Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02784424 2012-08-02
SELF-CONSOLIDATING CONCRETE (SCC) MIXTURE HAVING A
COMPRESSIVE STRENGTH OF AT LEAST 25 MPa AT 28 DAYS OF AGE
TECHNICAL FIELD
[0001] The present disclosure relates to self-consolidating
concrete (SCC),
and more particularly to a SCC mixture having a compressive strength of at
least
25 MPa at 28 days of age.
BACKGROUND
[0002] Workability of concrete refers to the effort (or energy)
required to
manipulate a freshly mixed quantity of concrete with minimum loss of
homogeneity.
The manipulation may refer to pumping, placing, consolidation and/or finishing
of
the concrete. Workability of concrete is quantified in terms of "slump" or
"slump
flow". The slump flow test has been standardized as ASTM C 1611, "Slump Flow
of
Self-Consolidating Concrete." Slump and slump flow are measurements of
concrete
rheology and is determined using a slump cone. A slump cone is standardized
measurement cone having a predefined volume and angle. FIG. 1A illustrates a
standard slump cone 100 which includes a top opening 102 and a bottom opening
104.
[0003] The slump cone 100 is used by placing the slump cone 100 on
a flat
surface and filling the slump cone 100 with fresh concrete through the top
opening
102 as shown in FIG. 1B. The slump cone 100 is completely filled and any
excess
concrete at the top of the slump cone 100 is scraped off. The slump cone 100
is
lifted directly upwards. The concrete 110 slowly spreads out over the flat
surface
without the support of the slump cone 100 to hold the concrete 110 in place.
The
spreading action causes the height of the concrete 110 to decrease to a height
112
from an initial height 116 corresponding to the height of the slump cone 100.
The
distance 114 represented by the change in height of the concrete 110 is
referred to
as the "slump". The "slump" is indicative of the yield value of the concrete.
The
concrete 110 ultimately spreads out over the flat surface to form a crude disc
or
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CA 02784424 2012-08-02
pancake shape as shown in FIG. 1C. The diameter 118 of the disc formed by the
concrete 110 is referred to as the "slump flow".
[0004] Another measurement of the workability of the concrete is
the T50 test.
The T50 test quantifies the viscosity of the concrete 110 and measures the
amount
of time in seconds for the concrete in the slump flow test to spread to a
diameter of
50 cm or 500 mm). The T50 test has been standardized as ASTM C 1611. The T50
time is indicative of the viscosity of the concrete. The slump, slump flow and
T50
are used to assess the rheological properties of the concrete and predict how
it will
flow or move under the force of gravity or positive force into a desired shape
or
position.
[0005] Conventional concrete has a slump flow of 80 mm to 120 mm.
The
placement and finishing of concrete floors in residential and commercial
applications
using a conventional concrete is difficult, labour intensive and time
consuming due
to this low slump. Conventional concrete having a minimum compressive strength
of 25 MPa is typically designed to have a maximum slump flow of 100 mm;
however, water is added in the field to raise the slump flow to 200 mm to
improve
the workability of the concrete, and in particular the placeability of the
concrete.
The consequences of adding extra water to increase the water/cement ratio, is
to
decrease ultimate strength and increase shrinkage.
[0006] SCC is a type of concrete characterized by a low yield, moderate
viscosity which can be used to ensure a uniform suspension of aggregate during
transportation, placement and finishing until the concrete sets. SCC has
properties
which are desirable in the construction of the concrete floors in residential
and
commercial applications; however, known SCC compositions are more costly to
produce than conventional concrete and provide a surface which is prone to
tearing
and peeling in response to mechanical working/finishing (smoothing and/or
hardening) such as when power trowelled. This results in surface defects such
as
blisters and delaminations which are unacceptable for most applications.
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CA 02784424 2012-08-02
[0007] Accordingly, a SCC mixture is desired which is comparable in
cost to
conventional concrete used in residential and industrial floor construction
but which
requires less time to place and finish, thus increasing the productivity of
the
concrete supplier and user.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1A is a perspective view of a standard slump cone.
[0009] FIG. 1B is an elevational view of the standard slump cone of
FIG. 1A
and a poured concrete schematically illustrating the use of the slump cone for
measuring the slump.
