U.S. patent application number 10/389188 was filed with the patent office on 2003-10-02 for concrete admixture, mortar admixture and blended cement.
This patent application is currently assigned to MOTOYUKI SUZUKI. Invention is credited to Ando, Hisashi, Kasai, Kazuhiro, Kawamura, Toshihiko, Nishiura, Kazuyuki, Suzuki, Motoyuki, Terazawa, Masato.
Application Number | 20030183129 10/389188 |
Document ID | / |
Family ID | 28456271 |
Filed Date | 2003-10-02 |
United States Patent
Application |
20030183129 |
Kind Code |
A1 |
Suzuki, Motoyuki ; et
al. |
October 2, 2003 |
Concrete admixture, mortar admixture and blended cement
Abstract
A concrete admixture or a mortar admixture which is obtained by
mixing a silicate with an acid in the presence of water and then
solidifying the mixture. It is preferable that the silicate is
sodium silicate and the acid is a carboxylic acid. This admixture
can improve a tensile strength of a concrete or a mortar. Since a
concrete or a mortar containing the admixture, cement, an aggregate
and water is high in tensile strength, it can advantageously be
used in various concrete structures, concrete products or mortar
products.
Inventors: |
Suzuki, Motoyuki;
(Sendai-shi, JP) ; Kasai, Kazuhiro; (Chiyoda-ku,
JP) ; Terazawa, Masato; (Chiyoda-ku, JP) ;
Nishiura, Kazuyuki; (Chiyoda-ku, JP) ; Ando,
Hisashi; (Hiroshima-shi, JP) ; Kawamura,
Toshihiko; (Nerima-ku, JP) |
Correspondence
Address: |
Koda & Androlia
2029 Century Park East
Suite 1430
Los Angeles
CA
90067-3024
US
|
Assignee: |
MOTOYUKI SUZUKI
TOBISHIMA CORPORATION
ASTON CO., LTD.
|
Family ID: |
28456271 |
Appl. No.: |
10/389188 |
Filed: |
March 14, 2003 |
Current U.S.
Class: |
106/634 ;
106/608 |
Current CPC
Class: |
C04B 28/02 20130101;
C04B 24/04 20130101; C04B 12/04 20130101; C04B 12/04 20130101; C04B
40/0042 20130101; C04B 20/023 20130101; C04B 40/0042 20130101; C04B
12/04 20130101 |
Class at
Publication: |
106/634 ;
106/608 |
International
Class: |
C04B 012/04 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 26, 2002 |
JP |
2002-086976 |
Aug 29, 2002 |
JP |
2002-251249 |
Claims
What is claimed is:
1. A concrete admixture which is obtained by mixing a silicate with
an acid in the presence of water and then solidifying the
mixture.
2. The concrete admixture as claimed in claim 1, wherein the
silicate is sodium silicate.
3. The concrete admixture as claimed in claim 1, wherein the acid
is a carboxylic acid.
4. The concrete admixture as claimed in claim 1, which is a powder
or granules.
5. A concrete admixture comprising a powder or granules containing
a reaction product of a silicate and an acid.
6. A process for producing a concrete admixture, which comprises
mixing a silicate with an acid in an aqueous solution, and then
removing water from the aqueous solution for solidification.
7. A concrete comprising the concrete admixture as claimed in claim
1, cement, an aggregate and water.
8. A process for constructing a concrete structure, which comprises
placing a fluid concrete comprising cement, an aggregate, the
concrete admixture as claimed in claim 1 and water in a form, and
curing the fluid concrete.
9. The process for constructing the concrete structure as claimed
in claim 8, wherein the concrete admixture is added to a fluid
concrete comprising cement, an aggregate and water, and the blend
is then placed in a form.
10. A process for producing a concrete product, which comprises
placing a fluid concrete comprising cement, an aggregate, the
concrete admixture as claimed in claim 1 and water in a form, and
curing the fluid concrete.
11. The process for producing the concrete product as claimed in
claim 10, wherein the concrete admixture is added to a fluid
concrete comprising cement, an aggregate and water, and the blend
is then placed in a form.
12. A mortar admixture which is obtained by mixing a silicate with
an acid in the presence of water and then solidifying the
mixture.
13. A mortar admixture comprising a powder or granules containing a
reaction product of a silicate and an acid.
14. A process for producing a mortar admixture, which comprises
mixing a silicate with an acid in an aqueous solution, and then
removing water from the aqueous solution for solidification.
15. A mortar comprising the mortar admixture as claimed in claim
12, cement, a fine aggregate and water.
16. A process for producing a mortar product, which comprises
molding a fluid mortar comprising cement, a fine aggregate, the
mortar admixture as claimed in claim 12 and water, and curing the
fluid mortar.
17. Blended cement which is obtained by blending cement with a
powder or granules obtained by mixing a silicate with an acid in
the presence of water and then solidifying the mixture.
18. Blended cement which is obtained by blending cement with a
powder or granules containing a reaction product of a silicate and
an acid.
19. The blended cement as claimed in claim 17, wherein the water
content of the powder or the granules is 10% by weight or less.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a concrete admixture which
is added to a concrete. More specifically, it relates to a concrete
admixture which is obtained by mixing a silicate with an acid in
the presence of water and then solidifying the mixture, a process
for producing the same, a concrete using the concrete admixture, a
process for constructing a concrete structure using the concrete
admixture, and a process for producing a concrete product using the
concrete admixture. Further, it relates to a mortar admixture which
is added to a mortar, a process for producing the same, a mortar
using the mortal admixture, and a process for producing a mortar
product using the mortal admixture. Still further, the invention
relates to blended cement.
[0003] 2. Description of the Related Art
[0004] Since a concrete is high in compressive strength, easy to
mold and less costly, it has so far found wide acceptance in the
construction field. In recent years, since structures in particular
are large-sized and diversified, many studies have been made for
more enhancing a compressive strength of a concrete. In order to
increase a strength of a concrete, for example, a method using
various admixtures has been reported. This is the same with a
mortar.
[0005] JP-A-61-155237 (U.S. Pat. No. 4,892,586) discloses a method
for producing a dam concrete characterized in that an organic acid
and a set accelerating inorganic salt are contained therein. It
describes that a strength can be increased by containing an organic
acid and a set accelerating inorganic salt without the increase in
exothermic heat, and that the method is suited for placing a large
amount of a concrete such as a dam concrete. Examples of the
organic acid used here include various carboxylic acids such as
citric acid and fumaric acid, and examples of the set accelerating
inorganic salt include alkali metal salts such as sodium carbonate
and sodium silicate. In Examples of this document, the improvement
in compressive strength is specifically confirmed.
[0006] JP-A-2001-294461 describes a concrete modifier containing
water glass and a polycarboxylic acid or derivatives thereof. This
concrete modifier is coated on a surface of a concrete after cured
in solution. It is described that deterioration due to
neutralization of a concrete or occurrence of cracks can thereby be
prevented or suppressed.
[0007] The most important mechanical characteristics of a concrete
are that a compressive strength is high while a tensile strength, a
shear strength and a flexural strength are low. In general,
although a compressive strength of a concrete can be increased, a
tensile strength of a concrete is limited. Thus, it is difficult to
increase a tensile strength beyond the limit. Accordingly, in a
site where a concrete structure is constructed, occurrence of
cracks owing to an insufficient tensile strength is a serious
problem.
[0008] Since a concrete is low in tensile strength in comparison to
a compressive strength, the strength designing is performed using
separately a reinforcement against a tensile force upon neglecting
a tensile strength of a concrete for securing a safety. As the
reinforcement, a reinforcing steel and a prestressing steel are
listed. A strength in a whole structure is actually secured upon
using these members. However, since structures are large-sized and
diversified as stated above, an amount of steel used for securing
the strength of the concrete structures is increased, and excessive
bar arrangement is thus unavoidable. In this case, a fluid concrete
is not satisfactorily charged when placed in a form, or a work of
bar arrangement is itself intricate, which leads to the increase in
costs.
