derivative
thermogravimetric
curves (DTG) allow identifying different decomposition processes as shown in
Figure 6.
Four peaks can be distinguished on DTG curves. Weight loss associated to the
loss of
combined water of calcium silicates hydrates (CSH) (peak 1), ettringite (AFt)
(calcium
aluminate hydrates) (peak 2), decomposition of mono- (Me) and hemicarbonate
calcium
aluminate (He) (peak 3). Weight loss peak that occurs at temperature range 450-
500 C
is related to the dehydroxilation of portlandite (CH) (peak 4). It is clear
that the intensity
of the endothermic peak for Me/H, increases as the amount of TOSW increases
which
implies the increase in Me/He formation.
Compressive Strength
Figure 7 shows the compressive strength results for mixtures incorporating
different percentages of TOSW. Generally, the compressive strength had
increased for
all paste mixtures with time. However, addition of TOSW resulted in some
reduction in
the achieved compressive strength; the higher the TOSW, the greater the
reduction in
the compressive strength. For instance, mixtures incorporating 10% and 30% of
TOSW
as a partial replacement of cement exhibited 12% and 34% reduction in the 7
days
compressive strength with respect to that of the control mixture. This can be
explained
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based on both dilution and filler phenomena. At early ages, the strength
development
rate depends mainly on the rate of hydration and formation of hydration
products.
Addition of a fine filler to cement modifies the early hydration rate
primarily due to
dilution effect. Replacing cement by TOSW decreases the total cement content
leading
to a lower formation for hydration products. However, the large specific
surface of the
TOSW small particles increases its potential as nucleation sites that promote
the
precipitation of hydration products.
Although nucleation is a physical process, it accelerates the hydration
process of
cement. This can partially compensate for the reduction in the hydration rate
due to the
dilution effect. Consequently, at low replacement rates (i.e. 10%), the
dilution effect will
have lower influence on strength development than at high replacement rates
(i.e.
30%). This is in agreement with previous heat of hydration (Figure 4) and DTG
results
(Figure 5). At later ages, the rate of hydration is very slow and consequently
the
strength gain rate is low. On the other hand, at this later age, filler
materials are able to
reduce gaps and spaces needed to be filled by hydration products, which can
compensate for the dilution effect leading to a recovery in the strength.
Figure 8 shows the reduction in the compressive strength with respect to
control
mixtures at different ages. Figure 8 indicates that the percentage reduction
in
compressive strength of the paste mixtures decreased as sample age increased.
Moreover, it seems that partially replacing cement by TOSW with a rate higher
than
20% causes significant reduction in the compressive strength. For instance,
reductions
in the compressive strength for mixtures incorporating up to 20% and more than
20%
TOSW as partial replacement of cement were <15% and >30% regardless of the
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sample age, respectively. This indicates that the dilution effect in pastes
with TOSW >
20% will dominate, leading to a reduction in strength. It should be mentioned
that even
though the compressive strength decreased due to the addition of TOSW, it is
still within
the range for several construction applications. For example, in micropile
applications,
the Federal Highway Administration (FHWA) specified the minimum design
compressive strength as 28 MPa for the gout used.
Drying Shrinkage
Figures 9 and 10 illustrate the drying shrinkage and mass loss results for
mixtures incorporating different percentage of TOSW. Regardless of the
percentage of
TOSW, shrinkages and mass losses for tested cement paste mixtures
incorporating
TOSW are practically higher than that of the control mixture without TOSW, and
the
measured shrinkage was greater for mixtures with higher percentage of TOSW.
For
instant, mixtures incorporating 10% and 20% of TOSW as partial replacement of
cement exhibited 11% and 19% higher shrinkage than that of the control at age
28
days, respectively. Thermal shrinkage of the cement paste mixture may be
ignored due
to the small size of the tested specimens which assure quick dissipation of
the hydration
heat. Therefore, shrinkage was mainly due to the evacuation of water from the
test
specimens.
Hardened cement paste is a porous medium. The formation of the pore structure
largely depends on the degree of hydration and water content. Pore structure
provides
an indication of the degree of interconnection between the pores and the pore
size
distribution in the hardened cement. From shrinkage point of view, capillary
pores are
the most important type of pores as their sizes will control the amount of
internal tensile
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stresses and consequently shrinkage. The finer the capillary pores, the higher
the
shrinkage. Capillary pores are formed because the hydration products do not
fill all the
space between hydrated cement particles. Hence, the presence of TOSW will
influence
the microstructure of the cement paste including the total porosity and the
critical pore
diameter along with the connectivity of capillary pores and thus water
exchange.
Therefore, shrinkage and mass loss results can be explained based on the two
concurrently effects induced by TOSW addition: Filling and diluting. Adding
the TOSW,
which is a very fine material, act as a filler leading to finer pores, which
in turn leads to
higher shrinkage. Figure 11 shows the porosity measured for the tested
mixtures. It is
clear from Figure 11 that the addition of TOSW had refined the pore sizes.
Meanwhile,
replacing cement with TOSW reduces the cement content leading to formation of
lower
amounts of hydration products.
Consequently, a lower amount of water is consumed in the hydration reactions,
besides the depercolation/disconnection of capillary pores is delayed. Hence,
more free
water became available for evaporation and can easily find its path to the
surrounding
environment, leading to a higher mass loss, i.e. higher mass loss occurs as
the TOSW
percentage increases. For instant, mixtures incorporating 20% and 50% TOSW as
a
replacement of cement exhibited 5% and 29% higher mass loss than that of the
control
specimens at age 7 days, respectively. Thus, the measured shrinkage for the
tested
mixtures is attributed to the combined effects of: refined pores leading to
higher capillary
stresses and lower hydration product formation leading to greater availability
of free
water.
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Leaching
Based on the previous results, it seems that adding TOSW more than 20% as a
partial replacement of cement will adversely affect the cementitious material
performance. Therefore, the leaching test was conducted only on specimens
incorporating 10% and 20% of TOSW as a partial replacement of cement. In order
to
identify the leaching properties of heavy metals that existed in the TOSW,
leaching test
was conducted on TOSW before being incorporated into the cementitious
material.
Table 4 shows the results of heavy metal leaching test for TOSW sample and
cement
paste samples incorporating 10% and 20% TOSW. It is clear that both tested
cementitious samples with 10% and 20% TOSW showed a reduction in metal
leaching
compared to that of the raw TOSW sample. Moreover, metal leaching results was
below groundwater standard of the Canadian Council of Ministers of Environment
(CCME). For instance, leaching of Aluminum, Arsenic, Cadmium, Copper, Nickel,
and
Vanadium from cement mixtures incorporating TOSW was below CCME standards
within the range of 22% to 96%. This can be attributed to the solidifying of
the TOSW in
the microstructure of the cementitious mixtures.