[0010] FIG. 1C is an elevational view of the standard slump cone of
FIG. 1A
and a poured concrete schematically illustrating the use of the slump cone for
measuring the slump flow.
[0011] FIG. 2 is an example of a 0.45 power gradation chart.
[0012] FIG. 3 is a sieve comparison chart.
[0013] FIG. 4 show properties of example embodiments of SCC mixtures
prepared in accordance with the present disclosure.
BRIEF SUMMARY OF DISCLOSURE
[0014] The present disclosure provides a SCC mixture which seeks to
address
one or more of the foregoing shortcomings of known SCC mixtures. The present
disclosure describes an SCC mixture which forms a surface of partially set
concrete
which can be hardened by finishing with power trowelling equipment. The
hardening increases the density of the surface of the concrete, thereby
increases its
resistance to wear with little or no tearing or peeling of the surface. This
allows
ready mix trucks to spend less time at the jobsite and less time and labour is
required to place and finish the concrete, thereby increasing the productivity
of the
concrete supplier and user.
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CA 02784424 2012-08-02
[0015] In accordance with one example embodiment, there is provided
a
self-consolidating concrete (SCC) mixture, comprising: a mixture of coarse
aggregate (CA), fine aggregate (FA), very fine aggregate (VFA), Portland
cement
or Portland limestone cement, an ASTM C494 Type F polycarboxylate ether high
range water reducer (also known as a superplasticizer), and water, wherein the
VFA has a particle size distribution in which 95% to 100% passes a 2.5 mm
sieve
and in which 20% to 100% passes a 75 pm sieve.
[0016] In some embodiments, the SCC mixture further comprises
supplementary cementitious materials. In some embodiments, the amount of
supplementary cementitious materials ranges between 5% and 70% by weight of
the total cementitious materials, preferably between 5% and 50% by weight of
the
total cementitious materials.
[0017] In some embodiments, the VFA has a methylene blue value of
less
than 0.75 mg/g at 3 minutes.
[0018] In some embodiments, the polycarboxylate ether high range water
reducer is present in an amount such that a percent of polycarboxylate solids
relative to total cementitious materials ranges between 0.1 and 0.28.
[0019] In some embodiments, the SCC mixture has a water-to-cement
ratio
which ranges between 0.4 and 0.8.
[0020] In some embodiments, the VFA principally comprises dust-of-fracture
fines. The dust-of-fracture fines may principally comprise non-reactive
particles
having a significant quantity of particles (at least 20%) of less than 75 pm
in size.
[0021] In some embodiments, the VFA principally comprises crushed
sedimentary aggregate, crushed igneous aggregate, crushed siliceous aggregate
or
any combination thereof. The crushed sedimentary aggregate may comprise
crushed limestone particles. The crushed siliceous aggregate may comprise
crushed granite particles. The crushed siliceous aggregate may comprise
crushed
quartz particles.
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CA 02784424 2012-08-02
[0022] In some embodiments, the CA may principally comprise crushed
aggregate or natural aggregate (such as gravel), preferably crushed aggregate.
The
CA principally comprises one or any combination of particles having nominal
maximum sizes of 10, 14 and 20 mm.
[0023] In some embodiments, the CA principally comprises particles having a
nominal maximum size between 10 and 14 mm and the SCC mixture has a slump
flow between 350 mm and 750 mm, preferably a slump flow between 550 mm and
650 mm.
[0024] In some embodiments, the CA principally comprises particles
having a
nominal maximum size of 20 mm and the SCC mixture has a slump flow between
350 mm and 650 mm, preferably a slump flow between 450 and 550 mm.
[0025] In some embodiments of the above-described embodiments, the
SCC
mixture has a slump flow of 500 mm or more and a T50 time of 5 seconds or
less,
preferably 4 seconds or less, and more preferably 3 seconds or less. The SCC
mixture is non-segregating at the slump flow of 500 mm or more at the
specified
T50 times.
[0026] In some embodiments, the SCC mixture has a total amount of
VFA
particles less than 75 pm has a range between 300 and 500 kg/m3, preferably
between 300 and 400 kg/m3.
[0027] In some embodiments, the SCC mixture has a compressive strength of
at least 25 MPa at 28 days of age, typically between 25 MPa and 40 MPa at 28
days
of age.