[0009] A concrete of which the temperature is increased by heat
generation owing to a hydration reaction after placing is shrunk in
cooling. When both ends of a concrete are confined in shrinking, a
tensile stress is generated, whereby occurrence of cracks is often
induced. It is thus important to increase a tensile strength of a
concrete within a relatively short period of ageing time during
which a hydration reaction proceeds. Further, a concrete
immediately after placing is wet. However, when a concrete is
exposed to air, it is shrunk by drying. To cope with shrinkage by
long-term drying, it is important to increase a tensile strength of
a concrete.
[0010] A method in which a short fiber reinforcement made of
inorganic fibers such as asbestos and glass fibers or synthetic
fibers is used to improve a tensile strength of a concrete has been
known. In this method, however, a fluidity might be impaired, or a
dispersibility of a reinforcement might be insufficient to form
clumps, which leads to the increase in costs. Accordingly, this
method is used only in limited applications.
[0011] In the method described in JP-A-61-155237, a strength is
increased by adding an admixture to a concrete. However, only a
compressive strength is increased, and there is no description on a
tensile strength. In the method described in JP-A-2001-294461, the
modifier is coated on the surface of the cured concrete, and the
deterioration of the concrete such as occurrence of cracks can be
prevented, but a tensile strength is not positively increased.
SUMMARY OF THE INVENTION
[0012] The invention has been made for solving the problems, and it
is to provide an admixture which can improve a tensile strength by
being added to a concrete and a process for producing the same.
Further, it is to provide a concrete using the concrete admixture,
a process for constructing a concrete structure using the same, and
a process for producing a concrete product using the same.
[0013] The problems associated with the concrete are also applied
to a mortar. The invention has been made to solve such problems
too, and it is to provide an admixture which can improve a tensile
strength by being added to a mortar, and a process for producing
the same. Further, it is to provide a mortar using the mortar
admixture, and a process for producing a mortar product using the
same. Still further, the invention is to provide blended cement
which is advantageously used in such a concrete or mortar.
[0014] The foregoing problems are attained by providing a concrete
admixture which is obtained by mixing a silicate with an acid in
the presence of water and then solidifying the mixture. That is,
the concrete admixture of the invention is obtained by mixing a
silicate with an acid in the presence of water and then solidifying
the mixture. The cause that the addition of such an admixture
increases the tensile strength of the cured concrete is not
altogether clarified. However, the following mechanism is
presumed.
[0015] The mechanism of the hydration reaction of cement is
complicated, and has not completely been clarified at present.
However, a typical hydration reaction is represented by, for
example, the following reaction formula (1). The numerical values
in formula (1) are only illustrative, and in an actual reaction,
they are to be understood within certain ranges. Further, compounds
not shown here participate in a hydration reaction.
2(2CaO.SiO.sub.2)+4H.sub.2O.fwdarw.3CaO.2SiO.sub.2.3H.sub.2O+Ca(OH).sub.2
(1)
[0016] Thus, as a result of the hydration reaction, calcium
silicate hydrate [xCaO.SiO.sub.2.yH.sub.2O] (usually, x is a value
of from 1.5 to 2.0, and y is a value in a slightly wider range) and
calcium hydroxide Ca(OH).sub.2 are formed as main hydration
reaction products. Of these, the calcium silicate hydrate is a main
component that usually occupies more than a half volume in portland
cement completely cured. It is deemed that the calcium silicate
hydrate takes a fibrous or network shape and can strongly be bonded
by the van der Waals force. Meanwhile, since calcium hydroxide is a
hexagonal prism crystal having a small surface area, the van der
Waals force is low, and it is liable to tear owing to crystal
orientation, less contributing to a bonding strength.
[0017] A position in a concrete which has the lowest strength and
tends to crack due to a tensile stress is deemed to be a so-called
transition zone formed mainly in an interface between a coarse
aggregate and a mortar. When a concrete is placed in a form, a
water film is formed by bleeding around a large aggregate or a
reinforcement, especially under it, and a transition zone, a region
in which a water content based on cement is high occurs. In this
transition zone, a proportion of calcium hydroxide is higher than
in a mortar portion. This is deemed to be a factor of decreasing a
strength of a transition zone and also a tensile strength of a
concrete.
[0018] It is presumed that the concrete admixture of the invention
helps convert calcium hydroxide present in this transition zone
into strong calcium silicate hydrate by the following reaction.
Formation of calcium silicate hydrate by a reaction of sodium
metasilicate and calcium hydroxide is represented by, for example,
the following reaction formula (2).
2Na.sub.2SiO.sub.3+3Ca(OH).sub.2+2H.sub.2O.fwdarw.3CaO.2SiO.sub.2.3H.sub.2-
O+4NaOH (2)
[0019] The actual chemical reaction in a concrete is not such a
quantitative reaction, and the numerical values in formula (2) have
to be understood in certain ranges as is the case with formula
(1).
[0020] However, when an aqueous solution obtained by mixing a
silicate, an acid and water is added as such to a fluid concrete, a
fluidity of the concrete is decreased, and the concrete is hardly
placed in a form. This is presumably because the reaction of
formula (2) proceeds too rapidly in a concrete.
[0021] With respect to the concrete admixture of the invention, it
is presumed that while the fluidity of the concrete is maintained
in placing, the reaction of formula (2) can proceed in the
transition zone in curing after placing. It is further presumed
that when the admixture obtained by mixing a silicate with an acid
in the presence of water and then solidifying the mixture is added
to the concrete, the fluidity of the concrete is not impaired and
the hydration reaction of formula (2) then proceeds, with the
result that the silicate component can be fed to the transition
zone.
[0022] In fact, the present inventors have confirmed that an
admixture obtained by mixing a silicate with an acid in the
presence of water and then drying the mixture for solidification
is, unlike an admixture obtained by only drying a silicate for
solidification, much decreased in water solubility showing a
behavior of slow dissolution in water over a long period of time.
It is presumed that since silicic acid such as orthosilicic acid or
metasilicic acid is a very weak acid, an acid-base reaction
(neutralization reaction) proceeds in which a weak acid (silicic
acid) is liberated through a reaction with a stronger acid (for
example, a carboxylic acid) to form a stronger acid salt.
[0023] The problems of the invention are solved by the concrete
admixture obtained by mixing the silicate with the acid in the
presence of water and then solidifying the mixture through the
above-presumed mechanism. In the concrete admixture of the
invention, the silicate is preferably sodium silicate, and the acid
is preferably a carboxylic acid. The concrete admixture is
preferably a powder or granules. The problems of the invention are
solved by providing a concrete admixture including a powder or
granules containing a reaction product of a silicate and an
acid.
[0024] The problems of the invention are also solved by providing a
process for producing a concrete admixture, which includes mixing a
silicate with an acid in an aqueous solution, and then removing
water from the aqueous solution for solidification.
[0025] A preferred embodiment of the invention is a concrete
including the concrete admixture, cement, an aggregate and water. A
process for constructing a concrete structure, which includes
placing a fluid concrete containing cement, an aggregate, the
concrete admixture and water in a form, and curing the fluid
concrete is also a preferred embodiment of the invention. At this
time, it is preferable that the concrete admixture is added to a
fluid concrete containing cement, an aggregate and water and the
blend is then placed in a form. Further, a process for producing a
concrete product, which includes placing a fluid concrete
containing cement, an aggregate, the concrete admixture and water
in a form, and curing the fluid concrete is also a preferred
embodiment. At this time as well, it is preferable that the
concrete admixture is added to a fluid concrete containing cement,
an aggregate and water and the blend is then placed in a form.