) ______________ 1 Raw El TOSW leaching Cementitious material
leaching (mg/I)
ement Symbol
(mg/I) 10% TOSW 20% TOSW
1
Silver Ag i 0.005 0.002 0.001
Aluminum Al I 1.656 0.349 0.815
______________________________________________________________ -
Arsenic As 1 0.012 0.003 0.006
Barium Ba . 1.100 0.066 0.101
- ___________________________________
Cadmium Cd 0.066 0.001 0.004
Chromium Cr 0.006 0.003 0.004
Copper Cu 0.012 0.007 MX*
Potassium K 80.580 3.586 24.84
Lithium Li 0.013 BDL* BDL*
Magnesium Mg 4.852 0.571 0.39
Manganese Mn 0.011 MIL* BDL*
Molybdenum Mo 0.056 0.005 0.005
_ ________________
Sodium Na 116.358 1.746 6.438
Nickel Ni 0.017 0.009 0.006
Strontium Sr 3.604 0.059 0.123
Vanadium V _ 0.038 0.018 0.026
*BDL: Below Detecting Limits
Table 4. Leaching test results of TOSW
In addition, the fine particles of TOSW act as a filler decreasing the void
spaces
and blocking the pores and thus higher amount of metal is entrapped.
Conclusions
The results disclosed herein show that employing TOSW as a construction
material
can represent an interesting and viable alternative to final landfill
disposal. Based on the
results of this study, the following conclusions can be drawn. First, water of
consistency
of cement paste mixtures slightly decreases as the percentage of TOSW
increases.
Secondly, as the proportion of TOSW in the mixture was increased, the
compressive
strength decreased; above 20% TOSW, the strength reduction was more than 30%.
Therefore, it would be appropriate to use TOSW within 10% to 20% content by
weight.
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Thirdly, addition of TOSW was found to induce higher shrinkage, hence, when
using
TOSW in cementitious materials, it would be appropriate to apply a shrinkage
mitigation
method (i.e. the use of shrinkage reducing admixture). This point needs
further
investigation. Lastly, the leaching tests carried out on cementitious mixtures
incorporating TOSW confirmed that the process makes it possible to obtain
materials
with a pollutant potential lower than that characterizing the TOSW.
CLSM FORMULATIONS
Controlled low-strength material (CLSM) is a flowable self-levelling
cementitious
material widely used as a replacement for soil-cement materials in many
geotechnical
in .. applications such as structural backfill, pipeline beddings, void fill,
pavement bases and
bridge approaches. Because of its low strength requirements, CLSM can be a
perfect
host for many waste and by-products assuming that these materials have been
proven
environmentally safe. Many studies have evaluated the effect of incorporating
different
by-products, such as spent foundry sand, cement kiln dust, wood ash, scrap
tire rubber
and coal combustion by-products on the properties of CLSM. The main properties
for
CLSM performance are flowability, density, and compressive strength. However,
other
properties such shrinkage, bleeding and subsidence were also evaluated. The
upper
limit of compressive strength of CLSM can be up to 8 MPa, however, maintaining
a low
strength is essential for projects where later excavation is required. CLSM
with a
compressive strength of 0.7 MPa and lower can be easily excavated manually if
there is
no high content of coarse aggregate in the mixture. The removability modulus
(RE) can
be used to assess the excavatability of a CLSM mixture based on its strength
and dry
density (Equation 1).
22
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W1.5 X 0.619 x C .5
RE = (1)
106
Where W is the dry density of the mixture in (kg/m3), C is the compressive
strength at 28 days in (kPa). The CLSM mixture is considered easily removable
if RE is
less than one (1).
The present disclosure presents the potential of incorporating TOSW in CSLM as
a fine filler material in order to produce green CLSM. Using TOSW as a fine
filler will
alter the properties of CLSM either chemically or physically, or both,
therefore, it is
important to evaluate the properties of the new CLSM to maintain the
performance
within the requirements of ACI committee 229 for different geotechnical
applications.
Materials
Type 10 Ordinary Portland Cement (OPC) with Blaine fineness of 360 m2/kg and
specific gravity of 3.15 and Class F fly ash according to ASTM C618 were used
as
binding materials in CLSM mixtures. OPC contained 61% Tricalcium Silicate
(C3S), 11%
Dicalcium Silicate (C2S), 9% Tricalcium Aluminate (C3A), 7% Tetracalcium
Aluminoferrite (C4AF), 0.82% equivalent alkalis and 5% limestone. Treated Oil
Sand
Waste (TOSW) was used as a silicate base fine filler material with a Blaine
fineness of
1440 m2/kg and specific gravity of 2.23. The chemical composition and the
physical
properties of the cement, fly ash and TOSW are shown in Table 5.
Three groups of mixtures were prepared and tested in the current study: Group
1
included control mixtures prepared based on proportion guidelines reported by
AC!
committee 229. All mixtures were mixed with natural river bed sand with a
specific
gravity of 2.65. Group 2 included six mixtures where TOSW was added as a
partial
replacement of sand by volume at rates of 5%, 10%, and 15%. Group 3 was
comprised
23
= CA 2961137 2017-03-17
of nine mixtures prepared with TOSW as a replacement of 100% of the fly ash
along
with partial replacement of sand by volume at rates 5%, 10% and 15%. Mixture
proportions are shown in Table 6.
Chemical
OPC TOSW Fly ash
Composition
SiO2 21.60 61.24 43.39
A1203 6.00 8.73 22.08
Fe2O3 3.10 3.00 7.74
CaO 61.41 5.55 15.63
MgO 3.40 0.92 -
K20 0.83 1.60
Na2O 0.20 0.85 1.01
P205 0.11 0.15 -
SO3 1.76 3.00 1.72
TiO2 0.46
Physical
properties
Surface area
360 1440 280
(m2/kg)
Specific gravity 3.15 2.23 2.5
Table 5. Chemical composition and physical properties of cementitious
materials
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Mixture Cement Fly ash Aggregate TOSW Water w/Powderl
Code kg/m3 kg/m3 kg/m3 kg/m3 kg/m3 kg/m3
0130 30 148 1727 0 297 4.3
(Group 1) 0160 60 148 1691 0 297 3.8
Control
Mixtures 0190 90 148 1655 0 297 3.4
0260W5 60 148 1606 84 221 1.9
(Group 2) G260W10 60 148 1522 168 226 1.5
TOSW G260W15 60 148 1437 253 221 1.2
replacing G290W5 90 148 1572 82 270 2.2
aggregate 0290W10 90 148 1490 165 245 1.5
0290W15 90 148 1407 247 244 1.13
G330W5 30 0 1641 205 209 2.1
G330W10 30 0 1554 277 177 1.3
(Group 3) G330W15 30 0 1468 350 165 1.0
TOSW
G360W5 60 0 1606 205 246 2.2
replacing fly
G360W10 60 0 1522 274 227 1.6
ash andregate
G360W15 60 0 1437 341 232 1.3
agg
0390W5 90 0 1572 205 224 1.9
0390W10 90 0 1490 274 212 1.4
G390W15 90 0 1407 341 213 1.2
1The ratio of water content to fly ash, cement and TOSW
Table 6. Mixtures proportions
Mixing Procedure
Dry mixture components (i.e. cement, fly ash and TOSW) were mixed for 1 minute
without addition of water to ensure a homogeneous distribution. About half of
the mixing
water was then added gradually to the mixture and mixed for 1 more minute and
the
rest of the mixing water was then added and mixed for another minute. The
mixture was
allowed to rest for 1 minute after adding the water and then mixed for another
2 minutes
lo before sampling. No special admixtures were needed to adjust the
properties of the
mixture. The flowability of the mixture was continuously measured during the
addition of
water to reach the desired normal flowability range of 150 mm to 200 mm.