[0028] In some embodiments, wherein the SCC mixture exhibits a
drying
shrinkage of less than 0.06%.
[0029] In some embodiments, the SCC mixture forms a surface layer which is
sufficiently non-segregating after an initial setting so as to be capable of
being
finished with a power trowel without significant adhesion of concrete to
blades of
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= - = = - - =
- = "
the power trowel and without formation of blisters or delamlnation of the
surface
layer.
[00301 The embodiments of the present disclosure described herein
are
intended to be examples only. Some alterations, modifications and variations
to
the described embodiments may be made without departing from the intended
scope of the present disclosure. The described embodiments may be combined in
many instances unless otherwise stated or unless Incompatible with the
teachings
of the present disclosure. In addition, one or more features of the described
embodiments may be used in isolation as a sub-combination or may be combined
with other embodiments or sub-combinations in alternate embodiments not
explicitly described herein but consistent with the teachings of the present
disclosure. Features suitable for such combinations and sub-combinations would
be
readily apparent to persons skilled in the art upon review of the present
disclosure
as a whole.
[0031] These and other advantages and features of the present disclosure
will
become more fully apparent from the following description of example
embodiments and the appended claims, or may be learned by the practice of the
present disclosure as set forth below.
=
DETAILED DESCRIPTION 9F EXAMPLE EMBODIMENTS
[0032] The present disclosure describes an SCC mixture which forms a
surface of partially set concrete which can be hardened by finishing with
power
trowelling equipment. The hardening increases the density of the surface of
the
concrete, thereby increases its resistance to wear with little or no tearing
or peeling
of the surface. This allows ready mix trucks to spend less time at the jobsite
and
less time and labour is required to place and finish the concrete, thereby
increasing
the productivity of the concrete supplier and user.
[0033] The present disclosure provides a SCC mixture which, in at
least some
embodiments, has a compressive strength of at least 25 MPa at 28 days of age,
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CA 02784424 2012-08-02
typically between 25 MPa and 40 MPa at 28 days of age. Preferably, the SCC
mixture is comprised of components which allow the SCC mixture to be
manufactured at relatively low cost, thereby providing a low cost SCC mixture.
The
SCC mixture, in at least some embodiments, includes one or by-products of the
manufacture of concrete aggregates from limestone to reduce the cost of the
SCC
mixture and to provide waste diversion as such by-products are typically
disposed
of in landfills. Accordingly, the SCC mixture, in at least some embodiments,
allows
waste products to be beneficially utilized. The by-products of the manufacture
of
concrete aggregates may comprise very fine aggregate in the form of dust-of-
fracture having a substantial quantity of particles (at least 20%) with a size
less
than 75 pm.
[0034] The SCC mixture, in one example embodiment, comprises a
mixture
of coarse aggregate, fine aggregate, very fine aggregate, cement, an ASTM C494
Type F polycarboxylate ether high range water reducer, and water. The very
fine
aggregate has a particle size distribution in which 95% to 100% passes a 2.5
mm
sieve and in which 20% to 100% passes a 75 pm sieve.
Cement
[0035] The cement is Portland cement or Portland limestone cement.
The
cement may be an ASTM C150 Type I, Type II, Type I/II Portland cement, or
limestone modified cements such as CSA A3000 Type GU and GUL. Blended
cements conforming to ASTM C595 and CSA A3000 may also be used.
[0036] As appreciated by persons skilled in the art, Portland cement
is made
by heating a source of calcium carbonate (such as limestone) with small
quantities
of an aluminosilicate such as clay or similar material at a sintering
temperature
(typically about 1450 C) in a kiln in a process known as calcination. During
calcination a molecule of carbon dioxide is liberated from the calcium
carbonate to
form calcium oxide which is blended with the secondary materials. The
resulting
hard substance, called "clinker", is ground with a small amount of gypsum
(calcium
sulfate dihydrate) and/or anhydrite into a powder. Portland cement reacts with
7
CA 02784424 2012-08-02
water to form primarily calcium silicate hydrate. The strength of the
resultant
concrete results from a hydration reaction between the silicate phases of
Portland
cement and water to form calcium aluminate hydrate Ca3Si2011H8 (3 Ca0 = 2 Si02
=
4 H20, or C3S2H4 in Cement chemist notation (CCN)) and calcium hydroxide
(lime)
as a by-product.