[0026] The foregoing problems are also attained by providing a
mortar admixture which is obtained by mixing a silicate with an
acid in the presence of water and then solidifying the mixture, as
well as a mortar admixture including a powder or granules
containing a reaction product of a silicate and an acid. Further,
the problems are attained by providing a process for producing a
mortar admixture, which includes mixing a silicate with an acid in
an aqueous solution, and then removing water from the aqueous
solution for solidification. A preferred embodiment of the
invention is a mortar including the mortar admixture, cement, a
fine aggregate and water. A process for producing a mortar product,
which includes forming a fluid mortar containing cement, a fine
aggregate, the mortar admixture and water, and curing the blend is
also a preferred embodiment of the invention.
[0027] Moreover, the problems are attained by providing blended
cement which is obtained by blending cement with a powder or
granules obtained by mixing a silicate with an acid in the presence
of water and then solidifying the mixture, as well as blended
cement which is obtained by blending cement with a powder or
granules containing a reaction product of a silicate and an acid.
At this time, it is preferable that the water content of the powder
or the granules is 10% by weight or less.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a graph showing a pore size distribution of a
concrete in Example 4;
[0029] FIG. 2 is a graph showing a pore size distribution of a
concrete in Comparative Example 1;
[0030] FIG. 3 is a photo of a broken surface of the concrete in
Example 4;
[0031] FIG. 4 is a photo of a broken surface of the concrete in
Comparative Example 1;
[0032] FIG. 5 is a graph showing a change in split tensile strength
with time;
[0033] FIG. 6 is a graph showing a change in compressive strength
with time; and
[0034] FIG. 7 is a graph showing a relation of a compressive
strength and a split tensile strength.
PREFERRED EMBODIMENTS OF THE INVENTION
[0035] The concrete admixture of the invention is obtained by
mixing a silicate with an acid in the presence of water and then
solidifying the mixture.
[0036] The silicate used in the invention is not particularly
limited. Its cationic species may be not only a metal ion but also
an ammonium ion, and the metal ion is preferable. With respect to
the metal ion, an alkali metal ion is preferable. A sodium ion is
more preferable in view of easy procurement of a starting material
and cost. An anionic species of the silicate used in the invention
is not particularly limited. It may be not only an anionic species
such as orthosilicate anion [SiO.sub.4.sup.4-] or metasilicate
anion [SiO.sub.3.sup.2-] but also an anionic species in which
plural silicate [SiO.sub.2] units are bound.
[0037] Specific examples of the compound include sodium
orthosilicate, potassium orthosilicate, lithium orthosilicate,
sodium metasilicate, potassium metasilicate, lithium metasilicate
and water glass.
[0038] Of these, water glass is preferably used in the invention.
Water glass is an aqueous solution of an alkali metal silicate in
which plural silicate [SiO.sub.2] units are bound to form an
anionic species. The alkali metal used here is usually sodium, and
potassium is also available. Sodium silicate as a solid content is
represented by the formula Na.sub.2O.nSiO.sub.2.
[0039] A ratio of a metal atom to a silicon atom [metal/silicon] in
the silicate is preferably from 0.1 to 2. When the [metal/silicon]
ratio is less than 0.1, the water solubility is reduced, and the
silicate might be less mixed with a carboxylic acid in the presence
of water. It is more preferably 0.2 or more, further preferably 0.3
or more. When the [metal/silicon] ratio exceeds 2, the water
solubility of the silicate is too high, which might worsen the
fluidity of the concrete. It is more preferably 1.5 or less,
further preferably 1 or less.
[0040] The type of the acid mixed with the silicate in the
invention is not particularly limited. It may be an inorganic acid
such as sulfuric acid or phosphoric acid, or an organic acid such
as a carboxylic acid. Of these, a carboxylic acid is preferably
used. The carboxylic acid used is not particularly limited.
Examples thereof can include monocarboxylic acids such as formic
acid, acetic acid and propionic acid; oxymonocarboxylic acids such
as glycolic acid, lactic acid and gluconic acid; polycarboxylic
acids such as oxalic acid, malonic acid, succinic acid, pimelic
acid, adipic acid, glutaric acid, maleic acid, fumaric acid,
phthalic acid and terephthalic acid; hydroxypolycarboxylic acids
such as malic acid and citric acid; and polycarboxylic acid
polymers such as an acrylic acid polymer and a maleic anhydride
polymer. Of these, oxycarboxylic acids and polycarboxylic acids
which are low in volatility and good in water solubility are
preferable, and polycarboxylic acids are more preferable.
Unsaturated polycarboxylic acids such as maleic acid and fumaric
acid are also preferable.
[0041] When a metal silicate and a carboxylic acid are used in the
concrete admixture of the invention, a ratio of a metal atom of the
silicate to a carboxyl group of the carboxylic acid [metal/carboxyl
group] is preferably from 1 to 200. When the [metal/carboxyl group]
ratio is less than 1, the silicic acid component is insoluble in
water, and an insoluble matter might be generated in mixing the
silicate with the carboxylic acid in the presence of water, making
it impossible to uniformly mix them. It is more preferably 2 or
more, further preferably 5 or more, most preferably 10 or more.
Meanwhile, when the [metal/carboxyl group] ratio exceeds 200, the
water solubility of the silicate is too high, which might decrease
the fluidity of the concrete. It is more preferably 100 or less,
further preferably 50 or less.
[0042] The concrete admixture of the invention is produced by
mixing the silicate with the acid in the presence of water as
stated above. It is presumed that by the mixing in the presence of
water, a neutralization reaction (salt formation) can proceed
between the cationic species constituting the silicate and the acid
to properly decrease the water solubility of the silicate. The
amount of water present in the mixing is preferably 1 part by
weight or more, more preferably 10 parts by weight or more, further
preferably 100 parts by weight or more per 100 parts by weight in
total of the silicate and the acid. The mixing method is not
particularly limited so long as these components are mixed in a
fluid state. A method in which the silicate and the acid are mixed
with stirring in the state of an aqueous solution is preferable.
For example, a method in which a carboxylic acid or its aqueous
solution is added to water glass and the mixture is stirred is
mentioned. For facilitating the stirring, it is advisable that they
are mixed at elevated temperature.
[0043] The concrete admixture of the invention is produced by
mixing the components as stated above and then solidifying the
mixture. The mixture may be solidified by removing water or by
cooling. A method in which, after mixing the silicate with the
acid, water is removed from an aqueous solution for solidification
is preferable. A method for removing water is not particularly
limited. Water may be volatilized by allowing the aqueous solution
to stand at room temperature or by heating it. After removing
water, the water content is preferably 50% by weight or less, more
preferably 40% by weight or less, further preferably 30% by weight
or less. The concrete admixture of the invention, even in the solid
state, contains a considerable amount of water therein. As will be
later described, when producing blended cement in which the
concrete admixture has been incorporated, it is preferable that the
water content is further reduced. The water content here referred
to is a value measured by the method described in JIS
K0101-16.2.
[0044] The concrete admixture of the invention is a concrete
admixture comprising a powder or granules containing the reaction
product of the silicate and the acid. The reaction product here
referred to is a product obtained by an acid-base reaction
(neutralization reaction) in which a weak acid (silicic acid) is
liberated to form a stronger acid salt. The concrete admixture
containing such a reaction product in the invention can bring forth
the effects of the invention. As stated above, it is preferable
that the concrete admixture is produced by mixing the silicate with
the acid in the presence of water and then solidifying the mixture.
However, the concrete admixture produced by this method is not
critical, and a concrete admixture finally containing the reaction
product is also available. A powder or granules containing such a
reaction product can be used as a mortar admixture or a raw
material of blended cement to be described later.
[0045] The concrete admixture of the invention is preferably a
powder or granules. A method for forming a powder or granules is
not particularly limited. It includes a method in which the product
is solidified and then pulverized, and a method in which droplets
are solidified. Further, a powder or granules may be formed during
solidification. In case of the powder or the granules, the particle
size is not particularly limited. However, it is advisable that
fine particles having a particle size of, for example, less than
100 .mu.m, are not used as main particles. Meanwhile, it is
advisable that coarse particles having a particle size of, for
example, more than 10 mm, are not used as main particles.