CA 2961137 2017-03-17
Testing
Fresh properties, including flowability, unit weight and bleeding, were
evaluated
for fresh mixtures according to ASTM standards D6103-04 (Flow Consistency of
Controlled Low Strength Material), ASTM D6023-07 (Density, Yield, Cement
Content,
and Air Content (Gravimetric) of Controlled Low-Strength Material) and ASTM
test
method C232 (Standard Test Method for Bleeding of Concrete), respectively.
To assess the effect of mixing materials on drying shrinkage, a drying
shrinkage
test was conducted following the ASTM test method C490-11 (Standard Practice
for
Use of Apparatus for the Determination of Length Change of Hardened Cement
Paste,
Mortar, and Concrete). Four 25mm x 25mm x 280mm prismatic samples were
prepared
for each mixture. The prisms were kept in plastic bags for 7 days to reduce
water
evaporation. The samples were then demolded and the initial readings were
taken
before wrapping the samples in plastic bags and storing until testing ages.
The
shrinkage readings were taken daily until no change was recorded.
The compressive strength was determined as per ASTM test method D4832-10
(Standard Test Method for Preparation and Testing of Controlled Low Strength
Material
(CLSM) Test Cylinders). Due to the low early age strength of CLSM mixtures,
samples
were matured in their uncovered molds inside a 98% relative humidity curing
room until
testing ages. Compressive tests were conducted after 7, 14 and 28 days of
mixing using
a strain controlled unconfined compressive strength machine. The compressive
loading
was applied at a strain rate of 1.14 mm/min, which ensured that failure of the
tested
sample would not occur in less than 2 minutes (ASTM D 4832-10, 2010). The
stress-
strain curve was plotted and the secant elastic modulus was calculated as the
slope of
26
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the line from origin to the point of 50% of maximum stress. The CLSM specimens
were
also tested for splitting tensile strength at age of 28 days following ASTM
standards
C496/C496M (Standard Test Method for Splitting Tensile Strength of Cylindrical
Concrete Specimens).
The environmental assessment of incorporating TOSW in CLSM mixtures was
evaluated by investigating heavy metals leaching from the hardened CLSM
samples
immersed in distilled water. As aforementioned, three different replacement
rates of
TOSW were used; however, environmental assessment was conducted only on
samples having the highest content of TOSW, which is 15%, to represent the
most
critical impact of using TOSW as a fine material in CLSM mixtures. The results
were
compared with the groundwater standards of the Canadian Council of Ministers
of
Environment (CCME, 2004). In addition, tests were conducted on the raw TOSW
separately in order to evaluate its leaching properties. Cubic samples of 50 x
50 x 50
(mm) were used following the procedure of method 1315 of the US Environmental
Protection Agency (Mass Transfer Rates of Constituents in Monolithic or
Compacted
Granular Materials Using a Semi-Dynamic Tank Leaching Procedure). Leachates
samples were collected after 2, 7 and 28 days of immersion in distilled water
and
analyzed using coupled plasma mass spectrometry (ICP-MS).
RESULTS AND DISCUSSION
Flowability
Flowability of CLSM mixtures is generally controlled by the amount of added
water to achieve the targeted flow of 150 to 200 mm. Results show that
changing the
cement content while maintaining the same fly ash content has an insignificant
effect on
27
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the flowability of CLSM, in agreement with previous work (Qian, Xiang , Qiao,
Jianming ,
& Baoshan , 2015). Figure 12 presents the results of the flowability for
tested CLSM
mixtures. The flowability of CLSM control mixtures ranged from 185 to 250 mm,
which
falls within the normal to high flowability category according to the ACI
committee 229R
report. The incorporation of TOSW reduced the amount of water required to
achieve the
same flowability range of control mixtures with about 25%.
As shown in Figure 12, mixtures containing TOSW required considerably lower
water/powder ratios while maintaining a normal flowability. Incorporating very
fine
material, such as TOSW, increases the surface area of the particles in the
mixture,
which leads to a higher water demand. On the other hand, the small particle
size in
TOSW enhances the powder packing and releases the water entrapped between
cement particles making it available for lubrication and consequently
increasing the
flowability of the mixture. In addition to filling voids between coarser
particles, the very
fine TOSW acts as a "lubricant" between them, reducing the particle
interference and
consequently the viscosity. This was confirmed in Group 3 mixtures at which
fly ash was
replaced by TOSW. TOSW addition was more efficient in increasing flowability
than fly
ash (Figure 12).
Density
Density of the fresh and hardened CLSM samples were measured at different
ages up to 28 days of curing. Table 7 presents the fresh and hardened density
of the
different tested mixtures. The fresh density of the control mixtures ranged
from 2190 to
2195 kg/rin3. It can be noticed from Table 7 that the density of Group 2
ranged from
1816 to 1901 kg/m3. This represents a reduction of density up to 17% compared
to that
28
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of the control mixtures but the density still lies within the range of normal
density CLSM
mixtures reported by ACI Committee 229. The reduction in density can be
attributed to
the low specific gravity of TOSW compared with sand. For Group 3 mixtures, in
which
fly ash was replaced by TOSW, the fresh density increased up to 6% for G390
and
G360 mixtures, then it started to decrease with age at a rate slower than
Group 2
mixtures. The fresh density ranged from 2067 to 2325 kg/m3 for all Group 3
mixtures,
which is also within the range of normal density CLSM mixtures.