[0037] Supplementary cementitious materials (SCMs) may, in some
embodiments, be partially substituted for Portland cement to improve the
durability
and ultimate strength of the resultant concrete, react with calcium hydroxide,
a by-
product of Portland cement hydration to form additional binder which further
increases durability and ultimate strength and reduce material costs. The SCMs
are
silicate or aluminosilicate materials which exhibits pozzolanic properties and
may
include one or any combination of ground granulated blast furnace slag (GGBFS)
(ASTM C989), coal combustion ash (ASTM C618), silica fume (ASTM C1240), rice
husk ash or any fine silicate or aluminosilicate material which exhibits
pozzolanic
properties. Fine silicate or aluminosilicate materials typically have an
average
particle size of less than 15 microns. The substitution range of Portland
cement
with the various supplementary cementitious materials will typically range
between
5 and 70% by weight, preferably between 5 and 50% by weight to reduce the
impact of lower strengths of caused by higher levels of SCMs. Accordingly, in
such
instances the amount the supplementary cementitious materials ranges between
5% and 70% by weight of the total cementitious materials (i.e., Portland
cement or
Portland limestone cement and supplementary cementitious materials),
preferably
between 5% and 50% by weight of the total cementitious materials.
Aggregates
[0038] The SCC mixture includes aggregate comprising coarse aggregate
(CA), fine aggregate (FA) and very fine aggregate (VFA). The CA may be a
crushed
aggregate or natural aggregate. In some embodiments, the CA may be crushed
calcitic limestone, dolomitic limestone, limestone gravel, crushed granite or
other
aggregate conforming to the requirements of ASTM C33 or CSA A23.1, or possibly
a
mixture of two or more thereof.
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[0039] In some embodiments, the CA principally comprises one or any
combination of particles having nominal maximum sizes of 10, 14 and 20 mm
meeting CSA or ASTM requirements depending on availability and desired plastic
and hardened properties. At the nominal maximum size, no more than 5% of the
particles exceed the stated size of 10, 14 or 20 mm. The smaller particles
have a
lower tendency to settle in the SCC mixture but shrinkage of the concrete may
be
higher whereas larger particles typically settle faster and exhibit less
shrinkage.
Moreover, the proportion of the various sizes affects particle packing, which
in turn
affects rheology and strength of the concrete.
[0040] In other embodiments, the CA principally comprises particles having
a
nominal maximum size between 10 and 14 mm and the SCC mixture has a slump
flow between 350 mm and 750 mm, preferably a slump flow between 550 mm and
650 mm. In other embodiments, the CA principally comprises particles having a
nominal maximum size of 20 mm and the SCC mixture has a slump flow between
350 mm and 650 mm, preferably a slump flow between 450 mm and 550 mm.
[0041] Unexpectedly, research has shown that larger sized CA is
preferred for
minimizing the potential for plastic and drying shrinkage cracking, however,
this
lowers the maximum slump flow which can be achieved while increasing the
potential for segregation. Intermediate sized CA aggregate, e.g. CA particles
having nominal maximum sizes of 10 and 14 mm, is preferred for achieving
higher
slump flows and minimizing segregation.
[0042] The FA may be calcitic (or calcareous) sand, dolomitic sand,
siliceous
sand or other fine material conforming to the requirements of ASTM C33 or CSA
C23.1, or possibly a mixture of two or more thereof. The particular size
distribution
for the FA is 100% passing through a 10 mm sieve and a maximum per cent of 3%
passing through a 150 pm sieve. In some embodiment, synthetic materials, such
as a light weight aggregate, having the same or similar particle size
distribution
may be used instead of or in addition to sand to reduce the density of the
concrete,
when required to reduce load or improve insulating properties. The synthetic
light
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CA 02784424 2012-08-02
weight aggregate may be haydite and/or pelletized blast furnace slag or other
similar material conforming to ASTM C330 or ASTM C332.