[0046] When the particle size is too small, the fluidity of the
concrete might be decreased in adding the concrete admixture of the
invention to the concrete. Meanwhile, when the particle size is too
large, the cured concrete might be nonuniform. Further, when the
particle size is too small or too large, the tensile strength tends
to be less improved. The tensile strength is greatly improved by
using particles having an appropriate particle size. Although the
reason is not clear, it is presumed that with an appropriate
particle size, the silicate component can properly be fed to the
transition zone when the hydration reaction proceeds well after
placing the concrete.
[0047] Preferable particle size varies with a chemical composition
or a water content of the concrete admixture or a method in which
the concrete admixture is added to the concrete. Thus, it has to be
properly adjusted. It is advisable that an amount of particles
having a small particle size is not too large. For example, the
amount of particles which are not passed through a 1.25 mm-mesh
sieve is preferably 50% by weight or more, more preferably 80% by
weight or more. Meanwhile, it is advisable that an amount of
particles having a large particle size is not too large. For
example, the amount of particles which are passed through a 2.5
mm-mesh sieve is 50% by weight or more, more preferably 80% by
weight or more. By the way, the size of the mesh is as defined in
JIS Z8801.
[0048] The concrete obtained in the invention comprises cement, an
aggregate, water and the concrete admixture. The concrete here
referred to includes both a fluid concrete (fresh concrete) before
placing and a cured concrete after placing.
[0049] Cement used at this time may be hydraulic cement containing
calcium silicate, and portland cement and blast furnace cement can
be used.
[0050] The concrete of the invention contains the aggregate. As
noted above, it is presumed that the concrete admixture of the
invention improves a bonding strength mainly in the transition zone
which is an interface between the coarse aggregate and the mortar.
Accordingly, it is significant that the concrete admixture is added
to the concrete containing the aggregate. The aggregate used is not
particularly limited. An aggregate obtained from natural minerals,
an aggregate using a blast-furnace slag, a fly ash or a waste
concrete as a raw material, and an artificial aggregate can be
used. The amount of the aggregate is preferably from 300 to 1,200
parts by weight, more preferably from 500 to 800 parts by weight
per 100 parts by weight of cement.
[0051] The size of the aggregate is not particularly limited. A
fine aggregate and a coarse aggregate may be used either singly or
in combination. The fine aggregate is passed through a 5 mm-mesh
sieve, and usually remains on a 75 .mu.m-mesh sieve. The coarse
aggregate remains on a 5 mm-mesh sieve, and its size is usually up
to approximately 200 mm. The larger the size of the aggregate, the
more the transition zone tends to be formed therearound.
Accordingly, the concrete admixture of the invention is used quite
advantageously in the concrete containing the coarse aggregate. The
amount of the coarse aggregate is preferably from 100 to 800 parts
by weight, more preferably from 150 to 500 parts by weight per 100
parts by weight of cement. It is preferable to contain the fine
aggregate in addition to the coarse aggregate. The amount of the
fine aggregate is preferably from 100 to 800 parts by weight, more
preferably from 150 to 500 parts by weight per 100 parts by weight
of cement.
[0052] The amount of water incorporated in the concrete of the
invention is preferably from 20 to 75 parts by weight, more
preferably from 30 to 60 parts by weight per 100 parts by weight of
cement.
[0053] The concrete of the invention contains the concrete
admixture in addition to cement, an aggregate and water. The amount
of the concrete admixture is preferably from 0.1 to 20 parts by
weight per 100 parts by weight of cement. When the amount is less
than 0.1 part by weight, the tensile strength might be less
improved. The amount is more preferably 0.5 part by weight or more,
further preferably 1 part by weight or more. When the amount
exceeds 20 parts by weight, the fluidity of a concrete might be
decreased, and the tensile strength might be rather less improved.
The amount is more preferably 10 parts by weight or less, further
preferably 5 parts by weight or less.
[0054] The concrete may contain components other than the foregoing
components unless the effects of the invention are impaired. Known
additives such as a water reducing agent, an air entraining agent,
a superplasticizer and a setting retarder can be incorporated
according to applications and properties required. In some
applications, it is advisable to incorporate a short fiber
reinforcement made of inorganic fibers such as asbestos and glass
fibers or synthetic fibers.
[0055] A process for producing the concrete of the invention is not
particularly limited. The foregoing materials may be simultaneously
blended and kneaded, or successively added and blended. For
example, the concrete may be produced by kneading the materials at
once in a ready mixed concrete plant. However, for keeping good a
fluid state before placing, it is preferable that the concrete
admixture of the invention is added to a fluid concrete comprising
cement, an aggregate and water. This makes it possible to improve
the tensile strength of the cured concrete while keeping good the
fluidity of the concrete in placing. Specifically, a method in
which a ready mixed concrete produced in a ready mixed concrete
plant is transported to a site with a truck mixer and the concrete
admixture of the invention is charged into the mixer in the site
and placed soon after kneaded is preferable. It is also possible
that, as will be later described, blended cement which is obtained
by blending cement with a powder or granules obtained by mixing a
silicate with an acid in the presence of water and then solidifying
the mixture is used as a raw material and an aggregate and water
are added thereto.
[0056] The thus-obtained concrete of the invention is placed in a
form in a fluid state, and cured. Since the cured concrete is
increased in tensile strength, the amount of reinforcing steel used
can be reduced in comparison to ordinary concrete structures.
Meanwhile, when the concrete is placed in a form with steel
arranged, especially in a form with steel intricately arranged, the
invention can be practiced quite advantageously. The reason is that
brittle portions that occur under a reinforcement due to bleeding
can be reinforced by adding the concrete admixture of the
invention.
[0057] The concrete of the invention can be used to construct
various structures. Since the concrete structures using the
concrete of the invention are high in tensile strength, they are
effectively used in members in which a tensile stress tends to be
generated due to an external force or a thermal stress or members
which tend to be influenced by fatigue. Further, the concrete of
the invention is effectively used to construct structures with
complicated shapes. It can specifically be applied to road and
railway installations such as pavements, piers and tunnels, port
installations, airport installations, river and shore installations
such as retaining walls and banks, energy plants such as a nuclear
power plant and a thermal power generation plant, water treatment
installations such as dams and channels, and general buildings.
[0058] The concrete of the invention can be used to produce various
concrete products (concrete secondary products). In this case,
concrete products of the same shape can be mass-produced in a
factory. The concrete of the invention is placed in a form, and
then cured to produce a concrete product. Since concrete products
can be produced in a factory, various moldings such as extrusion
molding, press molding, pressure molding, vibration molding, roller
molding and centrifugal molding can be employed. The concrete
products using the concrete of the invention are, because of the
high tensile strength, useful as products susceptible to a tensile
stress due to an external force or a thermal stress or as products
which tend to be influenced by fatigue. Further, they are useful as
products with complicated shapes or thin products. Specific
examples of the concrete products include blocks, pipes, columns,
piles, retaining walls and gutters.
[0059] Such are the concrete admixture, the process for producing
the same and the applications thereof. The mortar admixture is
described below. A mortar is a concrete without a coarse aggregate,
and cement, a fine aggregate (sand) and water are commonly used as
its main raw materials.
[0060] The mortar admixture of the invention is obtained by mixing
a silicate with an acid in the presence of water and then
solidifying the mixture. As the components constituting the mortar
admixture of the invention, the components constituting the
concrete admixture of the invention can be used.
[0061] The mortar obtained in the invention comprises cement, the
fine aggregate, water and the mortar admixture. The mortar here
referred to includes both of a fluid mortar before curing and a
cured mortar. As the cement used here, the cement used in the
concrete is available.