Fresh Hardened Density (kg/m3)
Mixture Code Density
(kg/m3) 7 days 14 days 28 days
(Group 1) G130 2195 2201 2231 2226
ACI-229R G160 2190 2244 2218 2207
Control G190 2192 2217 2201 2207
Mixtures
G260W5 1939 1872 1900 1897
(Group 2)
G260W10 1901 1849 1846 1860
TOSW
G260W15 1928 1932 1935 1918
replacing
G290W5 1942 1963 1955 1935
sand
G290W10 1816 1930 1913 1988
G290W15 1939 1935 1932 1952
G330W5 2087 1765 1774 1774
G330W10 2067 1677 1761 1761
(Group 3) G330W15 2134 1785 1796 1796
TOSW G360W5 2325 1977 1977 2002
replacing fly G360W10 2214 1915 1930 1938
ash and G360W15 2308 1990 1962 1968
sand G390W5 2249 1897 1927 1914
G390W10 2313 1946 1948 1947
G390W15 2302 1919 1934 1949
Table 7: Fresh and hardened densities of CLSM mixtures
Bleeding
Increasing the cement content reduced the bleeding in all mixtures as more
water was consumed in hydration resulting in less free water. For instance,
increasing
29
the cement content in control mixtures from 30 to 90kg/m3 reduced bleeding
with about
34%. The bleeding results range matches the range found in the literature for
CLSM
mixed with fly ash. The settlement during placement was also measured based on
volume reduction due to released water and entrapped air; the subsidence
results
ranged from 1.8% to 3.1%. Mixtures with TOSW showed a significant reduction in
bleeding ranging from 76% to ¨100% for G260 mixtures and from 17% to 95% for
G290
mixtures and up to 17% and 70% for G360 and G390 mixtures compared with
bleeding
control mixtures as shown in Figure 13. This reduction can be attributed to
the increase
in fine materials content in the mixture which is directly related to the
water/powder
ratio. Incorporating waste that includes large amounts of fines (i.e. large
surface area)
increases the amount of water needed to cover the fine particles, which keeps
water
from escaping to the surface as bleed water during setting of the mixture.
Bleeding
values of all mixtures, however, were well below the maximum of 5% for stable
CLSM.
Drying shrinkage
Drying shrinkage of all mixtures was measured as the change of the sample
initial length. Measurements were taken until no significant change was
recorded.
Measurements for control mixtures G160 and G190 (Group 1 with cement content
of 60
kg/m3 and 90 kg/m3, respectively) showed that increasing cement content
reduced the
shrinkage as the hydration products were increased, leading to less free water
for
evaporation.
Mixtures containing TOSW experienced increases in shrinkage. For example,
shrinkage of G260 and G290 (see Figures 14(a) and 14(b)) mixtures increased
from
0.031% to 0.082% and from 0.038% to 0.072% compared to that of the control
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CA 2961137 2017-03-17
mixtures, respectively. This behaviour is related to the water/powder ratio
and amount
of bleeding observed. Mixtures with high bleeding values exhibited lower
shrinkage as
the water dried from the surface rather than from the bulk of the material.
Moreover, incorporating a fine inert material like TOSW refine capillary pores
in
the hardened mixtures, which increased the internal tensile stresses leading
to more
shrinkage.
The normal range of ultimate shrinkage in CLSM is between 0.02% and 0.05%
(ACI Committee 229R, 2013). The range of the measured shrinkage for G260
mixtures
exceeded the normal range for CLSM yet was still below the typical ultimate
shrinkage
of 0.1% for concrete. The mixture design can be optimized to keep the
shrinkage closer
to the lower limit (i.e. 0.031%). However, shrinkage has minor effect on the
performance
of CSLM (ACI Committee 229R, 2013).
Leaching of Heavy Metals
Table 8, Figures 15 and 16 show the results of the conducted (ICP-MS) analysis
on the leachates. It is noticed from Figure 15 that the TOSW has little to no
contribution
to the concentration of Lithium and Chromium of the leached material. The
concentration of these metals increased with age only for mixtures containing
cementitious materials, while measurements for the same elements in raw TOSW
samples were within minimum detectable concentration. On the other hand,
leaching of
Arsenic, Strontium, Cadmium and Barium were prominent for the raw TOSW sample
and greatly reduced for samples containing cementitious materials, which
indicates
stabilization of these elements in CLSM mixtures. However, concentration of
Strontium
and Barium were noticeably higher in Group 3 mixtures as the amount of
cementitious
31
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materials reduced by replacing fly ash with TOSW. Figure 16 shows a clear
reduction in
the concentrations of Lithium and Chromium for samples with TOSW as a
replacement
for fly ash (Group 3) compared with mixtures containing fly ash (Group 2)
after 28 days
of leaching. All leaching results were below the concentration limits of the
groundwater
standard of the Canadian Council of Ministers of Environment (CCME),
Lithium Chromium Arsenic Strontium
Cadmium Barium
Elements:
(Li) (Cr) (As) (Sr) (Cd) (Ba)
Conc. Conc. (p g/L) Conc. (p Conc.
(p Conc. (p Conc. (p
Mix code age (pg/L) g/L) g/L) g/L) g/L)
G260W15 2 days 5.29 6.43 1.55 179.45 ND 153.45
G260W15 7 days 7.70 11.09 1.94 455.31 ND 146.11
G260W15 28 days 21.97 30.29 1.67 1148.03 ND 118.08
G290W15 2 days 5.29 3.03 0.93 81.40 ND 131.21
G290W15 7 days 12.32 9.38 0.64 480.47 ND 180.43
G290W15 28 days 38.03 21.32 1.11 977.09 ND 320.43
G360W15 28 days 16.86 12.10 1.31 3887.84 <0.05
874.63
G390W15 28 days 12.58 9.07 0.98 3699.30 <0.05
792.48
Raw G2 2 days <5.29 <0.26 13.20 1040.43 0.34
394.81
Raw G2 7 days <5.29 0.32 16.74 1201.91 0.21
381.74
Raw G2 28 days <5.29 <0.26 13.93 1485.15 0.33
477.06
Raw G3 28 days 12.85 0.38 23.09 1920.81 0.27
371.45
ND=lower than method detection limit
Table 8: Results of (ICP-MS) analysis of leachates
Compressive Strength
1.0 The compressive strength was evaluated for the three control CLSM
mixtures
and 15 CLSM mixtures with different cement, TOSW and fly ash contents, after
7, 14
and 28 days of curing. The compressive strength values of the tested mixtures
are
presented in Table 9 and Figures 17(a) and 17(b). Control mixtures with cement
content of 30 and 60 kg/m3 (i.e. G130 and G160) exhibited a very slow strength
gain
32
CA 2961137 2017-03-17
rate compared with 90 kg/m3 mixture (G190). This can be attributed to the
dilution effect
and reduction in pozzolanic reaction of fly ash. The class F fly ash used in
these
mixtures has no cementitious properties and needs cement in order for the
pozzolanic
reaction to take place; in the presence of cement, the silicate minerals in
fly ash react
with the calcium hydroxide released during the hydration process of the
cement.
For mixtures incorporating TOSW, the compressive strength depends mainly on
the water/powder ratio. As shown in Figures 12 and 17(a), the strength of G290
mixtures increased with the decrease of water/powder ratio regardless of the
waste
content. However, in Group 2 mixtures, the ability of the TOSW to enhance
flowability
reduced the amount of water needed for the mixture, which led to an increase
in
strength when the same flowability was maintained as noticed for G260
mixtures. On
the other hand, replacing fly ash with TOSW in Group 3 mixtures resulted in a
significant reduction in strength. This is attributed to reduced bonding
between particles
due to the lack of the pozzolanic activity of fly ash that was available in
Group 2
mixtures. However, this reduced strength can be compensated for by increasing
the
cement content. For example, increasing the cement content from 60kg/m3 to 90
kg/m3,
led to an increase in the achieved compressive strength of about 300% (i.e.
from 423
kPa for G360 mixture to 1233 kPa for G390 mixture). In addition, for some CLSM
applications, it may be important to maintain a low strength to facilitate
future
excavation. The ACI committee 229 recommends a compressive strength lower than
2.1 (MPa) if future excavation is anticipated (ACI Committee 229R, 2013).