[0043] The VFA has a particle size distribution in which 95% to 100%
passes
a 2.5 mm sieve and a minimum of 20% passes a 75 pm sieve. The VFA typically
comprises non-reactive particles. Non-reactive VFA particles less than 75 pm
in
size, such as crushed or ground limestone, granite or quartz are considered
fillers
and are used to substitute a portion of the cementitious components and
increase
the volume of fine particles paste fraction of the concrete. The VFA, in at
least
embodiments, comprises crushed or ground sedimentary aggregate, crushed or
[0044] Preferably, the VFA originates from the crushing, grinding
and/or
washing of coarse aggregate for concrete commonly known as dust-of-fracture
[0045] Research has shown that, unexpectedly, the beneficial
rheological
properties imparted by VFA do not appear to be due to the optimization of
particle
packing when the combined size distributions of cementitious materials, VFA,
sand
and coarse aggregate mixtures are analyzed according to the 0.45 power curve
plot
CA 02784424 2012-08-02
gradation chart) is based on the mathematically combined percent gradation and
has been used to develop uniform gradations for cement mixtures such as
Portland
cement mixtures.
[0046] As illustrated in Figure 2, the 0.45 power curve plot is a
curve plot of
the mathematically combined percent gradation for each sieve on a semi-log
chart
having percent passing on the y-axis and the sieve sizes (in microns) raised
to the
0.45 power on the x-axis. In the 0.45 power curve plot shown in Figure 2, the
sieve sizes include the 1 1/2 in. (37.5 mm), 1 in. (25.0 mm), 3/4 in. (19.0
mm), 1/2 in.
(12.5 mm), 3/8 in. (9.5 mm), No. 4 (4.75 mm), No. 8 (2.36 mm), No. 16 (1.18
mm), No. 30 (600 pm), No. 50 (300 pm), No. 100 (150 pm) and No. 750 (75 pm).
While not shown in Figure 2, data obtained from a seize analysis of the
aggregate
under test is plotted and the corresponding data points are connected. A
maximum
density line is then plotted. As shown in Figure 2, the maximum density line
extends from an origin of the 0.45 power gradation chart to one size larger
than
first sieve to show 90% or less passing. A well-graded aggregate will follow
the
maximum density line closely between the largest sieve and 1.18 mm sieve. The
combined grading should follow the maximum density line 7 % deviation for
each
percent passing. A minor deviation below the maximum density line can be
expected from the 1.18 mm sieve to the 75 pm sieve as a result of fines of the
FA
and VFA.
[0047] Instead of the performance of the SCC mixture following the
0.45
power curve plot as expected, the performance of the SCC mixture is primarily
due
to the amount of fine particles smaller than 75 pm, which typically comprises
all of
the cement, SCMs and fine fractions of the FA and VFA. Particles having a size
less
than 75 pm contribute to the volume of the concrete paste which is principally
comprised of water, cement, SCMs, FA and VFA.
[0048] The total content of VFA particles less than 75 pm in the SCC
mixtures
of the present disclosure ranges from 300 and 500 kg/m3, and preferably
between
300 to 400 kg/m3. This is significantly lower than typical or conventional SCC
mixtures which have a total VFA particle content between 475 and 600 kg/m3 to
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=
= , . = = , .. =
achieve a non-segregating mixture. Conventional SCC mixtures typically use
cementitious materials and ground limestone with an average particle size
between
3 pm and 15 pm as the source of filler to achieve the required volume of fine
particles. Without wishing to be being bound by theory, It Is noted that
particles
greater than 75 pm and less than 2.5 mm, which are considered fine aggregate,
may play a functional role in the SCC mixtures of the present disclosure
because
the total content of particles less than 75 pm is considered insufficient to
provide
the required flow characteristics and resistance to segregation.
[0049] The VFA should have a suitable methylene blue value. The
methylene
blue value is an indicator of the amount and type of clay present in aggregate
and
can therefore be useful In distinguishing between harmful and beneficial
fines. One
example of a methylene blue test is provided the Grace Rapid Clay Test
procedure,
which is described in the Grace Rapid Clay Test Kit, Step-by-Step Procedure,
Version C2, February 2011. In embodiments In which the SCC mixture includes a
plasticizer, the VFA should have a methylene blue value of less than 0.75 mg/g
at 3
minutes, preferably 0.4 mg/g at 3 minutes, to avoid excessive adsorption of
the
plasticizer, such as polycarboxylate ether type high range water reducers.