[0062] The mortar of the invention contains the fine aggregate, but
not the coarse aggregate. In the concrete admixture of the
invention, as stated above, the tensile strength seems likely to be
improved by improving the bonding strength in the transition zone
which is the interface between the coarse aggregate and the mortar.
Since the tensile strength is improved in the mortar of the
invention, the bonding strength seems likely to be improved also in
the interface between the fine aggregate and the cement paste.
[0063] The fine aggregate is passed through a 5 mm-mesh sieve, and
usually remains on a 75 .mu.m-mesh sieve. The fine aggregate used
in the mortar of the invention is not particularly limited. A fine
aggregate obtained from natural minerals such as sand, a fine
aggregate using a blast furnace slag, a fly ash or a waste concrete
as a raw material, and an artificial aggregate can be used. The
amount of the fine aggregate is preferably from 100 to 800 parts by
weight, more preferably from 150 to 500 parts by weight per 100
parts by weight of cement.
[0064] The amount of water incorporated in the mortar of the
invention is preferably from 20 to 75 parts by weight, more
preferably from 30 to 60 parts by weight per 100 parts by weight of
cement. The amount of the mortar admixture added to the mortar of
the invention is preferably from 0.1 to 20 parts by weight per 100
parts by weight of cement. When the amount is less than 0.1 part by
weight, the tensile strength might be less improved. The amount is
more preferably 0.5 part by weight or more, further preferably 1
part by weight or more. When the amount exceeds 20 parts by weight,
the fluidity of the mortar before curing might be decreased, and
the tensile strength might be rather less improved. The amount is
more preferably 10 parts by weight or less, further preferably 5
parts by weight or less.
[0065] The mortar may contain components other than the foregoing
components unless the effects of the invention are impaired. Known
additives such as a water reducing agent, an air entraining agent,
a superplasticizer, a setting retarder, an expansive admixture and
a set accelerating agent can be incorporated according to
applications and properties required. In some applications, it is
advisable to incorporate a short fiber reinforcement made of
inorganic fibers such as asbestos and glass fibers or synthetic
fibers.
[0066] A process for producing the mortar of the invention is not
particularly limited. The foregoing materials may be simultaneously
blended and kneaded, or successively added and blended. Further, as
will be later described, it is also possible that blended cement
which is obtained by blending cement with a powder or granules
obtained by mixing a silicate with an acid in the presence of water
and then solidifying the mixture is used as a raw material and the
fine aggregate and water are added thereto.
[0067] The thus-obtained fluid mortar is molded and then cured to
produce a mortar product. The molding method is not particularly
limited. The mortar may be poured into a form and then cured, or
various moldings such as extrusion molding, press molding, pressure
molding, vibration molding, roller molding and centrifugal molding
can be employed. Further, the fluid mortar can be sprayed or
trowelled onto a base member.
[0068] Since the mortar products using the mortar of the invention
are high in tensile strength, they are useful as products which are
susceptible to a tensile stress due to an external force or a
thermal stress or products which tend to be influenced by fatigue.
Further, the mortar products are also useful as products with
complicated shapes or thin products. Specific examples of the
mortar products include blocks, pipes, retaining walls, curbs,
gutters and forms.
[0069] Such are the concrete admixture and the mortar admixture.
The blended cement which is the other embodiment of the invention
is described below. The blended cement of the invention is obtained
by blending cement with a powder or granules obtained by mixing a
silicate with an acid in the presence of water and then solidifying
the mixture.
[0070] As the powder or the granules used in the blended cement of
the invention, the powder or the granules used as the foregoing
concrete admixture or mortar admixture are used. However, since
blocking or weathering of cement has to be prevented over a long
period of time in a state where the powder or the granules are
blended with cement, it is advisable that the water content is low.
The water content is preferably 20% by weight or less, more
preferably 10% by weight or less, further more preferably 5% by
weight or less, most preferably 1% by weight or less.
[0071] In the invention, the amount of the powder or the granules
based on cement in the blended cement is preferably from 0.1 to 20
parts by weight per 100 parts by weight of cement. When it is less
than 0.1 part by weight, the tensile strength might be less
improved. The amount is more preferably 0.5 part by weight or more,
further preferably 1 part by weight or more. When the amount
exceeds 20 parts by weight, the fluidity of the concrete or the
mortar before curing might be decreased, and the tensile strength
might be rather less improved. The amount is more preferably 10
parts by weight or less, further preferably 5 parts by weight or
less. As the cement used here, the cement used in the foregoing
concrete or mortar is available.
[0072] This blended cement can advantageously be used as a raw
material of a concrete or a mortar. Since the cement contains an
appropriate amount of the powder or the granules in advance, it can
be used, like ordinary cements, only by being kneaded with water,
the aggregate and the like, and the procedure of blending raw
materials is easy. Further, the blended cement can be distributed
in the same manner as ordinary cements, and a concrete or a mortar
improved in tensile strength can easily be produced in a building
site or a factory.
EXAMPLES
[0073] The invention is illustrated more specifically below by
referring to Examples and Comparative Examples.
Example 1
Production of Admixtures A and B
[0074] 120 g of fumaric acid was charged into a vessel filled with
15 kg of water held at 60.degree. C., and dissolved with stirring.
Then, while stirring was continued, 25 kg of water glass ("JIS No.
3 Sodium Silicate", made by Toso Sangyo K.K.) was added. At this
time, a viscosity was much increased temporarily in a portion to
which the water glass was added, but the whole solution was
homogenized with stirring. This procedure was repeated, and a
wholly uniform aqueous solution free from an insoluble matter was
prepared by adding the total amount of the water glass.
[0075] The water glass used here contained from 9 to 10% by weight
of sodium oxide (Na.sub.2O: MW=61.98) and from 28 to 30% by weight
of silicon dioxide (SiO.sub.2: MW=60.09). Assuming the water glass
contained 9.5% by weight of sodium oxide and 29% by weight of
silicon dioxide upon employing the intermediate values, a
[metal/silicon] ratio was 0.64. Further, a [metal/carboxyl group]
ratio (ratio of a sodium atom to a carboxyl group of fumaric acid
(C.sub.4H.sub.4O.sub.4: MW=116.07) as a dibasic acid) was 37.
[0076] The resulting aqueous solution was poured on a plastic tray
to a thickness of 5 mm, and allowed to stand at room temperature
for 3 days to evaporate water for solidification. The resulting
solidified product was a hydrous gel having a slight flexibility.
This solidified product was charged on a 2.5 mm-mesh sieve, and
extruded through openings of the sieve with a rod. The extruded
particles were spread on a plastic sheet, and dried by blowing hot
air of 50.degree. C. with a fan for 24 hours. After the drying,
particles slightly stuck to one another were separated, and then
applied to a 2.5 mm-mesh sieve. The particles passed through the
sieve were designated admixture A used in this Example, and the
particles remaining on the sieve were designated admixture B used
in this Example. When admixture A was applied to a 1.25 mm-mesh
sieve, approximately 10% by weight thereof was passed through the
sieve, and approximately 90% by weight thereof remained on the
sieve. Admixture B contained particles having the maximum particle
size of 7 mm.
[0077] The water content of the thus-obtained admixtures A and B
was measured according to JIS K0101-16.2, and found to be 25.5% by
weight. Since these admixtures A and B had a moisture absorption,
they were stored in a polyethylene bag with a drying agent. They
were withdrawn and used whenever they were blended with a ready
mixed concrete or with a fine aggregate and sand to produce a
mortar.
Example 2
Production of Admixture C
[0078] An aqueous solution was prepared in the same manner as in
Example 1 except that 1,440 g of citric acid was used instead of
120 g of fumaric acid. A [metal/carboxyl group] ratio of a sodium
atom to a carboxyl group of citric acid (C.sub.6H.sub.8O.sub.7:
MW=192.13) as a tribasic acid was 3.4.