CLSM cylinders were also tested for tensile strength according to ASTM test
method C496/C496M (Standard Test Method for Splitting Tensile Strength of
Cylindrical
33
CA 2961137 2017-03-17
Concrete Specimens). Figure 17 shows a good linear relationship between the
tensile
strength and the compressive strength of the tested CLSM samples. The tensile
strength ranged from 7% to 17% of the compressive strength and this range is
very
close to the normal range of Portland cement concrete, which is 8% to 14%
(Qian
2015).
To assess the excavatability of tested mixtures, the removability modulus is
calculated according to (Equation 1) based on the results of the compressive
strength
and density of the samples. The requirements and limits of RE vary with the
application
of CSLM, CLSM is considered easily removable by hand tools if RE is equal or
less
than one (1). Replacing fly ash with TOSW lowered the RE producing more easily
removable CLSM while maintaining the other properties of CLSM within ACI
specifications. The results of removability modulus calculations are shown in
Table 9.
Elastic Modulus
The secant elastic modulus (E2) was calculated based on the stress-strain
curve
obtained from the unconfined compressive strength test at 50% of the maximum
strength at 28 days. The obtained results demonstrated that the secant elastic
modulus
increased as the compressive strength, as shown in Table 9. The secant elastic
modulus was found to be 46 to 210 times the corresponding compressive strength
which is within the range reported in the literature for CLSM.
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1 (E) Modulus (UCCS)
Mixture code of Elasticity Compressive E/UCCS
RE
(KPa) strength (KPa) .
G130 73324 595 122 1.59
(Group 1) G160 65887 1436 46 2.43
ACI-229R 489235 4771 102 4.43
Control
Mixtures G190
G260W5 181647 2894 63 2.75
(Group 2) G260W10 360617 2840 127 2.65
TOSW G260W15 322350 3172 101 2.93
replacing
G290W5 625374 4364 143 3.48
sand
G290W10 280892 4281 66 3.59
G290W15 676029 6848 98 4.42
G330W5 3154 72 54 0.39
G330W10 20174- 158 128 0.57
(Group 3) G330W15 26749 184 146 0.64
TOSW G360W5 18106 298 61 0.96
replacing fly G360W10 48877 370 135 1.02
ash and sand G360W15 88804 423 210 1.11
G390W5 57489 972 59 1.62
3390W10 119108 1043 114 1.72
3390W15 181206 1233 147 1.87
Table 9: Compressive strength, elastic modulus and removability modulus at age
of
28 days
Conclusions
The results of this study demonstrate that TOSW can be used as a filler
material
and as a replacement of fly ash in CLSM formulations producing a sustainable
and
environmentally safe CLSM that satisfies fresh and hardened properties.
Moreover,
some of the CLSM properties were enhanced after incorporating TOSW. There are
lo several significant advantages of using TOSW in the CLSM formulations.
For example, the incorporation of TOSW has increased the flowability of the
mixtures, which reduced the water demand to reach a specific flowability
value, which in
CA 2961137 2017-03-17
turn lead to higher compressive strength in Group 2 mixtures. TOSW was more
effective in increasing flowability compared with fly ash in Group 3 mixtures.
Lower dry density was achieved for mixtures with TOSW, which makes it suitable
for field applications encountering weak soils. Some of the mixtures can also
be
classified as Class VII low-density CLSM (LD-CLSM) according to ACI committee
229R,
which makes TOSW a suitable material for application in LD-CLSM mixtures.
Mixtures with TOSW showed higher drying shrinkage as the content of TOSW
increases), therefore it is recommended to use shrinkage control admixtures
for
applications where shrinkage control is required. Figure 19 is a photograph of
cementitious grout incorporating TOSW.
Incorporating TOSW in CLSM mixtures has significantly reduced bleed water.
Incorporating TOSW in CLSM mixtures lowered the pollutant potential of the
TOSW in terms of leaching of heavy metals with concentrations within the
limits of the
groundwater standard of the Canadian Council of Ministers of Environment
(CCME).
The unconfined compressive strength at 28 days of the tested CLSM mixtures
ranged from 0.6 MPa to 4.7 MPa for control mixtures with different cement
content and
from 2.8 MPa to 6.8 MPa for Group 2 mixtures with different cement and TOSW
content. Higher strength values were achieved for mixtures with higher TOSW
content
within the same group. Replacing fly ash with TOSW in Group 3 mixtures lowered
the
.. strength and elastic modulus of the mixtures compared to the control
mixtures, which
may be beneficial in some applications of CLSM where low strength is required
for
future excavation. Higher cement content can compensate for the reduced
strength due
36
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to elimination of fly ash. Increasing cement content from 60 kg/m3 to 90 kg/m3
increased the CLSM mixture strength from 423 kPa to 1233 kPa.
Finally, fly ash can be replaced by TOSW in CLSM mixtures while maintaining
the properties for CLSM within the limits of ACI committee 229 report. As
noted above,
the mechanical properties of CLSM formulations have been deliberately kept low
so that
it can be excavated easily. However, due to its pozzolanic nature, the use of
fly ash to
maintain high flowability will increase later ages strength making re-
excavation a
problem. Thus, very advantageously the use of the very fine SiO2 TOSW
particles
allows the production of flowable CLSM formulations at early ages and is easy
to
excavate at later ages.
Concrete formulations
Materials
Ordinary Portland cement (OPC) Type 10 was used in all mixtures as the main
binder. It consisted of 61% Tricalcium silicate(3Ca0Si02), 11% Dicalcium
silicate
(2Ca0Si02), 9% Tr-calcium aluminate (3Ca0 Al2O3), 7% tetracalcium
aluminoferrite
(4Ca0A1203Fe203)), 3% sulfur trioxide (SO3) and 0.82% equivalent alkalis was
used as
a binder material. TOSW was added as partial replacement of sand by volume.
Table
10 shows the trace elements of TOSW. Particle size distribution curves for OPC
and
TOSW are shown in Figure 2 as previously discussed.