High
levels of adsorption reduce the concentration of the polycarboxylate
superpiasticizer
and therefore reduce the slump flow of the SCC mixture.
Reinforcement
(0050] The SCC mixtures of the present disclosure may also
include fibers to
at partially replace, or possibly supplement, welded wire mesh as secondary
reinforcement In some embodiments. The fibers provide resistance to impact by
increasing the flexural and tensile strength of the concrete. Reinforcement
increases the amount of energy required to cause rupture and complete failure.
The fibers and other reinforcing materials provide strength when cracks form
in the
concrete. When a crack forms In the concrete, the reinforcing materials bridge
the
void created by the crack and allow the concrete to deform in a ductile
manner.
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[0051] The fibers may be steel, polypropylene, nylon or a
combination
thereof. The fibers and welded wire reinforcement reduce cracking due to
drying
shrinkage. The steel fibers may range in length from 12.5 mm to 50 mm and have
an aspect ratio of 50 to 80. The volume fraction of steel fibers may range
between
0.25% and 3%. Polypropylene fibers may range in length from 25 mm to 40 mm
and have diameters between 0.2 mm to 0.6 mm. An example of polypropylene
fibers suitable for secondary reinforcement in concrete is STRUX 90/40,
manufactured by W. R. Grace & Co. (Connecticut, United States), which has a
length, diameter and aspect ratio of 40 mm, 0.43 mm and 90, respectively.
Fibrillated or monofilament polypropylene fibers having lengths of 6.25 mm to
20
mm and diameters of 15 pm to 40 pm (for the monofilament fibers) may be added
to reduce the potential for plastic shrinkage cracking when the estimated
evaporation rate exceeds 1 kg/m2-hr. An example of a fibrillated polypropylene
fiber suitable for this type of application is the 19 mm "Grace Fiber", and 19
mm
"Grace Microfiber" monofilament fiber manufactured by W. R. Grace & Co.
Admixture/additives
[0052] Any of the admixture types listed in ASTM C494 may be used
in the
SCC mixture of the present disclosure. Chloride and non-chloride based set
accelerators may be used when ambient temperatures are low (e.g., 1 C to 15 C
or
lower) whereas set retarders may be used when temperatures are high (e.g.,
greater than 28 C).
[0053] Preferably, the SCC mixture of the present disclosure
includes a
plasticizer, more preferably a superplasticizer such as polycarboxylate ether
(PCE)
high range water reducer conforming to the requirements of ASTM C 494 Type F
(water reducing, high range). At suitable dosage rates relative to the cement,
the
PCE high range water reducer imparts a very high fluidity to the SCC mixture
for 45
to 75 minutes without causing excessive retardation of hydration or
segregation.
Sulfonated naphthalene or melamine formaldehyde condensate based
superplasticers conforming to ASTM C494 Type F may be used instead of the PCE
high range water reducer with or without a viscosity modifying additive to
obtain a
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CA 02784424 2012-08-02
desired consistency. However, the amount of time available for transportation,
placement and finishing will be significantly less. It is contemplated that
other
superplasticizers or high range water reducers could be used in other
embodiments.
Special Admixtures/Additives
[0054] Viscosity modifiers may be used when required to reduce the
potential
for segregation of the concrete. Viscosity modifiers are particularly useful
with SCC
mixtures having a slump flow is greater than 650 mm and/or SCC mixtures with
larger coarse aggregate, such as 20 mm coarse aggregate. Defoaming admixtures
which de-entrain air from the SCC mixture may be used when required, typically
in
instances when the specific combination of materials results in air contents
greater
than 4%. Although generally unnecessary, shrinkage reducing admixtures (SRA)
may be added to reduce drying shrinkage when lower shrinkage values are
required, or a given combination of materials exhibit greater shrinkage or
placement conditions (e.g., lack of secondary reinforcement, low relative
humidity)
promote shrinkage.
SCC Mixture Properties
[0055] The SCC mixture of the present disclosure, in at least some
embodiments, has a compressive strength of at least 25 MPa at 28 days of age,
typically between 25 MPa and 40 MPa at 28 days of age. However, a compressive
strength of up to 50 to 60 MPa at 28 days of age is also possible for some
embodiments. The SCC mixture forms a surface layer which is sufficiently non-
segregating after an initial setting so as to be capable of finishing with a
power
trowel without significant adhesion of concrete to blades of the power trowel
and
without formation of blisters or delamination of the surface layer.