[0079] The resulting aqueous solution was solidified and dried as
in Example 1. After the drying, particles slightly stuck to one
another were separated, and then applied to a 2.5 mm-mesh sieve,
and particles passed through the sieve were designated admixture C.
When admixture C was applied to a 1.25 mm-mesh sieve, approximately
10% by weight thereof was passed through the sieve, and
approximately 90% by weight thereof remained on the sieve. The
water content of the thus-obtained admixture C was measured
according to JIS K0101-16.2, and found to be 30% by weight. Since
admixture C had a moisture absorption, it was stored and used as in
Example 1.
Example 3
Production of Admixture D
[0080] Admixture A produced in Example 1 was charged on a frying
pan, and heated on a gas heater. Since water in the admixture was
evaporated by the heating, the admixture particles were swollen.
However, 5 minutes later, the swelling was no longer observed, and
the heating was completed. After cooling, particles slightly stuck
to one another were separated, and then applied to a 2.5 mm-mesh
sieve. The particles passed through the sieve were designated
admixture D used in this Example. When admixture D was applied to a
1.25 mm-mesh sieve, approximately 10% by weight thereof was passed
through the sieve, and approximately 90% by weight thereof remained
on the sieve. The water content of the thus-obtained admixture D
was measured according to JIS K0101-16.2, and found to be 0% by
weight. Since admixture D had a moisture absorption, it was stored
and used as in Example 1. Thus, admixture D does not contain water.
Accordingly, even when cement is previously blended with the
admixture, it can be stored for a long period of time without
blocking or weathering, and distributed as blended cement.
Example 4
Production and Evaluation of a Concrete Containing Admixture A
[0081] For a ready mixed concrete used as a base concrete, the
following raw materials were used.
[0082] 1) Cement
[0083] normal portland cement made by Ube Industries Ltd., density
3.16 g/cm.sup.3, sodium content (calculated as Na.sub.2O) 0.68% by
weight
[0084] 2) Coarse aggregate
[0085] crushed stone (2005) from Kuzuu, particle size from 5 to 20
mm, solid volume percentage 60.0%, surface-dry condition density
2.70 g/cm.sup.3, water absorption 0.89% by weight
[0086] 3) Fine aggregate 1
[0087] crushed sand from Kuzuu, particle size 5 mm or less,
fineness modulus 3.20, surface-dry condition density 2.63
g/cm.sup.3, water absorption 1.22% by weight
[0088] 4) Fine aggregate 2
[0089] soil sand from Sawara, particle size 1.2 mm, fineness
modulus 1.80, surface-dry condition density 2.58 g/cm.sup.3, water
absorption 2.16% by weight
[0090] 5) Air entraining and water reducing agent
[0091] "Darlex WRDA" made by Grace Chemicals Co., Ltd.
[0092] The proportions of the foregoing components are as follows.
The parenthesized values are amounts per 100 parts by weight of
cement. A slump of this base concrete is 8 cm.
1 cement 283 kg/m.sup.3 (100 parts by weight) water 162 kg/m.sup.3
(57 parts by weight) coarse aggregate 1,058 kg/m.sup.3 (374 parts
by weight) fine aggregate 1 491 kg/m.sup.3 (173 parts by weight)
fine aggregate 2 321 kg/m.sup.3 (113 parts by weight) air
entraining agent 1.698 kg/m.sup.3 (0.6 part by weight)
[0093] 2.5 parts by weight, per 100 parts by weight of cement, of
admixture A obtained in Example 1 was added to the base concrete.
After the blend was stirred with a forced action mixer for 30
seconds, the resulting blend was poured in a cylindrical form
having a diameter of 100 mm and a height of 200 mm to form a
concrete sample. Plural such samples were produced, and cured in
air of 20.degree. C. In this Example 4 and Examples 5 and 6 and
Comparative Example 1 to be described later, samples were produced
on the same date using the same base concrete, and cured under the
same atmosphere.
[0094] The samples aged 7 days, 28 days and 91 days were subjected
to tests for measuring strengths. A compressive strength and a
split tensile strength were measured according to JIS A1108-1999
and JIS A1113-1999 respectively. At this time, three samples were
used in each test (n=3), and the average value thereof was
obtained. The resulting tensile strength, compressive strength and
a are all shown in Table 1. In this table, a is a value shown in
the following formula (3), indicating a correlation of a tensile
strength and a compressive strength.
(Tensile strength)=.alpha..times.(compressive strength).sup.2/3
(3)
[0095] The sample aged 28 days was measured for a secant modulus of
elasticity in compression with a compressometer according to
JSCE-G502-1999. The secant modulus of elasticity was approximately
30,000 N/mm.sup.2, and a strain was approximately 0.002 when a
compressive stress reached a maximum value. Further, the sample
aged 91 days was cut out, and measured for a pore size distribution
with a porosimeter. The results are shown in FIG. 1. A photo of a
broken surface of the sample aged 28 days and broken in the split
tensile strength test is shown in FIG. 3.
Example 5
Production and Evaluation of an Admixture B-Containing Concrete
[0096] Concrete samples were produced in the same manner as in
Example 4 except that 2.5 parts by weight of admixture B obtained
in Example 1 was used instead of 2.5 parts by weight of admixture
A. Samples aged 7 days and 28 days were subjected to the same tests
for measuring strengths as in Example 4. The resulting tensile
strength, compressive strength and .alpha. are all shown in Table
1. The sample aged 28 days was measured for a secant modulus of
elasticity in compression as in Example 4. The secant modulus of
elasticity was approximately 29,000 N/mm.sup.2, and a strain was
approximately 0.002 when a compressive stress reached a maximum
value.
Example 6
Production and Evaluation of a Concrete Containing Admixtures A and
B
[0097] Concrete samples were produced in the same manner as in
Example 4 except that 2.5 parts by weight of admixture A and 2.5
parts by weight of admixture B (5 parts by weight in total of
admixtures) obtained in Example 1 were used instead of 2.5 parts by
weight of admixture A. The samples aged 7 days and 28 days were
subjected to the same tests for measuring strengths as in Example
4. The resulting tensile strength, compressive strength and .alpha.
are all shown in Table 1.
Comparative Example 1
Production and Evaluation of a Concrete Without Admixture
[0098] Concrete samples were produced by pouring the base concrete
alone in the form without using admixture A in Example 4, and then
cured as in Example 4. The samples aged 7 days, 28 days and 91 days
were subjected to the same tests for measuring strengths as in
Example 4. The resulting tensile strength, compressive strength and
.alpha. are all shown in Table 1. The sample aged 28 days was
measured for a secant modulus of elasticity in compression as in
Example 4. The secant modulus of elasticity was approximately
26,000 N/mm.sup.2, and a strain was approximately 0.002 when a
compressive stress reached a maximum value. Further, the sample
aged 91 days was cut out, and measured for a pore size distribution
with a porosimeter. The results are shown in FIG. 2. A photo of a
broken surface of the sample aged 28 days and broken in the split
tensile strength test is shown in FIG. 4.
Comparative Example 2
Production of a Concrete Containing an Aqueous Solution Before
Solidification
[0099] A fumaric acid aqueous solution and water glass were mixed,
and dissolved with stirring as in Example 1. The thus-obtained
aqueous solution was added to the base concrete used in Example 4
without being solidified. The amount of the aqueous solution added
was 5 parts by weight per 100 parts by weight of cement.
Consequently, the fluidity of the concrete was extremely decreased
immediately after the addition, and it was difficult to pour the
concrete in the form.
2 TABLE 1 Compressive Tensile strength strength .alpha.*.sup.1)
(N/mm.sup.2) Ratio*.sup.2) (N/mm.sup.2) Ratio*.sup.2) Ratio*.sup.2)
aged 7 days Comp. Ex. 1 1.54 1.00 19.57 1.00 0.21 1.00 Ex. 4 2.44
1.58 24.34 1.24 0.29 1.38 Ex. 5 2.42 1.58 22.09 1.13 0.31 1.48 Ex.