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ICP-AES Analysis
Element Symbol
(pg/g)
Silver Ag <0.05
Aluminum Al 7399
Arsenic As 20
Barium Ba 4795
Cadmium Cd <0.05
Cobalt Co 5
Copper Cu 13
Iron Fe 14024
Manganese Mn 201
Molybdenum Mo < 0.05
Nickel Ni 25
Vanadium V 30
Zinc Zn 101
Lithium _ Li 4
Lead Pb 33
Table 10. Analysis of the TOSW
Coarse aggregate was a washed round gravel with sizes 5 to 10 mm, absorption
of 0.8% and fines content lower than 1%. Natural siliceous sand with an
absorption of
1.5% was used as fine aggregates. A water to cement ratio of 0.42 was used in
all
tested mixtures. A polycarboxylate ether based superplasticizer (HRWRA) was
used to
adjust mixture flowability. Air entraining admixture complying with ASTM C260
was
used. In order to satisfy strength, workability and durability requirements
for CFA piles,
all mixtures were designed to achieve a slump of 220 mm 50 mm and minimum 28-
day compressive strength of 35 MPa. Table 11 shows the composition for all
tested
mixtures.
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40 /0
Property Control 10% TOSW 20% TOSW 30% TOSW
TOSW
Cement 1 1 1 1 1
Sand 1.79 1.6 1.42 1.24 1.07
Gravel 2.45 2.45 2.45 2.45 2.45
TOSW (%) 0 10 20 30 40
Superplasticizer (%) 0.80% 0.85% 1.0% 1.15% 1.6%
Air entrainment (%) 0.05 0.05 0.05 0.05 0.05
Slump (mm) 225 225 220 220 215
Concrete temperature (C ) 17 18 18 23 23
Air temperature (C ) 22 24 24 23 23
Table 11. Mixtures composition
Testing Procedures
Fresh properties
Slump and bleeding tests were conducted according to ASTM C143 (Standard
Test Method for Slump of Hydraulic-Cement Concrete) and ASTM C232 (Standard
Test
Method for Bleeding of Concrete) to evaluate fresh properties for concrete
mixtures,
respectively. Moreover, the slump retention for concrete mixtures was
conducted by
measuring the slump loss at specific time intervals over the investigated
period.
Hardened Properties
Mechanical properties including compressive and tensile strengths, and modulus
of elasticity were evaluated according to ASTM C39, ASTM C496, respectively.
Flexural
strength was evaluated using 100 x 100 x 400 mm specimens according to ASTM
C78.
In addition, the bond strength between the concrete and the rebar was
evaluated by
pulling a steel rebar out of the 150 x 300 mm concrete cylinder. All specimens
were
produced in triplicate and were cured in a moist curing room (i.e. temperature
(T) 23
C 2 C and relative humidity (RH) = 95% 5%) until testing ages 7, 28 and
120 days.
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Durability performance
Freezing and thawing test was conducted on prismatic concrete specimens
following ASTM C666. Initially, specimens were inserted in metal boxes and
then water
was added up to 3 mm above the upper face of the concrete specimens (Method A
of
ASTM C666). Specimens were subjected to the freeze and thaw cycles adjusted
according to ASTM 0666 inside a freeze and thaw chamber. Meanwhile, non-
destructive ultrasonic pulse velocity test was performed.
For corrosion testing, the electrochemical linear polarization resistance
method
was utilized to determine the corrosion current density (Icon). In this
method, a three-
10, ,1 =
electrode system is used to measure /corr. More details about the test setup
can be
found elsewhere.
After a suitable initial delay, typically 60 s, the steel was polarized. The
product of
surface area of rebar under polarization and the slope of applied potential
versus
measured current plot was taken as the linear polarization resistance Rp (kS/
cm2) and
icorr (A/crin2) can be calculated using Equation 2:
icorr ¨ 2
Rp
B is a constant, in case of steel in passive state, it has a value 52 mV while
in case of
steel in active state, it has a value of 26 mV. The value of B used in this
test was 26 mV.
All specimens were exposed to an accelerated scenario adopted from previous
study at
which specimens were connected to a direct electric current while being
immersed in a
3.5% sodium chloride (NaCI) solution.
CA 2961137 2017-03-17
Leaching test
Leaching testing was conducted according to EPA 1315 method (1315, 2013).
Test was conducted on an unsolidified sample of TOSW soaked as a row material
in a
certain volume of water. Simultaneously, concrete specimen with and without
TOSW
were immerged separately in the same water volume. Water samples were analyzed
every 3 days using inductively coupled plasma mass spectrometry (ICP-MS).
Results And Discussion
Fresh properties
Fresh properties of concrete have a significant effect on its placement
quality.
Concrete with adequate workability and stability against segregation will have
high
strength and durability performance. In order to examine the effect of TOSW
addition on
the workability, all concrete mixtures slump was adjusted to 220 5 mm while
monitoring the change in HRWRA demand. Several trial concrete batches were
conducted in order to identify the optimum HRWRA dosage that meets the
targeted
slump. As shown in Table 11, addition of TOSW reduced slump, hence, an
increasing
in HRWRA dosage was required to maintain the slump within the desired range.
For
instance, mixture incorporating 20% TOSW required an increase in the HRWRA
with
about 0.2% to achieve the same slump of that of the control mixture. This can
be
ascribed to the fact that TOSW is a very fine material which confers a very
high
viscosity to the fresh mixture leading to a greater cohesivity and lower slump
(Frontera,
Candamano, lacobini and Crea, 2014). Eventually, all tested mixtures had not
shown
any sign of segregation or bleeding. On the other hand, from practicality
point of view,
failing to maintain the concrete workable for at least 30 min can jeopardize
the entire
41
CA 2961137 2017-03-17
installation process of CFA piles. This time frame is required to finish
concrete pumping
and reinforcement steel cage installation. Figure 20 illustrates the change in
slump with
time for all tested mixtures. All concrete mixtures incorporating TOSW had
satisfied the
30 minutes' slump retention time and maintained up to 90 min after mixing
within the
required slump range for CFA piles. Therefore, mixtures incorporating TOSW can
be
used successfully for CFA application from workability point of view.
Cornpressive Strength
Compressive strength results for control and TOSW mixtures are given in Figure
21. Compressive strength had decreased by the addition of TOSW as partial
replacement of sand. The higher the replacement rate, the greater was the
reduction in
the compressive strength. For instance, adding 10% and 30% of TOSW had induced
a
reduction in the compressive strength at age 28 days with about 4% and 16%
than that
of the control mixture, respectively. This reduction in strength can be
ascribed to the
increase in the amount of fine materials in mixtures (i.e. TOSW addition).
Simultaneously, inadequate dispersion of TOSW particles due to coagulation
could
induce weak points in the concrete microstructure resulting in a lower
achieved
strength. However, all tested mixtures meet the targeted compressive strength
for CFA
pile concrete mixtures at age 28 days (i.e. 35 MPa), except mixture
incorporating 40%
TOSW. For instance, compressive strength at age 28 days for mixtures
incorporating
20% and 30% were 52.31 MPa and 46.75 MPa, respectively. It is interesting to
note that
the development rate of concrete strength did not alter by the addition of
TOSW. The
increase in compressive strength for mixture with and without TOSW from age 7
to 28
days and from 28 to 120 days was about 10% 1% and 12% 2%, respectively.