[0056] The SCC mixture of the present disclosure, in at least some
embodiments, has a slump flow of 500 mm or more and a T50 time of 5 seconds or
less, preferably 4 seconds or less, and more preferably 3 seconds or less.
Testing
of the SCC mixtures has shown T50 times of 1 1/2 to 4 seconds, and more
typically 2
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CA 02784424 2012-08-02
to 3 seconds, have been achieved or projected. It will be appreciated that
such T50
times are lower than conventional SCC mixtures. It was also observed that the
SCC mixture is non-segregating at the slump flow of 500 mm or more at the
specified T50 times.
[0057] The SCC mixture, in at least some embodiments, exhibits a drying
shrinkage of less than 0.06% or less, preferably 0.05% or less, and more
preferably 0.04% or less. This amount of drying shrinkage was observed when
testing cast concrete prisms having dimensions of 100 mm x 100 mm x 250 mm
and exposed to a relative humidity of 50% according to CSA A23.2-21C. Concrete
with drying shrinkage values of less than 0.06% generally have a lower
tendency to
exhibit curling and cracking in concrete applications.
Examples
[0058] Non-limiting examples of SCC mixtures prepared in accordance
with
the present disclosure will now be described. Table 1 describes example
embodiments SCC mixtures which were found to form a surface layer which is
sufficiently non-segregating after an initial setting so as to be capable of
finishing
with a power trowel without significant adhesion of concrete to blades of the
power
trowel and without formation of blisters or delamination of the surface layer
and a
compressive strength of at least 25 MPa at 28 days of age.
CA 02784424 2012-08-02
Table 1: Example SCC Mixtures
Cement Type (CSA) Type 10 Type 10 Type 10 Type 10 Type
10
Basement Basement Basement Basement
Product Type Precast Floor Floor Floor
Floor
Estimated Cost
($/m3) 98.60 88.40 93.40 91.20
90.90
Admixture
(ml/100 kg)
G7700 550 650 645 600
600
PS1390 150 300 150 150
150
VMA362 150 150 150 150
150
Total Cementitious
(kg/m3) 329.1 252.1 276.0 280.0
281.2
Mixture Composition
(kg/m3)
Cement 246.8 189.1 207.0 210.0
210.9
Limestone Filler 0.0 0.0 0.0 0.0
0.0
GGBFS 82.3 63.0 69.0 70.0
70.3
Coarse Aggregate 688.5 795.0 746.1 708.1
705.0
Fine Aggregate 779 922 865 794
789
Very Fine Aggregate 251 274 257 270
271
Water 201.7 162.2 177.4 185.6
192.0
Density (kg/m3) 2252.4 2406.8 2324.0 2240.7
2240.7
Paste Content
(fraction) 0.401 0.300 0.328 0.375
0.381
W/C Ratio 0.62 0.65 0.65 0.67
0.69
Slump Flow (mm) 610 500 580 540
565
T50 (s) n/a n/a 4.3 4.31 3
Appearance (VSI) 0 0 0 0 0
Setting Time (hours)
Initial n/a n/a n/a n/a
n/a
Final n/a n/a n/a n/a
n/a
Compressive Strength MPa) - tested on 100 mm x 200 mnn cast concrete cylinder
1 day 10.9 n/a 11.3 n/a
10.7
7 day 26.9 n/a 28.7 n/a
26.0
28 day 37.9 n/a 40.5 n/a
37.2
56 day 44.6 n/a 45.4 n/a
42.2
[0059]
Figure 4 show properties of example SCC mixtures 2-1, 2-2 and 2-3
prepared in accordance with the present disclosure. As shown in Examples 2-1,
2-2
and 2-3, the SCC mixtures exhibited a compressive strength of at least 25 MPa
at
28 days of age, typically between 25 MPa and 40 MPa at 28 days of age. The SCC
16
CA 02784424 2012-08-02
mixtures in in Examples 2-1, 2-2 and 2-3 included VFA particles as described
above, which exhibited a content of 6, 8, 10 or 12% compared with a moisture
content of 1.75% for 10 mm gravel (coarse aggregate) and 4.0% for sand. The
moisture content of the VFAs may vary in other embodiments.