6 2.13 1.39 24.45 1.25 0.25 1.19 aged 28 days Comp. Ex. 1 2.32 1.00
30.09 1.00 0.24 1.00 Ex. 4 3.22 1.39 33.15 1.10 0.31 1.30 Ex. 5
2.91 1.26 31.87 1.06 0.29 1.21 Ex. 6 2.44 1.05 26.74 0.89 0.27 1.14
aged 91 days Comp. Ex. 1 2.54 1.00 32.31 1.00 0.25 1.00 Ex. 4 3.52
1.39 36.13 1.12 0.32 1.28 Comp. Ex. 1 Absence of an admixture Ex. 4
2.5 parts by weight of admixture A was added. Ex. 5 2.5 parts by
weight of admixture B was added. Ex. 6 Admixtures A and B were
added in an amount of 2.5 parts by weight each. *.sup.1)Tensile
strength = .alpha. .times. (compressive strength).sup.2/3
*.sup.2)Ratio when the value in Comparative Example 1 was defined
as 1.00.
[0100] Analysis of Results in Examples 4 to 6 and Comparative
Example 1
[0101] The change in split tensile strength with time and the
change in compressive strength with time on the concretes obtained
in Examples 4 to 6 and Comparative Example 1 are shown in FIGS. 5
and 6 respectively. In Example 4 (containing admixture A), as
compared to Comparative Example 1 (base concrete), the tensile
strength of the sample aged 7 days was much improved by
approximately 60%, and those of the samples aged 28 days and 91
days by approximately 40% respectively. Meanwhile, the compressive
strength thereof was improved by only from 10 to 20%. Further, in
Example 5 containing admixture B having a larger particle size than
admixture A, the tensile strength was less improved than in Example
4. Also in Example 6 in which the amount of the concrete admixture
was twice as large as those in Examples 4 and 5, the strengths were
less improved than in Examples 4 and 5.
[0102] With respect to strength data of the samples aged 7 days, 28
days and 91 days as obtained in Example 4 (containing admixture A)
and Comparative Example 1 (base concrete), the compressive strength
was plotted as abscissa and the split tensile strength as ordinate
respectively. The results are shown in FIG. 7.
[0103] Consequently, the strength data obtained in Example 4 was
close to a curve with .alpha. of 0.31 in formula (3), and the
strength data obtained in Comparative Example 1 to a curve with a
of 0.23 respectively.
[0104] That is, in Example 4 containing admixture A, as compared to
the base concrete, .alpha. was improved by approximately 35%, and
the tensile strength estimated from the same compressive strength
was much improved by 35%. Thus, the concrete of the invention has
the outstanding characteristic feature that the tensile strength is
by far more improved than the compressive strength.
[0105] In Example 4 (containing admixture A), Example 5 (containing
admixture B) and Comparative Example 1 (base concrete), the secant
modulus of elasticity in compression of the samples aged 28 days
was measured. Consequently, in all of the samples, the maximum
compressive stress was shown with the strain of approximately
0.002, and no great difference was found in the stress. That is,
although the secant modulus of elasticity in compression was
slightly increased by adding the admixture of the invention, no
great change was found in the compression behavior.
[0106] With respect to the concretes obtained in Example 4
(containing additive A) and Comparative Example 1 (base concrete),
the pore size distribution was measured with a porosimeter. The
results are shown in FIGS. 1 and 2 respectively. It was identified
that by adding the admixture of the invention, pores having a pore
size of from 0.5 to 10 .mu.m were decreased and pores having a pore
size of from 0.01 to 0.1 .mu.m were increased.
[0107] The photos of the broken surfaces in the tensile test on the
concretes obtained in Example 4 (containing admixture A) and
Comparative Example 1 (base concrete) are shown in FIGS. 3 and 4
respectively. As is clear from FIG. 4, in the base concrete, a
large number of broken portions are observed in the interface
between the coarse aggregate and the mortar, showing that the
transition zone is a brittle point. On the contrary, as shown in
FIG. 3, in case of containing the admixture of the invention, a
large number of broken portions are observed in the coarse
aggregate, suggesting that the bonding strength in the transition
zone is greatly improved.
Example 7
Production and Evaluation of a Concrete Containing Admixture C
[0108] For a ready mixed concrete used as a base concrete, the
following raw materials were used.
[0109] 1) Cement
[0110] normal portland cement made by Taiheiyo Cement Corp.,
density 3.16 g/cm.sup.3, sodium content (calculated as Na.sub.2O)
0.58% by weight
[0111] 2) Coarse aggregate 1
[0112] crushed stone No. 5 from Hachioji, particle size from 5 to
20 mm, fineness modulus 7.04, surface-dry condition density 2.67
g/cm.sup.3, water absorption 0.55% by weight
[0113] 3) Coarse aggregate 2
[0114] crushed stone No. 6 from Hachioji, particle size from 2.5 to
10 mm, fineness modulus 5.88, surface-dry condition density 2.67
g/cm.sup.3, water absorption 0.69% by weight
[0115] 4) Fine aggregate
[0116] soil sand from Kimitsu, particle size 5 mm or less, fineness
modulus 2.64, surface-dry condition density 2.60 g/cm.sup.3, water
absorption 2.23% by weight
[0117] The proportions of the foregoing components are as follows.
The parenthesized values are amounts per 100 parts by weight of
cement. A slump of this base concrete is 8 cm.
3 cement 320.0 kg/m.sup.3 (100 parts by weight) water 176.0
kg/m.sup.3 (55 parts by weight) coarse aggregate 1 564.3 kg/m.sup.3
(176 parts by weight) coarse aggregate 2 376.2 kg/m.sup.3 (118
parts by weight) fine aggregate 842.2 kg/m.sup.3 (263 parts by
weight)
[0118] A concrete sample was produced as in Example 4 except that
admixture C obtained in Example 2 was added to the base concrete in
an amount of 2 parts by weight per 100 parts by weight of cement.
Plural such samples were produced, and cured in air of 15.degree.
C. In this Example 7 and Comparative Example 3 to be described
later, samples were produced on the same date using the same base
concrete, and cured under the same atmosphere. The samples aged 7
days and 28 days were subjected to the same tests for measuring
strengths as in Example 4. The resulting tensile strength,
compressive strength and .alpha. are all shown in Table 2.
Comparative Example 3
Production and Evaluation of a Concrete Without Admixture
[0119] Concrete samples were produced by pouring the base concrete
alone in the form without using admixture C in Example 7, and then
cured as in Example 7. The samples aged 7 days and 28 days were
subjected to the same tests for measuring strengths as in Example
4. The resulting tensile strength, compressive strength and a are
all shown in Table 2.
4 TABLE 2 Compressive Tensile strength strength .alpha.*.sup.1)
(N/mm.sup.2) Ratio*.sup.3) (N/mm.sup.2) Ratio*.sup.3) Ratio*.sup.3)
aged 7 days Comp. Ex. 3 1.64 1.00 20.86 1.00 0.217 1.00 Ex. 7 2.21
1.35 19.69 0.94 0.303 1.40 aged 28 days Comp. Ex. 3 1.97 1.00 28.71
1.00 0.210 1.00 Ex. 7 2.45 1.24 28.14 0.98 0.265 1.26 Comp. Ex. 3
Absence of an admixture Ex. 7 2 parts by weight of admixture C was
added. *.sup.1)Tensile strength = .alpha. .times. (compressive
strength).sup.2/3 *.sup.3)Ratio when the value in Comparative
Example 3 was defined as 1.00.