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Splitting tensile strength
Figure 22 illustrates the variation of splitting tensile strength with time
for all
tested mixtures. Tensile strength results followed the same trend as that of
compressive
strength results. The higher the replacement rate, the greater was the
reduction in the
tensile strength. For instance, adding 10% and 40% of TOSW had induced a
reduction
in the tensile strength at age 28 days with about 6% and 23% than that of the
control
mixture, respectively. Similar to compressive strength, addition of TOSW had
insignificant effect on the development rate of the tensile strength. All
mixtures with and
without TOSW had tensile strength developing rate of about 14% from age 7 to
28 days
and less than 10% from age 28 to 120 days.
Generally, the ratio between tensile and compressive strengths for mixtures
with
and without TOSW at different concrete ages was about 10% which is a common
value
in the literature. Moreover, several national building codes had proposed
various
formulas for the relationship between splitting tensile and compressive
strengths for
concrete. In this study, ACI 318 (318, 2008), ACI 363R (ACI, 2010) and CEB-FIP
(Taerwe and Matthys, 2013) formulas were used to predict the TOSW mixture
splitting
tensile. The general formula is as follows (Equation 3):
3
Where, ftsp = splitting tensile strength, and fc. = compressive strength, in
MPa, a and b
are constants (i.e. ACI 318: a=0.56, b=0.50; ACI 363R: a=0.59, b=0.50; and CEB-
FIP:
a=0.3, b=0.67). The deviation between experimental data and predicted values
is
assessed statistically based on the integral absolute error (IAE,%), and it is
computed
from the following equation (Equation 4):
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CA 2961137 2017-03-17
Q¨
IAE= ______________________________ P x 100% 4
EQ
Where, C2 = observed value and P = predicted value. The IAE value reflects the
difference between predicted and observed values. If 1AE is zero, this
indicates that the
predicted and observed values are identical, which is rarely occurred. Hence,
if there
are different regression equations, the one having the smallest value of the
IAE is the
most reliable. Generally, an acceptable regression equation will have IAE in
the range
from 0 to 10%.
Figure 23 illustrates the correlation between the experimental data and
predicted
values for the splitting tensile strength. It seems that all the proposed
formulas
underestimate the splitting tensile strength of concrete mixtures
incorporating TOSW.
However, IAE values for CEB-FIP and ACI 363R were less than 10%, hence, both
equations can be used to estimate the splitting tensile strength of TOSW
concrete
mixtures based on the achieved compressive strength.
Flexural strength
Figure 24 shows the development of the flexural strength with time. It is
clear
that flexural strength results were consistent with compressive and tensile
strength
results. The flexural strength for control mixture was around 13% 1% of its
compressive strength at all testing ages. Similar trend was exhibited by
mixtures
incorporating different contents of TOSW. For instance, ratios between the
flexural and
compressive strength for mixtures incorporating 20% and 40% of TOSW were 11.6%
and 13.2% at age 28 days, respectively.
Similar to splitting tensile strength, various formulas for the relationship
between
flexural and compressive strengths were adopted. The ACI 318, ACI 363R and
formula
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CA 2961137 2017-03-17
proposed by Shah and Ahmad (Shah and Ahmad, 1985) were used to predict the
TOSW mixture flexural strength. The general formula is similar to that in
Equation 3 as
follows in Equation 5:
ff = a kb 5
Where, f1 = flexural strength, and L = compressive strength, in MPa, a and b
are
constants (i.e. ACI 318: a=0.62, b=0.50; ACI 363R: a=0.94, b=0.50; and Ahmad
and
Shah (1985): a=0.44, b=0.67). The deviation between experimental data and
predicted
values was also assessed on the basis of /AE (%). Figure 25 shows the
correlation
between the experimental data and predicted values for the flexural strength.
It can be
seen that Eq. 5 is capable to predict the flexural strength for mixtures
incorporating
TOSW with an acceptable accuracy (i.e. 1AE less than 10%).
Modulus Of Elasticity
The modulus of elasticity of concrete (E) represents the relationship between
the
stress and strain and provides an understanding of their effect on each other.
As shown
in Figure 26, increasing the TOSW content leads to a reduction in the measured
modulus of elasticity. For instance, at age 28 days, increasing the TOSW
content from
10% to 30 % resulted in a higher reduction in the modulus of elasticity with
about 12%.
Moreover, the reduction in the modulus of elasticity induced by TOSW addition
was in
the same reduction order of that of the compressive strength. This is in
agreement with
the literature as concrete modulus of elasticity is strongly related to its
compressive
strength. Generally, in the quality control program, modulus of elasticity is
expressed as
function of compressive strength which is determined routinely, while modulus
of
elasticity test is ignored as it is laborious and time-consuming. Therefore,
various
CA 2961137 2017-03-17
researchers have proposed a number of expressions that can be categorized into
two
groups. The first group of expressions may be written in the general formula
as shown
in (Equation 6):
E a Lb + c 6
Where a, b, and c are coefficients. This formula is recommended by ACI 363R (a
=3320, b=0.5, c=6900). In the second category, the expression is similar to
Equation 3.
The ACI 318 and CEB-FIP use values of 4730 and 8981 for a coefficient and 0.5
and
0.33 for b coefficient, respectively. Figure 27 shows the correlation between
the
experimental data and predicted values for the modulus of elasticity. All
proposed
formulas are capable to predict the modulus of elasticity for mixtures
incorporating
TOSW with an acceptable accuracy (i.e. IAE less than 10%).
Pullout Strength
One of the main assumptions in design of reinforced concrete structures is the
strain compatibility between concrete and reinforcement steel. Hence, bond
between
them (i.e. concrete and steel) is an essential parameter which is
significantly affected by
the quality and properties of the holding concrete (Valcuende and Parra,
2009). Figure
28 shows pullout strength development for all tested mixtures over the
investigated
period. All tested mixtures achieved more than 75% of the final pull-out
strength at age
7 days. For instance, control mixture and mixture incorporating 30% TOSW
exhibited
77% and 87% of their final pull-out strength at age 7 days, respectively.
Moreover, the
addition of TOSW has resulted in a lower pull-out strength with respect to
that of the
control mixture without TOSW. The higher the TOSW content, the higher was the
reduction in the pull-out strength.
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For example, increasing the TOSW content from 10% to 40% had led to a higher
reduction in pull-out strength with about 30% with respect to that of the
control mixture
at age 28 days. Figure 29 shows the compressive strength and pull-out strength
of the
tested mixtures at age 28 days as a percentage of the control mixture. The
reduction in
both compressive and pull-out strengths due to TOSW addition were almost the
same.
This is expected since the bond behaviour between the rebar and concrete is
mainly
controlled by concrete mechanical properties (i.e. compressive and tensile
strengths).