[0060] Table 2, shown below, describes the range of SCC mixture
compositions which are considered to form a surface layer which is
sufficiently non-
segregating after an initial setting so as to be capable of finishing with a
power
trowel without significant adhesion of concrete to blades of the power trowel
and
without formation of blisters or delamination of the surface layer and a
compressive
strength of at least 25 MPa at 28 days of age.
Table 2: SCC Mixture Compositions
kg/m3 Percent (%)
Component
Minimum Maximum Minimum Maximum
Total cementitious materials 260 375 10.5
16.5
Slag content (%)1 0 50
Fly ash (%)1 0 35
Silica fume (%)1 0 10
Coarse aggregate 700 1130 29 46
Fine Aggregate 481 1010 19.5 42
Very fine aggregate 135 500 5.5 20
water/total cementitious
materials ratio2 0.4 0.8
Polycarboxylic ether3 0.1 0.28
1 % relative total cementitious materials
2 total cementitious materials being comprised of Portland cement, slag fly
ash, silica fume
3 % polycarboxylate solids relative to total cementitious materials
[0061] It will be appreciated that the polycarboxylate ether high
range water
reducer is prepared as an admixture which is added to the SCC mixture during
preparation of the CC mixture. The admixture of the polycarboxylate ether high
range water may vary in concentration. Accordingly, the amount of the
polycarboxylate ether high range water reducer present in the SCC mixture is
quantified herein as a percent of polycarboxylate solids relative to total
cementitious materials in accordance with the convention in the art.
17
CA 02784424 2012-08-02
[0062]
Table 3, shown below, describes a preferred range of SCC mixture
compositions which are considered to form a surface layer which is
sufficiently non-
segregating after an initial setting so as to be capable of finishing with a
power
trowel without significant adhesion of concrete to blades of the power trowel
and
without formation of blisters or delamination of the surface layer and a
compressive
strength of at least 25 MPa at 28 days of age.
Table 3: SCC Mixture Compositions Preferred Ranges
kg/m3 Percent (%)
Component
Minimum Maximum Minimum Maximum
Total cementitious materials 280 335 11.6
13.5
Slag content (%)1 0
50
Fly ash (%)1 0
35
Silica fume (%)1 0
10
Coarse aggregate 900 1120 37
45
Fine Aggregate 481 805 19.5
32.5
Very fine aggregate 270 395 11
16
water/total cementitious
materials ratio2 0.45 0.65
Polycarboxylic ether3 0.1 0.28
1
/ zo
relative total cementitious materials
2 total cementitious materials being comprised of Portland cement, slag fly
ash, silica fume
3 % polycarboxylate solids relative to total cementitious materials
[0063] The present disclosure refers to particle sizes based on a
sieve
analysis. It will be appreciated by persons skilled in the art that seizes are
standardized to have specific aperture opening sizes and that different
standards
having different sieves exist. Figure 3 provides a sieve comparison chart
which
compares various sieves and the respective aperture sizes of the sieve
openings
according to some of the most common standards. Sieves on the same line are
generally considered to be functionally equivalent in some applications;
however, in
some cases sieves on adjacent lines (typically only immediately adjacent
lines) are
considered to be functionally equivalent. For example, the 2.36 mm and 2.5 mm
sieve are functionally equivalent ,the 9.5 mm and 10 mm sieves are
functionally
equivalent, the 13.2 mm and 14 mm sieves are functionally equivalent, and the
19
18
CA 02784424 2013-05-22
. 05/22/2013 WED 17:08 FAX
10014/02
mm and 20 mm sieves are functionally equivalent for the purposes of the SCC
= mixture of the present disclosure.
(0064] The present disclosure may be embodied in other specific
forms
= without departing from the subject matter of the claims. The described
example
embodiments are to be considered In all respects as being only illustrative
and not
restrictive. The scope of protection being sought Is defined by the following
claims
rather than the described embodiments in the foregoing description. The scope
of
the claims should not be limited by the preferred embodiments set forth in the
examples, but should be given the broadest interpretation consistent with the
description as a whole.
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