[0120] As is apparent from Table 2, the concrete containing
admixture C in Example 7 was clearly improved in tensile strength
as compared to the concrete without admixture in Comparative
Example 3. Meanwhile, the concrete in Example 7 was slightly
decreased in compressive strength as compared to the concrete in
Comparative Example 3. That is, only the tensile strength was
selectively improved in comparison to the compressive strength,
which was also shown by the increase in .alpha.. These test results
are the same as those in Examples 4 to 6 using fumaric acid as the
carboxylic acid, the raw material of the admixture. Thus, it was
found that the effects of the invention could be brought forth even
by using citric acid as the carboxylic acid.
Example 8
Production and Evaluation of a Concrete Containing Admixture D
[0121] A ready mixed concrete used as a base concrete was the same
as that used in Example 7. A concrete sample was produced as in
Example 4 except that admixture D obtained in Example 3 was added
to the base concrete in an amount of 1 part by weight per 100 parts
by weight of cement. Plural such samples were produced, and cured
in air of 20.degree. C. In this Example 8 and Comparative Example 4
to be described later, samples were produced on the same date using
the same base concrete, and cured under the same atmosphere. The
samples aged 7 days and 28 days were subjected to the same tests
for measuring strengths as in Example 4. The resulting tensile
strength, compressive strength and .alpha. are all shown in Table
3.
Comparative Example 4
Production and Evaluation of a Concrete Without Admixture
[0122] Concrete samples were produced by pouring the base concrete
alone in the form without using admixture D in Example 8, and then
cured as in Example 8. The samples aged 7 days and 28 days were
subjected to the same tests for measuring strengths as in Example
4. The resulting tensile strength, compressive strength and .alpha.
are all shown in Table 3.
5 TABLE 3 Compressive Tensile strength strength .alpha.*.sup.1)
(N/mm.sup.2) Ratio*.sup.4) (N/mm.sup.2) Ratio*.sup.4) Ratio*.sup.4)
aged 7 days Comp. Ex. 4 2.01 1.00 26.65 1.00 0.226 1.00 Ex. 8 2.40
1.19 24.83 0.93 0.283 1.25 aged 28 days Comp. Ex. 4 2.42 1.00 35.23
1.00 0.225 1.00 Ex. 8 2.73 1.13 34.44 0.98 0.258 1.15 Comp. Ex. 4
Absence of an admixture Ex. 8 1 part by weight of admixture D was
added. *.sup.1)Tensile strength = .alpha. .times. (compressive
strength).sup.2/3 *.sup.4)Ratio when the value in Comparative
Example 4 was defined as 1.00.
[0123] As is apparent from Table 3, the concrete containing
admixture D in Example 8 was clearly improved in tensile strength
as compared to the concrete without admixture in Comparative
Example 4. Although the amount of admixture D in Example 8 was as
small as 1 part by weight per 100 parts by weight of cement, the
tensile strength was no doubt improved. Meanwhile, the concrete in
Example 8 was slightly decreased in compressive strength as
compared to the concrete in Comparative Example 4. That is, in this
case as well, only the tensile strength was selectively improved in
comparison to the compressive strength, which was also shown by the
increase in .alpha.. Thus, it was found that even though the
admixture having the low water content was used in the small
amount, the tensile strength was improved.
Example 9
Production and Evaluation of a Mortar Containing Admixture A
[0124] The following raw materials were used in this Example.
[0125] 1) Cement
[0126] normal portland cement made by Taiheiyo Cement K.K., density
3.16 g/cm.sup.3, sodium content (calculated as Na.sub.2O) 0.58% by
weight
[0127] 2) Fine aggregate
[0128] soil sand from Kimitsu, particle size 5 mm or less, fineness
modulus 2.64, surface-dry condition density 2.60 g/cm.sup.3, water
absorption 2.23% by weight
[0129] The foregoing cement, fine aggregate and water were first
stirred with a forced action mixer for 1 minute, and admixture A
obtained in Example 1 was then added. The blend was further stirred
for 30 seconds. The proportions thereof are as follows. The
parenthesized values are amounts per 100 parts by weight of
cement.
6 cement 320.0 kg/m.sup.3 (100 parts by weight) water 176.0
kg/m.sup.3 (55 parts by weight) fine aggregate 842.2 kg/m.sup.3
(263 parts by weight) admixture A 6.4 kg/m.sup.3 (2 parts by
weight)
[0130] After stirred, the blend was poured in a cylindrical form
having a diameter of 50 mm and a height of 100 mm to produce a
mortar sample. This sample was formed according to JSCE-F506-1999.
Plural such samples were produced, and cured in air of 20.degree.
C. In this Example 9 and Comparative Example 5 to be described
later, samples were produced on the same date and cured under the
same atmosphere. The samples aged 7 days and 28 days were subjected
to the same tests for measuring strengths as in Example 4. The
resulting tensile strength, compressive strength and .alpha. are
all shown in Table 4.
Comparative Example 5
Production and Evaluation of a Mortar Without Admixture
[0131] Mortar samples were produced as in Example 9 except that
cement, water and the fine aggregate were incorporated without
using admixture A, and were cured as in Example 9. The samples aged
7 days and 28 days were subjected to the same tests for measuring
strengths as in Example 4. The resulting tensile strength,
compressive strength and .alpha. are all shown in Table 4.
7 TABLE 4 Compressive Tensile strength strength .alpha.*.sup.1)
(N/mm.sup.2) Ratio*.sup.5) (N/mm.sup.2) Ratio*.sup.5) Ratio*.sup.5)
aged 7 days Comp. Ex. 5 1.47 1.00 22.71 1.00 0.183 1.00 Ex. 9 1.67
1.14 22.14 0.97 0.212 1.16 aged 28 days Comp. Ex. 5 1.91 1.00 33.00
1.00 0.186 1.00 Ex. 9 2.36 1.24 32.05 0.97 0.233 1.25 Comp. Ex. 5
Absence of an admixture Ex. 9 2 parts by weight of admixture A was
added. *.sup.1)Tensile strength = .alpha. .times. (compressive
strength).sup.2/3 *.sup.5)Ratio when the value in Comparative
Example 5 was defined as 1.00.
[0132] As is apparent from Table 4, the mortar containing 2 parts
by weight of admixture A per 100 parts by weight of cement in
Example 9 was improved in tensile strength as compared to the
mortar without admixture in Comparative Example 5. The extent of
the improvement was less than the extent of the improvement in the
concrete containing 2.5 parts by weight of admixture A per 100
parts by weight of cement in Example 4. Thus, the effect of the
improvement in tensile strength provided by adding the admixture of
the invention is greater in the concrete than in the mortar.
However, in the mortar as well, the tensile strength is no doubt
improved, and the bonding strength seems likely to be improved also
on the surface of the fine aggregate, though its extent is not so
high as that on the surface of the coarse aggregate. Meanwhile, the
compressive strength of the mortar in Example 9 was slightly
decreased in comparison to the mortar in Comparative Example 4. In
the mortar, as in the concrete, the tensile strength was
selectively improved in comparison to the compressive strength,
which was also shown by the increase in .alpha.. That is, the
admixture of the invention, when added to the mortar, can also
improve the tensile strength.
[0133] As has been thus far described, the concrete containing the
concrete admixture of the invention is greatly improved in tensile
strength as compared to the compressive strength and can reduce
cracks in the concrete structure or decrease an amount of steel
used. This concrete admixture can be used only by adding it to a
fluid concrete, and the fluidity of the concrete can be maintained.
It is thus possible to provide a concrete which is advantageously
used in large-sized, diversified concrete structures, and further
to provide a concrete which is advantageously used in various
concrete products.
[0134] The mortar containing the mortar admixture of the invention
is also greatly improved in tensile strength as compared to the
compressive strength, and can advantageously be used in products
which are susceptible to a tensile stress due to an external force
or a thermal stress and products which tend to be influenced by
fatigue. Further, the mortar is also useful for products with
complicated shapes or thin products, and can therefore provide
various mortar products. The blended concrete of the invention is
useful for producing a concrete or a mortar excellent in tensile
strength.
* * * * *