Freeze And Thaw
Frost action is among the prominent durability problems of concrete structures
exposed to cold climates. Hence, the freeze-thaw resistance for each tested
mixtures
was assessed according to ASTM 0666 in which a durability factor (DF) is
calculated
after exposing each specimen to a number of freezing and thawing cycles (N)
equals to
M, which is a specified number of cycles at which the exposure is to be
terminated (i.e.
300 cycles according to ASTM C666) or until its relative dynamic modulus of
elasticity
(P) reaches 60 % of its initial value using Equation 7:
P x N
DF = ____________________________________________________________ 7
Durability factors for all tested concrete mixtures after 300 freezing and
thawing cycles
are shown in Figure 30. All mixtures incorporating TOSW met the 60% threshold
recommended by ASTM 0666 guidelines for durable concrete subjected to freezing-
thawing cycles, except mixture incorporating 40% TOSW. Mixture incorporating
40%
TOSW was markedly deteriorated at about 210 freezing-thawing cycles with a
durability
factor less than 50%.
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Generally, the relative dynamic modulus of elasticity was found to decrease as
the TOSW content increased. Addition of TOSW reduces the mechanical properties
of
concrete mixtures, especially tensile strength. Simultaneously, deterioration
of concrete
exposed to freezing and thawing cycles has been ascribed to the migration of
super-
s cooled water between small and large surface pores in order to freeze and
form ice.
The gradual build-up of ice in capillary pores exerts tensile stresses. As
these tensile
stress excessed the cement matrix tensile strength, micro cracks are formed
and start
to grow and propagate with the repeating of the freeze and thaw cycle. Hence,
the
addition of TOSW to concrete exposed to forest action makes it more vulnerable
to
crack due to the reduction in its tensile strength.
Corrosion
Figure 31 illustrates the variation of corrosion current density Ni(COrr,)
with exposure
time to NaCI solution for different specimens. It was observed that TOSW
addition
increases the corrosion current. However, the calculated corrosion current for
all
mixtures was below the threshold value of 0.10 pA/cm2indicating passive
condition
according to the criteria developed by Broomfield and Clear (Broomfield, 1996,
Clear,
1989).
Leaching
Concrete mixtures incorporating 40% TOSW did not meet the performance
requirements for CFA. Hence, the focus in the leaching evaluation was directed
to
concrete mixtures incorporating up to 30% of TOSW as partial replacement of
sand.
Leaching of heavy metals from the TOSW was initially identified through
testing a
sample of raw TOSW (Table 12). According to the Canadian Council of Ministers
of
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CA 2961137 2017-03-17
Environment (CCME) guideline limits, incorporation of TOSW in concrete
mixtures had
significantly reduced the leaching for different metals with respect to raw
TOSW as
shown in Table 12. For example, incorporation of TOSW in concrete had led to
leaching
values for Vanadium, Arsenic, Aluminum and Nickel, below CCME standards by
about
20% to 93%. This can be ascribed to the solidification of the TOSW in the
cementitious
matrix of concrete. In addition, the densification and reduction in porosity
of concrete
microstructure induced by the addition of the very fine TOSW assisted in
entrapping
higher amount of metals (Sabatini, Knox and American Chemical Society.
Division of
Colloid and Surface).
õ CCME Concrete leaching (mg/I)
Raw TOSW
Element Symbol guideline
(mg/1) leaching (mg/I) 10% 20% 30%
TOSW TOSW TOSW
Silver Ag N.A. 0.005 0.005
0.004 0.003
" Aluminum Al 5.000b -1.656 0.349 0.615 0.975
Arsenic As 0.005a 0.012 0.004
0.002 BDL*
Barium Ba N.A. 1.113 0.700 0.105 0.119
Cadmium Cd N.A. 0.066 0.010
0.004 BDL
Cobalt Co , 0.0500 0.001 BDL BDL BDL
Copper Cu 0.004a 0.012 BDL BDL BDL
Iron Fe 0.300a 0.451 0.028 0.013 0.004
Manganese Mn 0.2000 0.011 BDL BDL BDL
Molybdenum MD 0.073' 0.056 0.005 0.005 0.004
Nickel Ni 0.150a 0.017 0.030 0.027 0.023
Vanadium V 0.1000 0.038 0.026
0.018 0.011
Zinc Zn 0.030a 0.001 BDL BDL BDL
Lithium Li 2.500b 0.013 0.023 0.025 0.024
Lead Pb 0.006a 0.004 0.001
0.002 0.002
a CCME (Canadian Council of Ministers of Environment) guide lines for
protection of fresh water
b CCME guide lines for protection of agriculture (irrigation)
*BDL: Below Detecting Limits
Table 12. Measured metals in TOSW compared to different standards
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CA 2961137 2017-03-17
Conclusions
This study provides a new thought about TOSW. It proved experimentally the
high potential of recycling/reusing TOSW in concrete mixtures for different
construction
applications. Besides converting TOSW to a valuable product, this study
provides an
alternative solution for waste management of TOSW instead of sending to
landfill. The
following conclusions can be drawn from the above discussed results on
concrete
containing TOSW particles.
First, increasing the HRWRA dosage can overcome the reduction in concrete
slump induced by TOSW addition and maintain its workability within the
required range
for CFA application. Second, concrete mixtures incorporating up 30% TOSW as a
partial replacement of sand met the targeted compressive strength for CFA pile
concrete mixtures at age 28 days (i.e. 35 MPa) along with adequate durability
performance. Third, addition of TOSW did not alter the correlation between
compressive
strength and other mechanical properties. Finally, solidification of TOSW in
the
cementitious matrix of concrete along with reduction in concrete porosity due
to TOSW
addition increase the potential of producing materials with a lower pollution
potential
than that characterizing the TOSW disposal.
The use of the TOSW silicon dioxide particles in concrete is very advantageous
in that it addresses a fundamental structural problem associated with
concrete.
Specifically, bleeding is an inherent property of concrete, where water comes
out to the
surface of the concrete, it being lowest specific gravity among all the
ingredients of
concrete. Bleeding increases concrete permeability thereby jeopardizing its
durability
performance, it reduces the bonding between aggregate and cement paste leading
to a
CA 2961137 2017-03-17
lower strength, and it also reduces bond between the reinforcement and
concrete.
Using the very fine SiO2 waste in concrete formulations as disclosed herein
will reduce
bleeding significantly as it creates a longer path for the water to traverse
and it has a
high surface area. Further the inter-particle voids between aggregate
particles have
adverse effects on concrete strength and durability. Hence, using such very
fine SiO2
waste will fill these voids thereby improving the packing density of the
aggregate leading
to impermeable strong and durable concrete.
The foregoing description of the preferred embodiments of the invention has
been presented to illustrate the principles of the invention and not to limit
the invention
to the particular embodiment illustrated. It is intended that the scope of the
invention be
defined by all of the embodiments encompassed within the following claims and
their
equivalents.
References
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offshore
treatment of oil contaminated cuttings on the Norwegian continental shelf and
Martin Linge case study. Norway: Master thesis, University of Stavanger.
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